Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
-
Upload
recordtrac-city-of-oakland -
Category
Documents
-
view
222 -
download
0
Transcript of Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
1/63
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
16 Southwood Drive
Orinda, CA 94563
510-520-5592
ENGINEERING GEOLOGY GEOLOGIC HAZARD ASSESSMENT HYDROLOGY GEOTECHNICAL ENGINEERING
LANDSLIDE INVESTIGATION REPORT
CHELTON DRIVE LANDSLIDE
CHELTON DRIVE AND GIRVIN DRIVE
OAKLAND, CALIFORNIA
UNAUTHORIZED USE OR COPYING OF THIS DOCUMENT IS STRICTLY PROHIBITED BY ANYONE OTHER THAN THE
CLIENT AND PROJECT OWNER FOR THIS SPECIFIC PROJECT.
July 25, 2012
Job No. 1082.100
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
2/63
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
16 Southwood Drive
Orinda, CA 94563
510-520-5592
ENGINEERING GEOLOGY GEOLOGIC HAZARD ASSESSMENT HYDROLOGY GEOTECHNICAL ENGINEERING
TABLE OF CONTENTS
INTRODUCTION ............................................................................................................................................ - 1 -
LANDSLIDE HISTORY ................................................................................................................................. - 1 -
PURPOSE AND SCOPE OF SERVICES ......................................................................................................... - 2 -
FIELD INVESTIGATION .............................................................................................................................. - 2 -
SLOPE INCLINOMETER INSTALLATION ..................................................................................................... - 3 -
LABORATORY TESTING ............................................................................................................................. - 3 -
EXISTING GEOTECHNICAL INFORMATION ............................................................................................... - 3 -
Landslide Records at the City of Oakland ............................................................................................ - 3 -
Dames & Moore geotechnical investigation dated October 15, 1969 ................................................ - 4 -
Un-published landslide mapping by the City of Oakland ..................................................................... - 4 -
Geotechnical Investigations of Lot 2344 .............................................................................................. - 5 -
FINDINGS ...................................................................................................................................................... - 5 -
SITE DESCRIPTION .................................................................................................................................... - 5 -
AERIAL PHOTOGRAPH INTERPRETATION ................................................................................................. - 5 -
REGIONAL GEOLOGY ................................................................................................................................ - 6 -
SUBSURFACE CONDITIONS ...................................................................................................................... - 6 -
Landslide Conditions ............................................................................................................................ - 7 -
Bedrock Conditions .............................................................................................................................. - 8 -
Groundwater ........................................................................................................................................ - 8 -
SEISMIC HAZARDS .................................................................................................................................... - 9 -
CONCLUSIONS AND RECOMMENDATIONS ................................................................................................ - 10 -
GENERAL ................................................................................................................................................ - 10 -CHELTON DRIVE LANDSLIDE ACTIVITY ................................................................................................... - 10 -
SLOPE STABILITY ANALYSIS .................................................................................................................... - 11 -
EARTHQUAKE-INDUCED LANDSLIDE POTENTIAL ................................................................................... - 12 -
SEISMIC DESIGN CRITERIA...................................................................................................................... - 12 -
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
3/63
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
16 Southwood Drive
Orinda, Ca94563
510-520-5592
ENGINEERING GEOLOGY GEOLOGIC HAZARD ASSESSMENT HYDROLOGY GEOTECHNICAL ENGINEERING
DRAINAGE GALLERY CONDITIONS ......................................................................................................... - 13 -
SLOPE INCLINOMETER MONITORING .................................................................................................... - 13 -
LIMITATIONS .............................................................................................................................................. - 14 -
REFERENCES ............................................................................................................................................... - 15 -
LIST OF FIGURES
FIGURE 1VICINITY MAP
FIGURE 2SITE PLAN
FIGURE 3CROSS SECTION A-A
FIGURE 4AERIAL PHOTO INTERPRETATION
FIGURE 5REGIONAL GEOLOGIC MAP
FIGURE 6 - REGIONAL LANDSLIDES AND OTHER SURFACE DEPOSITS MAP
FIGURE 7 - OFFICIAL EARTHQUAKE FAULT ZONES MAP
FIGURE 8OFFICIAL SEISMIC HAZARD ZONE MAP, STATE OF CALIFORNIA
FIGURE 911 RESULTS OF SLOPE STABILITY ANALYSES
FIGURE 12SLOPE INCLINOMETER PLOT B-2A
FIGURE 13RING SHEAR TEST RESULTS
FIGURES 14ATTERBERG LIMITS TEST RESULTS
FIGURES 15 AND 16PARTICLE SIZE DISTRIBUTION TEST RESULTS
LIST OF APPENDICES
APPENDIX ACORE LOGS (2013 study)
APPENDIX BBORING LOGS, DAMES AND MOORE (1969)
APPENDIX CDIGITAL PHOTOGRAPHS OF 2013 CORE SAMPLES
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
4/63
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
16 Southwood Drive
Orinda, CA 94563
510-520-5592
ENGINEERING GEOLOGY GEOLOGIC HAZARD ASSESSMENT HYDROLOGY GEOTECHNICAL ENGINEERING
December 1, 2012
Job No. 1082.100
Mr. Edward De MeloC/O BERDING WEIL
2175 N California Blvd, Suite 500
Walnut Creek, California 94596
Attention: Mr. Chad T. Thomas
Subject: DRAFT
Landslide Investigation Report
Chelton Drive Landslide
Chelton Drive and Girvin Drive
Oakland, California
Dear Mr. Thomas:
INTRODUCTION
This report presents the results of our subsurface investigation of the Chelton Drive Landslide located
between Chelton Drive and Girvin Drive in Oakland California. The Chelton Drive Slidewas named
during the late 1960s following failure of the hillside beneath Chelton Drive. Herein we will use the
phrase Chelton Drive Landslide to be clear as to the site conditions. The Chelton Drive Landslidewas
mapped covering an area about 260 feet wide at the head scarp along Chelton Drive and extended
about 320 feet downslope to Girvin Drive at the toe of the landslide mass. The approximate site
location is shown on the Vicinity Map, Figure 1, and the approximate landslide limits are shown onFigure 2.
We previously conducted a preliminary engineering geologic review for Lot 2344 of the Piedmont Pines
development which is located at the base of the Chelton Drive Landslide along Girvin Drive. The review
focused on available geotechnical reports specific to Lot 2344 and landslide records at the City of
Oakland. The results of the review were summarized in our report dated December 1, 2012. The study
revealed that Lot 2344 was located at the base of a historically active deep-seated bedrock landslide
that additional without stabilization would preclude the safe development of Lot 2344 or any of the
surrounding lots.
LANDSLIDE HISTORY
The first reported indications of massive landslide movement occurred in April 1967. Chelton Drive
dropped as much as 10 feet over a period of about 1 week as the landslide slid downslope. Significant
damage resulted from the April 1967 landslide causing closure of Chelton Drive and forcing the
evacuation of 2 homes located within the landslide limits. The City of Oakland restored access through
Chelton Drive by placing fill on the top of the landslide mass and lowering the adjacent street grades.
In January 1969, the landslide mass began to show signs of additional movement along Chelton Drive.
This episode of landslide activity included up to 13 feet of movement over a 1-month period. The two
http://maps.yahoo.com/#tt=&q=2175+N+California+Blvd%2C+Walnut+Creek%2C+CA++94596-3540&conf=1&start=1&lat=37.9095&lon=-122.066238&zoom=16&mvt=m&trf=0http://maps.yahoo.com/#tt=&q=2175+N+California+Blvd%2C+Walnut+Creek%2C+CA++94596-3540&conf=1&start=1&lat=37.9095&lon=-122.066238&zoom=16&mvt=m&trf=0http://maps.yahoo.com/#tt=&q=2175+N+California+Blvd%2C+Walnut+Creek%2C+CA++94596-3540&conf=1&start=1&lat=37.9095&lon=-122.066238&zoom=16&mvt=m&trf=0http://maps.yahoo.com/#tt=&q=2175+N+California+Blvd%2C+Walnut+Creek%2C+CA++94596-3540&conf=1&start=1&lat=37.9095&lon=-122.066238&zoom=16&mvt=m&trf=0 -
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
5/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 2 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
homes located on the landslide that were evacuated in 1967 were demolished due to severe structural
damage and the potential for future damage to neighboring properties.
Following the second episode of massive sudden landslide movement in 1969, the City of Oakland
retained Dames & Moore, a reputable geotechnical engineering firm, to provide recommendations for
landslide stabilization. Dames & Moore (report summarized below) characterized the Chelton DriveLandlside as a bedrock landslide with a slip surface as deep as 45 feet below the ground surface. In
order to increase stability of the Chelton Drive Landslide, the City of Oakland installed extensive
drainage galleries to lower groundwater levels. The drainage galleries consisted of a series of vertical
drainage shafts connected at the bottom by corrugated metal pipes. The outlet pipes are visible on the
properties bordering the site and they discharge water below Girvin Drive. We were not able to obtain
the full plan set that shows the bottom elevations or construction details for the drainage galleries or for
any other aspects of the stabilization efforts undertaken by the City of Oakland. The approximate
locations of the drainage galleries are shown on the Site Plan, Figure 2.
The current conditions of Chelton Drive suggest that post-1970 movement of the Chelton Drive
Landslide has occurred. We observed an arcuate pattern of several inches of settlement along thedownslope side of Chelton Drive. The arcuate settlement pattern generally coincides with the landslide
limits reported for the 1967 and 1969 landslide events. Additionally, based on verbal reports, we
understand that lots on the east side of Chelton Drive may have experienced some settlement and
ground deformation. For reference, portions of the 1667 landslide limits were mapped extending into
some lots east of Chelton Drive.
PURPOSE AND SCOPE OF SERVICES
The purpose of this investigation was to evaluate the landslide conditions within and upslope of Lot
2344 of the Piedmont Pines development and to evaluate the feasibility of developing Lot 2344 for
single family residential use. Our scope of services for this project included:
1.
Review of readily available published geologic maps and reports covering the site vicinity.
2.
Reviewing readily available files from the City of Oakland Planning Department.
3.
Site reconnaissance by a State of California licensed Certified Engineering Geologist.
4.
Drilling and logging of 4 exploratory borings to depths between about 30 and 80 feet.
5.
Installation and monitoring of a slope inclinometer in one boring drilled on Lot 2344.
6.
Lab testing on selected slide plane materials.
7.
Evaluation and analysis of the information obtained during the course of this study.
8.
Preparation of this report.
FIELD INVESTIGATION
Our field investigation for this project was conducted in May, 2013. The main aspect of the investigationincluded the drilling and logging of 4 exploratory borings designated as Borings B-1, B-2, B-2A and B-3.
Borings were drilled by Gregg Drilling and Testing, Inc. out of Martinez, California using a six inch
diameter core barrel equipped with HQ coring systems. Borings B-1, B-2 and B-2A were drilled to depths
up to 80 feet below the ground surface using a small limited access Fraste Mito 4000 track-mounted drill
rig and B-3 was drilled using a truck-mounted CME 850 drill rig. Core samples recovered from B-2 were
disrupted by drill rig malfunctions. Therefore, the boring was terminated at a depth of 25 feet, the drill
rig moved about 10 feet south and re-drilled as B-2A. Borings were continuously sampled and logged
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
6/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 3 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
by a certified engineering geologist as samples were recovered. The borings were backfilled with
cement grout in accordance with drilling permit requirements, except for B-2A in which a slope
inclinometer was installed. The boring locations were surveyed in the field by Moran Engineering out of
Berkeley, California. Boring locations are shown on the Site Plan, Figure 2. Core Logs are provided in
Appendix A.
During the field investigation, we also conducted a reconnaissance of the hillside and adjacent streets.The reconnaissance was conducted in attempt to locate the piezometers noted on the 1969 Dames &
Moore map and to identify any other landslide related features at the site. We located man-holes (MH-
1 and MH-2) with PVC pipes above the mapped location of the drainage galleries and one piezometer
along the western shoulder of Chelton Drive. The man-hole locations were surveyed by Moran
Engineering at the locations shown on the Site Plan. The piezometer located along Chelton Drive
appears to coincide with the location of observation well Afrom the 1969 Dames & Moore report and
the approximate location is shown on the Site Plan.
SLOPE INCLINOMETER INSTALLATION
We installed 2.75-inch (70mm) slope inclinometer casing into the borehole at the B-2A location. The
inclinometer was positioned based on surface indications of landslide deformation and site access. Theinclinometer was installed to readable depth of 76 feet below the top of casing. The top of casing was
surveyed by Moran engineering to be at Elevation 1067.4 feet Mean Sea Level, about 1.5 feet above the
ground surface. The A+ groves within the casing were aligned downslope, an azimuth direction of about
270 degrees.
Baseline readings of the slope inclinometer were taken on April 2, 2013 and one set of subsequent
readings were taken on July 17, 2013. The current plots are inconclusive with respect to subsurface
landslide movement but do show minor blip at about 44 feet, about the same elevation as the slide
plane identified in the core samples. Plots of the slope inclinometer readings are provided on Figure 13.
LABORATORY TESTING
Representative samples of the slide plane materials encountered in B-2A were transmitted to Cooper
Testing Labs, Inc., in Palo Alto, California for laboratory analysis. Testing included performing residual
torsion ring shear tests (ASTM D 6467) to get residual strength values for the gouge zone in B-2A at a
depth of 42 feet. The sample was prepared over a -200 sieve and sheared at 2000, 4000 and 8000 ksf.
Atterberg limits and particle size distribution tests were run on slide plane materials in B-2A at 15 and 42
feet. Lab test reports label the samples as being from a depth of 40 feet which represents the middle of
the shear zone noted on the sample, however we provided the lab with the actual clay gouge material at
42 feet for testing. Lab tests indicate that the gouge materials at the base of the landslide have a
residual strength (phi angle) of 15 degrees and a plasticity index (PI) between about 15 and 17. Lab test
results are provided on Figures 16 through 20.
EXISTING GEOTECHNICAL INFORMATIONLandslide Records at the City of Oakland
The City of Oakland Planning Department has record files regarding a large bedrock landslide named the
Chelton Drive Slide that occurred in the Late 1960s. The subject files have the City file designation L
275-1 which is stamped on documents in the file. Movement of the landslide is reported to have
occurred in 1967 and again in 1969. The approximate historic limits of the Chelton Drive Landslide are
shown on the Site plan, Figure 2. The record documents in the City files that were reviewed as part of
this project include the following:
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
7/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 4 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
Proposal to conduct a landslide investigation by Dames & Moore dated June 11, 1969
Landslide investigation report by Dames and Moore dated October 15, 1969. Several enlarged
prints of the figures from this report are also in the City files.
Undated (circa 1969?) topographic map of the subject landslide area by the City of Oakland.
One sheet of a plan set titled Plans for the construction of drainage galleries in the vicinity of
Chelton Drive and Chelsea Drive. The sheet shows the limits of landslide movement prior to
1970, limits of repair grading at the top of the landslide and the location of drainage galleries.
The documents suggest that the first episode of landslide activity extended down to Girvin Drive based
on the map provided in the Dames & Moore proposal and the slide limits shown on the single plan
sheet. The 1969 Dames & Moore report shows the toe of the landslide as much as 50 feet upslope of
Girvin Drive, generally in the middle of Lot 2344. Both of the reported landslide limits are shown on the
Site Plan, Figure 2.
Dames & Moore geotechnical investigation dated October 15, 1969
The City of Oakland retained Dames & Moore to evaluate the Chelton Drive Landslide and provide
recommendations for stabilization. The results of the Dames & Moore study are provided in their reportdated October 15, 1969 which can be found on file at the City of Oakland. In summary, Dames & Moore
drilled 5 exploratory borings through the landslide mass. The earth materials encountered in the
borings were interpreted to indicate a bedrock landslide with a depth of sliding between about 30 and
45 feet deep. The landslide materials were described as highly weathered and fractured shale with
abundant clay seams. Additionally, a 4 to 10 foot thick zone of highly sheared and fractured bedrock
was encountered at the base of the landslide. Bedrock underlying the landslide was described as gray to
black fractured siltstone with little weathering. Groundwater levels were reported to include significant
seasonal fluctuations up to 30 feet which appeared to have been a significant contributing factor in the
landslide activity. The highest groundwater levels noted on the borings logs were up to 15 feet above
the interpreted basal slip plane except for in Boring B-4 which was noted about 11 feet below the
interpreted basal slip plane at that location. The toe of the landslide was described as poorly defined in
the field at that time and the mapping at the toe was inferred based on the occurrence of seepage on
the slope just above Girvin Drive. Additionally, Dames & Moore made some assumptions regarding the
depth of sliding coinciding with the depth at which wells were sheared-off during the 1969 movement.
It is not known if the wells sheared at the deepest portion of movement or if the wells sheared deeper,
possibly at multiple intervals. The approximate locations of borings drilled at the site by Dames and
Moore (1969) are shown on the Site Plan, Figure 2, copies of their boring logs are provided in Appendix
B.
Un-published landslide mapping by the City of Oakland
Historic landslides in the Oakland Hills were previously noted by the City engineer, Mr. Earl Buckingham.
Mr. Buckingham kept detailed unofficial notes of landslides and landslide features as they occurred in
the area between the early 1950s up to about 1970. Portions ofMr. Buckinghams maps and notes are
archived at the offices of Alan Kropp and Associates in Berkeley, California who allowed us to review the
Buckingham information located in their archives. We were able to locate pertinent maps for the
Piedmont Pines development but not the notes that would accompany each landslide feature. The
unpublished Buckingham maps show the subject Chelton Drive Landslide with the same general slide
limits as the 1969 Dames & Moore report. Buckingham noted the landslide as 11 A 34. Additionally,
Buckingham shows another separate landslide on the downhill side of Girvin Drive with the note 11 A
28.
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
8/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 5 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
Geotechnical Investigations of Lot 2344
Previous geotechnical investigations at Lot 2344 were summarized in our December 2012 report. At the
site geotechnical consultant Mohan Shrinivas and Purcell, Rhoades & Associates conducted a
geotechnical studies of Lot 2344 who presented their results in reports dated June 15, 2011 and
December 30, 2010, respectively. The investigation test pits and borings from those studies are shown
on the Site Plan, Figure 2. Since these studies did not detect, mention or evaluate the presence of the
Chelton Drive Landslide, they provide no pertinent data regarding site conditions.
FINDINGS
SITE DESCRIPTION
The site is defined as Lot 2344 of the Piedmont Pines development and the portion of the hillside
located directly above that is underlain by the Chelton Drive Landslide. The site is located between
Chelton Drive at the top of the hill and to Girvin Drive at the bottom. The area was developed well over
75 years ago; however, several lots in the site vicinity are vacant. Lot 2344 is a vacant lot located on the
east side of Girvin Drive in steep hillside terrain typical of the Oakland Hills. Lot 2344 is surrounded byundeveloped vacant lots on all sides, including downslope of Girvin Drive. We understand that these
lots are vacant largely due to the presence of the Chelton Drive Landslide that caused damage,
demolition and removal of 2 homes that were located along Chelton Drive. The approximate locations
on the demolished and removed homes are shown on the Site Plan, Figure 2. Large concrete blocks,
remnants from the former house foundations, were observed on the hillside.
Geomorphically, the site is situated near the head of a tributary drainage basin to Shepherd Canyon
Creek which is located downslope to the northwest. The ground surface at the site is steep with
topography ranging from about Elevation 1160 at the top along Chelton Drive to about Elevation 965 at
the bottom along Girvin Dive. Site topography slopes as steep as about 1 horizontal to 1 vertical (1H:1V)
along Girvin Drive and much flatter and irregular within the landslide mass. There is a subtle yet visiblebulge on the hillside within Lot 2344 that has the appearance of the leading edge of a landslide deposit.
A relatively horizontal (un-natural looking) bench traverses the hillside at the location of the lower tier
of drainage galleries installed in response to the Chelton Drive Landslide. Two man-hole covers (MH-1
and MH-2) were observed at the northern end of the bench at the locations shown on the Site Plan,
Figure 2. Several larger trees at the site are either severely leaning downslope or have fallen.
Chelton Drive currently has an arcuate-shaped cracking and settlement pattern that appears to coincide
with the late-1960s landslide limits. Corrugated metal drainage pipes traverse the slopes north and
south of Lot 2344 and discharge water to the slope below Girvin Drive. The pipes appear to be the
outfall pipes for the drainage galleries installed upslope. The pipes are separated slightly on the north
side of Lot 2344 at the approximate location shown on Figure 2. An erosion gully has formed along the
alignment of the southern pipe below Girvin Drive. We understand that these pipes are the outlet pipesfor the drainage galley installed above Lot 2344 to stabilize the Chelton Drive Landslide. Directly
downslope of the site, the outer edge of Girvin Drive is settling into the ravine.
AERIAL PHOTOGRAPH INTERPRETATION
We reviewed stereo-paired aerial photographs focusing on the years of reported landsliding including
review of aerial photographs from 1967, 1969 and 1970. Aerial photographs were obtained and viewed
at the archive library at Pacific Aerial Surveys office in Oakland, California.
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
9/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 6 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
The 1969 photography showed that Chelton Drive and Chelsea Drive had been recently paved where the
roadway was reported to be damaged and repaired following the 1967 event. The slope between
Chelton Drive and Girvin Drive was covered with trees and not readily viewable. The 1969 photography
provided the best viewing of landslide conditions and show several landslide related features as noted
below. We observed several subparallel cracks in the asphalt along Chelton Drive in the location of the
recent repaving noted in 1967. The slope between Chelton Drive and Girvin Drive appeared to bedisturbed based on tonal contrasts suggesting bare ground rather than vegetation. The area that
appeared disturbed extended down to Girvin Drive. In the 1970 photography, Chelton Drive appeared
repaved as the cracks were no longer visible. A portion of the 1969 photograph annotated with our
interpretations of landside-related features noted is provided on Figure 4.
REGIONAL GEOLOGY
The site is located within the Coast Ranges Geomorphic Province of California. The Coast Ranges are
characterized by northwest-southeast trending series of folded and faulted mountain ranges and valleys.
Folding, faulting and tectonic uplift of the region is the result of rightlateral and oblique relative
motions between the Pacific and North American tectonic plates which has deformed the region for the
past several million years. The San Andreas fault is the generally accepted boundary between theseplates, although in the San Francisco Bay Area, stresses and deformation are distributed across a broad
network of subparallel right-lateral strike slip faults.
The site is situated on the west flank of the Oakland-Berkeley hills which is a northwest-trending band of
uplifted bedrock units forming steep hillsides along the east side of the San Francisco Bay plain.
According to regional geologic maps prepared by the U.S. Geological Survey (Graymer, 2000; Graymer et
al, 1996; Radbruch, 1969; Radbruch and Case, 1967) several bedrock units have been tectonically
juxtaposed against each other in the area. In general, in the site vicinity, sedimentary bedrock units of
the Franciscan Complex are located on the west side of the Hayward fault, while several slivers of
volcanic, metamorphic and sedimentary rocks are located to the east of the fault.
Bedrock underlying the site includes siltstone and shale of the Shepherd Creek formation. The ShepherdCreek formation is a series of sea floor sedimentary layers that were deposited during the Late
Cretaceous Period of geologic time, roughly 65 to 144 million years before present. Outcrops along
Girvin Drive indicate the bedrock is steeply inclined and aligned with a northwest northwest-trending
structure. Regional geologic maps depict a northwest trend and variable dip of the bedrock layers that
is distorted by folding. Locally, based on our observation of several bedrock outcrops along Girvin Drive,
this portion of the Shepherd Creek formation consists of thinly bedded layers of sandstone and shale
that strike to the northwest and dip at inclinations between about 75 to 90 degrees, generally consistent
with the regional geologic maps. A portion of Graymers map is provided on Figure 5.
The site is located in an area of known landslides and relatively high landslide hazards. Regional
landslide maps prepared by the U.S. Geological Survey (Nilsen, 1975) shows a landslide featuredownslope of Girvin Drive but do not show a landslide deposit in the location of the Chelton Drive
Landslide. However, regional maps are generally created without site-specific investigation and are
considered guidelines for planning only. A portion of Nilsens landslide map is provided on Figure 6.
SUBSURFACE CONDITIONS
The site is underlain by the Chelton Drive Landslide which is a deep-seated bedrock landslide extending
to depths of about 45 to 50 feet below the ground surface. Artificial fill was placed along the top of the
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
10/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 7 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
landslide to re-establish the roadway along Chelton Drive following the 1967 and 1969 landslide events.
We did not investigate the fill. The landslide mass is composed of a displaced block of bedrock overlying
the Shepherd Creek formation. Descriptions of the landslide mass, basal shear zone and the underlying
bedrock are provided below.
Landslide ConditionsBased on the findings of this investigation and review of the 1969 Dames & Moore report, the Chelton
Drive Landslide is composed of a displaced mass of disrupted Shepherd Creek Formation with abundant
clay infilling. Many portions of the rock mass recovered in our borings have a block-in-matrix texture
with clay infilling between dilated fractures in the rock. The majority of clay infilling was interpreted to
be washed away during the drilling processes based on the recovery of rubble only at several intervals.
The landslide mass was found brown to orange brown, highly weathered, highly fractured to crushed
and weak.
Our borings were drilled in the northern half of the landslide, where we generally encountered deeper
landslide debris than encountered in Dames & Moores nearby borings. For example, we encountered
up to 42 feet of landslide debris in Boring B-2A, whereas Dames & Moore encountered only about 27feet of landslide debris in their nearby B-4 which was drilled more in the center of the landslide mass
(see Figure 2). This can be attributed to the underlying bedrock structure. While the landslide cuts
across dip, thereby shearing across beds, we believe that the northern edge of the landslide is, at least
in part, along one of the more resistant steep south-dipping sandstone or siltstone beds. Therefore, the
Chelton Drive Landslide is likely wedge-shaped across its width, resulting in deeper landslide deposits to
the north and a steep northern margin along bedrock structure.
The basal landslide slip plane was identified in Borings B-1 and B-2A. In Boring B-1, the slide plane
identified at 32 feet included a 2 foot thick shear zone consisting of angular rock fragments in a
sheared soil matrix demonstrating block-in-matrix textures. At the top of the shear zone, we identified a
1 inch thick layer of olive brown clay gouge with well-developed dip slip striations. The gouge layer was
measured dipping 17 degrees. Internal shearing within the landslide mass was also interpreted betweenabout 20 to 23 feet below the ground surface in Boring B-1.
In Boring B-2A, we encountered sheared zones at depths of about 15 and 42 feet below the ground
surface. The shear zone at 15 feet includes 8 inches of sheared clay gouge with a sub-horizontal foliated
shear fabric. We interpreted this zone to represent a higher slide plane within the landslide mass.
Samples of the sheared zone at 15 feet were submitted to the laboratory for Atterberg limits and
gradation tests. The lab tests indicate the slide plane clay gouge is moderately expansive with a
Plasticity Index (PI) of 27. Digital photographs of the slide plane recovered from the core samples at 15
feet are provided in Appendix C.
The basal shear zone was identified in Boring B-2A between about 38 and 42 feet below the ground
surface. Within this interval we identified a 12 to 18 inch zone of blue gray sheared clay with angular
rock fragments and a foliated shear fabric dipping 10 to 15 degrees. About 12 inches of rubble were
encountered that may be slough from the borehole above, however the driller insists they did not raise
the core barrel through this interval, therefore, the rubble may represent a block of fractured rock
within the shear zone. At the base of the shear zone, we identified the slide plane at a depth of about
42 feet. At this depth we identified a 6-inch thick layer of sheared black clay with a inch thick layer
of foliated clay gouge at the base. The clay gouge was measured dipping 10 degrees. The slide plane at
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
11/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 8 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
42 feet was submitted to the laboratory for torsional ring shear, Atterberg limits and gradation tests.
The lab tests indicate the slide plane gouge is relatively granular with a Plasticity Index (PI) of 15 and a
residual phi angle of 15 degrees. Digital photographs of the shear zone and slide plane recovered
between 37 and 42 feet are provided in Appendix C.
Bedrock Conditions
Bedrock underlying and surrounding the Chelton Drive Landslide belongs to the Shepherd Creek
formation. The Shepherd Creek formation was deposited as a series of sea floor sediments during the
Cretaceous Period of geologic time (65 to 144 million years before present). The Shepherd Creek
formation consists of thinly laminated clay rich shale, siltstone and occasional beds of sandstone. At the
site the in-place bedrock was found gray to dark gray, weak to moderately strong and thinly laminated.
Bedrock structure measured in outcrops along Girvin Drive shown a northwest strike of the beds that
dip steeply to the northeast and southwest between 75 to 90 degrees. This structure is typical of the
steeply bedded, occasionally overturned structures shown on the regional geologic maps.
We observed outcrops or relatively strong sandstone beds up to a few feet thick along the slope above
Girvin Drive, just north of the site. The beds were striking northwest and dipping south (towards thelandslide mass). The strike of the bedrock structure is about the same or at least similar to the direction
of movement of the Chelton Drive Landslide. Therefore, the steeply dipping stronger beds observed
near the northern margin of the landslide mass likely influences the subsurface geometry of the
landslide as noted above.
Groundwater
Groundwater conditions at the site are influenced by the presence of the drainage galleries installed by
the City of Oakland as their stabilization efforts of the Chelton Drive Landslide. The drainage galleries
include vertical drains connected at the base by horizontal shafts. We were not able to locate any
records of the drainage gallery construction other than the plan view locations that are shown on the
Site Plan, Figure 2. We made several inquiries to the City of Oaklands planning, engineering and
drainage departments. None of these departments had any knowledge or records regarding the
subsurface drainage system installed at the site.
Groundwater conditions were generally obscured during drilling of our borings due to the addition of
water as part of the HQ coring methods. We were able to obtain some groundwater information from
B-1, where water continually rose from the core barrels after the drilling system was shut off suggesting
some artesian conditions at about 50 feet below the ground surface. Groundwater information was not
obtained from Borings B-2, B-2A or B-3.
We located an 8-inch diameter Christy box along the western shoulder of Chelton Drive covering a near-
vertical, 1 inch diameter PVC pipe that appears to correspond to the location of observation well A
from the 1969 Dames & Moore report. We inserted a water level meter into the 1 inch diameter PVCpipe and found that the meter has trouble passing a blockage or kink at a depth of about 34 feet.
Groundwater was detected at a depth of 44 feet and the bottom of the PVC pipe appeared to be about
49 feet below the ground surface. The approximate location of observation well A is shown on the Site
Plan, Figure 2.
We located 2 man-holes along the northern limits of the Chelton Drive Landslide, located roughly mid
slope. The locations of the man-holes, MH-1 and MH-2, were surveyed in the field by Moran
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
12/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 9 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
Engineering at the locations shown on the Site Plan, Figure 2. Note that the surveyed man-hole
locations correspond to the north end of the middle row of the drainage galleries installed by the City of
Oakland. Therefore, we believe these are observation wells to check the drainage gallery conditions.
Manhole MH-1 covers an 8-inch diameter PVC pipe. We inserted the water level reader into the 8-inch
PVC pipe on the uphill side of the pipe. The water level meter hit the downhill side of the pipe at a
depth of about 20 feet demonstrating that the PVC pipe is severely out of plumb. The water level meterencountered a muddy bottom of the pipe at about 54 feet below the ground surface. Man-hole MH-2
covers a 2-inch diameter PVC pipe that is leaning over about 20 degrees at the ground surface. Similar
to MH-1, the water level reader encountered a muddy bottom of the pipe at about 49 feet below the
ground surface. Groundwater was not detected in the PVC pipes.
Our interpretations of the groundwater conditions underlying the site are shown on the Cross Section,
Figure 3. The following table summarizes the groundwater conditions described above.
LOCATION
GROUND SURFACE
ELEVATION
(Ft MSL)
DEPTH TO
GROUNDWATER
(Ft)
GROUNDWATER
ELEVATION
(Ft MSL)
B-1 1133.3* 50 feet 1083.3
Well A Estimated 1058 44 feet 1014
MH-1 1101.9* >54 feet 49 feet
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
13/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 10 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
Given the relatively high seismicity in the region, the site is expected to experience at least one
moderate to large magnitude earthquake in the future. The Working Group on Earthquake Probabilities
(1999) estimates there is a roughly 65% chance that the San Francisco Bay Area will experience a
magnitude 6.7 (or greater) earthquake within in the next 30 years. Interactive probabilistic seismic
analysis tools available at the U.S. Geological Survey and California Geological Survey websites suggest
the site is expected to experience peak ground accelerations (pga) with a 10% chance of being exceededin the next 50 years of 0.71g and 0.77g; respectively.
The site is located within a State of California designated Seismic Hazard Zone for earthquake-induced
landslide displacement (CGS, 2003). In contrast, seismic hazards maps covering the cities of Oakland
and Piedmont prepared by the U.S. Geological Survey (Miles and Keefer, 2001) shows the seismic
landslide hazard at the site to be low to very low. The official State of California seismic hazard map is
provided on Figure 8, the U.S. Geological Survey map is not provided to avoid confusion.
CONCLUSIONS AND RECOMMENDATIONS
GENERAL
Based on the results of this study, experience with similar large bedrock landslides, and professional
judgment, in our opinion none of the vacant lots between Chelton Drive and Girvin Drive or the vacant
lots below Girvin Drive are developable in the current conditions due to the high potential for the hazard
of damage resulting from movement of the Chelton Drive Landslide. The primary geologic hazards
impacting the site are the presence of the Chelton Drive Landslide and the potential for sudden mass
landslide displacement during a seismic event. Extensive movement of the existing landslide mass could
burry, knock over or destroy future improvements located within the landslide mass.
The current landslide conditions are considered marginally stable at best. The 1969 stability analysis
provided in the Dames & Moore report indicates that the landslide repair was designed to be marginally
stable in the static conditions, however, their analysis and parameters do not indicate the landslide is
stable in the pseudo-static (seismic) conditions. Based on our analysis, the Chelton Drive Landslide is
expected to undergo on the order of 5 to 10 feet of seismically induced deformation during a moderate
to large earthquake.
Based on the results of this study, we recommend the Chelton Drive Landslide be treated as an active
landslide feature for planning purposes.
CHELTON DRIVE LANDSLIDE ACTIVITY
Bedrock landslides in the region often creep along the basal slip surface at very slow rates for several
years, sometimes decades, without showing indications of activity such as cracks or bulges at the ground
surface. We believe there is physical evidence at the site that suggests the Chelton Drive Landslide hasexperienced episodic creep or movement since the historic landslide movement in 1969. The surface
indications of landslide activity include:
1)
There are several semi-arcuate cracks in the pavement along Chelton Drive, at about the
locations of the head scarp of the Chelton Drive Landslide.
2)
The leaning PVC pipes located at man-holes MH-1 and MH-2 suggest downslope movement
after installation.
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
14/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 11 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
3)
The bend or block in the PVC pipe at a depth of about 34 feet at observation well A which
corresponds to the approximate depth of the landslide at that location.
SLOPE STABILITY ANALYSIS
The stability analysis conducted by Dames & Moore in 1969 (for the shallowest condition) indicated that
the drainage galleries would only marginally stabilize the Chelton Drive Landslide. The analysis
calculated factor of safety of 1.2 for the non-seismic condition. With this relatively low calculated static
factor of safety, the existing landslide was expected to experience significant displacement during a
moderate to large earthquake event, specifically on the Hayward fault, which is located just mile west
of the site. It should be noted that the Dames and Moore analysis is well over 43 years old.
In order to model the static and seismic stability of the existing slope, we conducted a series of limit-
equilibrium slope stability analyses using the computer program SLOPE-W. Our slope stability analyses
were based on the interpreted slip surface geometry shown on the Cross Section (Figure 3).
Groundwater was modeled predominantly below the landslide mass due to the presence of the
drainage galleries and the results of our field investigation. The results of our various slope stability runs
are discussed in more detail below. . Plots of the slope stability analysis are provided on Figures 9though 11
In our initial static stability run, we modeled the slide plane gouge zone using a drained residual friction
angle of 15 degrees, which is consistent with the results of the laboratory ring shear test (Figure 13).
The analysis resulted in a factor of safety well below 1.0. These results are not supported by field data
or the initial inclinometer readings, which indicate the 15-degree drained friction angle measured in the
lab is not representative of the entire slide plane and likely represents the lower bound strength. In
addition, the slope stability analyses were performed using a two-dimensional model, which neglects
the three-dimensional effects of the potentially wedge-shaped landslide, which tend to increase the
actual factor of safety in the field. The results of the initial analysis using the 15-degree drained friction
angle are presented on Figure 11.
During our second slope stability run, we estimated the shear strength along the existing slide plane
through back-calculation, based on the assumption that the slope is currently at a static factor of safety
of about 1.0. The back-calculation using the two-dimensional slope stability model resulted in a drained
friction angle of about 24 degrees, as presented on Figure 11. The 24-degree strength is, in theory,
inflated due to the fact that it is influenced by the three-dimensional effects of the landslide present in
the field, which are not captured in the two-dimensional model. We conclude the assumed
approximate factor of safety of 1.0 is reasonable due to the observations of the arcuate cracking and
settlement pattern along Chelton Drive, roughly at the location of the 1967 and 1969 head scarp.
However, we believe the 24-degree strength likely represents an upper-bound for the strength of the
gouge zone, and therefore, our subsequent analyses utilize strength values between the 15- and 24-
degree values discussed above. The results of the back-calculation analysis are presented on Figure 11.
For our third run, we used a drained friction angle of about 20 degrees, which we believe is a realistic
strength approximation for long-term static conditions, given the available data and field observations.
As presented on Figure 12 this analysis resulted in a factor of safety of less than 1.0, which indicates
active failure, however, considering the shortcomings of two-dimensional modeling discussed above, we
believe 20 degrees represents a realistic average strength for the slide plane under static conditions. The
results of the analysis for the long-term static condition are presented on Figure 12.
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
15/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 12 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
Given that the slope is marginally stable under static conditions, we conclude the slope is subject to
significant deformations during moderate to large seismic events. As discussed in more detail in the
following section, we performed a deformation analysis to estimate the magnitude of potential
displacements during future earthquakes. We performed a fourth slope stability run in SLOPE-W toestimate the yield acceleration of the slide mass. The fourth run utilized a horizontal pseudo-static
coefficient to represent seismic loading. We also assigned an estimated undrained strength of 1,500 psf,
which is based on previous TxUU testing on the slide mass by Dames & Moore (1969) with consideration
of potential strength reduction due to the cyclic nature of seismic loading. We performed a series of
runs, increasing the horizontal pseudo-static coefficient until a factor of safety of 1.0 was achieved.
EARTHQUAKE-INDUCED LANDSLIDE POTENTIAL
The site is located within a State of California designated Seismic Hazard Zone for earthquake-induced
landslide displacement. The probabilistic seismic analysis web tools from the CGS and USGS indicate the
site is expected to experience relatively high peak ground accelerations. The stability of all slopes is
lowest during ground shaking from a large magnitude earthquake. Areas underlain by existinglandslides are generally considered to have the highest probability of coseismic displacement. Based on
our analysis, the potential for severe damage resulting from seismically-induced movement of the
Chelton Drive Landslide is the primary geologic hazard precluding development at the site. In our
opinion, the risk of earthquake-induced landslide damage at the site is very high.
As discussed in the previous section, to model the earthquake loading, we assigned an equivalent static
(pseudo-static) horizontal force equal to the soil weight multiplied by a seismic coefficient, k. Limit
equilibrium slope stability analyses were then performed to determine the critical (yield) seismic
coefficient (ky) that will reduce the static factor of safety against sliding of the potential slide mass to
unity. The analysis indicates ky for the slip surface defined in the geologic cross section (Figure 3) is
about 0.07g.
To estimate the amount of lateral movement the critical slide mass may experience during a seismic
event, we used the methodology developed by Bray and Travasarou (2007), which is presented in the
paper titled Simplified Procedure for Estimating Earthquake Induced Deviatoric Slope Displacements.
The method indicates the median displacement for the critical slip surface shown in Figure 3 is
approximately 5 to 10 feet, for a Mw7.33 earthquake occurring approximately 1.2 kilometers from the
site on the Hayward Fault.
SEISMIC DESIGN CRITERIA
Due to the relatively high seismicity of the San Francisco Bay region, the project should be expected to
undergo at least 1 moderate to strong earthquake during the lifespan of the project. Ground shaking
from a strong earthquake is a hazard that cannot be eliminated but can be partially mitigated throughproper attention to seismic structural design and observance of good construction practices. Based on
the an approximate center of the landslide located coordinates of 37.8264 degrees latitude and -
122.1953 degrees longitude, we recommend the structural engineer use the following design
parameters for seismic design in accordance with the ASCE 7-10 Standard, which is based on the 2008
USGS seismic hazard data.
SITE CLASS B - PERIOD (sec) 0.2 1.0
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
16/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 13 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
SPECTRAL RESPONSE Ss, S1 2.371g 0.986g
SITE COEFFICIENT Fa, Fv 1.0 1.0
MAXIMUM SPECTRAL RESPONSE
Sms, Sm1
2.371g 0.986g
DESIGN SPECTRAL RESPONSE
SDs, SD11.581g 0.657g
The above mentioned values are empirically generated and the actual ground response at the site can
vary.
DRAINAGE GALLERY CONDITIONS
The drainage galleries installed to lower groundwater levels from within the landslide area are over 40
years old and we could not find record of any maintenance activities by the City of Oakland. The
drainage galleries include vertical shafts connected at the base by metal pipes at the approximatelocations shown on the Site Plan, Figure 2. If the drainage galleries continually maintain groundwater
levels below the base of the landslide, they can be effective in lowering the potential for sudden massive
landslide movement.
Two man-hole covers (MH-1 and MH-2) were located along the alignment of the drainage galleries as
shown on the Site Plan, Figure 2. As previously discussed, both man-holes cover PVC pipes, both of
which were observed to have a significant downslope lean. Additionally, muddy sediments were
encountered at the bottom of each pipe. Based on our observations at the site, we have the following
concerns regarding the drainage galleries:
1)
We could not find any records of the as-built depths of the drainage galleries nor could we
locate any records of maintenance or knowledge of the system at the City of Oakland offices.
2)
Post-1970 movement of the Chelton Drive Landslide that has likely damaged some of the
vertical shafts allowing sediment to enter the pipes and the movement has deformed the
vertical PVC pipes.
3)
Some of the vertical shafts may not have penetrated through the deeper portions of the wedge
shaped landslide along the northern margin, above Lot 2344.
Properly functioning drainage galleries are essential to the stability of the Chelton Drive Landslide. As
previously mentioned there is a high risk of seismically-induced ground displacement of the Chelton
Drive Landslide which could severely damage the drainage gallery system. This can allow groundwater
to back up in the system and saturate the landslide mass which would increase the potential for
movement. The drainage galleries should be maintained in a functioning capacity for the lifespan of theneighboring developments.
SLOPE INCLINOMETER MONITORING
The slope inclinometer was installed in boring B-2A for the purpose of monitoring subsurface movement
of the Chelton Drive Landslide. Baseline readings of the slope inclinometer were taken on April 2, 2013
and one set readings were taken on July 17, 2013. The current plots are inconclusive with respect to
subsurface landslide movement but do show a very minor blip in the data plot at about 44 feet (below
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
17/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 14 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
the top of casing), corresponding to about the same elevation as the slide plane identified in the core
samples. At this time the readings are considered inconclusive with respect to landslide movement due
to the relatively short time period it has been installed. Slow landslide creep can take several months to
fully engage the inclinometer casing. We recommend the current quarterly monitoring period be
revised to take readings at 6 month intervals rather than every 3 months. Additionally, we recommend
the inclinometer be read as soon as possible following any small to large earthquake that causes groundshaking at the site. The post-earthquake readings should be performed to cross check the seismic
deformation analysis provided above, and to demonstrate activity of the Chelton Drive Landslide and
the magnitude of earthquake-induced movement of the landslide mass.
LIMITATIONS
The conclusions and recommendations contained in this report are based on the information provided
to us regarding the proposed improvements, the results of this investigation, our experience in the area
and professional judgment. This study has been conducted in accordance with currently accepted
standards of professional engineering geology; no other warranty is expressed or implied. The locations
of features discussed in the text above are those that existed at the time of our last site visit in July 2013and are not necessarily representative of other locations or times. If the subsurface conditions
encountered during any repair work or any future investigations of the Chelton Drive Landslide differ
from those interpreted in this report, our firm should be afforded the opportunity to review the changes
and respond accordingly.
Respectfully submitted,
RYAN GEOLOGICAL CONSULTING, INC.
Kevin James Ryan, P.G., C.E.G.
Principal Engineering Geologist
Copies: Addressee (1 pdf via email)
Attention: Mr. Chad Thomas
Mr. Ed De Melo (1 pdf via email, 2 hard copies via hand-delivery)
RGC_Landlside investigation report/Chelton Drive Landlside/1082.100.doc
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
18/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 15 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
REFERENCES
California Division of Mines and Geology, January 1, 1982, State of California special studies zones,
Oakland East, Revised official map.
California Geological Survey, February 14, 2003, State of California Seismic Hazard Zones, Oakland East
and part of the Las Trampas Ridge quadrangles, Official map.
California Geological Survey, 2003, Seismic hazard zone report for the Oakland East 7.5-minute
quadrangle, Alameda County, California: Seismic Hazard Zone Report 080.
Dames & Moore, October 15, 1969, Geological and soil engineering studies, Chelton Drive Slide, Chelton
Drive near Chelsea Drive, Oakland, California. Job No. 1363-005. Consulting report for the City of
Oakland.
Herd, D.H., 1978, Map of quaternary faulting along the northern Hayward fault zone: Mare Island,Richmond, Briones Valley, Oakland West, Oakland East, San Leandro, Hayward, and Newark 7
quadrangles, California: U.S. Geological Survey Open-File Report 78-308. Sheet 5 of 8.
Graymer, R.W.; 2000; Geologic map and database of the Oakland Metropolitan Area, Alameda, Contra
Costa, and San Francisco Counties, California: U.S. Geological Survey Miscellaneous Field Studies MF
2342, Online Version 1.0.
Graymer, R.W., Jones, D.L. and Brabb, E.E., 1996, Preliminary geologic map emphasizing bedrock
formations in Alameda County, California: A digital database: U.S. Geological survey Open File Report
96-252.
Leinkaemper, J.J.; 2008 (revised); Digital database of recently active traces of the Hayward fault: U.S.Geological Survey Data Series 177, Version 1.1.
Leinkaemper, J.J.; 1992; Map of recently active traces of the Hayward fault, Alameda and Contra Costa
Counties, California: U.S. Geological Survey Miscellaneous Field Studies Map MF-2196.
Miles, S.B. and Keefer, D.K., 2001, Seismic landslide hazard for the Cities of Oakland and Piedmont,
California: U.S. Geological Survey Miscellaneous Field Studies Map MF-2379.
Nilsen, T.W., 1975, Preliminary photointerpretation map of landslide and other surficial deposits of the
Oakland East quadrangle, Contra Costa and Alameda Counties, California: U.S. Geological Survey
Open File Map 75-277-41.
Purcell, Rhoades & Associates, December 30, 2012, Geotechnical Study, proposed single family home,
Lot 2344, Girvin Drive, Piedmont Pines, Oakland, California. Project No. 04-232/7500-01. Consulting
report for Mr. Edward De Melo.
Radbruch-Hall, D.H.; 1974; Map showing recently active breaks along the Hayward fault zone and the
southern Calaveras fault zone, California: U.S. Geological Survey Miscellaneous Investigations Series
Map I-813.
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
19/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
- 16 -
July 25, 2013
RYAN GEOLOGICAL CONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
Radbruch, D.H.; 1969; Aerial and engineering geology of the Oakland East quadrangle, California: U.S.
Geological Survey Geologic Quadrangle Maps GQ-769.
Radbruch, D. and Case, J.E., 1967, Preliminary geologic map and engineering geologic information,
Oakland and vicinity, California: U.S. Geological Survey Open-File Report 67-183.
Radbruch, D.H., 1967, Approximate location of fault traces and historic surface ruptures within the
Hayward Fault Zone between San Pablo and Warm Springs, California: U.S. Geological Survey
Miscellaneous Geologic Investigations Map I-522.
Roberts, S., Roberts, M.A., and Brennan, E.M., 1999, Landslides in Alameda County, California. A digital
database extracted from preliminary photointerpretation maps of landslides and other surficial
deposits by T.H. Nilsen in U.S.G.S. Open-File Report 75-277, U.S. Geological Survey Open-File Report
99-504.
Ryan Geological consulting, Inc., December 1, 2012, Preliminary engineering geologic review, Lot 2344
Piedmont Pines, Girvin Drive, Oakland, California. Consulting report for Mr. Ed De Melo, Job No.
1082.000.
Shrinivas, M., June 15, 2011, Geotechnical engineering investigation and design recommendations, new
residenceAPN 048D-7281-052Girvin Drive, Oakland, California. Consulting report for Mr. Edward
De Melo.
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
20/63
APPROXIMATESITE LOCATION
BASE: PORTIONS OF U.S.G.S. 7.5 MINUTE TOPOGRAPHIC QUADRANGLE, OAKLAND
EAST, CALIFORNIA AT A SCALE OF 1:24,000.
0 1000
1"=1000'
CHELTON DRIVE LANDSLIDE
CHELTON DRIVE AND GIRVIN DRIVE
OAKLAND , CA
DATE: 7-22-13 Figure 1Project No. 1082.100
RYAN GEOLOGICALCONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
21/63
0 50
1"=50'
BASE: DRAFT TOPOGRAPHIC SURVEY, PREPARED BY MORAN ENGINEERING, INC., DATED APRIL 20 13, AND CITY OF OAKLAND TOPO OF LANDSLIDE SURVEYED PRIOR TO 1970 LANDSLIDE MOVEMENT
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
22/63
0 50
1"=50'
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
23/63
?
?
TENSION CRACKS
ALONG CHELTON
DRIVE
APPROXIMATE LANDSLIDE
LIMITS BASED ON
APPARENT GROUND
DISTURBANCES
CHELTON
DRIVE
GIRVINDRIVE
CHELSEA DRIVE
BASE: PORTION OF AERIAL PHOTOGRAPH AV-902-09-26 FLOWN ON 5-16-1969
ACQUIRED FROM PACIFIC AERIAL SURVEYS IN OAKLAND CALIFORNIA
0 200
1"=200'
DATE: 7-22-13 Figure 4Project No. 1082.100
NOTE: LANDSLIDE FEATURES NOTED ABOVE ARE INTERPRETED
FROM STEREO-PAIRED AERIAL PHOTOGRAPHS DESIGNATED AS
FLIGHT AV-902, LINE 09, FRAMES 25 AND 26 FLOWN ON 5-16-1969
(APPROXIMATE)
RYAN GEOLOGICALCONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
CHELTON DRIVE LANDSLIDE
CHELTON DRIVE AND GIRVIN DRIVE
OAKLAND , CA
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
24/63
APPROXIMATE
SITE LOCATION
Ko
Kjm
Kfn
Qpaf
jb
0 1000
1"=1000'
DATE: 7-22-13 Figure 5Project No. 1082.100
RYAN GEOLOGICALCONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
CHELTON DRIVE LANDSLIDE
CHELTON DRIVE AND GIRVIN DRIVE
OAKLAND , CA
BASE: PORTION OF R.W. GRAYMER, 2000, GEOLOGIC MAP AND MAP DATABASE OF THE
OAKLAND METROPOLITAN AREA, ALAMEDA, CONTRA COSTA, AND SAN FRANCISCO
COUNTIES, CALIFORNIA: U.S. GEOLOGICAL SURVEY MISCELLANEOUS FIELD STUDIES
sp
EXPLANATION
CONTACT - DEPOSITIONAL OR
INTRUSIVE CONTACT, DASHED
WHERE APPROXIMATELY LOCATED,
DOTTED WHERE CONCEALED
REVERSE OR THRUST FAULT -
DASHED WHERE APPROXIMATELY
LOCATED, DOTTED WHERE
ONCEALED
STRIKE AND DIP OVERTURNED
BEDDING
STRIKE AND DIP OF BEDDING
ALLUVIAL FAN AND FLUVIAL
DEPOSITS (PLEISTOCENE)
FRANCISCAN COMPLEX
Qpaf
Ksc
Kr
CHERT BLOCKS
SHEPARD CREEK FORMATION
REDWOOD CANYON FORMATION
OAKLAND CONGLOMERATE
JOAQUIN MILLER FORMATION
SANDSTONE
fs
Ko
Kjm
Kfn
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
25/63
APPROXIMATESITE LOCATION
BASE: PORTION OF NILSEN, T.H. 1975 PRELIMINARY PHOTOINTERPRETATION MAP OF
LANDSLIDE AND OTHER SURFICIAL DEPOSITS OF THE OAKLAND EAST 7-1/2 QUADRANGLE
CONTRA COSTA AND ALAMEDA COUNTIES, CALIFORNIA, BY TOR H. NILSEN US
GEOLOGICAL SURVEY OPEN-FILE REPORT 75-277-41
0 1000
1"=1000'
DATE: 7-22-13 Figure 6Project No. 1082.100
RYAN GEOLOGICALCONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
REGIONAL LANDSLIDES AND OTHER
SURFICIAL DEPOSITS MAPCHELTON DRIVE LANDSLIDE
CHELTON DRIVE AND GIRVIN DRIVE
OAKLAND , CA
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
26/63
APPROXIMATESITE LOCATION
HAYWARD FAULT
NORTHERN SECTION
BASE: PORTIONS OF STATE OF CALIFORNIA SPECIAL STUDIES ZONES , OAKLAND
EAST, CALIFORNIA AT A SCALE OF 1:24,000.
0 1000
1"=1000'
DATE: 7-22-13 Figure 7Project No. 1082.100
OFFICIAL EARTHQUAKE FAULT ZONES MAP
RYAN GEOLOGICALCONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
CHELTON DRIVE LANDSLIDE
CHELTON DRIVE AND GIRVIN DRIVE
OAKLAND , CA
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
27/63
APPROXIMATE
SITE LOCATION
BASE: PORTIONS OF SEISMIC HAZARD ZONES , OAKLAND EAST AND PART
OF LAS TRAMPAS RIDGE, CALIFORNIA AT A SCALE OF 1:24,000.
0 1000
1"=1000'
DATE: 7-22-13 Figure 8Project No. 1082.100
OFFICIAL SEISMIC HAZARD ZONES MAP
STATE OF CALIFORNIA
RYAN GEOLOGICALCONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
CHELTON DRIVE LANDSLIDE
CHELTON DRIVE AND GIRVIN DRIVE
OAKLAND , CA
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
28/63
DATE: 7-31-13 Figure XProject No. 1082.100
RYAN GEOLOGICALCONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
CHELTON DRIVE LANDSLIDE
CHELTON DRIVE AND GIRVIN DRIVE
OAKLAND , CA
STATIC ANALYSIS - NO SESMIC LOAD
LANDSLIDE MASS
Wt: 130 pcf
C: 0 psf
Phi: 15 degrees
BEDROCK
Impenetrable
CHELTON DRIVE LANDSLIDE
GEOLOGIC SECTION A-A' - FULLY SPECIFIED FAILURE SURFACE
SLOPE STABILITY ANALYSIS
Residual Strength conditionsFactor of Safety = 0.6
9
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
29/63
DATE: 7-31-13 Figure XProject No. 1082.100
RYAN GEOLOGICALCONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
CHELTON DRIVE LANDSLIDE
CHELTON DRIVE AND GIRVIN DRIVE
OAKLAND , CA
STATIC ANALYSIS - NO SESMIC LOAD
LANDSLIDE MASS
Wt: 130 pcf
C: 0 psf
Phi: 24 degrees
BEDROCK
Impenetrable
SLOPE STABILITY ANALYSIS
Back-CalculationFactor of Safety = 1.2
10
CHELTON DRIVE LANDSLIDE
GEOLOGIC SECTION A-A' - FULLY SPECIFIED FAILURE SURFACE
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
30/63
DATE: 7-31-13 Figure XProject No. 1082.100
RYAN GEOLOGICALCONSULTING, INC.PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
CHELTON DRIVE LANDSLIDE
CHELTON DRIVE AND GIRVIN DRIVE
OAKLAND , CA
STATIC ANALYSIS - NO SESMIC LOAD
LANDSLIDE MASS
Wt: 130 pcf
C: 0 psf
Phi: 20 degrees
BEDROCK
Impenetrable
SLOPE STABILITY ANALYSIS
Long-Term Static ConditionFactor of Safety = 0.8
CHELTON DRIVE LANDSLIDE
GEOLOGIC SECTION A-A' - FULLY SPECIFIED FAILURE SURFACE
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
31/63
RSTInstrumentsLtd.
Inclinalsis
.2.44.3
CUM
ULATIVEDISPLACEMENT
Borehole:B
2GIRVIN
Project:RYAN
Location:
Northing:
Easting:
Collar:
SpiralCorrection:NA
CollarEle
ation:0.0feet
Bore
holeTotalDepth:76.0feet
AG
roo
eA
imuth:270degrees
BaseReading:2013Apr0214:48
AppliedA
imuth:0.0degrees
A
is-A
CumulatieDisplacement(inches)
-1.00
-0.80
-0.60
-0.40
-0.20
-0.00
0.20
0.40
0.60
0.80
1.00
Depth(feet)
2.00.0
-2.0
-4.0
-6.0
-8.0
-10.0
-12.0
-14.0
-16.0
-18.0
-20.0
-22.0
-24.0
-26.0
-28.0
-30.0
-32.0
-34.0
-36.0
-38.0
-40.0
-42.0
-44.0
-46.0
-48.0
-50.0
-52.0
-54.0
-56.0
-58.0
-60.0
-62.0
-64.0
-66.0
-68.0
-70.0
-72.0
-74.0
-76.0
-78.0
-80.0
-82.0
B
2GIRVIN(3)
17-Jul-13
B
2GIRVIN(2)
02-Apr-13
A
is-B
CumulatieDisplacement(inch
es)
-1.00
-0.80
-0.60
-0.40
-0.20
-0.00
0.20
0.40
0.60
0.80
1.00
Depth(feet)
2.00.0
-2.0
-4.0
-6.0
-8.0
-10.0
-12.0
-14.0
-16.0
-18.0
-20.0
-22.0
-24.0
-26.0
-28.0
-30.0
-32.0
-34.0
-36.0
-38.0
-40.0
-42.0
-44.0
-46.0
-48.0
-50.0
-52.0
-54.0
-56.0
-58.0
-60.0
-62.0
-64.0
-66.0
-68.0
-70.0
-72.0
-74.0
-76.0
-78.0
-80.0
-82.0
B
2GIRVIN(3)17-Jul-13
B
2GIRVIN(2)02-Apr-13
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
32/63
Job No.: Boring: Date: 05/03/2013
Client: Sample: By: PJ
Project: Depth: Checked: DC
Soil Type: Clay, %: 13 X
Remarks:
LL: 30
2000 4000 8000 PL: 15 Residual: X
16 15 15
804-001 Undisturbed:
Peak:
Residual:
B-2A
40'
Ryan Geological
Chelton Drive Slide - 1082.100
Normal Stress, psf
Secant Phi, deg.
Fully Softened:
Peak:
Bluish Black Lean Clayey SAND w/ GravelThe sample was processed over the #200 sieve per
clients instructions. A small friction correction was
applied to each point.
564
1068
2140
0
2000
4000
6000
8000
0 2000 4000 6000 8000
ShearStress,psf
Normal Stress, psf
Secant Residual Friction Angles
0
500
1000
1500
2000
2500
0 10 20 30 40
She
arStress,psf
Degrees
Deformation Curves2000 psf
4000 psf
8000 psf
To convert degrees to inches of
Drained, Residual Torsional Ring ShearTest ASTM D 6467
0
2000
4000
6000
8000
0 2000 4000 6000 8000
ShearStress,psf
Normal Stress, psf
Strength Envelope
-0.001
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.010 0.2 0.4 0.6 0.8 1
Chan
gein
Height,inches
Deformation, inches
Vertical Deformation
2000 psf4000 psf
8000 psf
FIGURE 13
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
33/63
Project:Remarks:Client:Project No.
%
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
34/63
Project No.:
Project:
Client:
Cu
Cc
COEFFICIENTSD10
D30
D60
REMARKS:GRAIN SIZE
SOIL DESCRIPTIONPERCENT FINERSIEVEPERCENT FINERSIEVE
LLPLAASHTOUSCS% CLAY% SILT% SAND% GRAVEL
sizesizenumber
Particle Size Distribution Report
10
20
30
40
50
60
70
80
90
0
100
PERCENTFINER
100 10 1 0.1 0.01 0.00200
GRAIN SIZE - mm
6in.
3in.
2in.
1-1/2in.
1in.
3/4in.
1/2in.
3/8in.
#4
#10
#20#30#40
#60
#100
#140
#200
Figure
% COBBLES
804-001
Chelton Drive Slide - 1082.100
Ryan Geological
Source: B-2A Elev./Depth: 15'
0.0112
43.216.3CL37.839.223.0
inches Olive Lean CLAY w/ Sand
COOPER TESTING LABORATORY
100.089.286.684.080.077.075.6
#10#30#40#50
#100#200#270
FIGURE
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
35/63
Project No.:
Project:
Client:
Cu
Cc
COEFFICIENTSD10
D30
D60
REMARKS:GRAIN SIZE
SOIL DESCRIPTIONPERCENT FINERSIEVEPERCENT FINERSIEVE
LLPLAASHTOUSCS% CLAY% SILT% SAND% GRAVEL
sizesizenumber
Particle Size Distribution Report
10
20
30
40
50
60
70
80
90
0
100
PERCENTFINER
100 10 1 0.1 0.01 0.00200
GRAIN SIZE - mm
6in.
3in.
2in.
1-1/2in.
1in.
3/4in.
1/2in.
3/8in.
#4
#10
#20#30#40
#60
#100
#140
#200
Figure
% COBBLES
804-001
Chelton Drive Slide - 1082.100
Ryan Geological
Source: B-2A Elev./Depth: 40-42'
0.0115
0.861
30.014.7SM13.133.132.920.9
inches Bluish Black Lean Clayey SAND w/ Gravel
COOPER TESTING LABORATORY
79.170.256.153.150.748.046.245.4
#4#10#30#40#50
#100#200#270
100.087.0
3/4"3/8"
FIGUR
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
36/63
Chelton Drive Landslide
Oakland, California
Job No. 1082.100
ENGINEERING GEOLOGY GEOLOGIC HAZARD ASSESSMENT HYDROLOGY GEOTECHNICAL ENGINEERING
RYAN GEOLOGICAL CONSULTING, INC.
PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
APPENDIX A
CORE LOGS
BORINGS B-1 THROUGH B-3
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
37/63
CORE LOG
PROJECT:DRILLING COMPANY:
NUMBER OF CORE BOXES:
DRILLING METHOD:
LOGGED BY:
BORING NO.:DATE INITIATED:DATE COMPLETED:TOTAL DEPTH OF HOLE:BOREHOLE ELEVATION:
JOB NO.:Gregg DrillingMud Rotary
4K. Ryan
B-13-5-13
3-6-1355 Feet1133 Feet MSL
1082.100
RUNNO.
DRILLING
PRESSURE(ps
i)
CUT
RECOVERED
%R
ECOVERY
%D
RILLING
FLUIDLOSS
RQD(%)
DEPTH
LOG
DESCRIPTION
2
4
6
8
10
12
14
Chelton Drive Landslide
DRILLRATE
(MIN/FT)
DRILL RIG: Fraste MITO 4000
CASING TYPE: Steel (During Drilling Only)GROUNDWATER ELEVATION:CASING ELEVATION: n/a
Not encountered
A-1
1
1
1
1
1
1/2
1/2
1
1
1
5
5
2.8
2.5
56
50
70
70
n/a
0
1
drilled to 5 feet without sampling
GRAVELLY CLAY, tan-brown, moist, stiff, angularfragments of sandstone and shale
SILTY CLAY, dark gray-brown, moist
SANDSTONE interbedded with SHALE mixed with CLAY,dark yellowish orange to yellow-brown, weak, highlydisrupted with abundant clay, block-in-matrix texture
2
RYAN GEOLOGICALCONSULTING, INC.
PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
38/63
CORE LOG
A-2
RUN
NO.
DRIL
LING
PRESSU
RE(psi)
CU
T
RECOV
ERED
%R
ECOVERY
%D
RI
LLING
FLUID
LOSS
RQD
(%)
DEP
TH
LO
G
DESCRIPTION
16
18
20
22
24
26
28
DRILL
RATE
(MIN
/FT)
1
1
1
1
1
1
1
1
0
1.5
1.5
3
2
3
0
2
2
4
1
2.5
2.5
2.5
2.5
3.3
1/2
2.5
2.2
1.5
2.5
50
100
88
72
100
70
70
70
30
30
30
0
0
0
0
0
0
3
4
5
6
7
8
SANDSTONE interbedded with SHALE mixed with CLAY,dark yellowish orange to moderate yellow-brown, friable,highly disrupted with abundant clay, block-in-matrix texture
clayey crushed zone
planar J 40 dip SHEAR ZONEbetween 20.3 to 23 feet with
multiple clay-lined shear planes 50-70 dip
*set casing to 20 feet to control water loss
SANDY SILTSTONE and SANDSTONE, severelyfractured into gravel-size pieces bound with clay
brecciated rock fragments in clay
remnant bedding 70 dip interbedded shale and sandstone predominately silty sandstone (less fractured than
above)
J 40 dipJ 30 dip
PROJECT:
RYAN GEOLOGICALCONSULTING, INC.
PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
Chelton Drive Landslide BORING NO.:TOTAL DEPTH OF HOLE:CORE LOG PAGE:
JOB NO.:B-155 Feet2 of 4
1082.100BORE HOLE ELEVATION: 1133 Feet MSLLOGGED BY: K. Ryan
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
39/63
A-3
RUN
NO.
DRIL
LING
PRESSU
RE(psi)
CU
T
RECOV
ERED
%R
ECOVERY
%D
RI
LLING
FLUID
LOSS
RQD
(%)
DEP
TH
LO
G
DESCRIPTION
31
33
35
37
39
41
43
DRILL
RATE
(MIN
/FT)
2
2
2
2
2
3
3
3
5
2
2
5
5
2
2
2
2.5
2.5
2.5
1.5
2
1.5
2.5
1.8
2.5
0
0
0.5
1.5
1.25
72
100
0
0
25
100
50
30
30
30
30
30
30
30
0
0
0
0
0
0
0
9 SANDY SILTSTONE and hard SANDSTONE, severelyfractured into gravel-size pieces
SLIDE PLANEat 32.5 feet, 1 inch clay gouge with welldeveloped dip-slip striations, 17 dip at top ofshear zone containing angular rock fragments in clay
matrix, block-in-matrix texture
samples being washed out during drilling.Water in mud tub is black, suggesting black shale
driller reports much harder drilling, below 40 feet
rubble
1/2 inch clay seam 70 dip
10
11
12
13
14
15
CORE LOG
BORING NO.:TOTAL DEPTH OF HOLE:CORE LOG PAGE:
JOB NO.:B-155 Feet3 of 4
1082.100
RYAN GEOLOGICALCONSULTING, INC.
PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
PROJECT: Chelton Drive LandslideBORE HOLE ELEVATION: 1133 Feet MSLLOGGED BY: K. Ryan
LANDSLIDE DEBRIS
SHEPHERD CREEK FORMATION
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
40/63
A-4
RUN
NO.
DRIL
LING
PRESSU
RE(psi)
CU
T
RECOV
ERED
%R
ECOVERY
%D
RI
LLING
FLUID
LOSS
RQD
(%)
DEP
TH
LO
G
DESCRIPTION
46
48
50
52
54
56
58
DRILL
RATE
(MIN
/FT)
2
2
2
5
5
5
13
8
8
8
2
1
2
1
3
0
1
1.5
0.9
0
0
100
75
90
0
75
80
80
0
0
0
0
0
SANDY SILTSTONE and hard SANDSTONE, severelyfractured into gravel-size pieces
rubble
J 30 and 70 dip
ground up clay zone
water rising out of borehole after drilling stoppedsuggesting groundwater at about 50 to 51 feet
rubble ground up clay zone with rock chards
Boring terminated at 55 feetBorehole backfilled with cement groutfluid loss estimated by driller
B - BeddingJ - Joint
S - Shear
area of no recovery
16
18
19
20
17
CORE LOG
BORING NO.:TOTAL DEPTH OF HOLE:CORE LOG PAGE:
JOB NO.:B-155 Feet4 of 4
1082.100
RYAN GEOLOGICALCONSULTING, INC.
PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
PROJECT: Chelton Drive LandslideBORE HOLE ELEVATION: 1133 Feet MSLLOGGED BY: K. Ryan
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
41/63
CORE LOG
PROJECT:DRILLING COMPANY:
NUMBER OF CORE BOXES:
DRILLING METHOD:
LOGGED BY:
BORING NO.:DATE INITIATED:DATE COMPLETED:TOTAL DEPTH OF HOLE:BOREHOLE ELEVATION:
JOB NO.:Gregg DrillingMud Rotary
1K. Ryan
B-23-7-13
3-7-1325 Feet1063 Feet MSL
1082.100
RUNNO.
DRILLING
PRESSURE(ps
i)
CUT
RECOVERED
%R
ECOVERY
%D
RILLING
FLUIDLOSS
RQD(%)
DEPTH
LOG
DESCRIPTION
2
4
6
8
10
12
14
Chelton Drive Landslide
DRILLRATE
(MIN/FT)
DRILL RIG:
CASING TYPE:GROUNDWATER ELEVATION:CASING ELEVATION: n/a
Not encountered
A-5
1
1
1
1
1
1
1
1
1
1
1
1
1
5
4
3.5
2.5
2
1
2.4
2
1.4
2.5
48
50
100
50
50
50
50
n/a
n/a
0
0
2
SILTY SANDY CLAY, brown to tan-brown, moist, stiff
(FILL FOR DRILLING PAD)
GRAVELLY CLAY, tan-brown, moist, stiff, angularfragments of shale up to 1 inch
driller reports very hard drilling, below 9 feet
3 SILTSTONE, highly weathered, weak to moderatelystrong, crushed, thinly bedded
*set casing to 10 feet
remnant bedding laminations 30 dip
crushed clay zone 30 dip
1
4
Fraste MITO 4000
Steel (During Drilling Only)
RYAN GEOLOGICALCONSULTING, INC.
PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
42/63
A-6
RUN
NO.
DRIL
LING
PRESSU
RE(psi)
CU
T
RECOV
ERED
%R
ECOVERY
%D
RI
LLING
FLUID
LOSS
RQD
(%)
DEP
TH
LO
G
DESCRIPTION
16
18
20
22
24
26
28
DRILL
RATE
(MIN
/FT)
1
1
1
2
1
2
1
1
1
1
1
2.5
2.5
2.5
1
0.5
0.5
0.5
5
5
20
20
20
50
50
50
50
50
0
0
0
0
0
5
7
6
SILTSTONE, highly weathered, weak to moderately strong rubble
rubble
rubble
rubble
LANDSLIDE DEBRIS
8
9
Boring terminated at 55 feetBorehole backfilled with cement groutfluid loss estimated by driller
B - BeddingJ - Joint
S - Shear
area of no recovery
*Core barrel not properlyengaging, runs #8 and #9 bothrecovered 5 feet of sloughfrom previous runs. Boringterminated due to drilling
malfunctions and drill rig. Holemoved 10 feet south to re-drill.See log for boring B-2A
CORE LOG
BORING NO.:TOTAL DEPTH OF HOLE:CORE LOG PAGE:
JOB NO.:B-225 Feet2 of 2
1082.100
RYAN GEOLOGICALCONSULTING, INC.
PROVIDING LOGICAL GEOLOGICAL SOLUTIONS
PROJECT: Chelton Drive LandslideBORE HOLE ELEVATION: 1063 Feet MSLLOGGED BY: K. Ryan
-
8/21/2019 Prr 5509 DRAFT Landlside Investigation Report Chelton Drive
43/63
CORE LOG
PROJECT:DRILLING COMPANY:
NUMBER OF CORE BOXES:
DRILLING METHOD:
LOGGED BY:
BORING NO.:DATE INITIATED:DATE COMPLETED:TOTAL DEPTH OF HOLE:BOREHOLE ELEVATION:
JOB NO.:Gregg DrillingMud Rotary
5K. Ryan
B-2A3-7-13
3-9-1380 Feet
1065.9 Feet MSL
1082.100
RUNNO.
DRILLING
PRESSURE(ps
i)
CUT
RECOVERED
%R
ECOVERY
%D
RILLING
FLUIDLOSS
RQD(%)
DEPTH
LOG
DESCRIPTION
2
4
6
8
10
12
14
Chelton Drive Landslide
DRILLRATE
(MIN/FT)
DRILL RIG: FRASTE MITO 4000
CASING TYPE: 2.75-Inch Slope InclinometerGROUNDWATER ELEVATION:CASING ELEVATION: 1067.4 Feet MSL
Not encountered
A-7
1
1
1
1
2
2
2
3
2
4
5
5
2
3
40