MANUAL F ROCKFALL INVENTORY - Pages - Welcome to The … · manual for rockfall inventory prepared...
Transcript of MANUAL F ROCKFALL INVENTORY - Pages - Welcome to The … · manual for rockfall inventory prepared...
MANUAL FOR
ROCKFALL INVENTORY
PREPARED BY:
THE OHIO DEPARTMENT OF TRANSPORTATION
OFFICE OF GEOTECHNICAL ENGINEERING
1980 WEST BROAD STREET
COLUMBUS, OHIO 43223 DECEMBER 2016
Manual for Rockfall Inventory – Revised 12/2016 i
TABLE OF CONTENTS
SECTION 100 INTRODUCTION .................................................................................................................. 1
SECTION 200 ROCK SLOPE INVENTORY AND DATA COLLECTION ................................................ 2
201 PURPOSE AND GENERAL PROCESS ....................................................................................................... 2 202 SITE INVENTORY AND PRELIMINARY RATING ...................................................................................... 6
202.1 General ....................................................................................................................................... 6 202.2 Office Procedures ....................................................................................................................... 6
202.2.1 ODOT Interview(s) .............................................................................................................................. 6 202.2.2 Digital Photolog ................................................................................................................................... 7 202.2.3 Other Photographic Alternatives .......................................................................................................... 8 202.2.4 Geological Reference ........................................................................................................................... 8
202.3 Field Procedures ......................................................................................................................... 9 202.3.1 Inventory Site Determination ............................................................................................................... 9
202.3.1 a) Site Determination for Ramps ................................................................................................ 11 202.3.2 Preliminary Rating of Inventory Site.................................................................................................. 14
202.3.2 a) Inventory Site Location .......................................................................................................... 14 202.3.2 aa) Beginning Mile Point (BMP) ........................................................................................... 16 202.3.2 bb) Inventory Site Length ....................................................................................................... 17 202.3.2 cc) Ending Mile Point (EMP) ................................................................................................. 17 202.3.2 dd) BMP Position ................................................................................................................... 18
203.2.2 Preliminary Rating Scoring ................................................................................................................ 19 203 TIER 1 DATA COLLECTION ..................................................................................................................25
203.1 Field Procedures ........................................................................................................................25 203.1.1 Slope Configuration ........................................................................................................................... 25
Figure 200-10. EXAMPLES OF CUT SLOPES ...........................................................................................26 203.1.2 Slope Condition .................................................................................................................................. 27 203.1.3 Photographic Documentation of Inventory Site ................................................................................. 27
204 DETAILED RATING OF INVENTORY SITES - GENERAL .........................................................................28 205 TIER 2 SITE DATA COLLECTION ..........................................................................................................29
205.1 Tier 2 Data Procedures ..............................................................................................................29 205.1.1 Geometrics and Traffic ....................................................................................................................... 30
205.1.1 a) Traffic Survey Reports ........................................................................................................... 30 205.1.1 b) Actual Site Distance (ASD) ................................................................................................... 30 205.1.1 c) Decision Site Distance (DSD) ................................................................................................ 31 205.1.1 d) Percent Decision Site Distance (PDSD) ................................................................................. 31
205.1.2 Slope Information ............................................................................................................................... 32 205.1.2 a) Slope Height ................................................................................................................................... 32 205.1.2 b) Slope Elevations............................................................................................................................. 34 205.1.2 c) Slope Undercutting/Raveling ......................................................................................................... 34 205.1.2 d) Slope Jointing ................................................................................................................................ 34 205.1.2 e) Rockfall Source Information .......................................................................................................... 35
205.1.2 f) Hydrologic Conditions ............................................................................................................ 38 205.1.2 g) Corrective Actions ................................................................................................................. 39 205.1.2 h) Catchment .............................................................................................................................. 42
205.1.2 aa) Catchment Area Shape ..................................................................................................... 42 205.1.2 bb) Catchment Area Depth ..................................................................................................... 44 205.1.2 cc) Catchment Area Width ..................................................................................................... 45 205.1.2 dd) Foreslope Angle ............................................................................................................... 45 205.1.2 ee) Slope Face Angle .............................................................................................................. 46 205.1.2 ff) Remedial Effectiveness ..................................................................................................... 48
205.1.2 i) Additional Information ........................................................................................................... 48 206 TIER 3 & TIER 4 SITE DATA COLLECTION ...........................................................................................49
206.1 Slope Geological Conditions......................................................................................................49 206.1.1 Number of Cut Slope Benches ................................................................................................... 50 206.1.2 Number of Cut Slope Angles ..................................................................................................... 50 206.1.3 Cut Slope Angles ....................................................................................................................... 50 206.1.4 Average Cut Slope Angle........................................................................................................... 52 206.1.5 Cut Slope Angles Elevations ...................................................................................................... 53 206.1.6 Bench Elevations ....................................................................................................................... 53
Manual for Rockfall Inventory – Revised 12/2016 ii
206.1.7 Bench Width .............................................................................................................................. 54 206.1.8 Competent Bedding.................................................................................................................... 54 206.1.9 Incompetent Bedding ................................................................................................................. 54 206.1.10 Undercutting Information........................................................................................................... 54 206.1.11 Joint Information ........................................................................................................................ 56 206.1.12 Potential Rockfall Estimation..................................................................................................... 58 206.1.13 Talus Accumulation ................................................................................................................... 59 206.1.14 Vegetation .................................................................................................................................. 60 206.1.15 Additional Information .............................................................................................................. 60
206.2 Slope Hydrological Conditions ..................................................................................................61 206.3 Tier 3 & Tier 4 Testing Data .....................................................................................................65 206.4 Tier 3 & Tier 4 Office Data........................................................................................................67
207 DATA COLLECTION ACKNOWLEDGEMENT ..........................................................................................67
300 RISK SCORING FOR INVENTORY SITES ........................................................................................ 68
301 ROCKFALL INVENTORY SITE RISK SCORING .......................................................................................68 302 DIFFERENTIAL WEATHERING ..............................................................................................................68 303 DISCONTINUITY ROLE ........................................................................................................................69 304 BLOCK SIZE/VOLUME OF ROCKFALL PER EVENT ...............................................................................69 305 HYDROLOGIC CONDITIONS (SEEPS AND SPRINGS) ...............................................................................70 306 ROCK SLOPE HEIGHT ..........................................................................................................................70 307 CATCHMENT/CONTAINMENT ..............................................................................................................70 308 EXPOSURE RISK ..................................................................................................................................71 309 PERCENT DECISION SIGHT DISTANCE (PDSD) ...................................................................................71 311 ACCIDENT HISTORY ............................................................................................................................72
400 INSPECTION FREQUENCY ................................................................................................................ 74
LIST OF APPENDIXES
APPENDIX A:
GLOSSARY OF TERMS
APPENDIX B:
CRITERIA FOR EVALUATION OF CATCHMENT
APPENDIX C:
FIELD GEOLOGIC PARAMETERS
APPENDIX D:
PHOTO EXAMPLES OF TIERED SITES
PHOTO EXAMPLES OF ROCKFALL RETENTION DEVICES
APPENDIX E:
GPS OUTLINE
Manual for Rockfall Inventory – Revised 12/2016 iii
LIST OF FIGURES
FIGURE NUMBER TITLE OR DESCRIPTION PAGE NUMBER
200-01 Rockfall Slope Inventory Rating Data Collection Process 4
200-02 Rockfall Slope Inventory Process…………..…………. 5
200-03 Screen Capture from ODOT Digital Photolog………… 8
200-04 Rock Slope Evaluation Based on Road Type…………. 10
200-05 Example of Rock Slope vs. Inventory Site……………. 12
200-06 Example of Curved Rock Slope vs. Inventory Site…… 13
200-07 Determined of Ramp BMP’s …………………………. 13
200-08 Positions of an Inventory Site……….……………….... 19
200-09 Potential of Rockfall to Impact Roadway
– Below the Roadway……….……………….... 23
200-10 Examples of Cut Slopes……………………………….. 26
200-11 Examples of Preliminary Rating (Tier 1) Photographs.. 28
200-11 Relationship between slope height and geometric
parameters……………………………………………... 33
200-13 Block Size Determinations……………………………… 37
200-13a Block Size Before Falling……………………………… 37
200-13b Block Size After Falling…………….…………….....… 37
200-14 Rockfall Volume Determination………………………. 38
200-15 Hydrologic Conditions………..………………………. 39
200-16 Typical Types of Corrective Actions………………….. 40-41
200-17 Catchment Area Shapes……………...………………... 43
200-18a Catchment Area……………………………………….. 44
200-18b Hydraulic Control Ditch NOT as Catchment…………. 45
200-18c Hydraulic Control Ditch as Catchment ……………….. 45
200-19 Catchment Area Configuration………………………... 47
200-20 Example of Mine Openings…………………………… 49
200-21 Slope Angle Determination…….……………………… 51
200-22 Recording Slope Angle along a Blast Hole Using a
Pocket Transit…………………………………………. 51
200-23 Recording Slope Angle using a Pocket Transit and
Non-ferric Clipboard………………………….. 52
200-24 Average Slope Calculation……………………………. 53
200-25 Example of Cut Slope Description……………………. 55
200-26 Orthogonal Joint Set/Spacing…………………………. 57
200-27 Joint Infilling…………….…………………………….. 57
200-28 Example Rockfall Shapes.…………………………….. 58
200-29 Estimating Talus Accumulation ……………………… 60
200-30 Hydrologic Conditions Winter Conditions…………… 63
200-31 Hydrologic Conditions Spring Conditions……………. 64
Manual for Rockfall Inventory – Revised 12/2016 iv
LIST OF TABLES
TITLE NUMBER TITLE OR DESCRIPTION PAGE NUMBER
200-01 Tier Type Based on Preliminary Rating Score .….…….... 20
200-02A Preliminary Rating Criteria
(Slopes Above Roadway) …………..………. 21
200-02B Preliminary Rating Criteria
(Slopes Below Roadway) …………..………. 22
200-03 Decision Sight Distance ...……………………….…………. 31
200-04 Typical Slope Values for Rock Cut Sections ..………… 52
200-05 Rockfall Parameters ..……………………………............... 58
200-06 Hydrological Prefixes ……………………………..………... 62
300-01 Hydrological Conditions (Seeps and Springs) …………. 70
300-02 Rockfall History Risk Score ...…………………………..... 73
300-03 Accident History Risk Score ...……………………………. 73
400-01 Re-Inspection Frequency ...……………………………. 74
LIST OF EXAMPLES
EXAMPLE NUMBER TITLE OR DESCRIPTION PAGE NUMBER
200-01 NFLID Coding Standard………………………………….. 15
200-02 Sites with DMI Readings starting at SLM 0.00…………... 17
200-03 Sites with DMI Readings not starting at SLM 0.00…......... 17
200-04 BMP Position Data………………………………………... 18
200-05 Preliminary Rating Score of an Inventory Site…………… 24
200-06 Determination of the Slope Configuration of the
Inventory Site…………………………………….. 25
200-07 Percent Decision Sight Distance…………………….......... 32
200-08 Calculating the Slope Height……………………………… 34
200-09 Weighted Average Calculation for Multi-Angled
Cut Slopes…………………………………........... 53
200-10 Calculation of Bench Width and Elevation………………. 54
200-11 Slope Geological and Natural Conditions………………… 55
200-12 Collection of Joint Information…………………………… 56
200-13 Hydrological Conditions of Cut Slope and Natural
Backslope………………………………………… 63
200-14 Hydrological Conditions of Cut Slope and Natural
Backslope………………………………………… 64
200-15 Slake Durability Index Test Sample Collection…………... 66
Manual for Rockfall Inventory – Revised 12/2016 v
LIST OF EQUATIONS
EQUATION NUMBER TITLE OR DESCRIPTION PAGE NUMBER
1 Percent Decision Sight Distance …………………………. 31
2 Vertical Height Calculation ………………………………. 33
3 Foreslope Angle Calculation …………..…………………. 46
4 Slope Face Angle Calculation ……………………………. 47
5 Average Slope Angle Calculation ………………………... 53 6 Exposure Risk…………………… ………………………... 71
Manual for Rockfall Inventory – Revised 12/2016 1
Section 100 Introduction
Rockfalls can constitute a major hazard along Ohio roadways, posing a risk to life, property,
and traffic safety. As a result of rockfalls, maintenance problems are constantly occurring,
resulting in a strain on the Ohio Department of Transportation (ODOT) funds and manpower.
The following terms have been defined for use in this Manual:
Rockfall: The down-slope gravitational movement of material that is comprised of at
least 51 percent rock. Where, rock is defined as: Any material found along a slope that
when freshly exposed has the characteristics of in-place bedrock. Bedrock includes, but
not limited to, sandstone, siltstone, shale, limestone, dolomite, coal, claystone, and
conglomerate.
Rock Slope: Any slope, either natural or man-made, that has in-place bedrock exposed at
the surface.
Rockfall Event: A distinct period of time during which a single or multiple rock(s) and
associated debris dislodges from a rock slope.
This Manual was developed by ODOT, Office of Geotechnical Engineering (OGE) to
inventory rock slopes, to identify potential hazardous rock slopes, to assess relative risk for
those slopes, to determine degree of monitoring required, and to allow for actions to be taken
to reduce, minimize, or eliminate the risk to the public’s safety and to protect the highway
system.
This document is not a design manual. The intent of this Manual is to facilitate the
creation of a statewide rockfall inventory process through the development of a statewide
inventory procedure and the establishment of office and field methods. These methods
should be used during the initial population of the inventory, inventory of new sites
following the initial population, and for maintenance and monitoring of the sites.
The data collection procedures are grouped into four (4) primary sections with subsections:
Site Inventory and Preliminary Rating
Tier 1 Site Rating
Tier 2 Site Rating
Tier 3 and Tier 4 Site Rating
A rockfall inventory will be performed for the state highway system as noted in ODOT’s
policy on geohazards. This inventory will include all natural and man-made slopes with
exposed bedrock. The field portion of the inventory shall be completed by a Field Team(s).
For safety concerns, a Field Team should consist of a minimum of two members. For a
multi-discipline approach, the Field Team shall consist of a geologist and either an
engineering geologist or geotechnical engineer. The optimum time for the performance of
Manual for Rockfall Inventory – Revised 12/2016 2
the field work along slopes that have high relief and/or are highly vegetated is October
through April. However, it should be noted that snow may also limit field activities in
December through February. Field activities may be suspended during periods of inclement
weather as directed by ODOT. Slopes that have low relief and/or low to moderate vegetation
may be evaluated year round.
Within this Manual, slopes which are being inventoried will generally be referred to as a
“rock slope”. All rock slopes shall receive a Preliminary Rating based on basic site
characteristics. The Preliminary Rating will also segregate the lower priority sites from the
groups that will receive detailed data collection efforts. This Manual will outline a tiered
data collection methodology which will allow rock slopes within Ohio to be rated for relative
rockfall risk to the public and Ohio’s highway system. The data collected from each site will
be incorporated into an Enterprise Database and integrated into a GIS system. All
information collected by personnel in the field or office should be presented in standard
database format, Excel spreadsheets, and GIS ArcView file(s) utilizing ODOT’s standardized
file naming conventions.
The data collected from the inventory process will be stored within the Geologic Hazard
Management System (GHMS) and other related components of the ODOT GeoMS.
Appendix A presents a Glossary of Terms that should be used in association with this
Manual.
Section 200 Rock Slope Inventory and Data Collection
201 Purpose and General Process
The inventory will consist of identifying and locating Inventory Sites within the rock
slopes situated along Ohio’s highway system. Generally, this inventory will be
concerned with rock slopes located above the roadway, unless a rockfall event below the
road could result in adverse impacts to the highway system. As part of the rock slope
inventory, a Preliminary Rating of each Inventory Site will be performed on each site.
The Preliminary Rating will provide guidance as to what level of data collection
(Detailed Rating) is required.
The Preliminary Rating will be completed by the Field Team(s) by visually evaluating
two criteria for each Inventory Site. These criteria are: 1) the potential of a rockfall
occurrence from the slope and 2) if a rockfall was to occur, the potential of the rock to
reach the traffic lane. This evaluation will be based upon best professional judgment and
past experience of the Field Team(s). A rating of Low, Moderate, High, or Very High
will be used for each criteria with an associated numerical value assigned. Section
202.3.1 Inventory Site Determination discusses in detail how to select an Inventory Site
and perform the Preliminary Rating.
For those sites where a Detailed Rating is not required, the slope will be listed as a Tier 1
site, or non-rated within the GHMS, with assigned data parameters required during the
Manual for Rockfall Inventory – Revised 12/2016 3
field data collection. The following Tiers are considered as Rated Sites within the
GHMS. A detailed explanation of the procedures will be presented in the subsequent
sections with a brief description of each Tiered Rating as follows:
A Tier 1, or non-rated, site will consist of rock slopes that have a low or moderate
potential of rockfall occurring from the slope, and a low or moderate potential of any
rockfall reaching the travel lane of the roadway. It should be noted that if both potentials
are moderate to very high then the site is not a Tier 1 site, but a rated site and will require
Detailed Rating data collection.
Tier 2 sites will consist of sites where the potential of a rockfall occurrence is moderate to
high, and the potential of the rockfall reaching the traffic lane is moderate.
Tier 3 and Tier 4 sites are sites that the potential of a rockfall occurrence is high to very
high and the potential of the rockfall reaching the traffic lane is high to very high. The
difference between a Tier 3 and Tier 4 site is that a Tier 4 site poses an immediate threat
to the safety of the public and/or the roadway.
The methodology for data collection is outlined in the following sections:
Section 202 Site Inventory and Preliminary Rating
Section 203 Tier 1 Data Collection
Section 205 Tier 2 Data Collection
Section 206 Tier 3 and Tier 4 Data Collection
Each section will outline the office and field procedures to collect all the required data for
the site.
All sites will require the Tier 1 data collection, which is the minimum required data
inputs, for the Rockfall Slope Inventory. Sites that are categorized as a Tier 2 site from
the Preliminary Rating will require Tier 1 augmented with Tier 2 data collection. For
sites that are categorized as either Tier 3 or Tier 4 sites from the Preliminary Rating will
require all levels (Tier 1, 2, 3 & Tier 4) of data collection. The Tiered sites are also
referenced as Non-Rated for Tier 1 locations or Rated if they are a Tier 2, 3, or 4
location.
If a debris fragment greater than 6 inches in any dimension, or debris greater than one
cubic foot in total volume, occupies the shoulder, travel lane(s) or median, the District
Geotechnical Engineer (DGE) and the Office of Geotechnical Engineering (OGE) shall
be notified within one week and the site shall be re-evaluated within one month of the
Manual for Rockfall Inventory – Revised 12/2016 4
event. If an Inventory Site is determined to be a Tier 4 designation, the DGE and OGE
shall be notified within 24 hours from completion of the evaluation.
Figure 200-01 is a generalized flow chart outlining the data collection process for the
Rockfall Inventory.
Figure 200-02 is a generalized Organization Chart for the initial population of the
Rockfall Inventory and Slope Rating System.
Figure 200-01. ROCKFALL SLOPE INVENTORY RATING DATA COLLECTION PROCESS
Tier 1 Site: Data Collection Completed
Tier 2 Data Collection
(Refer to Section 205 Tier 2 Site Data
Collection)
Tier 2 Site: Data Collection Completed
Tier 3 & Tier 4 Data Collection (Refer to Section 206 Tier3 & 4 Data
Collection)
Tier 3 Site: Data Collection Completed
Tier 4 Site: Data Collection Completed
Rock Slope Identification and
Inventory Site Identification
Preliminary Rating Completed (Refer to Section 202 Site Inventory and
Preliminary Rating)
Tier 1 Data Collection
(Refer to Section 203 Tier 1 Site Data
Collection)
Notify DGE & OGE Immediately if
Tier 4 Site Identified
Populate
Database with
Inventory Site
Inventory Site
Routine
Monitoring
Manual for Rockfall Inventory – Revised 12/2016 5
Figure 200-02. ROCKFALL SLOPE INVENTORY PROCESS
Field Team(s)
Preliminary Office
Data Collection
Site Inventory &
Preliminary Rating Tier 1
Detailed Field
Rating
Detailed Office
Data Collection
Database Input
ODOT Testing
Training QA/QC Progress
Reports Scheduling
ODOT
Project Manager
Tier 2, 3, or 4
Consultant
Testing
Tier 3 & 4
Sampling
Manual for Rockfall Inventory – Revised 12/2016 6
202 SITE INVENTORY AND PRELIMINARY RATING
202.1 General
The Project Manager and Field Team(s) will begin their work based upon the
selection of the counties and routes as designated by OGE and District personnel.
Study routes will encompass Interstate Routes, US Routes, and State Routes
throughout the state including routes within municipalities. The Project Manager and
Field Team(s) will evaluate and select the most efficient travel pattern or routes for
completion of the fieldwork prior to starting the field data collection.
Priority selection of counties will be based on National Highway System (NHS)
Routes (Interstate Routes, US Routes, and designated State Routes), then the
remaining State Routes (non-arterial) within those counties. Routes that have had
historical rockfall events should be completed before routes that do not have a
historical record of rockfall.
202.2 Office Procedures
Prior to commencement of the field work, the Project Manager and Field Team(s)
should have an idea as to the location of rock slopes that have a rockfall potential in
relation to Ohio’s highways. The following sections outline the general office
procedures for the development of a work plan for site investigations.
202.2.1 ODOT Interview(s)
Prior to commencing the fieldwork, the Field Team(s) shall contact and schedule
interviews with the ODOT DGE/Geologist for each respective District, the ODOT
County/Transportation Manager(s) for each respective county, and any other
applicable ODOT personnel (e.g. highway workers) who are familiar with the
rockfall maintenance for the selected area. In addition, interviews may be
conducted with county and/or city engineers or maintenance crews for locations
where personnel outside of ODOT perform the roadway maintenance or have
additional knowledge of the roadway.
The Field Team(s) will interview all applicable ODOT personnel as to locations
of rock slopes within their county and/or District. Additionally, the interviews
should reveal where rockfall is actively occurring or has been a historical
problem. Information from these interviews should include, but is not limited to:
Manual for Rockfall Inventory – Revised 12/2016 7
Straight Line Mile (SLM) location(s) of natural or cut slope(s) with exposed
bedrock
SLM locations of rockfall and frequency
Date and amount (size and volume) of rockfall
Length and width, referenced to the roadway, where rockfall debris has
accumulated
Accidents resulting from rockfall including date, damage to State or private
property, injuries, and/or fatalities
Scheduled maintenance of rock slope(s) and associated ditch line, including
but not limited to, ditch cleaning of rockfall debris, bench cleaning along cut
slopes, rock removal from shoulder or roadway, etc.
Any rockfall remediation work performed in the past
A Personnel Interview Data Form, included in Appendix G – Field Forms, should
be completed for each person or group interviewed recording the information
collected. The Interviewee data will be stored in the GHMS within Part A:
Interview Info. If paper forms are being utilized then the interviewee data will be
recorded on the Rockfall Site Inventory Site Field Form (Rockfall Form) in
Section B: ODOT INTERVIEWS. Additionally, this information will be necessary to
complete Section I: REMEDIAL WORK OBSERVATIONS to identify if, when, and/or
where corrective actions have been completed.
202.2.2 Digital Photolog
The Project Manager and/or Field Team(s) may review available Digital
Photolog(s) via the ODOT Pathweb System for each selected site or route. The
Digital Photolog System (Pathweb) was updated in 2011 to allow the user to view
the roadway, including a limited view of the side of the roadway, prior to
commencing their fieldwork. Digital Photolog(s) are available from ODOT
Office of Technical Services (OTS) and is not available through the internet.
The digital photolog is a digital recording created by driving a route with a digital
video recording device mounted on the front, back and sides of the vehicle. A
digital image of the roadway and shoulder is collected at an interval of every
0.005 mile (200 shots per mile). As part of the photolog a Log-Mileage, based on
a digital measurement instrument (DMI), and a GPS recording of latitude and
longitude are presented. The GPS readings are drift corrected geospatial data.
From the Log Mileage information, the Field Team(s) can determine the
approximate mile marker where the anticipated rock slope(s) is located.
Additionally, a GPS map will show spatially the approximate location of the
screen shots. Figure 200-03 shows a screen capture from the photolog
application.
Manual for Rockfall Inventory – Revised 12/2016 8
Figure 200-03. SCREEN CAPTURE FROM ODOT PATHWEB
202.2.3 Other Photographic Alternatives
Additionally, the Field Team(s) can review available aerial stereopairs, high
resolution digital aerial photos, and orthophoto quadrangle sheets or Google Earth
Street View in an attempt to refine the rock slope locations that may be a source
of rockfall. Aerial images, including stereopairs and obliques, orthophoto
quadrangle sheets (DOQ), USGS 7.5 minute topographic quadrangle sheet (topo),
and photogrammetric maps are available from ODOT Office of Cadd and
Mapping Services. Additionally, the DOQ’s and topos can be obtained from the
United States Geological Survey.
202.2.4 Geological Reference
General geological data shall be collected for each county prior to commencement
of the fieldwork. This data can be collected from the Geologic Map of Ohio
Camera Views
County
Route
Section Coordinates
Manual for Rockfall Inventory – Revised 12/2016 9
and/or the County Quadrangle Bedrock Geology Map for the respective USGS
Quadrangle. A rock description for each Geologic Map Unit associated with the
County Quadrangle Bedrock Geology Map is produced by the Ohio Department
of Natural Resources (ODNR) Geological Survey. The Geologic System/Period,
Group(s)/Formation(s), and primary rock types should be identified. Many of
these maps and others (e.g. bedrock geology, bedrock structure, bedrock
topography) are available as electronic files for GIS applications.
Additionally, the study area(s) should be evaluated for the potential presence of
known surface and underground mining, either abandoned or active. Mining
activities, both current and past, can be obtained from ODNR or ODOT as GIS
layers.
This data will be recorded in the GHMS in Part C: Geological, additional
information tab and on the Rockfall Form in Section I: GENERAL GEOLOGIC
DESCRIPTION.
202.3 Field Procedures
202.3.1 Inventory Site Determination
For each route, it is preferred that the Field Team begin at County Log Mile
(CLM) 0.00, which will have a corresponding Straight Line Mile (SLM) 0.00.
However, any known SLM referenced point can be utilized as a beginning point.
To begin, the DMI should be adjusted to zero at the county line or beginning of
the route. If starting at a known referenced point (e.g. structure or interchange)
adjust the DMI reading to the corresponding SLM. If the Field Team has to stop
for the day, or the need to re-zero the DMI is required, each structure has a SLM
recorded at its right side of the rear abutment in the cardinal direction, and a SLM
is available for each center point of roadway intersections. All mile marker
records for the rockfall inventory should be referenced to SLMs. The DMI
records will be in a True Log Mile format and will need to be adjusted to the
corresponding SLM. Straight Line diagrams referencing the SLM can be
obtained from OTS.
Using a zeroed DMI reading (from a reference point), proceed in the cardinal or
non-cardinal direction, until a rock slope is encountered.
The Field Team should evaluate each rock slope encountered. For bifurcated
highways with rock slopes encountered on both sides of the travel lane, the rock
slopes for both sides of the travel direction should be evaluated at the same time.
For divided highway, all rock slopes along the right side of the roadway should be
evaluated. Then, all the rock slopes on the opposite side of the roadway should be
evaluated while driving in the opposite direction. For non-divided highways rock
slopes can be evaluated on both sides of the roadway at the same time. Care must
be taken in correcting for the Beginning Mile Point (BMP) along the opposite
rock face. Figure 200-04 provides examples of how the rock slope shall be
evaluated based upon roadway type.
Manual for Rockfall Inventory – Revised 12/2016 10
Cardinal
Direction
Non-Cardinal
Direction
Evaluate
Both
Cardinal
Direction
Non-Cardinal
Direction
Evaluate
Both
Bifurcated Roadway
Divided Highway
Non-divided Highway
Figure 200-04. ROCK SLOPE EVALUATION BASED ON ROAD TYPE
Each rock slope location can be evaluated as a single or multiple Inventory
Site(s). An Inventory Site is defined as: any continuous roadway section where a
rock slope has the same characteristics. A minimum slope height of 10-feet is
required to be an Inventory Site, unless the Field Team determines that a slope
with a height less than 10 feet poses a danger to safety of the traveling public.
These characteristics shall be based upon:
Cardinal
Direction
Non-Cardinal
Direction
Evaluate
Only
Evaluate
Only
Cardinal
Direction
Non-Cardinal
Direction
Evaluate
Only
Evaluate
Only
Cardinal
Direction
Non-Cardinal
Direction
Evaluate
Only Evaluate
Both
Cardinal
Direction
Non-Cardinal
Direction
Evaluate
Only Evaluate
Both
Manual for Rockfall Inventory – Revised 12/2016 11
limits of the exposed rock face
natural breaks in the cut face or natural backslope (e.g. natural drainage
features, but not man-made drainage features)
changes in slope orientation relative to the roadway (e.g. roadway curves
around the nose of a hillside that contains a continuous cut section)
changes in the slope orientation relative to the regional joint patterns
changes in the cut face angle(s)
changes in the quality of the bedrock mass
Additionally, the following guidelines should be followed in establishing
Inventory Sites:
1. For cut slopes that contain intermittent rock exposures through
vegetation, but was obviously constructed as a single continuous cut, the
site should be inventoried as a single Inventory Site.
2. A series of small cuts should not be combined into a single Inventory
Site; because, if a problem arises from just one of the cuts, corrective
actions will only apply to the single cut in question, not all of the cuts.
3. The ends of the cuts should not be split out into short sites based only on
the change in height of the cut slope. If work is to be performed on a
large site typically the ends will be included within the project.
4. When a cut height is disrupted due to the presence of a structure abutment
with similar characteristics on either side of the abutment, the slope
should not be broken into two sites, unless the slope characteristics
change.
5. Prior to extending an Inventory Site to a distance of more than one-
half mile (+/-), contact the District Geotechnical Engineer (DGE) or
the Office of Geotechnical Engineering (OGE). In no case should an
Inventory Site extend more than one mile (+/-) or cross county lines.
A new Inventory Site should be created at a county border.
Figures 200-05 and 200-06 show examples of Inventory Sites relative to a
rock slope and Figure 200-07 shows an example for Ramp BMP’s.
202.3.1 a) Site Determination for Ramps
Sites located on ramps will be referenced to the SLM of the mainline. The
selected mainline for the SLM referencing will use the following conventions:
Interstates over US Routes and State Routes
US Routes over State Routes
If there are two Interstates, US Routes or State Routes, the lower
numbered route will be the referenced route
Manual for Rockfall Inventory – Revised 12/2016 12
Figure 200-05. EXAMPLE OF ROCK SLOPE VS. INVENTORY SITE
Comments: The total extent of the rock slope is approximately 1.9 miles, or 10,032 feet. The
10,032 feet of rock slope can be divided into 4 basic segments based on topography and major
local drainage indicated in the circles. From these basic segments a total of 8 Inventory Sites
should be evaluated based upon minor drainage features, change of slope face orientation
relative to the roadway, change in slope face orientation relative to the regional joint patterns,
and change in cut slope angle(s).
N
2
EXTENT OF ROCK SLOPE
10,032 ft (1.9 miles)
Natural Drainage –
No Rock Slope
Inventory Site #5
Inventory Site #3
Inventory Site #6
Inventory Site #7
Inventory Site #8
Natural Drainage –
No Rock Slope
1
3
4
Inventory Site #2
Inventory Site #1
Inventory Site #4
Natural Drainage –
with Rock Slope
Rock Slope
Manual for Rockfall Inventory – Revised 12/2016 13
Figure 200-06. EXAMPLE OF CURVED ROCK SLOPE VS. INVENTORY SITE
Approximate Ramp BMP Location Traffic Flow of Ramp
Figure 200-07. DETERMINATION OF RAMP BMP’s
1
4
3
3
2
Top of
Cut
Approximate
Roadway
Centerline N
Inventory Site
N
Manual for Rockfall Inventory – Revised 12/2016 14
202.3.2 Preliminary Rating of Inventory Site
The Preliminary Rating of a site should be completed for all Inventory Sites as the
first step to populate the rockfall inventory. The Preliminary Rating is basically a
two part process:
1) Inventory Site Location
2) Preliminary Rating Score
202.3.2 a) Inventory Site Location
For each rockfall Inventory Site, location data will need to be recorded to
identifying the site’s specific location. The following data is required to
identify the Inventory Site Location. This data is recorded in Part A: Site
Location of the GHMS or within Section A: PROJECT LOCATION AND
INFORMATION of the Rockfall Form.
The following data is included under the Basic Information tab within the
GHMS Section Site Location.
District
County
Route System
Route Number (5-digit ODOT designated route number)
Jurisdiction Code
(C-County, H-Turnpike Commission, M-Municipal, S-State, T-Township)
Slope orientation (in degrees from north (azimuth coordinate), relative to
the BMP, running parallel to the direction of traffic flow)
Measured length of the Inventory Sites (in feet) along roadway
Beginning Mileage Point (BMP) (as the SLM value determined from the
DMI reading [Note that the BMP is the lowest SLM value for the site])
Ending Mileage Point (EMP) (as a SLM value determined based upon the
Inventory Site length and BMP)
Record if the site is located along the roadway in the cardinal direction
(Yes = northbound or eastbound, No = southbound or westbound)
Horizontal Position of the Rock Slope
(Right or Left relative to cardinal mainline direction or to driving direction
for ramps)
Driving direction: (North, South, East, West)
Vertical Position (Above, Below or Both)
USGS Quadrangle Name
Manual for Rockfall Inventory – Revised 12/2016 15
The Network Linear Feature Identification Code (NLFID Code) will be auto
generated for the location (update button). The NFLID designation is a
tracking code consisting of:
Jurisdiction Code
County
Classification Code
Route Number
Default code to complete the NLFID Code (**C)
Example 200-01 presents the format for the NFLID Code
Optional Information concerning the site consists of:
Classification of roadway
Hazard width perpendicular to the road (from toe of cut)
Distance from Toe of cut to shoulder
EXAMPLE 200-01: NLFID Coding Standard
NLFID CODE - STUSUS00250**C
S TUS US 00250 **C
A B C D E
Where:
A is the Jurisdiction Code
B is the County Code
C is the Classification Code
D is the Route Number
E is the default code
The following data is included under the Roadway Information tab within the
GHMS Section Site Location:
Position Relative to the Roadway
(Mainline, On-ramp, Off-ramp)
Pavement Type
Median
Manual for Rockfall Inventory – Revised 12/2016 16
Optional Information concerning the site consists of:
Classification of roadway
Hazard width perpendicular to the road (from toe of cut)
Distance from Toe of cut to shoulder
The following data is included under the GPS Information tab within the
GHMS:
Beginning Latitude
Beginning Longitude
Beginning Elevation
Offset Distance, in feet, and Bearing, in degrees from north (azimuth
coordinate), if the positional data is not able to be collected at the exact
position of the BMP location
For Rockfall Inventory Sites, only the BMP coordinates will required.
However, if field personnel have a strong GPS signal, additional points can be
collected and coordinates recorded for the Centroid and EMP locations.
The beginning and end of the Inventory Site should be indicated in the field
by placing a minimum 18-inch long white line perpendicular to the roadway
made with surveyor’s paint at either end of the site along the edge of the
pavement. The BMP should be indicated with a “B”, and the EMP should be
indicated with an “E”.
Note: it can be helpful for large sites, if while measuring the Inventory Site
length, place tick marks along the roadway shoulder at regular intervals (say
100 or 200 feet) to use in locating features.
202.3.2 aa) Beginning Mile Point (BMP)
The BMP shall be determined based upon the DMI reading recorded at the
beginning point of the Inventory Site. The BMP shall always be the lowest
SLM point of the Inventory Site. If the DMI reading at the BMP was started
at SLM 0.00 then the BMP is the adjusted DMI reading. However, if the
DMI reading recorded at the BMP was started at a location other than SLM
0.00, the BMP needs to be calculated by adding the starting point SLM and
the adjusted DMI reading. The adjusted DMI reading is the true log mile
reading adjusted for the station equations to calculate the SLM.
Record the BMP value to the nearest 0.01 miles.
Place a PK nail into the paved shoulder or the roadway to indicate the BMP.
If no paved shoulder is present, place the PK nail into the white edge line.
The PK nail should be driven either flush with, or below, the top of
pavement.
BMP of Inventory Site
Manual for Rockfall Inventory – Revised 12/2016 17
202.3.2 bb) Inventory Site Length
The length of the Inventory Site is a direct measurement between the BMP
and the EMP. Generally, this measurement is made with either a measuring
tape, measuring wheel, or a laser range finder.
Record the Inventory Site Length to the nearest foot.
202.3.2 cc) Ending Mile Point (EMP)
For mainline sections, the EMP can be calculated based upon the length of
the Inventory Site divided by 5280 ft/mile then added to the BMP, and/or
recorded utilizing the adjusted DMI reading as outlined in Section 202.3.2
aa) Beginning Mile Point (BMP).
The EMP should be determined by establishing the offset location to its
referenced mainline then calculating this offset point utilizing either the
DMI or other measuring device.
Record the EMP value to the nearest 0.01 miles.
EXAMPLE 200-02: Sites with DMI Readings starting at SLM 0.00:
Inventory Site Attribute SLM
DMI Reading from SLM 0.00 = 2.91
Beginning SLM (BMP) = 2.91
Length of Site = 1850 ft
1850ft ÷ 5280ft/mile = 0.35 mile
Ending SLM (EMP) = 3.26
BMP 2.91 + 0.35 mile
Manual for Rockfall Inventory – Revised 12/2016 18
EXAMPLE 200-03: Sites with DMI Readings not starting at SLM 0.00:
Inventory Site Attribute SLM
SLM at Starting Intersection = 12.58
DMI Reading from Intersection = 2.91
Beginning SLM (BMP) = 15.49
Length of Site = 1850 ft
1850ft ÷ 5280ft/mile = 0.35 mile
Ending SLM (EMP)
BMP 15.49 + 0.35 mile = 15.84
For ramps where the BMP and/or the EMP is not visible from the mainline
then that value does not need to be recorded.
202.3.2 dd) BMP Position
Record the BMP position as a GPS point at the right shoulder of the BMP.
The BMP position shall include the latitude, longitude, and elevation and be
determined using a Trimble GPS unit, or equivalent or better, as a point in
decimal degrees to six (6) digits to the right of the decimal. GPS guidelines
for data collection are presented in Appendix E.
If a GPS reading cannot be taken along the shoulder of the roadway at the
BMP of the Inventory Site due to poor signal, or physical obstruction, use an
offset reference point which has good access and an adequate GPS signal.
After recording the GPS coordinates at the offset location, collect and record
a bearing, the offset distance from the reference point to the BMP, and
change in ground surface elevation to the shoulder location at the Inventory
Site BMP position. The bearing value should be obtained in degrees from
north (azimuth coordinate), and the offset distance and change in ground
height need to be recorded as a physical measurement to the nearest foot.
The raw data collected at the site will be recorded as an .ssf file. A separate
.cor file should be created for each Inventory Site upon completion of the
post processing of the raw data. Both the .ssf and .cor files should be saved.
EXAMPLE 200-04: BMP Position Data:
BMP Latitude = 40.125524958
BMP Longitude = -81.789859546
BMP Elevation = 765 ft
Offset Bearing = 127º
Offset Distance = 185 ft
Change in Elevation = 7 ft
Manual for Rockfall Inventory – Revised 12/2016 19
Figure 200-08 is a generalized diagram indicating how to determine the
positions of the rockfall Inventory Site.
203.2.2 Preliminary Rating Scoring
There are two components of the preliminary rating. The first part is the
determination of the probability of a rockfall event using best professional
judgment. Rockfall debris can be generated from either the cut slope or from the
natural backslope. Second, evaluate the potential of a rock or debris impacting
the roadway. Typically the impact to the roadway is a result of rockfall debris
reaching the traffic lane. Traffic Lane is defined for use in this Manual as: The
inside edge of the right vehicular lane in a given travel direction or the white
edge line. Potentials of Very High, High, Moderate, or Low are used, with
numerical values (10, 8, 4, 1, respectively) assigned for each potential. The
numerical value for the potential of rockfall occurrence is added to the numerical
value for the potential of the rockfall to impact the travel lane to determine the
Top of Natural Backslope
Rockfall Zone
DRAINAGE
FEATURE
DRAINAGE
FEATURE
Beginning of Inventory Site BMP @ MP 2.91
BMP Position
Latitude: 40.125524958
Longitude: -81.789859546
Elev.: 765 ft
1851 Ft.
Top of Rock Cut
Rock outcropping in
Natural Backslope
Ending of
Inventory Site EMP @ MP 3.26
“BMP” “EMP”
Inventory
Site
Length
Figure 200-08. POSITIONS OF AN INVENTORY SITE
Manual for Rockfall Inventory – Revised 12/2016 20
Preliminary Rating Score. Preliminary Rating Score values may range between 2
and 20 points which is then used to determine the level of data collection, or Tier,
required for the Inventory Site.
For locations where the Preliminary Rating Scores fall between 2 and 5 points, the
Inventory Site is considered a Tier 1 site. No Detailed Rating data collection is
required for Tier 1 sites.
For Preliminary Rating Scores over 5 points, the Inventory Site is either a Tier 2,
Tier 3, or Tier 4 site requiring a Detailed Rating which will result in additional
data collection.
Table 200-01 outlines the Preliminary Rating Score breakdown for each Tier.
TABLE 200-01
Tier Type Based on Preliminary Rating Score
Preliminary Rating
Score
Tier Type
Action
2 to 5 TIER 1 SITE
No Detailed Rating Needed
8 to 11 TIER 2 SITE
Detailed Rating Needed
12 to 16 TIER 3 SITE
Detailed Rating Needed
18 to 20 TIER 4 SITE
Detailed Rating Needed
For rockfall sources located at such a distance that any rockfall debris will not
reach the travel lane, these areas do not need to be inventoried. Additionally, if
the slope contains an area where the catchment (ditch or barrier) does not contain
sufficient storage between either the back of the barrier or the white edge line to
contain the anticipated volume of rock and debris that could be dislodged in an
event, the Potential of Rockfall Reaching the Roadway needs to be shifted to Very
High. The Catchment Storage is defined as: the calculated volume based on the
width by depth of the catchment area based on the length of the catchment
relative to the area where rockfall could occur. The calculated volume should
take in account any barrier height along the edge of the catchment.
Table 200-02 outlines general criteria for each of the category utilized in the
Preliminary Rating.
Manual for Rockfall Inventory – Revised 12/2016 21
TABLE 200-02A - PRELIMINARY RATING CRITERIA (Slopes Above Roadway)
Category LOW
(1 POINT)
MODERATE
(4 POINTS)
HIGH
(8 POINTS)
VERY HIGH
(10 POINTS) P
ote
nti
al
of
Rock
fall
Occ
urr
ence
No fresh exposures
No adverse joint
patterns
No undercutting
evident
Few to some fresh
exposures
Moderate weathering
of rock strata within a
cut section
Some jointing present
Minor undercutting
is present
Occasional cleaning
required of catchment
area
Some to many fresh
exposures
Observed minor stability
issues within slope face
Weathered rock strata
within a cut section
Significant jointing, or
adverse jointing present
Significant undercutting
present
Annual cleaning required
of catchment area
Minor amounts of rockfall
debris evident within
catchment area or
evidence of recent
cleaning of the catchment
area
Many fresh exposures
Stability issues within
slope face
Highly weathered to
decomposed rock strata
within a cut section
Major adverse joint, or
intersecting jointing
present
Severe undercutting
present
Significant amounts of
debris is evident within
the catchment area,
especially along the
shoulder
Frequent cleaning
required of catchment
area
Pote
nti
al
of
Rock
fall
to I
mpact
Roadw
ay
The distance from the
slope face to the travel
lane is greater than the
anticipated roll out
distance **
The distance from the
slope face to the
travel lane is greater
than the impact zone,
but less than the
rollout zone **
The distance from the
slope face to the travel
lane is within the impact
zone **
Slope is within three feet
of roadway
OR
Rockfall or evidence of
rockfall within the travel
lane, median, or opposite
shoulder is present
OR OR
OR
OR
An appropriately sized
barrier exists between
the slope face and the
roadway
Rockfall or evidence
of rockfall is present
along the edge of the
shoulder
Rockfall or evidence of
rockfall within the
shoulder is present
Documentation of
rockfall debris reaching
the roadway including
accidents or injury
** Impact zone and rollout width based upon the Appendix B guidelines. These guidelines provide distances based upon the cut slope angle and
height within a rock cut section. Generalized tables of distances are provided in Appendix B.
Manual for Rockfall Inventory – Revised 12/2016 22
Table 200-02B - PRELIMINARY RATING CRITERIA (Slopes Below Roadway)
Category LOW
(1 POINT)
MODERATE
(4 POINTS)
HIGH
(8 POINTS)
VERY HIGH
(10 POINTS) P
ote
nti
al
of
Rock
fall
Occ
urr
ence
No fresh exposures
No adverse joint
patterns
No undercutting
evident
Few to some fresh
exposures
Moderate weathering
of rock strata within a
cut section.
Some jointing present
Minor undercutting
is present
Occasional cleaning
required of catchment
area
Some to many fresh
exposures
Observed minor stability
issues within slope face
Weathered rock strata
within a cut section
Significant jointing, or
adverse jointing present
Significant undercutting
present
Annual cleaning required
of catchment area
Minor amounts of rockfall
debris evident within
catchment area or
evidence of recent
cleaning of the catchment
area
Many fresh exposures
Stability issues within
slope face
Highly weathered to
decomposed rock strata
within a cut section
Major adverse joint, or
intersecting jointing
present
Severe undercutting
present
Significant amounts of
debris is evident within
the catchment area,
especially along the
shoulder
Frequent cleaning
required of catchment
area
Pote
nti
al
of
Rock
fall
to I
mpact
Ro
adw
ay
***
Failure within slope
will not affect
roadway
Failure within slope
will affect Right of
Way, but not
shoulder or roadway
Failure within slope will
affect shoulder, but not
roadway
Failure within slope will
affect roadway
*** Refer to Figure 200-09. POTENTIAL OF ROCKFALL TO IMPACT ROADWAY - BELOW THE ROADWAY for clarification.
Further discussions within this Manual will be limited to rockfall impacting the
roadway from sources above the roadway.
The Preliminary Rating Data is reported within the GHMS in Part A: Preliminary
Rating tab.
Manual for Rockfall Inventory – Revised 12/2016 23
Figure 200-09. POTENITAL OF ROCKFALL TO IMPACT ROADWAY – BELOW THE ROADWAY
Low Risk of Rockfall to Impact the Roadway Moderate Risk of Rockfall to Impact the Roadway
High Risk of Rockfall to Impact the Roadway Very High Risk of Rockfall to Impact the Roadway
Edge of Road
Edge of
Shoulder
Right-of-Way
Edge of Road
Edge of
Shoulder
Right-of-Way
Edge of
Road
Edge of
Shoulder
Right-of-Way
Edge of
Shoulder
Right-of-Way
Edge of
Road
Manual for Rockfall Inventory – Revised 12/2016 24
EXAMPLE 200-05: Preliminary Rating Score of an Inventory Site:
A site has a high potential of rockfall occurrence due to the presence of debris
within the ditch along the road shoulder “and” a moderate potential of rockfall
reaching the travel lane due to the distance from the rock face to the shoulder is
slightly less than the rollout zone for the slope height.
PRELIMINARY RATING
Potential of a
Rockfall
Occurrence
Potential of Rockfall Impacting the Traffic Lane
Very High
(10)
High
(8)
Moderate
(4)
Low
(1)
Very High
(10)
High
(8)
Moderate
(4)
Low
(1)
High Potential of Rockfall Occurrence = 8 points
Moderate Potential of Rockfall Reaching the Traffic Lane = 4 points
Total Preliminary Rating Score for Inventory Site = (8 + 4) = 12 points
Therefore:
Preliminary Rating – Tiered Scoring
Preliminary Rating
Scale
TIER Type
Action
2 to 5 TIER 1 SITE
No Detailed Rating Needed
8 to 11 TIER 2 SITE
Detailed Rating Needed
12 to 16 TIER 3 SITE
Detailed Rating Needed
18 to 20 TIER 4 SITE
Detailed Rating Needed
Comments: Based on the Preliminary Rating Score of
12, this site is considered a Tier 3 Site requiring a
detailed site rating including the collection of all Tier 1
and Tier 2 data.
Manual for Rockfall Inventory – Revised 12/2016 25
203 TIER 1 DATA COLLECTION
Typically, the field data collection process will be completed within ODOT right-of-way.
However, occasionally, the slope will extend onto private property, especially for natural
backslopes above the cut slope. When this occurs the Field Team should make all
possible attempts to contact the property owner to obtain permission prior to entry onto
the property.
203.1 Field Procedures
For all Inventory Sites, rated and non-rated, the Tier 1 Field Data must be completed.
This data will be recorded within Part A of the GHMS or recorded on the Rockfall
Form in Section C: TIER 1 FIELD DATA.
203.1.1 Slope Configuration
Determine the slope configuration of the cut slope. Within the GHMS this data is
reported in Part A: General Information, Basic Slope Information tab. Figure
200-10 shows examples of different slope configurations, and the following are
descriptions of each criteria:
Single-angle Slope (SA): Slope that contains the same general slope
geometry from the road to the crest of the slope
Multi-angle Slope (MA): Slope that contains at least two slope angles
from the road to the crest of the slope
Single-angle Benched Slope (SB): Slope that contains the same general
slope angles and a relatively flat bench or break between the angles from
the road to the crest of the slope
Multi-angle Benched Slope (MB): Slope that contains at least 2 slope
angles and a relatively flat bench or break between any of the slope angles
from the road to the crest of the slope
EXAMPLE 200-06: Determination of the Slope Configuration of the Inventory Site
Slope Configuration: SA MA SB MB
Where: SA is for Single-angle Slopes
MA is for Multi-angle Slopes
SB is for Benched Slope Single-angled
MB is for Benched Slope Multi-angled
Manual for Rockfall Inventory – Revised 12/2016 26
Single-angle Slope (SA)
Single-angle Benched Slope (SB)
Multi-angle Slope (MA)
Multi-angle Benched Slope (MB)
Figure 200-10. EXAMPLES OF CUT SLOPES
Manual for Rockfall Inventory – Revised 12/2016 27
203.1.2 Slope Condition
Record general comments about the rock slope within the Inventory Site.
Comments that can be recorded can be the amount of vegetation along the slope,
talus buildup, if any, weathering of the exposed rock strata, general performance
of the slope, etc. It should be noted that if the site will have a detailed rating
performed, these comments can be very brief, since the slope will be discussed in
detail during the Detailed Data Collection.
Within the GHMS in Part A: General Information, Slope Condition several field
are available for the general description of the slope.
Vegetation coverage: with percentage of slope coverage by shrub, trees,
grass, and other (if other is used then a text description is required).
Weathering condition: None, Slight, Moderate, Complete
Talus buildup: Yes, No
General slope performance: stable, potentially instable, unstable
Exposed rock: click all that apply
203.1.3 Photographic Documentation of Inventory Site
Upon completion of the Tier 1 Field Data measurements, take representative
pictures of the Inventory Site. For Tier 1 sites three pictures should be taken.
One picture should be taken at an acute angle from each end (BMP and EMP) of
the site, and one picture should be taken perpendicular to the maximum slope
height (MHT) of the Inventory Site. Within the GHMS, these pictures should be
uploaded in Part A: General Information, Pic/Doc Information tab. At the tab
heading a count of the number of items located in the directory are present.
It should be noted that additional pictures may be required for Rated Sites (Tier 2,
Tier 3, or Tier 4) data collection. The requirements of these pictures are presented
within each of these respective sections.
The proper naming convention for the labeling of the pictures is presented within
Appendix D. Appendix D presents examples, including photographs and
discussions, of Tier 1, Tier 2, Tier 3, and Tier 4 sites.
Manual for Rockfall Inventory – Revised 12/2016 28
End Pictures of Rockfall Inventory Site
(SCI-335-2.05 looking east and west, respectively)
Picture of the Maximum Height of the Rock Slope
Figure 200-11. EXAMPLES OF PRELIMINARY RATING (TIER 1) PHOTOGRAPHS
204 Detailed Rating of Inventory Sites - General
For sites where rockfall poses a potential risk to traffic (Preliminary Rating Score >5), the
site is considered a Rated Site and a detailed site rating needs to be performed. The
amount of information required for the Detailed Data Collection is based upon the
Preliminary Rating Score completed in Section 202 - Site Inventory and Preliminary
Rating. For sites that score as Tier 2 sites, collect the information required in Section 205
– Tier 2 Site Data Collection. For sites that score as either a Tier 3 or Tier 4 site,
complete the Tier 2 data collection in addition to Section 206 - Tier 3 and Tier 4 Data
Collection.
Prior to commencement of the Detailed Data Collection, the Field Team should observe
the cut slope and natural back slope and evaluate the following:
“BMP” “EMP”
“MHT”
Manual for Rockfall Inventory – Revised 12/2016 29
Limits of the Inventory Site (BMP, EMP)
Location of all potential sources of rockfall
Number of slope angles
Number of benches that comprise the rockfall section
Location of any joint/fracture set(s) (orthogonal or stress relief)
Groundwater
Surface water flow or evidence of surface water flow
General condition of the cut slope
(e.g. where undercutting may be occurring, talus buildup)
Any mine opening (sealed or non-sealed), coal seams, clay seam, or mineable
mineral seam visually present
Evidence of possible slope instability within the soil mass above the rock cut
The Field Team should then determine the most efficient and safe way to collect the field
data from the rock slope. All slope angles and benches should be numbered sequentially
from the bottom of the rock slope (ditch line) to the top of the rock slope independent of
how the data was collected.
If the Field Team feels that no safe way of collecting the field data is evident within
an Inventory Site contact OGE.
If the Field Team feels that the slope possess an immediate threat to the welfare of
the traffic on the roadway, contact the respective ODOT County/Transportation
Manager, the DGE, and OGE within 24-hours to inform them of the situation to
provide appropriate traffic control measures.
If necessary, ODOT will arrange for traffic control measures such as lane closures or
temporary barriers.
205 TIER 2 SITE DATA COLLECTION
205.1 Tier 2 Data Procedures
Upon completion of the Preliminary Rating, sites which are Rated (Tier 2, Tier 3, or
Tier 4) need to have additional information collected. The following sections outline
the detailed breakdown on the methodology for the field and office data collection.
For low height rock slopes, where both the cut slope and the natural backslope are
observable and all features are visible from the roadway, the data may be collected
from the roadway. Slope angles can be collected from the roadway with a clinometer
or profiler; otherwise, the angles should be collected as a direct measurement from
the slope. If the entire slope is not observable from the road surface, the slope face
shall be inspected and evaluated by either climbing the face or repelling from the top.
The preferred method of data collection is by direct measurements taken from the
slope face or the use of a profiler. Generally, the best way to complete direct
measurements from the slope face is by performing horizontal and vertical line
survey(s).
Manual for Rockfall Inventory – Revised 12/2016 30
205.1.1 Geometrics and Traffic
The following are the office and field procedures for completion of TIER 2 -
GEOMETRICS AND TRAFFIC DATA. For the respective data locations within the
GHMS, refer to the individual item. The majority of the geometric and traffic
data within this section can be obtained through the ODOT Transportation
Information Management System (TIMS) or other resources of the Office of
Technical Services. However, it should be noted that these data fields can be
collected through physical observation or measurements.
205.1.1 a) Traffic Survey Reports
Record the Average Daily Traffic (ADT), Average Vehicular Traffic,
including Type A commercial vehicles, (AVT), and Average Truck Traffic
(ATT) values, for the section of roadway which contains the Inventory Site.
These values can be obtained from the Traffic Survey Reports which can be
accessed from the web. The traffic reports allow the user to select a report
based upon county and year that the survey was completed. A complete
report for each selected county is then provided that includes all state
highways. Each Route is subdivided based on straight line miles within a
“Traffic Section”, which gives a general description of where the data was
recorded, section length in miles, and columns for passenger & type A
commercial vehicles, type B & C commercial vehicles, and total vehicular
traffic. The passenger & A commercial vehicle column refers to the AVT
value, B & C commercial traffic column refers to the ATT value, and the total
vehicular traffic column refers to the ADT. The most recent survey should be
utilized to determine the individual counts. This data will be recorded within
the GHMS in Part B: Traffic Information.
205.1.1 b) Actual Site Distance (ASD)
The Actual Site Distance (ASD) is the shortest distance along a roadway over
which a six inch object is continuously visible to a driver, and is a physical
measurement based on the following method:
Place a 6-inch high traffic cone or hard hat near the edge of the roadway
within the rockfall section. From that point move away from the object until
it is no longer visible from a height of 3.5 feet above the road surface
(estimated height for a driver’s field of vision). From this point measure the
distance to the object. All observations should be made in the direction of the
traffic flow.
For Inventory Sites having relatively long lengths, curves, and/or varying road
slopes, collect a series of ASD beginning at the BMP and proceeding toward
the EMP. Compare the ASD values collected and utilize the smallest
recorded value as the ASD for the Inventory Site. This data will be recorded
within the GHMS in Part B: Traffic Information.
Manual for Rockfall Inventory – Revised 12/2016 31
205.1.1 c) Decision Site Distance (DSD)
The Decision Site Distance (DSD) shall be determined by the latest version of
the “Geometric Design of Highways and Streets”. The following table
outlines the general DSD values for highways.
TABLE 200-03
Decision Sight Distance
Design Speed
(MPH)
DSD (ft)*
25 > 375
30 450
35 525
40 600
45 675
50 750
55 865
60 990
65 1050
70 1105
75 1180
* Based upon the 2005 edition, Exhibit 3-3, Avoidance Maneuver C.
Note: For Design Speeds less than 25 MPH use a DSD of 375 feet.
205.1.1 d) Percent Decision Site Distance (PDSD)
After the DSD has been determined for the Inventory Site, calculate the
percent decision site distance (PDSD). The following equation shall be
utilized to calculate the PDSD:
Eq. #1: PDSD = ASD / DSD * 100
If the calculated value is greater than 100 percent it is assumed that a driver
will have sufficient time to stop prior to striking a rock within the roadway.
The PDSD is an auto-calculated field within the GHMS in Part B: Traffic
Information. Example 200-07 presents the calculation of the PDSD.
Manual for Rockfall Inventory – Revised 12/2016 32
Example 200-07: Percent Decision Site Distance
Inventory Site with the following field data:
BMP @ MP 2.91
EMP @ MP 3.26
Inventory Site Length = 1851 ft.
Speed Limit = 55 mph
DSD = 865 ft.
ASD Readings = 850 ft., 865 ft., 799 ft., 860 ft., 579 ft.
Site ASD = 579 ft.
PDSD = ASD / DSD * 100
PDSD = (579 / 865) * 100
PDSD = 67%
205.1.2 Slope Information
The following are the field procedures for completion on the Rockfall Form in
Section E: TIER 2 - SLOPE INFORMATION. For the respective locations within the
GHMS, refer to the individual item. It should be noted that these data fields can
be collected through either physical measurements utilizing a measuring wheel or
tape, or through calculated methods. The following sections outline in detail
procedures for the collection of the required data.
205.1.2 a) Slope Height
All slope height measurements made for the Inventory Site shall be recorded
as a vertical height recorded to the nearest foot. This data will be recorded
within the GHMS in Part C: Slope Information, Geometric Information tab.
Separate height measurements need to be recorded for the rock cut, any soil
cut, and any backslope. Additionally, in extreme cases where large ranges of
slope heights are present, especially along the Ohio River, the minimum and
maximum ranges of the slope heights should be recorded within comments
fields. Three methods of measurement can be performed to determine the
slope height.
The preferred method to determine the slope height is through the use of a
rangefinder. Using the rangefinder, the total height can be calculated through
trigonometric calculation based on the angle and distance from a fixed
reference point. Automated profilers, such as laser face profilers, will
internally calculate the distances and heights for the users. If heavy
vegetation is present across the slope obscuring the slope geometry then
this method may not be applicable.
Manual for Rockfall Inventory – Revised 12/2016 33
An alternative to the profiler method is to calculate the slope height involving
trigonometric calculations using field measurements collected with a pocket
transit compass, clinometer, or transit, from the shoulder, median or roadway
surface and measured distances. This method requires the collection of
angles and and distances needed for the calculations outlined in Figure
200-12. A minimum of three measurements should be collected of each angle
and the average angle recorded to the nearest whole degree. If heavy
vegetation is present across the slope obscuring the slope geometry, then
this method should not be utilized.
Another method is to perform physical measurement of the slope. For
relatively short slope heights, a survey rod or measuring tape can be used for
the height measurement. Generally, a survey rod can be used for a slope
height less than 25 feet in height. If a measuring tape is utilized make sure
that the tape is taunt and vertical, possibly utilizing a face-pole. Additionally,
the slope height can be measured utilizing a hand or abney level and shooting
spot heights up the slope. This method may be the most applicable for
slopes that are heavily vegetated.
Pavement fromHeight HIsin
sinsinxHeight Vertical
Comments: HI =height of instrument (ft)
x = distance between the two points used for measurement of angles (ft)
and = angles measured from horizontal (degrees)
EP = edge of pavement
x
HI
Tot
al s
lope
hei
ght
EP EP
Total slope height= (x) sin * sin + HI
sin (-)
Figure 200-12. RELATIONSHIP BETWEEN SLOPE
HEIGHT AND GEOMETRICAL PARAMETERS
(adapted from Pierson et al., 1991)
Eq. #2
Manual for Rockfall Inventory – Revised 12/2016 34
EXAMPLE 200-08: Calculating the Slope Height
Recorded Angle = 42º, 43.5º, 43.1º
Avg. Angle = 42.9º
Recorded Angle = 24.5º, 25º, 24.8º
Avg. Angle = 24.8º
X = 24 ft. HI = 5.3 ft
3.58.249.42sin
8.24sin9.42sin)24(Height Slope
+ 0.0
205.1.2 b) Slope Elevations
All slope height measurements collected in Section 205.1.2.a should be
converted to slope elevations based upon a Section Base Elevation. This data
will be recorded within the GHMS in Part C: Slope Information, Geometric
Information tab. The Section Base Elevation is the approximated ground
surface elevation at the edge of pavement where the height measurements
were collected. The Section Base Elevation is estimated based on the change
in ground surface height relative to the Inventory Site BMP Elevation
collected as part of the BMP position. All elevations should be recorded to
the nearest foot.
205.1.2 c) Slope Undercutting/Raveling
For each Inventory Site, estimate the percentage of the slope experiencing
undercutting and raveling. This data will be recorded within the GHMS in
Part C: Slope Information, Slope Information tab. For sites where
undercutting is occurring, any portion of the slope above the lowest location
of undercutting should be considered as experiencing undercutting.
Additionally, record the number of locations where undercutting is occurring
for both the cut slope and natural backslope. Record the maximum, and
average depth of undercutting being experienced in both the cut slope and the
backslope.
Raveling occurs when bedrock comprising the slope is completely broken
either by natural jointing and weathering or due to blast damage generated
during construction.
205.1.2 d) Slope Jointing
Record the joint pattern(s) expressed within the Inventory Site relative to the
orientation of the roadway. It is anticipated that generally this will only be
accomplished for cut slopes. Natural slopes usually will not present sufficient
Slope Height = 27 feet
Manual for Rockfall Inventory – Revised 12/2016 35
bedrock exposures, except where massive competent beds are present, to
establish joint information. For sites where multiple joint patterns are
expressed, record up to 3 principal or secondary joint sets.
This data will be recorded within the GHMS in Part C: Geological
Information, Joint Information tab.
205.1.2 e) Rockfall Source Information
Determine source zone(s), or potential source zone(s), of rockfall debris along
the rock slope. Typical source zones include, but not limited to:
1. more durable rock strata underlain by a less durable rock strata
2. intersection joint sets that are susceptible to freeze-thaw and ice
wedging
3. weathered zones that are highly fractured
4. cut slope faces that have extensive blast damage from construction
5. any combinations of source zones 1 through 4
It should be noted that rockfall source zones can and are located in both
the cut slope and or natural backslope of a slope. In some areas, the
natural backslope will be a greater source of rockfall debris than the cut slope.
Estimate the percentage of the slope that contains a rockfall source zone. The
percentage of the slope is calculated by summing all the potential rockfall
source zone heights located in the cut slope and the natural backslope and
dividing by the total slope height (cut slope height added to the natural
backslope height).
Record the estimated potential rockfall that may occur from either the cut
slope or the natural backslope. Estimate the maximum and average block size
that may be produced as well as the anticipated volume which may be
produced during a single rockfall event to a tenth cubic foot (0.1 ft3).
The block size can be determined by evaluating the discontinuities (joints,
bedding, etc.) within the slope. Three components to the block size which
need to be evaluated, with measurements recorded to the nearest tenth of a
foot (0.1 ft), are; height (x), width (y), and thickness (z):
Height (x): generally the distance from top of the rock strata to the
bottom of the rock strata; or the persistence of the joint (total length
that a joint is present within intact bedrock possibly crossing bedding
surfaces) with the slope face
Width (y): distance from one joint to another joint along the face
Thickness (z): depth at which either the joints intersect or the
thickness of the undercut or the distance to a joint set depth which
runs parallel to the slope face
Manual for Rockfall Inventory – Revised 12/2016 36
Figure 200-13 demonstrates the dimensions of a block before and after falling.
Estimate the anticipated total volume of debris that could be produced during
a single rockfall event. At sites where thick competent beds are broken by
regular repeating joint sets, as exhibited in the previous figure, the volume
will be equal close to the maximum block size. However, in thin to thick
bedded competent rock which is exhibiting raveling, the volume generated
during a single event may be much greater than the maximum block size.
When this is the case, debris volume can be estimated by evaluating the
discontinuities (joints, bedding, etc.) within the slope and comparing them to
how they are interlocked. Three components of the volume which need to be
evaluated, with measurements recorded to the nearest tenth of a foot (0.1 ft),
are; height (x), width (y), and thickness (z):
Height (x): generally the distance along a persistent joint within the
slope face which broken rock is located along which could dislodge
during a rockfall event
Width (y): lateral distance along the slope face along which uniformly
broken rock is located
Thickness (z): depth into the slope to which the persistent joint set
which the height is being measured along
Figure 200-14 demonstrates the dimensions of a block with the potential of
falling.
Manual for Rockfall Inventory – Revised 12/2016 37
Note: The block height is dictated by both the strata thickness
and joint persistence which are the same dimensions.
Figure 200-13. BLOCK SIZE DETERMINATION
X = 7.2 ft
Y = 14.6 ft
Z = 4.9 ft Size: 7.2*4.9*14.6 = 515.1 ft3
Figure 200-13b. Block Size After Falling
Figure 200-13a. Block Size Before Falling
X = 7.2 ft
Y = 14.6 ft
Z = 4.9 ft Size: 7.2*4.9*14.6 = 515.1 ft3
Manual for Rockfall Inventory – Revised 12/2016 38
Figure 200-14. ROCKFALL VOLUME DETERMINATION
Comment: Green Outline
represents the area of
potential rockfall debris
which could be generated
during an event based on
open jointing and
raveling. The arrows
indicate the dimensions.
X = 15.3 ft
Y = 13.5 ft
Z = 3.8 ft
Volume: 15.3*3.8*13.5
= 29.1 yd3
205.1.2 f) Hydrologic Conditions
Evaluate the cut slope and the natural backslope for the presence of
hydrologic conditions, both groundwater and surface water. The estimate of
the hydrologic conditions should be based on the entire surface area of either
the cut slope or the natural backslope. This data will be recorded within the
GHMS in Part C: Hydrogeologic Information, Cut Slope Information, Natural
Backslope Information, and Precipitation tabs.
Groundwater can be either flowing (spring) or non-flow (seepage) that is
discharging from the bedrock at the slope face, either the cut slope or natural
backslope. Indicate if groundwater is present in the cut slope and/or the
natural backslope. Record the percentage of the slope, cut slope and
backslope respectively, to the nearest whole percentage. If the site inventory
is conducted during winter months, the presence of groundwater may be
masked due to ice buildup on the slope face from an isolated area of
groundwater further up the slope. In this case, if the source of groundwater
cannot be isolated, then the ‘yes’ for groundwater needs to be recorded, but
the slope will need to be re-evaluated after the ice has melted and the natural
conditions can be sufficiently evaluated.
Manual for Rockfall Inventory – Revised 12/2016 39
Additionally, record if surface water is present in the cut slope and/or the
natural backslope. If erosion channels are present during dry seasons record
‘yes’ for surface water. Record the percentage, to the nearest whole percent,
of the cut slope and/or the natural backslope.
Comment:
Note that heavy
seepage appears to
be originating at
the cut slope/
natural backslope
interface which is
then creating an
ice cover over the
slope masking
potential areas of
additional seepage.
Figure 200-15. HYDROLOGIC CONDITIONS
205.1.2 g) Corrective Actions
Typical types of corrective actions for rock slopes include installation of
concrete D-50 barrier, barrier fencing, construction of protective berm,
construction of catchment area, scaling the slope, and re-grading the slope.
The presence of guardrail along the road is not considered a type of corrective
actions or method of catchment.
Indicate if corrective actions were performed in the past. Define the type and
location of the corrective actions. If known, record the date of the corrective
actions, or ‘NK’ if not known. If the slope was modified, record the
percentage of the slope re-graded. If the catchment was modified, record the
retention type, if applicable. This data will be recorded within the GHMS in
Part C: Slope Information, Corrective Actions tab. The data is presented on
the Rockfall Form in Section E: TIER 2 – SLOPE INFORMATION.
Figure 200-16 presents typical types of catchment corrective actions found
along Ohio roadways.
Manual for Rockfall Inventory – Revised 12/2016 40
Figure 200-16. TYPICAL TYPES OF CATCHMENT CORRECTIVE ACTIONS
Type of
Corrective
Action
Barrier Example Example Photograph
Catchment
Area:
Sufficient
area for
adequate
rockfall
debris
containment
None
PCB:
(Portable
Concrete
Barrier)
Catchment Area
Rockfall Debris
Limited Catchment Area
D50
D32
Manual for Rockfall Inventory – Revised 12/2016 41
Figure 200-16. TYPICAL TYPES OF CATCHMENT CORRECTIVE ACTIONS (cont.)
CIP:
(Cast in
Place
Concrete
Barrier)
ODOT
Rockfall
Fence:
Earthen
Berm.
Limited Catchment
Area
Limited Catchment
Area
Manual for Rockfall Inventory – Revised 12/2016 42
205.1.2 h) Catchment
Catchment Area is defined for use in this Manual as: The area between the
face of the rock slope and the edge of the travel lane capable of reducing the
velocity of a rock particle traveling in a downslope trajectory from a source
location along the rock slope. This definition differs from the design
catchment area as a distinction is made between design and actual rockfall
conditions.
It should be noted that the area between the rock slope face and the roadway,
which has a positive slope toward the roadway and/or is higher than the
roadway, should not be considered catchment areas. If a stream is located
between the slope and roadway, it can be counted as part of the catchment
area.
The catchment area shall be evaluated at its critical section. The critical
section is the smallest ratio based upon the width of the catchment area versus
the rock slope height, or largest volume that could be produced along the
length of the Inventory Site.
This data will be recorded within the GHMS in Part C: Slope Information,
Catchment Area tab. The data is presented on the Rockfall Form in Section E:
TIER 2 – SLOPE INFORMATION.
205.1.2 aa) Catchment Area Shape
The catchment area shape is based upon the simplified geometry of the
catchment area. The catchment area shape should not be influenced based
solely on the hydraulic control ditch, unless this ditch has sufficient size or
geometry to act as a catchment area for rockfall debris.
Basic catchment area shapes are flat, elliptical, circular, trapezoidal, or
triangular. The standard “Ritchie Ditch” utilizes a trapezoidal catchment
shape. The current FHWA/Oregon “Catchment Ditch” should be
considered a triangular catchment area shape. When the majority of the
catchment area is flatter than 8H:1V (7º from horizontal), the catchment area
should be considered flat.
Figure 200-17 presents simplified schematics of catchment area shapes and
example photos.
Manual for Rockfall Inventory – Revised 12/2016 43
General Schematic Shape/ Abbrev.
Picture Example
Flat
F
Triangle
V
Trapezoidal
T
Elliptical
E
Circular
C
Figure 200-17. Catchment Area Shapes
Manual for Rockfall Inventory – Revised 12/2016 44
205.1.2 bb) Catchment Area Depth
The catchment area depth is a physical measurement from the deepest point
of the catchment area referenced to the road elevation. The ditch depth of
the hydraulic control ditch (control of water runoff only) is not considered
part of the catchment system unless the ditch is wide enough to act in the
capacity of rockfall control.
To collect the depth measurement, extend a plane from the road surface,
such as a measuring tape or steel tape measure pulled taut, and determine
the distance from the base of the catchment area to the extended plane using
a folding scale or another tape measure. The depth should be an average of
five recorded depths along the length of the ditch, unless the critical section
is shallower than the remaining catchment area. The measurements shall be
recorded to the nearest 0.1-foot. For catchment areas where a barrier wall or
fence is located along the roadway shoulder, extend the plane from the top
of the footing as the reference plane and add the height of the barrier to the
depth.
Figure 200-18 shows a series of examples of the catchment area depth.
Catchment Ditch Depth
Hydraulic Ditch Depth
(NOT COUNTED since insufficient
to retain rockfall debris)
Road Elevation
Figure 200-18a. CATCHMENT AREA
Catchment Width
Manual for Rockfall Inventory – Revised 12/2016 45
Figure 200-18b.
Hydraulic Control Ditch NOT as Catchment
Note: The flow line of the hydraulic control ditch
should not be measured as catchment depth due to
insufficient width for rockfall catchment.
Figure 200-18c. Hydraulic Control Ditch as Catchment
Note: This hydraulic control ditch can be
measured as catchment depth due to sufficient
width which will result in rockfall catchment.
205.1.2 cc) Catchment Area Width
The catchment area width is a physical measurement from the edge of the
travel lane to the face of the rock slope. The distance should be measured to
the rock slope face, and not the outer edge of any talus buildup, since talus
buildup can be removed as part of the ditch maintenance.
To collect the width measurement, extend a plane from the road surface to
the rock slope face, as outline in Section 205.1.2.bb Catchment Area Depth.
The measurement shall be recorded to the nearest 1-foot. For a catchment
area with a uniform width across the slope, take an average of five
measurements. If the catchment area has an area which is wider than the
remaining catchment area, such as for a drainage basin, this area should be
excluded from the measurements. However, if a section of the catchment
area is narrower than the remaining catchment area this should be
considered a critical section and the catchment width should be based on the
average width of this section.
Figure 200-18 shows an example of the catchment area width.
205.1.2 dd) Foreslope Angle
The foreslope angle is the angle measurement of the slope between the
shoulder or edge of the travel lane and the bottom of the catchment area.
This measurement shall be made from a horizontal plane extended from the
road elevation and recorded to the nearest whole degree. If multiple angles
are present within the foreslope then an average angle of the foreslope needs
Catchment Depth
Hydraulic Control Ditch
(Not Counted)
Catchment Depth
Catchment Width
Catchment Width
Manual for Rockfall Inventory – Revised 12/2016 46
to be recorded. A minimum of five measurements should be recorded
across the length of the Inventory Site and averaged, excluding areas which
have been drastically modified and are not representative of the catchment
area.
To collect the foreslope angle two options are available. The preferred
method is by physical measurement by placing a two (2) or four (4) foot
level along the foreslope and then record the angle measurement utilizing a
clinometer. This method is not feasible at foreslopes where multiple angles
are present. However, the angle can be estimated utilizing a pocket transit
and visually estimating the average angle.
An alternative method is by determining the angle trigonometrically by
extending a plane from the road surface to the point of the catchment area
depth (l) measurement and record the value to the nearest foot, and the
catchment area depth (D) to the nearest foot. Use the following equation
(equation #3) to determine the foreslope angle:
Eq. #3: tan A = D / l
205.1.2 ee) Slope Face Angle
The slope face angle is the angle of the rock slope face where the slope
intersects the catchment area. This angle may not be the angle of the base of
the ditch due to modification through past maintenance activities and should
be reflective of the cut slope angle.
The foreslope angle is the angle measurement of the slope between the
shoulder or edge of the travel lane and the bottom of the catchment area.
This measurement shall be made from a horizontal plane extended from the
road elevation and recorded to the nearest whole degree. If multiple angles
are present within the foreslope, an average angle of the foreslope needs to
be recorded.
To collect the angle measurement, two options are available. The preferred
method is a physical measurement by placing a two (2) or four (4) foot level
along the rock slope face and recording the angle utilizing a clinometer.
This method is not feasible at foreslopes where large amount of talus
D
l
A
Manual for Rockfall Inventory – Revised 12/2016 47
buildup is present. However, the angle can be estimated utilizing a pocket
transit and visually estimating the average angle.
An alternative method is by determining the angle trigonometrically by
extending a plane along the same elevation as the road surface and measure
the distance from the point of the catchment area depth to the rock slope
face (f), record to the nearest foot, and utilize the catchment area depth (D),
as determined in Section 205.1.2.bb Catchment Area Depth, to the nearest
foot. Use the following equation to determine the slope face angle:
Eq. #4: tan = D / f
This angle shall be recorded to the nearest whole degree less than 90º.
Figure 200-19. Catchment Area Configuration
D
f
D
f
A
l
D
l f
A
Manual for Rockfall Inventory – Revised 12/2016 48
205.1.2 ff) Remedial Effectiveness
For areas were catchment areas are present or where past corrective
measures have been implemented, estimate the effectiveness of the work
expressed to the nearest 10 percent.
The work effectiveness should be based on existing catchment geometry
compared to the current guidelines outlined in Appendix B in addition to
past history or evidence of rockfall debris relative to the slope and roadway.
Inventory Sites where barrier corrective actions have been constructed does
not mean that the effectiveness is 100 percent. Barrier effectiveness should
be based on the barrier type relative to the debris type, size, volume, and
ditch geometry between the barrier and the cut slope. For example a very
large block size (>5 ft in diameter) will not be retained by a D36 or D50 cast
in place wall if the catchment width is very narrow; or if the block is
stopped by the wall the amount of debris as a result of the damage to the
wall may pose a risk to the travelling public.
Also, for Inventory Sites which may produce a large volume of debris with a
narrow catchment area and a barrier along the shoulder, check the catchment
capacity versus the potential rockfall volume. The catchment capacity is the
calculated volume based on the barrier height and catchment width relative
to the volume at the location where the high potential from which rockfall
debris could be generated. If the debris volume calculation is greater than
the catchment capacity, the remedial effectiveness should be less than 100
percent relative to the volume over the capacity.
205.1.2 i) Additional Information
Record if mine openings are evident within the cut slope or the natural
backslope as either yes or no. If yes, record within the comments section the
number of openings, including condition of the opening(s) (sealed, open,
collapsed, discharging drainage) and approximate location relative to the
BMP. Also, note if acid mine drainage is present within the ditchline. Figure
200-20 shows examples of mine openings within slopes.
Record if any evidence of slope instability is noted in either the soil cut
section or backslope as a yes or no under slope instability. If yes note the
observations within the comments field and approximate location relative to
the BMP. This data will be recorded within the GHMS in Part C: Slope
Information, Corrective Actions tab. The data is presented on the Rockfall
Form in Section E: TIER 2 – SLOPE INFORMATION.
Manual for Rockfall Inventory – Revised 12/2016 49
Abandoned mine opening
not sealed but collapsed
Abandoned mine opening
Entrance sealed with bricks
Mine subsidence within a cut slope Acid mine drainage within ditch
Figure 200-20. EXAMPLE OF MINE OPENINGS
206 TIER 3 & TIER 4 SITE DATA COLLECTION
Upon completion of the Tier 2 Data Collection any site which scored as a Tier 3 or Tier 4
site should have the final data sets completed. There is no difference in data collection
between a Tier 3 and Tier 4 site. However, if a Tier 4 site is identified, OGE and the
respective DGE or designated District Rockfall Inventory Coordinator needs to be
notified within 24 hours so that appropriate actions can be taken.
Generally, the best way to complete the data collection is through direct measurements
from the slope face by performing horizontal and vertical line survey(s). If the entire
slope is not obtainable from the road surface, the slope face shall be inspected, evaluated
and sampled by either climbing the face or repelling from the top.
206.1 Slope Geological Conditions
The following information needs to be complied in Section F: Tier 3 & Tier 4 - Slope
Geological Conditions. As previously noted, the slope information should be
recorded relative from the ditch to the crest of the cut.
Manual for Rockfall Inventory – Revised 12/2016 50
206.1.1 Number of Cut Slope Benches
Record the number of benches located on the cut slope by physically counting the
number of benches from the base of the slope to the top of the slope. This data
will be recorded within the GHMS in Part C: Slope Information, Slope
Information tab.
206.1.2 Number of Cut Slope Angles
Record the number of slope angles located on the cut slope by physically counting
the number of significantly different slope angles from the base of the slope to the
top of the slope. The differentiation of slope angles should be relative to gross
changes in the slope angles since cut slope angles can have variations across the
length of a cut due to construction techniques, minor physical property changes
within a rock strata, and differences on weathering over time. Typically, during a
cut slope design and construction, “slope angles” will change dramatically (i.e.
0.25:1 increment or greater). Minor incremental changes in the slope angles are
typically not discernable by the naked eye and should be considered one slope
angle. This data will be recorded within the GHMS in Part C: Slope Information,
Slope Information tab.
206.1.3 Cut Slope Angles
Collect the cut slope angle(s) along the cut slope face by recording the slope angle
from a horizontal plane using either a pocket transit, structural compass, or
clinometer. To record the slope angle use a non-ferric (aluminum or plastic)
clipboard or a 2- to 4-foot level placed against the cut slope face to estimate the
slope angle. If blast holes (half casts) are still evident within the cut slope face
record the slope angle along the central axis of the blast hole. An alternative
method is to visually line up the slope angle with the edge of a pocket transit,
structural compass, or clinometer and then determine the angle using the
clinometers needle. Figure 200-21 presents diagrams on how to determine these
angles. Collect a minimum of three readings per slope angle and use the average
value rounded to a whole degree. This data will be recorded within the GHMS in
Part C: Geological Information, Slope Information tab.
Manual for Rockfall Inventory – Revised 12/2016 51
Use of a pocket transit or
structural compass for direct
measurement for the slope
surface.
(From Brunton GeoTransit
Operators Manual, 2001)
Use of a pocket transit or
structural compass for a visual
measurement of the slope angle.
(From Brunton GeoTransit
Operators Manual, 2001)
Figure 200-21. SLOPE ANGLE DETERMINATION
For slopes were talus buildup is present at the base of the slope angle, take either
direct measurement from the slope above the talus, or estimate through sighting
assuming the talus material is not present.
Figures 200-22 and 200-23 show the collection of a slope angle utilizing a pocket
transit for both a slope face and along a blast hole, respectively.
Figure 200-22. Recording slope
angle along a blast
hole using a pocket
transit
Manual for Rockfall Inventory – Revised 12/2016 52
Figure 200-23. Recording slope angle
using a pocket transit
and non-ferric
clipboard
206.1.4 Average Cut Slope Angle
After all the slope angles have been recorded, the average slope angle shall be
calculated for the cut slope. The average slope angle shall be a weighted average
of all the cut slope angles recorded to the nearest whole degree. Table 200-04
provides typical design cut slope angles. Figure 200-24 and associated example
outlines the calculation of the weighted average of the slope angle.
TABLE 200-04
TYPICAL SLOPE ANGLES FOR ROCK CUTS
Slope Angle Cut Slope Ratio
76º 0.25H:1.0V
63º 0.50H:1.0V
53º 0.75H:1.0V
45º 1.0H:1.0V
34º 1.5H:1.0V
26º 2.0H:1.0V
22º 2.5H:1.0V
18º 3.0H:1.0V
Manual for Rockfall Inventory – Revised 12/2016 53
206.1.5 Cut Slope Angles Elevations
Record the elevation(s) at which the cut slope angle changes using a measuring
tape, survey rod, hand level, abney level, or methods outlined in Section 205.1.2.a
Slope Height. Record the elevation to the nearest foot. This data will be recorded
within the GHMS in Part C: Geological, Single-angle tab.
206.1.6 Bench Elevations
Record the height (elevation) at which the benches are located along the cut slope
using a measuring tape, survey rod, hand level, abney level, or methods outlined
in Section 205.1.2.a Slope Height. Record the elevation to the nearest foot.
If the bench is not a true horizontal bench, but a sloping bench (such as a
stratigraphic bench), record the percent (%) slope for the bench.
This data will be recorded within the GHMS in Part C: Geological tab.
63º
Catchment Area
Figure 200-24. AVERAGE SLOPE CALCULATION
20 ft
15 ft
10 ft
30 ft
45º
26º
76º
Avg. Slope Angle = {(0.27*45º) + (0.20*63º) + (0.13*26º) + (0.40*76º)}
= 58.5º or 59º
75 ft
Roadway
Weighted Heights
A1 Height =
20’/75’ = 0.27
A2 Height =
15’/75’ = 0.20
A3 Height =
10’/75’ = 0.13
A4 Height =
30’/75’ = 0.40
Slope Angles
Angle A1 = 45º
Angle A2 = 63º
Angle A3 = 26º
Angle A4 = 76º
Bench Width
B1 = 10 ft.
A1
A2
A3
A4
B1
Eq. 5 Avg. Slope Angle = (An* Hn)
EXAMPLE 200-09: Weighted average calculation for multi-angled cut slopes.
Manual for Rockfall Inventory – Revised 12/2016 54
206.1.7 Bench Width
The bench width measurement is a physical measurement made with either a
measuring tape or distance wheel. If talus material covers part, or all, of the
bench, use an estimated width for the original bench width. Record this width to
the nearest foot.
This data will be recorded within the GHMS in Part C: Geological, Bedding
information tab.
EXAMPLE 200-10: Calculation of Bench width and Elevation (From Figure 200-24)
Road Elevation (Section Base Elev.) = 879 Ft
Bench B1 Height (Elevation) = 35 Ft (914 Ft)
Bench B1 Width (Ft) = 10 Ft
206.1.8 Competent Bedding
Record the number of competent beds present within the cut slope including the
bed lithology, bedding, bedding JRC (see Appendix F for listing), and aggregate
thickness of all competent beds. Record this measurement to the nearest foot.
This data will be recorded within the GHMS in Part C: Geological Information,
Bedding Information tab.
206.1.9 Incompetent Bedding
Record the number of incompetent beds present within the cut slope including the
bed lithology, bedding, bedding JRC (see Appendix F for listing), and aggregate
thickness of all incompetent beds. Record this measurement to the nearest foot.
This data will be recorded within the GHMS in Part C: Geological Information,
Bedding Information tab.
206.1.10 Undercutting Information
Record the number of competent beds that have undercutting within the cut slope
including the maximum and average depth of undercutting and average thickness
of undercutting. Additionally, note any undercutting that may be occurring within
the natural backslope including maximum and average depth of undercutting and
thickness of undercutting. Record the measurements to the nearest tenth foot over
an average of five measurements. This data will be recorded within the GHMS in
Part C: Geological Information, Bedding Information tab.
Manual for Rockfall Inventory – Revised 12/2016 55
Figure 200-25. EXAMPLE OF CUT SLOPE DESCRIPTION
EXAMPLE 200-11: Slope Geological and Natural Conditions (from Figure 200-25)
Comments: In this example the coal/carbonaceous shale layer (4) and the
claystone layer (2) would be considered incompetent beds due to the overlying
more durable siltstone layers (3 & 5). The shale (6) located above the siltstone
(5), toward the top of the cut slope, would be considered a durable layer since
the overlying clayey shale (7) is not a more resistant layer.
Basal Talus Accumulation: 15 ft
Number of Competent Bed(s): 4
Aggregate Thickness of Competent Bed(s): 51 ft
Competent Bedding: thin to thick
Number of Incompetent Bed(s): 2
Aggregate Thickness of Incompetent Bed(s): 14 ft
Incompetent Bedding: thin to thick
Number of Competent Bed(s) with Undercutting: 2
Maximum Undercut Thickness: 3.5 ft
Average Undercut: 2.0 ft
Average Depth of Undercut: 4.0 ft
Ratio: Number of Competent to Incompetent Beds: 2.0
Ratio: Aggregate Thickness of Competent to Incompetent Beds: 3.6
(Note that the Ratios will be an auto-calculated field within the database)
Undercutting of incompetent bed beneath competent siltstone bed
6: Shale, thin bedded
7: Clayey shale, thin bedded
with partial vegetation
5: Siltstone, thick bedded
4: Coal/Carbonaceous Shale
2: Claystone, thick
bedded
3: Siltstone, thick bedded
1: Talus
80 f
t.
4ft
3ft
15ft
31ft
15ft
2ft
Block from Face
10ft
Manual for Rockfall Inventory – Revised 12/2016 56
206.1.11 Joint Information
Record the information concerning the jointing of the cut slope face. Natural
backslopes may present adequate bedrock exposures within massive, competent
bedrock types in which joint information may be determined.
Indicate the type of joint(s) present within the slopes as either Orthogonal Joints
(ORTH) or Valley Stress Relief Joints (VSRJ) and the number of joint sets.
Appendix F outlines the general difference between these two types of joints.
Record the orientation of the joint set(s) utilizing a Brunton or lensatic compass,
recorded to a whole degree. Measure and record the average width of each joint
and the spacing between the joints within a joint set(s) for each of the competent
and incompetent beds using either a tape measure, folding scale, or a distance
wheel. These measurements should be recorded to the nearest tenth foot.
Visually estimate the average percentage of the joints within each joint set(s) that
contains infilling for each of the competent and incompetent beds. Record the
estimate as a whole percent. Additionally, note the type of infilling present within
the joint set (examples clay, iron precipitation, mineralization, etc.).
This data will be recorded within the GHMS in Part C: Geological Information,
Joint Information tab.
Figures 200-26 and 200-27 present examples of joints and joint infilling for strata
within a cut slope.
EXAMPLE 200-12: Collection of Joint Information
Joint Orientation: ORTH / VSRJ
Orientation of Joint Set(s) = 182º; 175º
Avg Spacing of Joint (competent) = 15 ft.
Joint Width (competent) = 0.7 ft.
% of infilling of Joint = 55 %
Type of Infilling = Clay
Avg Spacing of Joint (incompetent) = 15 ft.
Joint Width (incompetent) = 0.5 ft.
% of infilling of Joint = 100 %
Type of Infilling = Clay
Manual for Rockfall Inventory – Revised 12/2016 57
Figure 200-27. JOINT INFILLING
Joint Spacing
Figure 200-26. ORTHOGONAL JOINT SET/SPACING
Joint Width
100% Clay
Infilling
Joint Width
50% Clay
Infilling
No Clay
Infilling
Manual for Rockfall Inventory – Revised 12/2016 58
206.1.12 Potential Rockfall Estimation
Estimate the anticipated shape of the blocks that may occur during a rockfall
event relative to the shapes modeled with the Colorado Rockfall Simulation
Program (CRSP). Three basic shapes utilized by CRSP are:
Spherical: a rock with uniform size and shape in all dimensions
Cylindrical: a rock that has one axis longer (length) than the other two
axes which are roughly equal in size
Discoidal: a rock that has a uniform diameter and length, but the thickness
is significantly less than the length or diameter (slab or flagstone)
A slab type rock typically seen within the interbedded strata typically found
within Ohio would fall into the discoidal category. All the parameters should be
recorded to the nearest 0.5-foot. Table 200-05 outlines each of the parameters
required for each particle shape. Figure 200-28 shows examples of each:
TABLE 200-05: ROCKFALL PARAMETERS
Shape Diameter Length Thickness
Spherical
Cylindrical
Discoidal
: Indicates the parameter measurement required for rock shape.
Figure 200-28. EXAMPLE ROCKFALL SHAPES
Spherical
Cylindrical
Discoidal
Manual for Rockfall Inventory – Revised 12/2016 59
Estimate the maximum extent that a single rockfall event will impact the
roadway. Record the estimated limits of impact as a linear distance relative to the
roadway, both parallel and perpendicular to the slope. The impact length should
be measured as a lateral distance parallel to the slope from which debris may be
produced. The length may be greater than the estimated width (y) estimated for
Section 205.1.2 e) Rockfall Source Information. The impact width should be
estimated as the lateral distance parallel from the base of the cut slope face to
which the rockfall debris will extend. These estimates should be recorded to the
nearest foot.
This data will be recorded within the GHMS in Part C: Geological Information,
Additional Information tab.
206.1.13 Talus Accumulation
For estimation of the talus accumulation, both basal and along benches, look at
the location where the maximum accumulation is present and evaluate this
location as a ‘worst case’ situation. Evaluate the ‘worst case’ location as a section
to determine the percentage of talus build up relative to the catchment or bench
width. Record this value to the nearest whole percentage. Figure 200-29
illustrates the calculation of the talus buildup along a bench.
Each bench should be calculated separately with a percentage value recorded for
each bench location.
This data will be recorded within the GHMS in Part C: Geological Information,
Bedding Information tab.
Manual for Rockfall Inventory – Revised 12/2016 60
206.1.14 Vegetation
Estimate the percentage of both the cut slope and natural backslope that contains
vegetation based on aerial extent of the slope. Record the estimate to a whole
percent. Additionally, within the comments section, record the type and size of
the vegetation. Typical category types () and sizes () are:
Grasses
Shrubs/scrub
Trees
0” - 6”
6” - 12”
> 12”
This data will be recorded within the GHMS in Part A: General Information.
206.1.15 Additional Information
Upon completion of the Tier 3 and Tier 4 Slope Geological Conditions, record
within the comments section if any anomalies are noted within the slopes (e.g.
faults, coal riders, etc.). This data will be recorded within the GHMS in Part C:
Geological Information, Additional Information tab.
Figure 200-29. ESTIMATING TALUS ACCUMULATION ON A BENCH
0 2.5ft 5.0ft 7.5ft 10.0ft
Bench Width = 10 ft.
Talus Accumulation
Along Bench Width
25%
50%
75%
100%
Manual for Rockfall Inventory – Revised 12/2016 61
206.2 Slope Hydrological Conditions
The following are the procedures for completion of the GHMS Part C:
Hydrogeological Information which is also found in the Rockfall Form in Section G:
TIER 3 & TIER 4 FIELD –SLOPE HYDROLOGICAL CONDITIONS. This basic information
pertains to the groundwater and surface water conditions of the cut slope and/or
natural backslope within an Inventory Site. This data is collected through visual
evaluation and by performing physical measurements of the slope.
Evaluate the cut slope and the natural backslope for the presence of groundwater.
Groundwater can be noted as either flowing (spring) or non-flowing (seepage) that is
discharging from the bedrock or soil cover along the slope face. Record if
groundwater is present in the cut slope and/or the natural backslope. Hydrological
conditions should be noted on the site plan and details, including the location based
on the discharge point(s). All measurements should be noted from the BMP location.
Distances should be determined based along the edge of pavement until perpendicular
to the referenced location. Elevations should be determined as outlined in Section
205.1.2.a Slope Height and Section 205.1.2.b Slope Elevation. The following types
of hydrological conditions should be noted:
Spring: An isolated point within the slope where groundwater is discharging
Spring Line: A series of springs which are located along the same elevation
Seep: An isolated point of moisture within the slope which is not comprised
of flowing groundwater
Seep Line: A series of seeps which are located along the same elevation
Seep Zone: An area within the slope where seepage is noted from multiple
sources in close proximity to each other at varying elevations
Surface Flow: An erosional channel developed form the channelization of
surface water runoff
Additional measurements are required for spring and seep lines and seep zones. For
spring or seep lines, the length that the line extends along the slope face needs to be
recorded. For seep zones, the distance from the BMP should be referenced to the first
noted edge of the zone with the length being referenced to the furthest edge of the
zone. The elevation of a seep zone will be referenced to the base of the seep zone.
The hydrologic conditions for the Inventory Site should be recorded across the
Inventory Site beginning at the BMP at the base of the slope proceeding upslope then
across the site to the EMP. All springs and seepage should be assigned a site specific
ID referencing and numerically numbered in the order that they are encountered with
a prefix designation outlined in Table 200-6.
Manual for Rockfall Inventory – Revised 12/2016 62
TABLE 200-6:
HYDROLOGICAL PREFIXES
Hydrogeological
Condition Abbreviation
Spring(s) SP
Spring Lines(s) SL
Seep(s) SE
Seep Line(s) SH
Seep Zones(s) SZ
Surface Flow SF
The following examples demonstrate the general outline of how to reference the site
hydrological conditions.
Manual for Rockfall Inventory – Revised 12/2016 63
Figure 200-30. HYDROLOGIC CONDITIONS WINTER CONDITIONS
Example 200-13: Hydrologic Conditions of Cut Slope and Natural Backslope
Comments: Note that water is present at overburden and rock interface. However, due to the cold
conditions at the time of the site inventory the groundwater has resulted in ice formation along the
entire slope face. Thus reducing the potential for observations and identification of possible additional
hydrologic conditions within the lower slope. Surface flows are evident within the picture where the
ice buildup along the face is greatly reduced or voided, and deep erosional rills are present in the soils
natural backslope. These locations should be noted as Surface Flows within the natural backslope
since this is where they originate as evidence of the rills.
Cut Slope Info:
Site ID# Dist. From BMP (ft) Length (ft) Elevation (ft) Flow Rate (gpm)
SL1 10 520 1002 <1.0 gpm
Pictures taken at all locations: Y / N
Backslope Info:
Site ID# Dist. From BMP (ft) Length (ft) Elevation (ft) Flow Rate (gpm)
SF1 350 NA 1085 NA
SF2 380 NA 1085 NA
SF3 460 NA 1085 NA
Pictures taken at all locations: Y / N
Spring Line
Surface Flow
BMP
GPS Obtained
Elev. 960
960
1002
1085
Elev. Ft.
Manual for Rockfall Inventory – Revised 12/2016 64
Figure 200-31. HYDROLOGIC CONDITIONS SPRING CONDITIONS
25 60 115 123 148
Example 200-14: Hydrologic Conditions of Cut Slope and Natural Backslope
Comments: Note that seepage is prevalent throughout the slope. Dashed red line indicates the cut
slope/backslope interface. Areas of seepage have saturated the slope, but are not part of the seep itself.
Cut Slope Info:
Site ID# Dist. From BMP (ft) Length (ft) Elevation (ft) Flow Rate (gpm)
SZ1 25 50 765 < 1.0
SH1 60 55 760 < 1.0
SE1 115 NA 786 < 1.0
SE3 148 NA 765 < 1.0
Comments: SZ1 is located just below natural backslope interface;
SH1 is located along a bedding plane.
Pictures taken at all locations: Y / N
Backslope Info:
Site ID# Dist. From BMP (ft) Length (ft) Elevation (ft) Flow Rate (gpm)
SE2 123 NA 771 < 1.0
Comments: SE2 is located just above the cut slope/backslope interface.
Pictures taken at all locations: Y / N
Seepage Zone
Seepage Line
Seeps
Saturated Surface
from Seepage
Saturated Surface
from Seepage
786
771
765
760
746 (BMP Elev.) Left Side of
Picture
Manual for Rockfall Inventory – Revised 12/2016 65
206.3 Tier 3 & Tier 4 Testing Data
The following are the procedures for completion of the GHMS Part C: Rock
Sampling Information which is also found in the Rockfall Form in Section H: TIER 3
& TIER 4 TESTING DATA.
Section H records the information concerning sample collection for Tier 3 and Tier 4
site. Slake Durability Index testing (SDI) will be performed on selected
representative samples collected from the slope of the rockfall sites rated as either
Tier 3 or Tier 4 from the Preliminary Slope Rating. For large sites that have many
different rock strata, collect a maximum of six samples for SDI testing. If more than
six incompetent beds are present within an Inventory Site, collect samples from the
six deepest, or worst, locations across the site.
Collect bag samples of fresh rock material from each incompetent bed located within
the slope. Coal, limestone and moderately hard sandstone strata should not be
sampled for testing. The weathered rock surface should be removed from the slope
face using a shovel, geologic hammer, mattock, and/or chisel until fresh competent
bedrock has been exposed. Once the fresh rock face has been exposed, collect a
sample of the fresh rock material and place it into a collection bag(s) or container for
preservation. The material should be collected in such a manner and placed in a
container that moisture loss and breakage of the sample will be minimal during
transport and storage prior to testing. During transport and storage the sample should
not be allowed to freeze. Refer to ASTM D 4644 for the type and amount of sample
specimen required to perform the test. On the plan view, record the approximate
locations where the samples were collected. Record the sample location by
referencing the location as a distance from the BMP to the nearest foot and elevation
relative to the BMP to the nearest foot.
Record the sample data on the sample container, or on a sample tag affixed to the
container, and on a completed chain of custody form, include the following
information:
Site Location as County-Route-Section
ODOT District
Travel Direction (Cardinal or Non-Cardinal)
Distance from BMP
Right or Left Offset
Sample ID#
Height relative to BMP
Number of containers collected per sample
Date sample collected
Person collecting the sample
The bag samples should be delivered to the respective testing laboratory within a
week of the sample collection.
Manual for Rockfall Inventory – Revised 12/2016 66
Upon completion of the testing data, record the sample test results in Section H: TIER
3 & TIER 4 TESTING DATA. For sites where multiple samples have been collected,
record the number of SDI tests performed with the high and low test results with an
average test results.
Example 200-15: Slake Durability Index Test Sample Collection
Removal of weathered
bedrock for SDI sample
collection
SDI Sample collected
(including field
identification)
SDI Sample
(prior to testing)
SDI Sample
(post testing)
Manual for Rockfall Inventory – Revised 12/2016 67
206.4 Tier 3 & Tier 4 Office Data
Tier 3 and Tier 4 sites, as determined from the Preliminary Rating, will require
additional traffic information not outlined in Section 205.1.1 Geometrics and Traffic.
This data includes:
Average Road Slope
Detour Distance
Detour Time – Auto
Detour Time - Truck
The detour information will not have been obtained during the interviewing process
outline in Section 202.2.1 ODOT Interview(s). The District Transportation Manager
will need to be contacted to obtain this information. ODOT has set guidelines for
how a roadway will be detoured based upon the road type and location. The District
Transportation Manager will have to determine this information for each Tier 3 and
Tier 4 site. This data will be presented in GHMS Part B: Traffic Information and in
the Rockfall Form in Section I: TIER 3 & TIER 4 OFFICE DATA.
Also, the precipitation history should be recorded for the site. The 1-day, 3-day, and
15-day precipitation history from the date of field data collection should be reviewed
and recorded. If more than one day was spent working on the field data collection for
the Inventory Site, the precipitation history should be referenced to the actual day that
site hydrogeology data was recorded. This information can be obtained commercially
from NOAA, or a request can be made to the Ohio Department of Natural Resources,
Division of Water. Web links for sites to obtain the precipitation histories are
available in Appendix B.
This data will be presented in GHMS Part C: Hydrogeological Information,
Precipitation tab and in the Rockfall Form in Section I: TIER 3 & TIER 4 OFFICE
DATA.
207 DATA COLLECTION ACKNOWLEDGEMENT
Upon completion of the field data collection, the Field Team should sign and date the
form to acknowledge that the all the information collected and presented is accurate to
the best of their knowledge. This signature can be either hand written or an electronic
stamp and is located in Section K: DATA COLLECTION ACKNOWLEDGMENT.
Manual for Rockfall Inventory – Revised 12/2016 68
300 Risk Scoring for Inventory Sites
301 Rockfall Inventory Site Risk Scoring
After completion of the field data collection, Inventory Sites which are Tier 2, Tier 3, or
Tier 4 risk sites will need an associated Inventory Site Risk Score (Risk Score)
developed. The Risk Score is calculated based on ten (10) factors which are:
1. Differential Weathering
2. Discontinuity Role
3. Block Size/Volume of Rockfall per Event
4. Hydrologic Conditions (seeps and springs)
5. Rock Slope Height
6. Catchment/Containment
7. Exposure Risk
8. PDSD
9. Rockfall History
10. Accident History
Each factor will develop a raw value score based on the recorded field data. Each
evaluation parameter has a specific equation in which the site specific raw value (RV) is
a field input. A weighting factor is applied to each evaluation parameter to provide an
evaluation parameter score. The evaluation parameters values are summed to calculate
the Inventory Site Risk Score
The following sections outline the scoring for each factor.
302 Differential Weathering
The differential weathering factor is a multi-variable factor based upon the Tier scoring.
For Tier 2 sites the score will be based upon the recorded maximum visible undercut
recorded within the cut section. This information is recorded in the Geological Hazard
Management System (GHMS), Part C Geology: Additional Information Tab. The
following scoring matrix should be utilized based on the depth of the undercut (RV):
5.6*(RV³) - 30.8*(RV²) + 62.4*RV - 34.2
For Tier 3 and Tier 4 sites, where slake durability (SDI) samples were collected and
tested, the score will be based on the highest value between the SDI and undercut scores.
The testing information is recorded in the GHMS, Part C Geology: Additional
Information Tab. The following scoring matrix should be utilized based on the test
results of the second cycle slake durability index (RV):
-0.0019*(RV³) + 0.4736*(RV²) - 39.268*RV + 1099.5
A minimum of 0 points and a maximum of 81 points need to be assigned for this section.
Manual for Rockfall Inventory – Revised 12/2016 69
303 Discontinuity Role
The Discontinuity Role factor is a multi-variable factor based upon the major type of
discontinuity producing the rockfall debris. Typically, one of two types of discontinuity
will be predominately controlling factor in production of rockfall debris. These are
jointing or raveling. Cut slopes can exhibit either one or both of these properties. The
slope should be evaluated for both types of discontinuities and scores based on the worst
case of the two. The following is a brief discussion of how to score each type.
Intersecting joint sets can produce blocks that can dislodge resulting in a potential hazard
to the roadway. However, if the joint sets do not intersect, then the resulting
discontinuity may not result in potential hazard to the traveling public. The scoring is
based upon how continuous the joint set(s) are and the orientation of the joint set(s)
relative to the roadway. This information is found in the GHMS in Part C: Geological
Information, Joint Information tab. The following scores are assigned based on how
continuous and the orientation of the joint(s):
Discontinuous joints with favorable orientation = 3 points
Discontinuous joints with random orientation = 9 points
Discontinuous joints with adverse orientation = 27 points
Continuous joints with adverse orientation = 81 points
For slopes where the raveling is the predominate feature producing the rockfall debris,
the score will be based on the percentage of the slope which is exhibiting the raveling
(RV). The following scoring matrix should be utilized based on the depth of the
undercut:
0.028*(RV³) - 1.36*(RV²) + 21.9*RV - 108
A minimum of 3 points and a maximum of 81 point need to be assigned for this section.
304 Block Size/Volume of Rockfall Per Event
This factor is based on the size and amount of debris which could be a potential hazard to
the traveling public. These variables are typically directly proportional to the type of
joint sets and raveling that the slope is experiencing. Typically, either large blocks
produced by the joint sets or small blocks produced by raveling is the predominate
mechanism of debris generation. Both should be evaluated and scores based on the worst
case of the two. The following is a brief discussion of how to score each type.
The first variable to look at is the maximum dimension of the anticipated or recorded
block size that could be produced for the slope. This information is recorded in the
GHMS, Part C Geology: Additional Information tab. The following scoring matrix
should be utilized based on the block size:
28*(RV³) - 136*(RV²) + 219*RV - 108
Manual for Rockfall Inventory – Revised 12/2016 70
The second variable to look at is the total volume of debris that could be produced for the
slope during a rockfall event. This information is recorded in the GHMS, Part C
Geology: Additional Information Tab. The following scoring matrix should be utilized
based on the block size:
1.037*(RV³) - 15.111*(RV²) + 73*RV - 108
A minimum of 0 points and a maximum of 81 point need to be assigned for this section.
305 Hydrologic Conditions (seeps and springs)
The Hydrologic Condition factor is based on the percentage of the slope which has
hydrologic conditions within the slope. This information can be found within the GHMS
in Part C: Hydrogeologic Information, Cut Slope Information, Natural Backslope
Information, and Precipitation tabs. The following scoring matrix should be utilized
based on the percentage of the slope with hydrological conditions:
0.0122*(RV³) - 0.4552*(RV²) + 5.8845*RV - 16.574
A minimum of 3 points and a maximum of 81 point need to be assigned for this section.
306 Rock Slope Height
The fifth factor to consider in the Risk Scoring is the rock slope height from which
potential rockfall debris could be generated. For Inventory Sites where the source zone is
solely within the cut slope, the Rock Slope Height will be the Rock Cut Height. If the
Inventory Site has a source zone located within the natural backslope, then the Rock
Slope Height will be recorded as the Backslope Height. This information can be found
within the GHMS in Part C: Slope Information, Geometric Information tab. The
following scoring matrix should be utilized based on the rock slope height:
0.0035*(RV³) - 0.55*(RV²) + 28.75*RV - 491
A minimum of 0 points and a maximum of 81 point need to be assigned for this section.
307 Catchment/Containment
The Catchment/Containment factor is a multi-variable factor based upon existing
catchment area and any past remedial activities. For sites where a retention
(containment) system is in place (e.g. D50 wall, rock fence), the system is evaluated on
whether the system is functional or not. For sites which do not have a containment
system the site is evaluated based on the catchment area effectiveness.
A reminder, just because a wall is in place does not necessarily mean that the wall will be
effective for either very large block sizes or large debris volumes with small catchment
storage capacity. This should be reflected in the estimated remedial work effectiveness.
This data will be recorded within the GHMS in Part C: Slope Information, Corrective
Actions tab. The following scores are assigned based whether there is a functional
retention (containment) system in place:
Manual for Rockfall Inventory – Revised 12/2016 71
Yes = 9 points
No = 81 points
Even though there is a functional barrier the site scores 9 points because there has been a
problem in the past which has warranted the installation of the barrier. Additionally, if
the barrier is subjected to repeated impacts the barrier may eventually fail, which is why a
score of 3 is not assigned for functional barriers.
For Inventory Sites which do not have a means of containment, all the debris control is
handled based on catchment width and geometry. The effectiveness of the catchment
area should be evaluated based on Appendix B. This data will be recorded within the
GHMS in Part C: Slope Information, Catchment Area tab. The following scoring
matrix should be utilized based on the catchment area effectiveness:
-0.0201*(RV³) + 5.2114*(RV²) - 449.15*RV + 12885
A minimum of 0 points and a maximum of 81 point need to be assigned for this section.
308 Exposure Risk
This factor is based on the exposure risk that the Inventory Site as expressed to the
travelling public. Exposure Risk can be calculated as following:
Eq. #6:
100*24/)*(
Risk Exposure
SpeedLimit
SiteLengthADT
Note: The site length should be reported in miles
ADT and speed limit values can be obtained from the GHMS in Part B: Traffic
Information. The site length is recorded in Part A: Site Location of the GHMS. The
following scoring matrix should be utilized to calculate the risk score for the exposure
risk of the inventory site:
0.0019*(RV³) - 0.2335*(RV²) + 9.4146*RV - 116.22
A minimum of 0 points and a maximum of 81 point need to be assigned for this section.
309 Percent Decision Sight Distance (PDSD)
This Risk Scoring factor is based on the percentage decision sight distance. This is
relative to the ability of a driver to react to an obstacle, such as rockfall debris, within the
roadway. Percent Decision Sight Distance can be calculated as following:
Eq. #1: PDSD = ASD / DSD
Manual for Rockfall Inventory – Revised 12/2016 72
This data will be recorded within the GHMS in Part B: Traffic Information. The
following scoring matrix should be utilized based on the Percent Decision Sight Distance:
-0.0018*(RV³) + 0.4544*(RV²) - 38.36*RV + 1087
A minimum of 0 points and a maximum of 81 point need to be assigned for this section.
310 Rockfall History
The Rockfall History factor is based on the Inventory Site’s rockfall maintenance
records. These records are obtained from the applicable County Garage, County or
Transportation Manager, or District Geotechnical Engineer. Rating scores are assigned
as follows:
Less than Annual Maintenance = 3 points
Annual Maintenance = 9 points
Semi Annual Maintenance = 27 points
Constant Maintenance = 81 points
Table 300-01 presents the Rockfall History section of the worksheet.
Table 300-01. Rockfall History
Evaluation Parameter Rating Scores for each Evaluation Parameter
3 9 27 81
Rockfall History < Annual
Maintenance
Annual
Maintenance
Semi
Annual
Maintenance
Constant
Score
311 Accident History
The final factor is the Accident History of the Inventory Site relative to past rockfall
events. Accidents which did not involve debris generated from a rockfall event should
not be considered. This factor is based on the County maintenance records and
Department of Public Safety records with scores assigned based as follows:
No Accidents = 3 points
Minor Property Damage = 9 points
Major Property Damage = 27 points
Death = 81 points
Manual for Rockfall Inventory – Revised 12/2016 73
Table 300-02 presents the Accident History section of the worksheet.
Table 300-02. Accident History
Evaluation Parameter Rating Scores for each Evaluation Parameter
3 9 27 81
Rockfall History
No Accident
Minor
Property
Damage
Major
Property
Damage
Death
Score
Manual for Rockfall Inventory – Revised 12/2016 74
400 Inspection Frequency
Each Inventory Site will require periodic re-inspection to determine if the site’s risk is
remaining relatively stable, or progressing as an increased risk relative to the public safety.
The frequency of re-inspection will be based on the Preliminary Rating of the previous
inspection as presented in Table 400-01.
Table 400-01. Re-Inspection Frequency
Rating Frequency
Non-rated
(Tier 1) 10 Years
Moderate Risk
(Tier 2) 5 Years
High Risk
(Tier 3) 3 Years
Very High Risk
(Tier 4) Annually
Re-inspection will be required outside of the prescribed inspection table if one of the
following events occur:
1. If rockfall debris fragment(s) greater than 6 inches in any dimension occupies the
shoulder, travel lane(s) or median: The District Geotechnical Engineer (DGE) and
the Office of Geotechnical Engineering (OGE) shall be notified within one week and
the site shall be re-evaluated within one month of the event.
2. If rockfall debris greater than one cubic foot in total volume, occupies the shoulder,
travel lane(s) or median: The District Geotechnical Engineer (DGE) and the Office
of Geotechnical Engineering (OGE) shall be notified within one week and the site
shall be re-evaluated within one month of the event.
3. A single rockfall event which produces debris volumes which occupies more than 70
percent of the estimated storage capacity over a length of 20 feet for the catchment
area: The site should be re-inspected within three months of the event.
4. Remedial activities to the slope, partial or full, are performed on a site to reduce the
overall relative risk: The site should be re-inspected within one year upon completion
of construction activities.
APPENDIX A
Glossary of Terms
APPENDIX A – GLOSSARY OF TERMS Rock Type Terms: The following are descriptions of the basic rock types found within Ohio rock slopes. This listing is not intended to be an all inclusive exhausting listing. The following listing is presented in alphabetical order. Breccia: A coarse-grained sedimentary rock comprised of >25% subangular to angular coarse-grained sand, gravel and/or cobbles. These grains are supported by a matrix of finer sands, silt and/or clay and cemented by calcite, hematite, silica or hardened clay. Color depends on the matrix and cementing agent with typical colors of white, gray, yellow, orange, brown, and red common. CHERT: A hard dense microcrystalline or crptocrystalline sedimentary rock consisting of quartz crystals and may contain amorphous silica. Chert may be a variety of colors, but commonly range from brown to black. When broken it produces conchoidal fractures. These fractures are smooth with sharp edges. Chert forms as nodular or concretionary segregations or nodules or as layered deposits in limestone and dolomite. CLAYSTONE: A fine-grained detrital rock formed from particles finer than silt. Claystone is comprised of indurated clay having the texture and composition of shale, but lacking the laminations and fissility of a shale. Claystone may range in color from red, gray, olive, or brown, and slickensides are common. COAL: A combustible rock containing >50%, by weight, and >70%, by volume, of carbonaceous material; formed from the compaction and induration of plant remains. Colors of coals range from brown to black. Generally light weight with a shiny appearance on fresh surfaces. CONGLOMERATE: A coarse-grained sedimentary rock comprised of >25% rounded to subrounded coarse-grained sand, gravel, cobbles, and/or boulders. These grains are supported by a matrix of finer sands, silt and/or clay and cemented by calcite, hematite, silica or hardened clay. Color depends on the matrix and cementing agent with typical colors of white, gray, yellow, orange, brown, and red common. DOLOMITE: A sedimentary rock of which >50% consists of the mineral dolomite (calcium magnesium carbonate – CaMg(CO3)2) and less than 10% is comprised of the mineral calcite. Commonly interbedded with limestone, and the magnesium can be replaced with ferrous iron. Dolomite is typically white to light colored and will be slow to react with cold dilute hydrochloric acid (HCl). Generally, for dolomite to react with HCl either a fresh or powdered surface is required. FIRECLAY: See Underclay for description. LIMESTONE: A sedimentary rock consisting of the mineral calcite (calcium carbonate – CaCO3). Very fine grains may not be visible to the naked eye. Impurities may included chert, clay and minor mineral crystals. May be crystalline (hard, pure, medium to coarse texture) and/or fossiliferous (remains of organisms). Limestone is typically white to dark gray in color and reacts vigorously with dilute HCl. SANDSTONE: Clastic sedimentary rock comprised of grains of angular or rounded sand in a matrix of silt and/or clay cemented together by silica, iron oxides, or calcium carbonate. Color depends on the cementing agent with white, gray, yellow, orange, brown, and red colors common. SHALE: Fine-grained detrital sedimentary rock formed be the compaction of clay, silt or mud. Shale is well indurated and has a laminated structure, which gives it fissility along which the rock splits readily. The predominate particle size is <0.002 mm (colloidal) and commonly interbedded with sandstone. Shale can be calcareous (contains calcite), carbonaceous (contains organic materials), and/or fossiliferous (contains remains of organisms). Carbonaceous shale often grades into coal. Typical colors may be red, brown, black, green or gray.
SILTSTONE: Fine-grained detrital sedimentary rock formed from particles finer than sand, but coarser than clay. Siltstone is comprised of indurated silt and have the texture and composition of shale, but lacking the lamination or fissility. Gray, olive, or brown are typical colors of siltstone. UNDERCLAY: A layer of clay lying immediately beneath a coal bed or carbonaceous shale. This layer may be bioturbated and indurated. Chiefly comprised of siliceous or aluminous clay capable of withstanding high temperatures without deformation, and may have a high shrink/swell potential. Technical Terms: The following are descriptions of basic terms utilized within the Rockfall Manual. The following listing is presented in alphabetical order. 1-Day Precipitation History: The recorded amount of precipitation, including but not limited
to, rainfall, ice, or snow, during the previous 24 hour period (1 day) prior to the field work.
3-Day Precipitation History: The recorded amount of precipitation, including but not limited to, rainfall, ice, or snow, during the previous 36 hour period (3 day) prior to the field work.
15-Day Precipitation History: The recorded amount of precipitation, including but not limited to, rainfall, ice, or snow, during the previous 360 hour period (15 day) prior to the field work.
AADT: (Adjusted Annual Daily Traffic)
Scaled adjustment of the annual daily traffic counts preformed within the field to account for increased traffic volume over time.
Accident: An incident that resulted in an injury of loss of private property due to a rockfall event.
ADT: (Average Daily Traffic)
The total amount of traffic, both truck and vehicle, for the given section of roadway over a 24-hour period.
Aggregate Thickness: The summed total of the thicknesses of a specified rock type for the total height of the cut slope and/or natural slope.
ASD: (Actual Sight Distance)
The shortest distance along a roadway over which a 6-inch object is continuously visible to a driver (assuming a height of 3.5 feet)
ATT: (Average Truck Traffic)
The total amount of truck traffic for the given section of roadway over a 24-hour period.
AVR: (Average Vehicle Risk)
A scaled factor for the risk to a vehicle associated with potential rock fall calculated as: ADT * Slope Length (miles) / 24 Posted Speed Limit
AVT: (Average Vehicle Traffic)
The total amount of vehicle traffic for the given section of roadway over a 24-hour period.
Bedding Plane: Break between the layering of sheet-like units, called laminations, beds or strata, indicating the change in lithology and/or physical characteristics.
* 100%
Bench: A low angle, or flat, step excavated into the cut slope with higher angle slopes above or below.
Block Size: The rock size that dislodged from the cut slope to become a rockfall. Estimated or measured in cubic feet.
Cardinal Direction: The cardinal direction of travel is based on the roadway description (i.e., I-70, West/East or I-71, South/North) and not a site specific compass direction or bearing. By convention, roadways are considered to be oriented in a south to north or west to east direction.
Cleanout: The removal of accumulated materials from ditches and benches including sediments and loose materials transported down slope from the cut slope face or natural slope.
Competent Bed: Rock strata composed of materials that are resistant to weathering processes relative to the underlying or overlying strata.
County Code The county that the site is located within using the ODOT three letter county designation. The county code consists of the first three letters of the county name with the exceptions of: County Code Ashland ASD Ashtabula ATB Champaign CHP Harrison HAS Meigs MEG Monroe MOE Montgomery MOT Morgan MRG Morrow MRW A full listing of the County Codes are included in Appendix X.
Crop Line: The general term “cropline”, if not further defined, refers to the line along the ground surface where the mined mineral seam is exposed in the existing grade. The term “cropline”, with further definition, can also be utilized to define the structural contour of the top of the mined mineral seam which is covered by a uniform depth of overburden. Example: On some ODNR abandoned underground mine maps, the notation on a map line may read “30 foot cropline”. This indicates the line on top on the mined mineral seam which was covered by 30 feet of natural overburden.
Cut Slope: The constructed slope along the roadway created by removal of overburden and/or bedrock from the ground surface to the road grade.
Cut Slope Angle: The angle from a horizontal datum/plane along the face of the constructed surface called the cut slope. (See Figure 1)
Cut Slope Height: The vertical distance measured from the top of the cut slope to
the base of the cut slope. (See Figure 1)
Cut Slope Length: The distance measured parallel along the road from which the material has been removed.
Ditch Depth: The vertical distance from the bottom of the ditch to the top of the ditch at the roadway shoulder. (See Figure 1)
Ditch Width: The horizontal distance of the ditch from the top of the ditch at the roadway shoulder to ground surface projected as a horizontal plane..
Drift Entry: A horizontal mine entry into the natural outcrop of the mined mineral seam.
DSD: (Decision Site Distance)
The required spacing along a roadway from which a driver has time to avoid an obstacle within the roadway. The value can be obtained from a design chart that considers speed limit, use of roadway, and possibly curvature and grade of the roadway. (Refer to Table 5 within the Manual Text)
%DSD: (Percentage Decision Site Distance)
Ratio between the DSD and the ASD, calculated as %DSD = (ASD/DSD) * 100
Durable Rock: Rock composed of materials that are resistant to weathering processes.
Field Team Field personnel consisting of a geologist and an engineering geologist or a geotechnical engineer, who will complete the required field data collection for the rockfall inventory.
Flow Rate: Rate at which water is discharging from the ground surface in gallons per minute (gpm).
Foreslope: The slope between the roadway shoulder and the bottom of the ditch. (See Figure 1)
Foreslope Angle: The angle of the slope between the roadway shoulder and the bottom of the ditch. (See Figure 1)
Gob: Coal refuse commonly abandoned on the surface in piles at or near the mining operation.
Ground Water: Flowing or non-flowing water discharging from the bedrock at the slope surface.
Haulage Shaft A mine shaft utilized for the transportation of mined mineral to the ground surface.
Joint: A discrete break or fracture within bedrock along which there has been little or no vertical displacement.
Joint Opening: The open distance between the joint faces measured in inches.
Joint Spacing: Distance between the centers of two joints (generally measured from center of joint opening to center of joint opening).
JRC: Joint Roughness Coefficient; Method used to describe the roughness of the joint surface by using a comparison on the discontinuity surface profile with reference profile.
Incompetent Bed: Rock strata composed of materials that are not resistant to weathering processes.
Infilling: Deposition (clay, silt, sand, minerals, etc.) within the joint opening.
Median: Area located between lanes of opposite directions of traffic. The median can consist as a divided, concrete barrier or fence, or undivided, open grass.
Mine Opening: A mine entry extending either vertically (shaft entry), horizontally (drift entry), or at an inclined angle (slope entry) to an underground mine.
Mine Subsidence: Sinking, settling or subsidence of the ground surface caused by the failed and collapse of the mine’s roof support.
Mineralization: The deposition of mineral deposits on a joint surface.
Natural Backslope: The original ground surface located above the top of the excavated surface of the cut slope. (See Figure 1)
Natural Backslope Height: The vertical distance from the top of the cut slope to the top of the natural ground surface, or to the upper limit of the source area for rockfall to occur within the Natural Backslope. (See Figure 1)
Orthogonal Joint Set: Series of deep-seated regional joints created by tectonic stress, which have a general regional trend.
Potential Rockfall Size: The estimated dimensions of a potential rock size that may dislodge from the cut slope or natural backslope to become a rockfall based upon bedding, the spacing and orientation of joints, and undercutting within the cut slope.
Potential Rockfall Volume: The estimated volume of material from a potential rockfall event that may dislodge from the cut slope or natural backslope to become a rockfall based upon the bedding, spacing and orientation of joints, and undercutting within the cut slope.
Ritchie Criteria: Catchment design criteria based upon the slope height and slope angle geometry.
Ritchie Score: A mathematical comparison of the Ritchie values compared to the actual ditch measurement. Ritchie Depth + Ritchie Width Actual Depth + Actual Width
Ritchie Score =
Rock Quality Designation: (RQD)
The RQD value is the percentage of the length of a rock core run which is made up of continuous pieces of core sample, that are four (4) inches in length or greater.
Rockfall: The detachment of rock mass(es) of variable size from along a cut slope or natural backslope with movement down slope toward the base of the slope.
Rockfall Chute: The clearing zone that results from the rockfall activities.
Rockfall Debris: The accumulation of material as a result of rockfall from the slope.
Rockfall Retention Device: Devices installed on the cut slope, natural backslope, or near the slope base, that inhibits the further movement, reduces the energy of, or collects the debris from, the down slope movement or tries to controls the rockfall from entering onto the roadway.
Rockfall Volume: The amount of accumulation of the rockfall from the slope measure in cubic yards.
Route Classification: State Route, US Route, or Interstate Route along which the field team will travel and complete the required inventory.
SDI: (Slake Durability Index)
Test for rock to determine its durability. Testing to be completed in accordance with ASTM D 4644: Standard Test Method for slake durability of shale and similar weak rocks.
Seepage: Non-flowing groundwater noted discharging from the slope surface measured in gallons per minute (gpm).
Shaft: A mine entry extending vertically from the ground surface down to the elevation of the mined interval.
Shoulder: The graveled or paved area between the outside travel lane and the ditch.
Site Number: Designation number for each specific inventory site assigned by ODOT.
SLM: (State Line Mile)
Numerical designation of any point along an ODOT maintained roadway, based on the actual centerline mileage as measured from the western or southern county line or other true beginning.
Spring: Flowing groundwater noted discharging from the slope surface measured in gallons per minute (gpm).
Surface Deformation: Area(s) of surface settlement or subsidence. Deformation may be indicated by the presence of irregular drainage conditions.
Surface Water Flow: Area of flowing water along either the face of the cut slope or along the natural backslope. Generally, surface water flow will be in a down slope direction and accumulates within the ditch at the base of the slope.
Talus: The accumulated of weathered rock particles and soil along the
cut slope, on benches, or at the foot of a slope.
Travel Lane or Lane: Paved section of roadway in which vehicular traffic moves.
Troughing: Linear surface deformation extending for some distance and having a gentle curvilinear profile when viewed in section.
Undercutting: The natural removal of materials as a result of weathering out of an incompetent bed overlain by a competent bed resulting in an overhang.
Underground Mine: An underground excavation from which mineral resources were extracted.
Valley Stress Relief Joint: Steeply dipping to vertical fractures that are a result of stress relief accompanying valley formation. Typically, these joint sets are oriented parallel to or sub-parallel to the valley walls. Stress relief joints tend to attenuate with distance away from the valley walls.
Cut Slope Height
D
Ditch Depth
Foreslope/ Foreslope Angle
Cut Slope Angle
Bench
Overburden Bench Natural Backslope
Natural Backslope
APPENDIX FIGURE #1
Not To Scale
Soil/Rock Interface
Catchment Area
APPENDIX B
Criteria for Evaluation of Catchment
Appendix B – Criteria for Evaluating Catchment Ditch Widths for Various Slope Angles
Cut Slope Height, H (ft) 0-40 50 60 70 80 >90*** Cut Slope Angle Catchment Ditch Width, W (ft)
2H:1V and 3H:1V Catchment Foreslope Angle* 0.25:1 10 15 15 15 20 25 min. 0.5:1 10 15 20 20 20 25 min. 1.0:1 15 20 20 20/25** 25 30 min. 1.5:1 15 20 20 20/25** 25 30 max.
4H:1V Catchment Foreslope Angle*
0.25:1 10/15** 15 20 20 25 30 min. 0.5:1 15 15 20 20 25 30 min. 1.0:1 15/20** 20 20/25** 25/30** 30 35 min. 1.5:1 15/20** 20 20/25** 25/30** 30 35 max.
6H:1V Catchment Foreslope Angle*
0.25:1 15 20 25 30 35 40 min. 0.5:1 20 20 25 30 35 40 min. 1.0:1 25/30** 25/30** 30 35 40 40 min. 1.5:1 25/30** 25/30** 30 35 40 40 max.
*If Slope under evaluation has a different foreslope angle than options listed above, round to nearest slope angle. **Single Angle Foreslope Catchment Ditch Width / Multi-Angle Foreslope (portion flat) Catchment Ditch Width *** Slopes with a height (H) greater than 90 feet should be evaulated with Appendix B width as minimum and adjusted according to specific site conditions For situations where the portion of the rock cut slope (backslope) intersecting the ditch is flatter than 1.5H:1V, use industry practices to evaluate width criteria.
APPENDIX C
Field Parameters
APPENDIX C – FIELD PARAMETERS
BEDROCK HARDNESS CRITERIA
Hardness Abbreviation Criteria - Field Criteria – Testing
(Schmidt Hammer)Very Soft VS Can be carved with a knife and excavated easily
with a point of a pick. Can be readily scratched by fingernail and pieces 1-inch of more in thickness can be broken by finger pressure.
Soft ST Can be grooved or gouged readily by a knife or pick. Can be excavated in small fragments by moderate blows of a pick point. Small, thin pieces can be broken by finger pressure.
Medium Hard MH Can be grooved or gouged 0.05-inch deep by hand pressure of a geologist’s pick. Hand specimens can be detached by moderate blows.
Hard HD Can be scratched with a knife or pick Very Hard VH Cannot be scratched by a knife or sharp pick.
Breaking of hand specimens require several hard blows of the geologist pick.
BEDROCK BEDDING CRITERIA
Bedding Type AbbreviationCriteria
English Metric Thinly Laminated TL <0.125-in <3 mm
Laminated LA 0.215-in to 0.400-in 3- to 10 mm Very Thinly Bedded VT 0.400- to 1.000-in 1.0- to 3.0 cm
Thin Bedded TH 1.000- to 4.000-in 3.0- to 10.0 cm Medium Bedded MB 4.000- to 12.00-in 10.0- to 30.0 cm
Thick Bedded TK 1- to 3.3-ft 30.0- to 100.0 cm Massive Bedded MS >3.3-ft >1.0 m
WEATHERING CHARACTERISTICS
Weathering Abbreviation Criteria Unweathered UW No evidence of any chemical or physical alteration of the rock
mass. Slightly Weathered SW Slight discoloration on rock mass surface, slight alteration along
discontinuities, less than 10% of the rock volume altered by either chemical or physical means.
Moderately Weathered MW Discoloration evident across the majority of the rock mass, surface pitting and alteration penetrating well below the rock mass surface, weathering “halos” evident, 10-25% of the rock volume has been altered.
Highly Weathered HW Entire rock mass discolored, alteration pervading nearly all of the rock mass surface with some pockets of slightly to moderately weathered rock noticeable, some materials may be leached away.
Decomposed DE Rock reduced to a soil like state with relict tock texture evident, generally molded and crumbled by hand pressure.
TEXTURE CHARACTERISTICS
Primary Component
Secondary Description
Grain Diameter (metric – mm)
Grain Diameter (english - inch)
Boulder Large >1025 >40.5
Medium 1025 – 500 40.5 - 20 Small 500 – 300 20 - 12
Cobble Large 300 – 125 12 - 5 Small 125 - 75 5 - 3
Gravel Coarse 75 – 19 3.0 - 0.75
Medium 19 – 8 0.75 - 0.31 Fine 8 – 2 0.31 - 0.08
Sand
Coarse 2.0 – 0.5 0.08 - 0.02 Medium 0.5 – 0.25 0.02 - 0.01
Fine 0.25 – 0.125 0.01 - 0.005 Very Fine 0.125 – 0.074 0.005 - 0.003
Silt --- 0.074 – 0.005 0.003 - 0.0002 Clay --- <0.005 <0.0002
BEDROCK MODIFIERS*
Modifier Definition Arenaceous Contains a sandy, or sandy-like appearance or texture. Arillaceous Contains silt and clay-sized particles. Calcareous Contains carbonate material as either a matrix or grains. Carbonaceous Contains an abundant amount of carbon material. Crystalline Contains crystalline grains or cementation composed of crystalline cement. Ferriferous Contains an abundance of iron rich minerals or grains. Fissile The rock mass has the ability to split along preferential planes. Friable The rock mass is easily crumbled, pulverized, or reduced. Micaceous Contains an abundance of mica grains within the rock mass. Pyritic Contains an abundance of pyrite nodules or crystals. Siliceous Contains an abundance of silica rich materials as either matrix or grains. Slickensided Contains polished striations indicating a plane along which differential movement
has occurred. Stylolitic Contains irregular, suture-like contacts called stylolotes. Variegated The rock mass has a variety of colors, usually intermixed or streaked. Vuggy Contains cavities within the rock mass. * This listing is only of common modifiers and is not intended to be all inclusive.
DISCONTINUITIES CHARACTERISTICS AND DESCRIPTION
VARIABLE TABLE NUMBER Discontinuity Dip Angle NA
Discontinuity Type C-1 Aperture C-2
Infilling Type C-3 Infilling Amount C-4 Infilling Profile C-5
Surface Roughness C-6 Spacing C-7
TABLE C-1
Type of Discontinuities
Abbreviation Characteristics
Bedding Plane BP
A well defined planar surface that indicates a marked break in the deposition within sedimentary rocks. With in Ohio this is the major discontinuity type, which generally dip to the southeast at angles ranging from horizontal to 10º. Isolated areas can have dip angle nearing 30º in areas of stratigraphic pinchouts have been recorded.
Valley Stress Relief Joint
VSRJ
Steeply dipping to vertical fractures that are present near the valley walls that are a result of the stress relief associated with the valley formation. This type of joint attenuates across beds of differing strength and becomes less frequent with depth below the valley floor and distance away from the valley walls and are generally parallel to sub-parallel to the valley walls.
Orthogonal Joint
ORTH Deep-seated regional joints created by tectonic stress that are more pervasive that the valley stress relief joints.
Shear SH
A discontinuity along which differential movement has taken place parallel to the discontinuity surface, sufficient to produce slickensides. May be accompanied by a zone of fractured rock up to a few inches wide.
Fault FT Major discontinuity along which there has been an appreciable displacement and accompanied by gouge and/or a severe fractured zone within the rock mass.
TABLE C-2
Type of Aperture Abbreviation Characteristics
English (inches) Metric (mm) Wide WD 0.5 – 2.0 13.0 – 50.0
Moderately Wide MW 0.1 – 0.5 2.5 – 13.0 Narrow NW 0.05 – 0.1 1.0 – 2.5
Very Narrow VN <0.005 <1 Tight TI 0.00 0.00
TABLE C-3
Type of Infilling Abbreviation Barite Ba Clay Cl
Calcite Ca Chlorite Ch
Iron Oxide Fe Gypsum/Talc Gy
Healed Hd Manganese Mn
None No Pyrite Py Quartz Qz Sand Sd Silica Si
Unknown Uk
TABLE C-4 Amount of Infilling Abbreviation Percentage of Infilling
None No 0% Surface Stain Su 0-2%
Spotty Sp 2-5% Partially Filled Pa 5-60%
Filled Fi >60%
TABLE C-5Infilling Profile Abbreviation
Planarity F Wavy Wa Planar Pl
Stepped St Irregular Ir
TABLE C-6
Surface Roughness Abbreviation Criteria
Slickensided SLK Surface has a smooth, glassy finish with visual evidence of striations.
Smooth SM Surface has a smooth appearance and feel.
Slightly Rough SR Asperities on the discontinuity surface are distinguishable and can be felt.
Rough RO Some ridges and side-angle steeps are evident; asperities are clearly visible, and discontinuity surface feels very abrasive.
Very Rough VR Near-vertical steps and ridges occur on the discontinuity surface.
TABLE C-7
Type of Aperture Abbreviation Characteristics
English (feet) Metric (m) Very Wide VW >10.0 >3
Wide W 3.0 – 10.0 1.0 – 3.0 Moderately Wide MW 1.0 – 3.0 0.3 – 1.0
Close C 0.2 – 1.0 0.06 – 0.3 Very Close VC >0.2 <0.06
FIELD PARAMETERS FOR DETERMINING JRC
From Hoek, et al., 1995
EXAMPLES OF DISCONTINUITIES TYPES
Bedding Plane
Orthogonal Joint
Valley Stress Relief Joint
EXAMPLES OF CATCHMENT TYPES
Grueberg Fence with D-36 Barrier in front of Fence
Grueberg Fence after rock catchment
ODOT Mesh Fence
Soil Berm
Open Catchment Area with Aggregate for Energy Dissipation
Open Catchment Area
Open Catchment Area with Grouted Rip Rap
D50 Concrete Wall with rock catchment
D50 Wall with Flat Catchment Area
APPENDIX D
Examples of Rockfall Tier Locations
TIER 1 EXAMPLES
BRO-62-9.6 +/-
COMMENTS: Notice that the cut section has a relatively short back slope height and has weathered with minor overhangs that would result in small amounts of rockfall due to the slope angle. Additionally, the ditch has adequate width and geometry to catch any rockfall that may occur. It should be noted that the on the other side of the road is not a Tier 1 site, but a Tier 3 site.
BRO-68-14.9 +/-
COMMENTS: Notice that the cut section has a relatively short back slope height and has weathered with minor overhangs that would result in small amounts of rockfall due to the slope angle. Additionally, the ditch has adequate width and geometry to catch any rockfall that may occur.
Slope Height = 15 ft
Minor overhangs of bedrock
HAM-52-35.2 +/-
COMMENTS: Notice that the cut section has weathered with minor overhangs that would result in small amounts of rockfall due to the slope angle.
HAM-52-35.2 +/- (Drainage Outfall)
COMMENTS: Notice that durable layers of limestone are present within the slope. However, with the talus accumulation over the durable layer they no longer become an issue along the rock slope. Additionally, the ditch has adequate width and geometry to catch any rockfall that may occur.
HAM-74-13.2
COMMENTS: Notice that the slope has weathered uniformly with no overhangs that would result in rockfall. Additionally, the ditch has adequate width and geometry to catch any rockfall that may occur.
LIC-70-26.5 +/-
COMMENTS: Notice that the slope has weathered uniformly with minimal overhangs that would result in rockfall. Additionally, the ditch has adequate width and geometry to catch any rockfall that may occur.
Minor overhangs of bedrock
MUS-70-8.1 +/-
COMMENTS: Notice that the slope has weathered uniformly with no overhangs that would result in rockfall. Additionally, the ditch has adequate width and geometry to catch any rockfall that may occur.
SCI-23-15.5
COMMENTS: Notice that the slope has weathered uniformly with no overhangs that would result in rockfall. Additionally, the ditch has adequate width and geometry to catch any rockfall that may occur.
TIER 2 EXAMPLES
BRO-62-6.5 +/-
COMMENTS: Notice that the slope has weathered relatively uniformly. However, overhangs that will result in rockfall are present throughout the slope including the along the slope crest. Additionally, the ditch width and geometry may be adequate to retain the rockfall from entering onto the roadway. It should be noted that the vegetation on the slope face will help reduce the rockfall energy resulting in less rocks reaching the roadway.
GUE-77-19.5 +/-
COMMENTS: Notice that the slope has not weathered uniformly. Differential weathering between the coal layer and the overlying sandstone layer has resulted in overhang rockfall. The ditch does not appear adequate to retain all rockfall from the roadway. A major portion of the sandstone blocks are not reaching the roadway, but are being retained on the highly weathered shale and coal layers within the lower portion of the slope.
Differential Weathering
with overhang
Rockfall block retained on
slope
LIC-70-19.8 +/-
COMMENTS: Notice that the lower slope has weathered relatively uniformly with little to no areas of overhang. However, within the upper vegetated slope a relatively thick to massive resistant sandstone layer has created an overhang that will result in rockfall.
LIC-70-21.2 +/-
COMMENTS: Notice that the slope has poorly weathered probably as a result of poor construction blasting that will result in rockfall. However, the ditch width appears to be adequate to retain any rockfall.
Sandstone overhang within highly vegetated slope
HAM-74-9.4
COMMENTS: Notice that the slope has weathered relatively uniformly with overhangs that will result in rockfall. It should be noted that the shale bedrock has apparently weathered to residual soil that is failing resulting in minor slope instability.
HAM-74-9.4 (D-50 Wall)
COMMENTS: The catchment area and D50 concrete wall appears to be retaining the rockfall from entering onto the roadway.
Rockfall being
retained within the catchment
area or by the D50 wall.
TUS-77-3.0 +/-
COMMENTS: Notice that the slope has weathered relatively poorly with several sources of rockfall present. However, the 42 ft width of the catchment area appears to be adequate to retain any rockfall that may be produced prior to encroachment of the roadway.
LIC-16-29.0 +/-
COMMENTS: Notice that the majority of the slope has weathered relatively well. However, the upper and outer portions of the slope are highly weathered with several sources of rockfall present. However, the width of the ditch appears to be adequate to retain any rockfall that may be produced prior to encroachment of the roadway.
52 ft
10 ft
Highly weathered, poorly performing section(s) of slope
Highly weathered,
poorly performing section(s) of
slope
Well performing section of
slope
TIER 3 EXAMPLES
ADA-52
COMMENTS: Notice that the slope has not weathered uniformly with overhangs present that will result in rockfall. It should be noted that a regional joint set is noticeable along which large blocks or volume of rockfall will occur in the future.
` ADA-52 (Ditch line)
COMMENTS: The catmint area appears to be only a hydraulic ditch, and does not appear to be adequate to retain a large rockfall that may occur from entering onto the roadway. It should be noted that the ditch line had been recently regarded and cleaned prior to photo.
Recent rockfall
ADA-52-24.1 +/- (looking East)
ADA-52-24.1 +/- (looking West)
COMMENTS: Notice that the slope has differential weathering resulting in an overhang of the massive sandstone that will result in rockfall. Additional, the ditch does not appear to be adequate to retain the large block size that will occur during the rockfall from entering onto the roadway. It should be noted that a regional joint set is noticeable along which large blocks of rockfall will occur in the future.
Valley Stress Relief Joint
Edge of Pavement
BEL-149-12.4 +/-
BEL-149-12.4 Top of slope BEL-149-12.4 Ditch COMMENTS: Notice that the slope has weathered poorly resulting in several sources that will result in rockfall. This includes the upper portion of the slope that is the natural backslope which is vegetated. Additional, the ditch dose not appears to be adequate to retain rockfall that will occur from entering onto the roadway.
Top of Cut Slope
BEL-147-33.2 +/- (Looking East)
COMMENTS: Notice that the slope has not weathered uniformly with overhangs throughout the cut slope that will result in rockfall.
BEL-147-33.2 +/- (Looking West)
COMMENTS: Notice that the hydraulic ditch has been grouted rip rap to prevent erosion during high flow events. This reduces the effectiveness of the catchment area since the grout will allow for a better “bounce” of a block instead of diminishing the rockfall.
GUE-70-4.9 +/-
GUE-70-4.9 +/-
COMMENTS: Notice that the slope has not weathered uniformly with overhangs at the top that will result in rockfall. Additional, it dose not appears that the ditch will be sufficient to retain the large blocks from the rockfall from entering onto the roadway. It should be noted that the where the highly weathered shale is present that a decrease in the rockfall reaching the ditch may occur.
Differential weathering within the rock slope
Anticipated block size during a rockfall
HAM-275-47.5 +/-
HAM-275-47.5 +/-
COMMENTS: Notice that the slope has not weathered uniformly with overhangs at the top of the cut backslope that will result in rockfall. Additional, it dose not appears that there is any ditch to retain rockfall from entering onto the roadway. It should be noted that the retaining wall is only 3 to 4 inches higher than the toe of the slope and does not appear to be affective as a rockfall catchment structure.
Rockfall from the cut back
TUS-77-5.1 (Ramp C to SR 36)
COMMENTS: Notice that the slope has not weathered uniformly with overhangs within the cut slope that will result in rockfall.
TUS-77-5.1 (Ramp C to SR 36)
COMMENTS: The catchment area does not appear adequate to retain all rockfall from the roadway. Note that several sizes of rock debris is evident within the catchment area.
Area(s) of rock overhang(s)
Typical Block Size during Rockfall
APPENDIX E
GPS Guidelines
APPENDIX E - GPS GUIDELINES
GGEENNEERRAALL The majority of the field data collected during the field evaluation of the Inventory Sites will be either collected utilizing a hand held gps unit, or referenced to coordinates collected with the hand held gps unit. Three basic types of gps data can and will be collected during the field evaluation of the Inventory Site. These data types are points, lines, and areas. The following sections outline the basic parameters and guidelines established for the field work associated with the Rockfall Inventory. GGPPSS GGEENNEERRAALL PPAARRAAMMEETTEERRSS Prior to collection of any gps data, make sure the Trimble GeoExplorer (or similar unit) is utilizing its WASS correction. A minimum of four satellites with a minimum elevation mask of 15º is required for an adequate signal. A PDOP (Position Dilution Of Precision) of less than six and a SNR (Signal to Noise Ratio) of greater than 39 is required. The antenna should always be held parallel to the ground at a constant height, approximately chest level. GGPPSS PPOOIINNTTSS A single referenced item, such as a seep, centroid location, etc, will be collected as a gps point. A gps point should be collected utilizing the hand held Trimble unit set to a one second log interval. This means that a data reading is collected every second. A minimum of twenty readings should be collected to establish the point. Start collecting the data readings and hold the gps unit as steady as possible until the required number of readings have been collected then stop of the readings. The recorded gps point will consist of the averaged value of the data readings collected. GGPPSS PPOOIINNTTSS OOFFFFSSEETTSS If an insufficient signal is present to collect the gps point (refereed to as the reference gps point) the point can be offset. To offset the gps point, find a location which is relatively close where the gps signal is adequate. At this area, collect a gps point as just outlined. Then with a compass obtain a bearing from where the gps point was collected to where the reference gps point should have been collected. The bearing is a whole degree azmuth reading from north. Then measure the distance from the area that the gps point was collected to the reference gps point. From the collected gps point, the bearing and offset distance can be used to calculate the reference gps point.
GGPPSS LLIINNEESS A horizontal feature, such as a spring line or seep line, will be collected as a gps line. A gps point should be collected utilizing the hand held Trimble unit set to a five second log interval. This means that a data reading is collected every five seconds. Start collecting data readings at one end of the horizontal feature and walk at a steady pace parallel to the feature to the opposite end where the data readings should be stopped. The gps line will consist of a “normalized line” of the readings collected. If the Field Team is unable to collect the readings on top of the horizontal features, the offset function should be utilized. GGPPSS AARREEAASS An area feature, such as a seep zone, will be collected as a gps area. A gps area should be collected utilizing the hand held Trimble unit set to a five second log interval. This means that a data reading is collected every five seconds. Start collecting data readings at one point of the area feature and walk at a steady pace along the perimeter of the area until the area has been outlined where the data readings should be stopped. The gps area will consist of a polygon based upon the readings collected. If the Field Team is unable to collect the readings at the area features, the offset function should be utilized.