REPORT GEOTECHNICAL ENGINEERING INVESTIGATION …

SANTA ROSA, CALIFORNIA
For BKF Engineers
TABLE OF CONTENTS
3.0 PURPOSE ................................................................................................................................3
6.0 GEOLOGY AND SEISMICITY ......................................................................................................7 6.1 Regional Geology .......................................................................................................................... 7 6.2 Seismicity ....................................................................................................................................... 8
7.0 SITE CONDITIONS .................................................................................................................. 10 7.1 Surface Conditions ...................................................................................................................... 10 7.2 Subsurface Conditions ................................................................................................................. 10 7.3 Groundwater ............................................................................................................................... 12
8.0 GEO-HAZARD EVALUATION ................................................................................................... 13 8.1 CBC 2016 Site Characterization ................................................................................................... 13 8.2 Expansive Soils ............................................................................................................................ 14 8.3 Flooding ....................................................................................................................................... 14
9.0 CONCLUSIONS AND RECOMMENDATIONS ............................................................................. 15 9.1 General ....................................................................................................................................... 15 9.2 Jacking and Receiving Pit Excavations ...................................................................................... 16 9.3 Drilling Fluid Migration .............................................................................................................. 17 9.4 Hydraulic Fracturing ................................................................................................................... 17 9.5 Site Grading ................................................................................................................................ 18 9.6 Lateral Design ............................................................................................................................. 18 9.7 Plan Review ................................................................................................................................. 19 9.8 Observation and Testing ............................................................................................................. 19
10.0 CLOSURE ............................................................................................................................... 19
11.0 REFERENCES ......................................................................................................................... 20
Attached Plates:
Plate 1 Vicinity Map Plate 2 Site Plan Plate 3 Area Geologic Map Plate 4 Regional Fault Map Plate 5 Unified Soil Classification System Plate 6 Soil Terminology Plate 7 Rock Terminology Plate 8 Boring Log Notes Plates 9A and 9B Key to Symbols Plates 10A thru 12C Boring & Well Logs Plate 13 Idealized Subsurface Profile A-A’ Plate 14 Atterberg Limits Test Data Plates 15A & 15B Gradation Test Data ASFE document titled “Important Information About Your Geotechnical Engineering Report”
REPORT
For BKF Engineers
This report presents the results of our geotechnical engineering investigation performed to address the
proposed construction of a temporary bypass tunnel for use in diverting flow within Santa Rosa Creek
during repair of the existing vortex tube beneath Montgomery Drive in Santa Rosa, California. The
attached Plate 1, Vicinity Map, shows the general location of the site and Plate 2, Site Plan, depicts the
existing site layout, location of the proposed improvements and the approximate locations of the three
exploratory borings advanced as part of this investigation. The study was carried out in accordance with
the scope of services outlined in our Proposal #19-262R, dated May 15, 2019.
For this investigation, we received the following supplemental document:
EXHIBIT, Vortex Tube Rehabilitation Project, Santa Rosa Creek, Sonoma Water, by BKF Engineers,
Job number 20180695, dated July, 2019.
The referenced document depicts the existing site layout, as well as two options for the approximate
configuration of the temporary bypass tunnel. These drawings provided the basis for selecting the boring
locations.
A summary of the laboratory tests, evaluations, and our recommendations for construction of the
proposed temporary bypass tunnel and the associated site improvements are presented in the following
sections of this report.
Vortex Tube Rehabilitation Project Job No: BKFEN-42-00 October 7, 2019 Page 3
2.0 SITE AND PROJECT DESCRIPTION
The proposed project will reportedly consist of repairing the existing vortex tube, which was constructed
in the mid 1960’s. The repair project will require a temporary bypass tunnel to carry the stream flow
during the repairs. We anticipate the bypass tunnel will be located immediately upstream of the existing
vortex tube, which traverses beneath Montgomery Drive, a little more than 200 feet northwest of Melita
Road and 0.6 miles east of Santa Rosa Creek Reservoir, in Santa Rosa, California. It is our understanding
that the proposed bypass will utilize trenchless technology in its construction, and the pipe will be roughly
14 feet below Montgomery Drive, varying from Elevation 305 to 303 feet. The bypass will flow from the
existing concrete-lined diversion channel and discharge on the northern side of Montgomery Drive.
The site area is underlain by predominantly granular alluvium of Pleistocene to early Pliocene age, which
in turn is underlain by Pliocene to early Miocene volcanic rocks. Old, 1958 boring logs from the general
vicinity indicate the soils vary from loose silt to very dense silty gravel with cobbles, underlain by dense to
very dense tuff. The boring logs indicate the tuff was encountered below Elevations varying from 295 to
314 feet. A short distance downstream, basalt was encountered around Elevation 304 and below.
3.0 PURPOSE The purpose of our services was to obtain pertinent information regarding the subsurface soil, rock, and
groundwater conditions in the vicinity of the proposed temporary bypass tunnel, and develop information
regarding the engineering properties of the earth materials within the vicinity of the proposed bypass
area. On this basis, our report addresses:
Geologic site conditions and seismicity of the project site, including distance to the active
faults in the region, and probability of a major earthquake on relevant faults,
Seismic parameters for the site per the 2016 edition of the California Building Code,
specific geotechnical conditions discovered by our borings, such as loose, saturated, very soft or very dense soils, gravelly/cobbly soils, or bedrock materials that may require special mitigation measures or impose restrictions on the project,
groundwater levels as measured in the borings
allowable active and passive soil pressures for jacking and receiving pits, and/or low retaining walls
criteria for placement of fills and backfills, allowable cut slopes, and general suitability of
the on-site soils for use as engineered fill,
criteria for support of concrete slabs on grade and/or channel lining
foundation support for minor retaining walls and any ancillary buildings, including criteria for vertical and lateral support for shallow foundations or drilled piers, as appropriate,
4.0 SCOPE OF SERVICES Information required to fulfill the above purposes was obtained from research of published data and
reports, a brief reconnaissance of the site, three exploratory borings, and a program of laboratory testing
of collected soil samples. Accordingly, the scope of our services consisted of the following specific tasks:
1. Research and review pertinent geotechnical and geological maps and reports
relevant to the site and vicinity. 2. Mark the planned boring locations in the field, and coordinate the drilling with
the client representatives. 3. Obtain drilling and well construction permits for the exploratory soil borings and
monitoring well construction, respectively, from the Sonoma County Permit and Resource Management Department. In addition, obtain an encroachment permit from the City of Santa Rosa for the drilling of the exploratory soil borings within Montgomery Drive.
4. Drill, log, and sample three borings with portable or track-mounted drilling
equipment equipped with solid-stem augers. The subsurface exploration was technically directed by one of our geologists, who also obtained Standard Penetration Test, and relatively undisturbed ring samples of the subsurface materials at 1- to 5-foot intervals for visual classification and laboratory testing. Convert one of the borings to a groundwater level observation well and leave the remaining two borings open overnight to allow for groundwater levels to stabilize somewhat. Upon recording the stabilized groundwater levels within the borings, the boreholes were sealed with cement grout per standard protocol. The drill cuttings generated during the subsurface exploration were stored at the site, environmentally profiled, and disposed of off-site in accordance with applicable regulations.
5. Perform a laboratory testing program on the collected soil samples to evaluate
the engineering characteristics of the subsurface soils. Tests included direct shear
tests, grain size analysis, Atterberg Limits tests, and moisture-density measurements, as judged appropriate.
6. Perform engineering analyses based on the results obtained from the above tasks
and oriented towards the above-described purpose of the investigation. 7. Confer with the design team and Contractor to answer specific questions.
8. Prepare a final report containing the results of our subsurface exploration and
laboratory testing, a vicinity map, site plan, a geologic map, a regional fault map, boring logs, subsurface profiles, and summarizing our findings, opinions, conclusions and recommendations regarding construction of the proposed temporary bypass tunnel.
5.0 FIELD EXPLORATION AND LABORATORY TESTING Subsurface conditions at the site were explored on August 23 and August 26, 2019 by drilling three borings
(designated as Borings B-1, B-2, and MW-1) to depths of approximately 30-, 26½- and 21-feet below the
existing ground surface, respectively, at the approximate locations shown on the attached Plate 2, Site
Plan.
Boring MW-1 was advanced on August 23, 2019 with a portable drilling rig equipped with 6-inch diameter
solid stem augers. Samples of the subsurface materials encountered in the boring were obtained with
the aid of a rope and cathead attached to a 140-lb drop-hammer. Following completion of the boring, the
borehole was developed as a 20-foot deep groundwater level observation well consisting of 2-inch
diameter, schedule 40 PVC, well casing encompassed by a filter pack consisting of #3 Monterey Sand and
capped with an annual seal consisting of hydrated bentonite chips overlain by cement grout.
Borings B-1 and B-2 were advanced on August 26, 2019 with a track-mounted DR8K drilling rig equipped
with 4-inch diameter solid stem augers. Samples of the subsurface materials encountered in the borings
were obtained with the aid of an automatic 140-lb drop-hammer. Following completion of the borings,
the boreholes were covered with traffic-rated covers and left open overnight to allow for groundwater
levels to stabilize. The boreholes were subsequently backfilled with neat cement grout on August 27,
2019 after the stabilized groundwater levels within the borings were recorded.
Our geologist technically directed the exploration, maintained a continuous log of the borings, and
obtained relatively undisturbed ring and Standard Penetration Test samples for laboratory testing and
visual examination in accordance with the sampling method described on Plates 9A and 9B, Key to
Symbols.
The subsurface materials were visually classified in the field; the classifications were then checked by
visual examination of samples in the laboratory. In addition to sample classification, the boring logs
contain interpretation of where stratum changes or gradational changes occur between samples. The
boring logs depict BAGG's interpretations of subsurface conditions only at the locations indicated on Plate
2, Site Plan, and only on the dates noted on the logs. The boring logs are intended for use only in
conjunction with this report, and only for the purposes outlined by this report.
The graphical representation of the materials encountered in the borings, and the results of laboratory
tests, as well as explanatory/illustrative data, are attached as follows.
Plate 5, Unified Soil Classification System, illustrates the general features of the soil classification system used on the boring logs.
Plate 6, Soil Terminology, lists and describes the soil engineering terms used on the boring logs.
Plate 7, Rock Terminology, lists and describes the engineering terms with respect to bedrock classification used on the boring logs.
Plate 8, Boring Log Notes, describes general and specific conditions that apply to the boring logs.
Plates 9A and 9B, Key to Symbols, describes various symbols used on the boring logs.
Plates 10A thru 12C, Boring & Well Logs, describe the subsurface materials encountered, show the depths and blow counts for the samples, and summarize the results of the strength tests, Atterberg Limits tests, classification tests, and moisture-density data.
Plate 13, Idealized Subsurface Profile A-A’, depicts our interpretation of the subsurface soil and bedrock conditions at the site based on extrapolation of the information obtained from the borings, site reconnaissance, and the available geologic literature.
Plate 14, Plasticity Data, graphs and presents the Atterberg Limits test data performed to classify selected soil samples obtained from the borings.
Plates 15A and 15B, Gradation Test Data, graphs and presents the results of gradation tests conducted on samples of the subsurface soils collected from the borings.
Selected undisturbed samples were tested in direct shear to evaluate the strength characteristics of the
subsurface soils encountered at the site. Direct shear tests were performed at natural (field) moisture
contents, while under various surcharge pressures. We also performed sieve analyses to aid in the
classification of the granular soil samples collected from the borings. Additionally, Atterberg Limits tests
were performed on clayey samples of the site materials to help define the expansion characteristics and
aid in the soil classification. The moisture content and dry density of several undisturbed samples were
also measured to aid in correlating their engineering properties. The results of our laboratory strength
tests, moisture-density measurements, Atterberg Limits tests, and classification tests are summarized on
the boring logs as well as the plates described above.
6.0 GEOLOGY AND SEISMICITY 6.1 Regional Geology
Review of the “Geologic and Geophysical Framework of the Santa Rosa 7.5’ Quadrangle, Sonoma County,
California," (USGS Open-File Report 2008-1009) compiled by R.J. McLaughlin, et al., 2008, indicates the
geology of the site area consists of Holocene channel deposits (Qhc) and Holocene to Pleistocene alluvial
deposits (Qt), described as consisting of:
Qhc - Channels (Holocene): Incised into older deposits. Map unit represents the most recent channels that incise Holocene alluvial deposits. This erosional unit is mapped on the basis of channel incision into older alluvial deposits and is not defined here by the character of the sediments in the channel. Qt – Alluvial deposits, undivided (Holocene and Pleistocene): This unit includes undivided Holocene and Pleistocene terrace deposits whose ages are not clearly Holocene or Pleistocene. Terraces of this unit probably are equivalent either to unit Qhf or Qhpf.
In addition, Late Tertiary volcanic rocks associated with the Pliocene and Miocene age Sonoma Volcanics
are also mapped south of the subject site and were found to underlie the project site at relatively shallow
depths. According to the above-referenced geologic report, the Sonoma Volcanics are reportedly
comprised of rhyolitic to dacitic ash-flow and air-fall tuff, andesitic water-lain tuff, and rhyolitic to basaltic
flows and flow breccia. In the vicinity of the project site, the Sonoma Volcanics are mapped as consisting
of andesite, basaltic andesite, and basalt (Tsb) as well as andesitic to dacitic tuff, breccia, and minor flows
(Tsbt), described as consisting of:
Tsb – Andesite, basaltic andesite and basalt (Pliocene and Miocene): Subaerial andesitic to basaltic flows, flow breccia, and tuff-breccia, local waterlain andesitic tuff and minor dacitic ash-flowtuff are aerially extensive between the Healdsburg and Southern Rodgers Creek segments of the Rodgers Creek Fault Zone, and the Mark West Fault Zone. Gravity data (Chapter B; Langenheim and others, 2006a) suggest that these andesitic rocks together with tuffs in the Sonoma Volcanics compose a relatively thin cover to the pre- Miocene basement over much of this area (cross sections AC). Geologic map relations consistent with a thin Tertiary volcanic cover are provided by local exposures of Franciscan Complex and ophiolitic rocks along the Rodgers Creek Fault and in the bottoms of a few drainages that deeply incise the volcanic section. Andesitic to basaltic rocks are intercalated with and underlain by estuarine, lacustrine and fluvial strata of the Petaluma Formation in the Bennett Valley area, along the Rodgers Creek and Healdsburg faults, on Taylor Mountain, and along the east side of Santa Rosa plain. Andesitic rocks are also intercalated with the numerous tuffs (Tst), and local rhyodacitic flows and intrusive rocks (Tsr)…Collectively, andesitic rocks between the Rodgers Creek-Healdsburg Fault Zone and the Maacama Fault range in age from ~5.4 to 4.4 Ma. Tsbt – Andesitic to dacitic tuff, breccia and minor flows (Pliocene and Miocene): This unit includes air-fall and ash-flow tuffs and some possibly reworked, waterlain tuff (Higgins, 1983). The unit underlies basaltic andesite flows of unit Tsb, dated at 4.7 ± 0.03 Ma. Younger andesitic tuff breccia overlies andesitic flows and breccias (Tsb) and rhyolitic rocks (Tsr) on the northeast side of Bennett Mountain that are probably correlative with the obsidian of Annadel State Park, dated at 4.5 ± 0.01 Ma (loc. 21, table 1 and fig. 4).
Plate 3, Area Geologic Map, shows the geologic setting of the site and vicinity, as mapped by McLaughlin
et al., 2008.
6.2 Seismicity
The San Francisco Bay Area lies within the Coast Ranges geomorphic province, a series of discontinuous
northwest trending mountain ranges, ridges, and intervening valleys characterized by complex folding and
faulting. These faults are in a zone that extends eastward from off the Pacific Coast through the
San Francisco Bay area to the western side of the Great Valley. This region has one of the highest rates of
seismic moment release per square mile of any urban area in the United States. It is emerging from the
stress shadow of the 1906 San Francisco Earthquake and future large earthquakes are considered a
certainty.
Three of the northwest-trending major earthquake faults included in the San Andreas fault system
extending through the northern San Francisco Bay Area include the San Andreas fault, the Maacama fault,
and the Rodgers Creek-Healdsburg fault, respectively located approximately 19.6 miles (31.5 km) west-
southwest, 2.7 miles (4.4 km) north, and 3.1 miles (5.0 km) west of the site. While the subject site is not
within any of an Alquist-Priolo Earthquake Fault Zones designated by the California Geological Survey, the
San Andreas, Maacama, and Rodgers Creek-Healdsburg faults are believed to be the principal seismic
hazards in this area because of their activity rates and proximity to the site. The Working Group on
California Earthquake Probabilities (2014) has estimated that the probability for a major earthquake
(MW6.7 or greater) within 30 years on the nearby north coast section of the San Andreas fault is about 13
percent and about 33 percent for a similar earthquake located anywhere on the Northern San Andreas
fault. The Maacama fault reportedly has a 23 percent probability for producing a major earthquake (MW
6.7 or greater) within 30 years. In addition, there is also about a 15 percent chance a MW 6.7 or greater
earthquake will be located on the Rodgers Creek-Healdsburg fault within 30 years.
Other significant regional faults are of greater distance or have lesser probabilities of a major earthquake
in the next 30 years or so. Of particular importance are the West Napa and Bennett Valley faults,
respectively located approximately 9.1 miles (14.7 km) east-northeast and 0.7 miles (1.1 km) west of the
subject site. The Working Group on California Earthquake Probabilities (2014) has estimated that the
probability for a major earthquake (MW6.7 or greater) within 30 years on the nearby West Napa fault is
about 23 percent and about 0.4 percent for a similar earthquake located on the Bennett Valley fault.
The predominant seismic hazard at this site will be from shaking caused by a large earthquake. ABAG
(Association of Bay Area Governments) has published earthquake intensity maps that indicate the
scenario earthquake listed for the entire northern San Andreas fault (1906-size earthquake) would
produce a “violent” shaking intensity at the site. The shaking intensity resulting from a scenario
earthquake (M7.4) on the Maacama fault will be "strong" and the shaking intensity resulting from a
scenario earthquake on the Rodgers Creek-Healdsburg fault will be “very strong” in nature. In addition,
the shaking intensity resulting from a scenario earthquake on the West Napa fault will be “moderate" in
nature.
The distances to the major active faults from the project site and the estimated probability of a MW≥6.7
within 30 years for each fault are listed on the following Table.
Table 1 Significant Earthquake Scenarios
Fault
30 Years2
N. San Andreas (Entire) 31.5 W-SW 33% San Andreas (North Coast) 31.5 W-SW 13.2%
Maacama 4.4 N 23.1% Rodgers Creek-Healdsburg 5.0 W-SW 14.5%
West Napa 14.7 E-NE 2.3% Bennett Valley 1.1 W 0.4%
1USGS Quaternary Fault Database - Google Earth 2Working Group on California Earthquake Probabilities, 2014.
The attached Plate 4, Regional Fault Map, depicts the major active fault locations with respect to the
subject site.
7.0 SITE CONDITIONS 7.1 Surface Conditions
The project site consists of two segments of Santa Rosa Creek separated by an artificial levee on which
Montgomery Drive was constructed. The upper surface of the existing levee in the vicinity of the project
site is surfaced with asphaltic concrete pavement that was observed to be approximately 6 to 6½ inches
thick and was observed to overlie approximately 3½ to 4 inches of aggregate base rock. The levee
embankments in the vicinity of the existing vortex tube and the proposed bypass tunnel are surfaced with
concrete of an unknown thickness.
7.2 Subsurface Conditions
The borings in the area of the proposed bypass tunnel beneath Montgomery Drive (Borings B-1 and B-2)
encountered approximately 7- and 5½-feet of fill materials, respectively. The fill materials encountered
are described as consisting of clayey gravel with sand, described as brown with dark-gray and yellow- to
red-brown mottling, dense to very dense, moist, and comprised of angular to subangular gravel with well-
graded sand and trace cobble size rock fragments. Based on our laboratory tests, the fines content (minus
#200 sieve fraction) of the clayey fill soils is on the order of 25%. It is inferred that the fill materials may
exist to deeper depths in the vicinity of the concrete-lined embankments along the margins of
Montgomery Drive and in the vicinity of the former alignment of Santa Rosa Creek as well as in areas
where grading may have been carried out as a part of previous developments.
The above-described fill soil encountered in Borings B-1 and B-2 were observed to be underlain by native
soils consisting of clayey sand and sandy moderate to high plasticity clay. The native alluvial soils
encountered are described as reddish-brown with yellow- to orange-brown and blue-gray mottling, very
dense/hard, slightly moist to moist, and predominantly comprised of fine- to medium-grained sand with
trace coarse-grained sand. The native soils encountered are interpreted to represent the residual alluvial
soils blanketing the sloping terrain prior to site grading. Based on our laboratory tests, the fines content
(minus #200 sieve fraction) of the native alluvial soils encountered in Borings B-1 and B-2 varies from
approximately 40 to 80 percent. Atterberg Limits tests conducted on samples of the clayey alluvial soils
indicates the soils are considered to be moderately to highly expansive in nature.
Bedrock consisting of primarily decomposed to intensely weathered basaltic andesite was encountered
at depths of approximately 18 and 15 feet below the ground surface in Borings B-1 and B-2, respectively.
The upper portion of the bedrock encountered was generally described as being weathered to a sandy fat
clay or clayey sand that are reddish-brown with minor yellow- to orange-brown, off-white, and dark-gray
coloration, hard/very dense, moist, and contain sand to gravel size bedrock fragments. Based on our
laboratory tests, the fines content (minus #200 sieve fraction) of the decomposed portion of the bedrock
encountered in Boring B-2 is on the order of approximately 50 percent. An Atterberg Limits test
conducted on a sample of the decomposed bedrock encountered in Boring B-2 indicates the clayey soils
generated during decomposition are considered to be highly expansive in nature. The decomposed to
intensely weathered portion of the bedrock encountered in Boring B-1 extended to the full depth explored
of 30 feet below the ground surface. However, moderately weathered basaltic andesite was encountered
at a depth of approximately 22 feet in Boring B-2. The moderately weathered portion of the bedrock
encountered in Boring B-2 is described as dark gray in color with yellow- to red-brown oxidation staining,
moderately soft and closely fractured.
The boring drilled in the area of the proposed bypass tunnel outfall (Boring MW-1) encountered
approximately 5¾-feet of predominantly fine-grained channel deposits consisting of approximately 3
feet of silty sand to poorly-graded sand with silt overlying approximately 2½ feet of silty lean clay. The
fine-grained channel deposits were generally observed to be brown to blue-gray in color, loose/soft to
medium stiff, and moist to very moist. Predominantly coarse-grained channel deposits consisting of silty
sand with gravel to silty gravel with sand were found to underlie the above-described fine-grained channel
deposits and extended to a depth of approximately 8 feet in Boring MW-1. The coarse-grained channel
deposits are described as gray to blue-gray in color, dense, wet and comprised of well-graded sand with
subangular to rounded gravel and trace subangular to subrounded cobbles. Based on our laboratory tests,
the fines content (minus #200 sieve fraction) of the coarse-grained channel deposits encountered in
Boring MW-1 is on the order of approximately 14 percent.
Bedrock consisting of olive-gray, olive brown and gray-brown andesitic tuff and andesitic tuff breccia was
encountered below a depth of approximately 8¼ feet below the ground surface in Borings MW-1. The
bedrock encountered in the boring is described as moderately to intensely weathered, soft to moderately
soft, slightly moist to moist, and contained sand and less commonly gravel size minerals and/or rock
fragments. Based on our laboratory tests, the fines content (minus #200 sieve fraction) of the upper
andesitic tuff deposits encountered in Boring MW-1 is on the order of approximately 40 percent.
For more information on the subsurface materials, we refer you to Plates 10A thru 12C, Boring & Well
Logs.
7.3 Groundwater
Groundwater was not encountered in Boring B-1 to the full depth explored of 30 feet below the ground
surface. However, the weathered bedrock encountered in the lowermost portion of the boring was
observed to be very moist. The following morning the depth to groundwater within the borehole was
measured to be 26¼ feet below the ground surface.
Groundwater was encountered at a depth of approximately 22 feet below the existing ground surface in
Boring B-2. The depth at which groundwater was encountered in the boring roughly coincided with the
transition between the highly and moderately weathered portions of the bedrock. A subsequent
measurement of the “static” groundwater elevation conducted on August 27, 2019 indicated that the
groundwater level within the borehole rose to within approximately 7 feet of the existing road surface.
Due to the discrepancy in groundwater measurements obtained in Boring B-1 and B-2, it is inferred that
the groundwater encountered within Boring B-2 is primarily sourced from open fractures within the
bedrock aquifer which is under substantial hydrostatic pressure.
Groundwater was encountered in Boring MW-1 at a depth of approximately 6 feet below the ground
surface. Following development of the boring as a groundwater level observation well, the depth to
groundwater was measured at approximately 5 feet below the ground surface. The depth to groundwater
measured in the boring appeared to be consistent with the water surface elevation within the nearby
Santa Rosa Creek channel.
It should be noted that groundwater levels typically fluctuate due to seasonal changes such as variations
in rainfall and temperature, hydrogeological variations such as groundwater pumping or recharging,
and/or other factors not evident at the time of exploration. In addition, due to the proximity of the project
site to the active Santa Rosa Creek Channel, it is anticipated that the localized fluctuations in the depth to
groundwater are likely attributed to variations in flow within Santa Rosa Creek. Furthermore, localized
fluctuations in the groundwater level resulting in seeps, springs, and perched water conditions may occur
across the site. For more information on the subsurface materials, we refer you to Plates 10A thru 12C,
Boring Logs.
8.0 GEO-HAZARD EVALUATION 8.1 CBC 2016 Site Characterization
Based on the boring data, the site is a Class C (Very Dense Soil and Soft Rock) site, with an average N value
in the top 100 feet greater than 50, an average shear wave velocity between 1,200 and 2,500 feet per
second (ft/s), and an average undrained shear strength greater than 2,000 pounds per square feet (psf).
Using the site coordinates of 38.4573° North Latitude and 122.6389° West Longitude, and the U.S. Seismic
Design Maps, by the USGS Earthquake Hazards Program, earthquake ground motion parameters were
computed utilizing the 2010 ASCE-7 option in accordance with the 2016 California Building Code and are
listed in the following table.
Table 2
Site Longitude 122.6389° W
Site Class, ASCE 7-10 Standard Class C, Very Dense Soil and Soft
Rock Risk Category II
Mapped Spectral Acceleration for Short Periods Ss 1.794g Mapped Spectral Acceleration for 1-second Period S1 0.715g
Site Coefficient Fa 1.0 Site Coefficient Fv 1.3
Site-Modified Spectral Acceleration for short Periods SMs 1.794g Site-Modified Spectral Acceleration for 1-second Period SM1 0.93g
Design Spectral Acceleration for short Periods SDs 1.196g Design Spectral Acceleration for 1-second Periods SD1 0.62g
8.2 Expansive Soils
The surface and near surface native soils as well as the decomposed portion of the underlying bedrock
consist of fat (moderate to high plasticity) clays. Based on the laboratory test data and experience, fat
clays can exhibit significant expansion characteristics. This subsurface condition is common within the
project area and poses a risk for post-construction heave and cracking of concrete slabs, as well as lightly
loaded foundations and pavements.
8.3 Flooding
The closest main drainage corridor, Santa Rosa Creek, as well as the adjoining diversion channel are
located immediately adjacent to the proposed bypass tunnel. Review of the National Flood Insurance
Program, Flood Insurance Rate Map for the site vicinity (Map Number 06097C0734E), prepared by the
Federal Emergency Management Agency (FEMA), and dated December 2, 2008, indicates the project site
is situated within an area designated as Zone X, defined as an area of minimal flood hazard. While not
specified, this designation has likely been made due to the presence of the existing levee and diversion
channel which may be used to redirect flow within Santa Rosa Creek during high flow events. However,
since the proposed project consists of constructing a temporary bypass tunnel and rehabilitating of the
existing vortex tube connecting the portions of the active channel on either side of Montgomery Drive,
the potential for flooding affecting the proposed project is considered to be high.
9.0 CONCLUSIONS AND RECOMMENDATIONS 9.1 General
Based on the subsurface exploration conducted as a part of this investigation and the results obtained
from our laboratory testing program, it is our opinion that the proposed project is feasible from a
geotechnical perspective, provided the recommendations presented in this report are incorporated into
the project design and construction. When the final development plans are available, they should be
reviewed by this office prior to construction to confirm that the intent of our recommendations is
reflected in the plans.
The boring data and laboratory test results indicate that the site materials generally have good consistency
and are capable of accommodating the proposed drilling of a temporary bypass tunnel and associated site
improvements. Based on the boring information, the area of the proposed bypass tunnel is underlain by
approximately 5½ to 7 feet of coarse-grained fill materials overlying approximately 10 feet of native
alluvial soils. Bedrock consisting of intensely weathered to decomposed basaltic andesite was
encountered at depths ranging from approximately 15 to 18 feet below the surface of Montgomery Drive
in the borings drilled with Montgomery Drive as part of this investigation (Borings B-1 and B-2). It is our
understanding that the proposed bypass tunnel beneath Montgomery Drive will range in elevation from
approximately 12 to 14 feet below the existing road surface (Elevation 305 to 303 feet), at the southern
and northern margins of the concrete lined embankments, respectively. The proposed bypass tunnel is
planned to extend an additional approximately 80 to 170 feet (Option 1 and 2, respectively) north of the
existing embankment for Montgomery Drive, and is planned to outlet at the eastern margin of Santa Rosa
Creek at an elevation of approximately 301 feet. Based on extrapolation of the information obtained
during our subsurface exploration, the proposed bypass tunnel will likely encounter weathered basaltic
andesite along the southernmost portion of the proposed alignment beneath Montgomery Drive and will
likely encounter relatively fine-grained alluvial deposits along the northernmost portion of the proposed
alignment beneath Montgomery Drive. It is also inferred that the proposed bypass tunnel will likely
encounter active channel deposits to the north of Montgomery Drive. While few cobbles were
encountered in Boring MW-1 between 5½ and 8½ feet, more significant cobble content in other areas of
the channel deposits cannot be ruled out. In addition, based on the groundwater information obtained
in our subsurface exploration, the proposed bypass tunnel will likely encounter shallow groundwater at
the initiation and termination points of the proposed bypass tunnel.
The surface and near surface native soils as well as the decomposed to intensely weathered portions of
the underlying volcanic bedrock at the site consist of fat (moderate to high plasticity) clays. Based on the
laboratory test data and experience, fat clays can exhibit significant expansion characteristics and
therefore pose a risk to lightly loaded structures.
Site grading is anticipated to consist of cuts and fills on the order of approximately 5 feet or less for the
construction of jacking and receiving pits as well as to accommodate access to the proposed work areas
(if necessary).
The site could experience very strong ground shaking from future earthquakes during the anticipated
lifetime of the project. The intensity of the ground shaking will depend on the magnitude of the
earthquake, distance to the epicenter, and the response characteristics of the on-site soils. While it is not
possible to totally preclude damage to structures during major earthquakes, strict adherence to good
engineering design and construction practices will help reduce the risk of damage to the proposed
improvements.
9.2 Jacking and Receiving Pit Excavations
Excavations within and adjacent to the active channel will likely require the use of temporary shoring due
to the presence of poorly consolidated granular soils and shallow groundwater. Temporary shoring should
be designed to withstand an active earth pressure of 30 pcf above the water table and 75 pcf below the
water table. Where a sloping surface will exist above the temporary shoring, these pressure should be
increased by 3pcf for every 5 degree increase in the slope angle. Surcharge loads will be in addition to the
active earth pressures.
Where a temporary sloped excavation is desired, it may be opened at a gradient of 1H:1V (horizontal to
vertical) within native alluvial soils and the weathered portion of the underlying bedrock, unless seepage
is encountered. If seepage is encountered within excavations into native alluvial soils and/or weathered
bedrock, cut slopes should be laid back at a maximum inclination of 1½H:1V. Excavations made within
close proximity to the active stream channel will likely expose poorly consolidated granular soils and
therefore should be sloped at an inclination no steeper than 2H:1V. Additionally, construction equipment
and material stockpiles should not be allowed within a distance equal to one-half the height of the
excavation.
The pit excavations for the bypass tunnel alignment should be observed by this office, to confirm the soil
conditions are stable and if supplemental recommendations for the pit excavations are deemed
appropriate.
9.3 Drilling Fluid Migration
Fluid migration is recognized by a decrease of fluid in the return tank, a drop in fluid pressure, or a
complete loss of drilling fluid. Drilling fluid migration typically occurs when the drilling bit encounters
fractures in rock or desiccated clay. Based on the boring information obtained as part of this study, the
proposed bypass tunnel beneath Montgomery Drive will likely encounter predominantly clayey alluvial
soils as well as the weathered portion of the underlying bedrock along the northern and southern ends of
the bypass alignment beneath Montgomery Drive, respectively. Based on the boring information, the
clayey alluvial soils were generally observed to be moist and void of desiccation cracks. In addition, the
upper approximately 3 to 5 feet of the basaltic bedrock encountered in Borings B-1 and B-2 was observed
to be weathered to a hard sandy fat clay that is moist and void of desiccation cracks. Due to the presence
of stiff clays lacking significant desiccation cracks along the tunnel alignment beneath Montgomery Drive,
it is inferred that the potential for fluid migration and loss of drilling fluid is considered to be low.
However, the underlying and relatively less weathered portion of the bedrock was observed to be highly
fractured and if encountered could create the potential for drilling fluid migration. In addition,
predominantly granular channel deposits were encountered within the upper several feet of Boring MW-
1. Due to the poorly consolidated and granular nature of the sediments within and adjacent to the active
stream channel, it is inferred that fluid migration and loss of drilling fluid is possible within the granular
materials located within close proximity to the active stream channel.
9.4 Hydraulic Fracturing
Hydraulic fracturing occurs when borehole pressure causes plastic deformation of the soil and/or rock
surrounding the borehole, initiating and propagating fractures in the soil/rock mass. The resistance to the
plastic deformation and fracturing is a function of soil shear strength, overburden pressure, and initial
pore pressure. Sufficient soil and bedrock cover should be maintained over the borehole to provide an
appropriate factor of safety against hydraulic fracturing.
In general, inadvertent returns of drilling fluid due to hydraulic fracturing of the borehole entry point is
rare since the drilling returns flow easily back up to the entry point. Inadvertent returns are generally
more common near the exit point, where the depth of cover decreases.
9.5 Site Grading
Site grading is anticipated to consist of the excavation and backfilling of jacking and receiving pits, and
miscellaneous minor cuts and fills. As used in this report, the term “compact” and its derivatives mean
that all on-site fills should be compacted to a minimum of 90 percent of the maximum dry density, as
determined by ASTM Test Method D1557-01, at a moisture content that is slightly over optimum. The fill
used to backfill the jacking pits can consist of the excavated material and/or imported granular materials.
A sample of imported material proposed to be used for backfilling the jacking pits should be submitted to
the project Geotechnical Engineer (BAGG Engineers) for approval before transporting it to the site. The
fill material should be compacted in thin layers not exceeding 12-inches in uncompacted thickness, and
should be compacted to a minimum of 90 percent relative compaction at near optimum moisture content.
Rocks larger than 6-inches should not be allowed within the backfill material.
It must be the Contractor’s responsibility to select equipment procedures that will accomplish the grading
as described above. The Contractor must also organize the work in such a manner that one of our field
representatives can observe and test the grading operations, including excavation, and compaction of fill
and backfill.
9.6 Lateral Design
Lateral resistance may be obtained from passive earth pressures acting on the sides of neat excavations.
For lateral resistance, a passive pressure of 400 pcf (equivalent fluid pressure) may be assumed within the
upper native alluvial soils. Below water level, passive pressure should be reduced to 250 pcf. Within
bedrock, a uniform pressure of 2,000 psf can be added to these pressures.
9.7 Plan Review
It is recommended that the Geotechnical Engineer (BAGG Engineers) be retained to review the final
project plans for the new temporary bypass tunnel, and associated site improvements. This review will
be to assess general suitability of the recommendations contained in this report, and to verify the
appropriate implementation of our recommendations into the project plans and specifications.
9.8 Observation and Testing
It is recommended that BAGG Engineers be retained to provide observation and testing services during
construction. This is to observe compliance with the design concept, specifications and
recommendations, and will allow for design changes in the event that subsurface conditions differ from
those anticipated prior to the start of construction. Unanticipated subsurface conditions may warrant
revised recommendations. For this reason, BAGG Engineers cannot accept responsibility or liability for
recommendations in this report, unless we are retained to provide observation and testing services during
construction.
10.0 CLOSURE This report has been prepared in accordance with generally-accepted engineering practices for the strict
use of BKF Engineers, and other professionals associated with the specific project described in this report.
The recommendations presented in this report are based on our understanding of the proposed
construction as described herein, and upon soil conditions encountered in three exploratory borings
drilled for this investigation.
The conclusions and recommendations contained in this report are based on subsurface conditions
revealed by widely-spaced borings. It is not uncommon for unanticipated conditions to be encountered
during site grading and/or foundation installation, and it is not possible for all such variations to be found
by a field exploration program appropriate for this type of project. The recommendations contained in
this report are therefore contingent upon the review of the final project plans, and upon geotechnical
observation and testing by this office of all pertinent aspects of construction.
Soil conditions and standards of practice change with time. Therefore, we should be consulted to update
this report, if the construction does not commence within 18 months from the date that this report is
submitted. Additionally, the recommendations of this report are only valid for the proposed development
as described herein. If the proposed project is modified, our recommendations should be reviewed and
approved or modified by this office in writing.
The following plates are attached and complete this report: Plate 1 Vicinity Map Plate 2 Site Plan Plate 3 Area Geologic Map Plate 4 Regional Fault Map Plate 5 Unified Soil Classification System Plate 6 Soil Terminology Plate 7 Rock Terminology Plate 8 Boring Log Notes Plates 9A and 9B Key to Symbols Plates 10A thru 12C Boring & Well Logs Plate 13 Idealized Subsurface Profile A-A’ Plate 14 Atterberg Limits Test Data Plates 15A & 15B Gradation Test Data ASFE document titled “Important Information About Your Geotechnical Engineering Report” 11.0 REFERENCES California Building Standard Commission, 2016 California Building Code, California Code of Regulations, Title 24, Part 2, Volume 2 of 2. California Department of Conservation, Division of Mines and Geology, 2000, Digital Images of Official
maps of Alquist-Priolo Earthquake Fault Zones of California, Central Coast Region California Department of Transportation, August 2011, Trenching and Shoring Manual, Issued by Office of
Structure Construction, Revision 1. California Geological Survey, 2003 & 2010, Seismic Shaking Hazards in California, Based on the USGS/CGS
Probabilistic Seismic Hazards Assessment (PSHA) Model 2002 (revised April 2003); 10% Probability of Being Exceed in 50 years last edited March 23, 2010.
McLaughlin, R.J., Langenheim, V.E., Sarna-Wojcicki, A.M., Fleck, R.J., McPhee, D.K., Roberts, C.W.,
McCabe, C.A., and Elmira Wan, 2008, Geologic and geophysical framework of the Santa Rosa 7.5' quadrangle, Sonoma County, California: U.S. Geological Survey Open-File Report 2008-1009, 51 p., three sheets, scale 1:24,000 [http://pubs.usgs.gov/of/2008/1009/].
U.S. Geological Survey (USGS), 2008, Documentation for the 2008 Update of the United States National Seismic Hazards Maps, Open-File Report 2008-1128.
U.S Geological Survey (USGS), 2013, U.S. Seismic Design Maps, USGS Earthquake Hazards Program
(http://earthquake.usgs.gov/designmaps/us/application.php). Working Group on California Earthquake Probabilities, 2014, Long-Term Time-Dependent Probabilities for
the Third Uniform California Earthquake Rupture Forecast (UCERF3), Bulletin of the Seismological Society of America, Vol. 105, No. 2A, April 2015
Working Group on California Earthquake Probabilities, 2008, The Uniform California Earthquake Rupture
Forecast, Version 2 (UCERF2), U. S. Geological Survey Open File Report 2007-1437. Working Group on Northern California Earthquake Potential, 1996, Database of Potential sources for
Earthquake Larger Than Magnitude 6 in Northern California, Open-File Report 96-705, U.S. Geological Survey.
SITE
SANTA ROSA CREEK DIVERSION CHANNEL SANTA ROSA, CALIFORNIA
PLATE: 2
SITE PLAN
Base: Modified from Exhibit, Vortex Tube Rehabilitation Project, Santa Rosa Creek, Sonoma Water, by BKF Engineers, Job no. 20180695, dated July, 2019.
E
20
B-2
B-1
Geotechnical Boring Locations - Approximate
Reference: Modified from Geologic and Geophysical Framework of the Santa Rosa 7.5’ Quadrangle, Sonoma County, California, U.S. Geological Survey Open-File Report 2008-1009, By R.J. McLaughlin et al., 2008, Map Scale 1:24,000
MAP EXPLANATION
DATUM IS MEAN SEA LEVEL
TERTIARY ROCKS
Reference: Taken from the 2002 California Geological Survey Fault Model
SITE
DATE: October, 2019
JOB NUMBER: BKFEN-42-00
UNIFIED SOIL CLASSIFICATION SYSTEM
GROUP SYMBOLS
SYMBOLS ILLUSTRATIVE GROUP NAMES MAJOR
DIVISIONS
GRAVELS More than
No. 4 sieve size
SILTS AND CLAYS
GP Poorly graded gravel Poorly graded gravel with sand
ML Silt Sandy silt with gravel
GM Silty gravel Silty gravel with sand
OL Organic clay Sandy organic clay with gravel
GC Clayey gravel Clayey gravel with sand
CH Fat clay Sandy fat clay with gravel SILTS AND
CLAYS liquid limit more than
50
SANDS More than
size
SP Poorly graded sand Poorly graded sand with gravel
OH Organic clay Sandy organic clay with gravel
SM Silty sand Silty sand with gravel
PT Peat Highly organic silt
HIGHLY ORGANIC
SC Clayey sand Clayey sand with gravel
NOTE: Coarse-grained soils receive dual symbols if: (1) their fines are CL-ML (e.g. SC-SM or GC-GM) or (2) they contain 5-12% fines (e.g. SW-SM, GP-GC, etc.)
NOTE: Fine-grained soils receive dual symbols if their limits in the hatched zone on the Plasticity Chart(L-M)
SOIL SIZES
4
7
10 20 30 40 50 60 70 80 90 100 110 0
10
20
30
40
50
60
0
SAND No. 200 to No.4
Coarse No. 10 to No. 4
Medium No. 40 to No. 10
Fine No. 200 to No. 40
*FINES: BELOW No. 200
NOTE: Classification is based on the portion of a sample that passes the 3-inch sieve.
Reference: ASTM D 2487-06, Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System).
GENERAL NOTES: The tables list 30 out of a possible 110 Group Names, all of which are assigned to unique proportions of constituent soils. Flow charts in ASTM D 2487-06 aid assignment of the Group Names. Some general rules for fine grained soils are: less than 15% sand or gravel is not mentioned; 15% to 25% sand or gravel is termed "with sand" or "with gravel", and 30% to 49% sand or gravel is termed "sandy" or "gravelly". Some general rules for coarse-grained soils are: uniformly-graded or gap-graded soils are "Poorly" graded (SP or GP); 15% or more sand or gravel is termed "with sand" or "with gravel", 15% to 25% clay and silt is termed clayey and silty and any cobbles or boulders are termed "with cobbles" or "with boulders".
Job No: BKFEN-42-00 Plate 6
SOIL TERMINOLOGY
(03/08)
SOIL TYPES (Ref 1) Boulders: particles of rock that will not pass a 12-inch screen. Cobbles: particles of rock that will pass a 12-inch screen, but not a 3-inch sieve. Gravel: particles of rock that will pass a 3-inch sieve, but not a #4 sieve. Sand: particles of rock that will pass a #4 sieve, but not a #200 sieve. Silt: soil that will pass a #200 sieve, that is non-plastic or very slightly plastic, and that exhibits little or no strength
when dry. Clay: soil that will pass a #200 sieve, that can be made to exhibit plasticity (putty-like properties) within a range of
water contents, and that exhibits considerable strength when dry.
MOISTURE AND DENSITY Moisture Condition: an observational term; dry, moist, wet, or saturated. Moisture Content: the weight of water in a sample divided by the weight of dry soil in the soil sample, expressed as a
percentage. Dry Density: the pounds of dry soil in a cubic foot of soil.
DESCRIPTORS OF CONSISTENCY (Ref 3) Liquid Limit: the water content at which a soil that will pass a #40 sieve is on the boundary between exhibiting liquid and
plastic characteristics. The consistency feels like soft butter. Plastic Limit: the water content at which a soil that will pass a #40 sieve is on the boundary between exhibiting plastic and
semi-solid characteristics. The consistency feels like stiff putty. Plasticity Index: the difference between the liquid limit and the plastic limit, i.e. the range in water contents over which the soil is
in a plastic state.
MEASURES OF CONSISTENCY OF COHESIVE SOILS (CLAYS) (Ref's 2 & 3) Very Soft N=0-1* C=0-250 psf Squeezes between fingers Soft N=2-4 C=250-500 psf Easily molded by finger pressure Medium Stiff N=5-8 C=500-1000 psf Molded by strong finger pressure Stiff N=9-15 C=1000-2000 psf Dented by strong finger pressure Very stiff N=16-30 C=2000-4000 psf Dented slightly by finger pressure Hard N>30 C>4000 psf Dented slightly by a pencil point
*N=blows per foot in the Standard Penetration Test. In cohesive soils, with the 3-inch-diameter ring sampler, 140- pound weight, divide the blow count by 1.2 to get N (Ref 4).
MEASURES OF RELATIVE DENSITY OF GRANULAR SOILS (GRAVELS, SANDS, AND SILTS) (Ref's 2 & 3) Very Loose N=0-4** RD=0-30 Easily push a ½-inch reinforcing rod by hand Loose N=5-10 RD=30-50 Push a ½-inch reinforcing rod by hand Medium Dense N=11-30 RD=50-70 Easily drive a ½-inch reinforcing rod Dense N=31-50 RD=70-90 Drive a ½-inch reinforcing rod 1 foot Very Dense N>50 RD=90-100 Drive a ½-inch reinforcing rod a few inches
**N=Blows per foot in the Standard Penetration Test. In granular soils, with the 3-inch-diameter ring sampler, 140- pound weight, divide the blow count by 2 to get N (Ref 4).
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Ref 1: ASTM Designation: D 2487-06, Standard Classification of Soils for Engineering Purposes (Unified Soil Classification
System). Ref 2: Terzaghi, Karl, and Peck, Ralph B., Soil Mechanics in Engineering Practice, John Wiley & Sons, New York, 2nd Ed., 1967,
pp. 30, 341, and 347. Ref 3: Sowers, George F., Introductory Soil Mechanics and Foundations: Geotechnical Engineering, Macmillan Publishing
Company, New York, 4th Ed., 1979, pp. 80, 81, and 312. Ref 4: Lowe, John III, and Zaccheo, Phillip F., Subsurface Explorations and Sampling, Chapter 1 in "Foundation Engineering
Handbook," Hsai-Yang Fang, Editor, Van Nostrand Reinhold Company, New York, 2nd Ed, 1991, p. 39.
Job No: BKFEN-42-00 Plate 7
ROCK TERMINOLOGY
WEATHERING DESCRIPTORS
Fresh No discoloration, not oxidized, no separation, hammer rings when crystalline rocks are struck. Slight Discoloration or oxidation is limited to surface of, or short distance from, fractures; some feldspar crystals are dull, no visible
separation, hammer rings when crystalline rocks are struck, body of rock not weakened. Moderate Discoloration extends from fractures, usually throughout; Fe-Mg materials are “rusty”, feldspar crystals are “cloudy”, all
fractures are discolored or oxidized, partial separation of boundaries visible, texture generally preserved, hammer dose not ring when rock is struck, body of rock is slightly weakened.
Intense Discoloration or oxidation throughout; all feldspars and Fe-Mg minerals are altered to clay to some extent; or chemical
alteration produces in situ disaggregation, all fracture surfaces are discolored or oxidized, surfaces friable, partial separation, texture altered by chemical disintegration, dull sound when struck with hammer, rock is significantly weakened.
Decomposed Discolored or oxidized throughout, but resistant mineral such as quartz may be unaltered, all feldspars and Fe-Mg minerals
are completely altered to clay, complete separation of grain boundaries, resembles a soil, partial or complete remnant of rock structure may be preserved, can be granulated by hand, resistant minerals such as quartz may be present as “stringers” or “dykes”.
BEDDING FOLIATION AND FRACTURE SPACING DESCRIPTORS Millimeters Feet Bedding Fracture Spacing >10 <0.03 Laminated Very Close 10-30 0.03-0.1 Very Thin Very Close 30-100 0.1-0.3 Thin Close 100-300 0.3-1 Moderate Moderate 300-1000 1-3 Thick Wide 1000-3000 3-10 Very Thick Very Wide >3000 >10 Massive Extremely Wide
ROCK HARDNESS/STRENGTH DESCRIPTORS* Extremely Hard Core, fragment, or exposure cannot be scratched with knife or sharp pick; can only be chipped with repeated heavy
hammer blows. Very Hard Cannot be scratched with knife or sharp pick. Core or fragment breaks with repeated heavy hammer blows. Hard Can be scratched with knife or sharp pick with difficulty (heavy pressure). Heavy hammer blow required to break
specimen. Moderately Hard Can be scratched with knife or sharp pick with light or moderate pressure. Core or fragment breaks with moderate
hammer blow. Moderately Soft Can be grooved 1/16 inch (2mm) deep by knife or sharp pick with moderate or heavy pressure. Core fragment breaks
with light hammer blow or heavy manual pressure. Soft Can be grooved or gouged easily by knife or sharp pick with light pressure, can be scratched with fingernail. Breaks wit
light to moderate manual pressure. Very Soft Can be readily indented, grooved, or gouged with fingernail, or carved with a knife. Breaks with light manual pressure. *Note: Although “sharp pick” is included in those definitions, descriptions of ability to be scratched, grooved, or gouged by a
knife is the preferred criteria. xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx "Engineering Geology Field Manual, Second Edition, Volume 1, by U.S. Department of Interior, Bureau of Reclamation, 1998
Job No. BKFEN-42-00 Plate 8
BORING LOG NOTES
GENERAL NOTES FOR BORING LOGS: The boring logs are intended for use only in conjunction with the text, and for only the purposes the text outlines for our services. The Plate "Soil Terminology" defines common terms used on the boring logs. The plate "Unified Soil Classification System," illustrates the method used to classify the soils. The soils were visually classified in the field; the classifications were modified by visual examination of samples in the laboratory, supported, where indicated on the logs, by tests of liquid limit, plasticity index, and/or gradation. In addition to the interpretations for sample classification, there are interpretations of where stratum changes occur between samples, where gradational changes substantively occur, and where minor changes within a stratum are significant enough to log. There may be variations in subsurface conditions between borings. Soil characteristics change with variations in moisture content, with exchange of ions, with loosening and densifying, and for other reasons. Groundwater levels change with seasons, with pumping, from leaks, and for other reasons. Thus boring logs depict interpretations of subsurface conditions only at the locations indicated, and only on the date(s) noted.
SPECIAL FIELD NOTES FOR THIS REPORT:
1. The boring drilled as part of the monitoring well installation was drilled on August 23, 2019 with a portable drilling rig using 6-inch diameter solid stem augers. The geotechnical borings were drilled on August 26, 2019 with a track-mounted drilling rig using 4-inch diameter solid stem augers. The geotechnical borings were covered and left open overnight to allow groundwater to equilibrate. The borings were sealed with cement grout on August 27, 2019.
2. The boring locations were approximately located by using a tape measure and/or pacing from
known points on the site, as shown on Plate 2, Site Plan. 3. The soils’ Group Names [e.g. SANDY LEAN CLAY] and Group Symbols [e.g. (CL)] were
determined or estimated per ASTM D 2487-06, Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System, see Plate 5). Other soil engineering terms used on the boring log are defined on Plate 6, Soil Terminology.
4. The “Blow Count” Column on the boring logs indicates the number of blows required to drive
the sampler below the bottom of the boring, with the blow counts given for each 6 inches of sampler penetration. The samples from the boring were driven with a 140-pound hammer.
5. Groundwater was encountered in the borings as indicated on the boring logs. 6. The shear strength values indicated on the boring logs are peak strength values.
Symbol Description
Strata symbols
Silty sand
Fat clay with sand
Water level at completion of boring
Boring continues
Soil Samplers
Modified California Sampler: 18" long, 2.375" ID by 3" OD, split-barrel sampler driven w/ 140-pound hammer falling 30 inches (ASTM D3550)
Standard Penetration Test: 18" long, 1.375" ID by 2" OD, split-spoon sampler driven w/ 140-pound hammer falling 30 inches (ASTM D 1586-11)
Line Types
Laboratory Data
DS Direct shear test performed on a sample at natural or field moisture content (ASTM D3080).
PI Plasticity Index established per ASTM D4318 Test Method.
LL Liquid Limit established per ASTM D4318Test Method.
KEY TO SYMBOLS
Plate 9 - A
Symbol Description
Laboratory Data
Gravel Percent soil particles finer than a 3" sieve and coarser than a No. 4 sieve (ASTM C136/C117)
Sand Percent soil particles finer than a No. 4 sieve and coarser than a No. 200 sieve (ASTM C136/C117)
Fines Percent soil particles finer than a No. 200 sieve (ASTM C117)
bgs Below the ground surface
KEY TO SYMBOLS
Plate 9 - B
13.2
24.9
87
6
4
ROCK
ROCK
SILTY SAND: light to medium brown, loose, slightly moist, fine sand, few medium to coarse sand
POORLY-GRADED SAND W/ SILT: gray-brown, loose, moist, fine to medium sand SILTY SAND: mottled brown and blue-gray, loose, moist to very moist, fine sand SILTY LEAN CLAY: blue- gray, soft to medium stiff, very moist, few fine sand
SILTY SAND W/ GRAVEL:gray to blue-gray, dense, wet, well-graded sand, some fine gravel, few coarse gravel, trace to few cobbles
ANDESITIC TUFF: olive-gray, moderately to intensely weathered, soft to moderately soft, slightly moist, contains fine to medium sand and trace to few coarse sand to fine gravel size rock fragments
ANDESITIC TUFF BRECCIA: olive-brown and red-brown,
Traffic-rated well cover
Transition Seal: Bentonite Pellets
Filter Pack: #3 Monterey Sand
% Sand=62 % Fines=38
BORING & WELL LOG Well No. MW-1
JOB NAME: Vortex Tube Rehabilitation Project JOB NO.: BKFEN-42-00 CLIENT: BKF Engineers DATE DRILLED: 8/23/19 LOCATION: East bank Santa Rosa Creek, Santa Rosa, CA ELEVATION: 305± feet DRILLER: Clear Heart Drilling, Inc. LOGGED BY: EW DRILL METHOD: Portable drilling rig w/ 6-inch diam. solid stem augers CHECKED BY:
T yp
22
moderately weathered, moderately soft, moist, contains well-graded sand and trace gravel-size rock fragments
ANDESITIC TUFF: gray- brown, moderately weathered, moderately soft, moist
The boring was terminated at approximately 21 feet bgs.
Following completion of the boring, the borehole was developed as a groundwater monitoring well per the details provided above.
Groundwater was encountered at approximately 6 feet bgs and subsequently measured at approximately 5 feet bgs on August 27, 2019.
Screw-on, PVC, bottom cap
JOB NAME: Vortex Tube Rehabilitation Project JOB NO.: BKFEN-42-00
T yp
Asphaltic concrete
Aggregate base CLAYEY GRAVEL W/ SAND: brown, yellow-brown, and gray-brown, dense, moist, well-graded sand, some coarse gravel, little fine gravel, few coarse gravel, trace to few cobbles
...approx. 1 foot thick zone of gray to gray-brown silty well- graded sand & gravel
CLAYEY SAND: red-brown, very dense, slightly moist, well- graded sand, few fine gravel
BORDERLINE SANDY FAT CLAY/CLAYEY SAND: mottled red-brown and orange- brown, hard/dense, moist, fine to medium sand, trace coarse sand, moderate to high plasticity fines
FAT CLAY W/ SAND: mottled blue-gray, red-brown, and yellow- to orange-brown, hard,
@6½" AC
Native
BORING LOG Boring No. B-1
JOB NAME: Vortex Tube Rehabilitation Project JOB NO.: BKFEN-42-00 CLIENT: BKF Engineers DATE DRILLED: 8/26/19 LOCATION: N. shoulder of westbound Montgomery Drive, Santa Rosa, CA ELEVATION: 317± feet DRILLER: Clear Heart Drilling, Inc. LOGGED BY: EW DRILL METHOD: DR8K track-mounted drilling rig w/ 4-inch solid stem augers
T yp
CH
SC
moist, fine sand, high plasticity fines BORDERLINE SANDY FAT CLAY/CLAYEY SAND: red- brown w/ yellow- to orange- brown and blue- to olive-gray mottling, hard/dense, fine to medium sand, trace coarse sand, moderate to high plasticity fines
...olive-gray w/ trace yellow- and red-brown oxidation staining, hard, moist, fine sand, trace medium sand
SANDY FAT CLAY: red- brown w/ trace off-white specks, hard, moist, fine sand, few medium to coarse sand, trace gravel size weathered rock fragments
CLAYEY SAND: red-brown w/ few off-white, dark gray, and yellow-brown specs,dense, moist, fine sand, trace to few medium sand
T yp
14
25
40
...trace orange-brown oxidation, dense, moist to very moist, fine to medium sand, trace coarse sand to gravel size weathered bedrock fragments
The boring was terminated at approximately 30 feet bgs.
Groundwater was not encountered in the boring.
The borehole was left open overnight and groundwater was subsequently measured at 26‚ feet bgs on August 27, 2019.
The borehole was backfilled with neat cement grout on August 27, 2019.
T yp
Asphaltic Concrete
Aggregate base CLAYEY GRAVEL W/ SAND: brown, red-brown, yellow-brown, and gray-brown, dense to very dense, moist, well-graded sand, little to some fine gravel, few coarse gravel, trace to few cobbles
...approx. 1 foot thick zone of gray to gray-brown silty well- graded sand & gravel
SANDY FAT CLAY: mottled blue-gray, red-brown and yellow- to olive-brown, hard, slightly moist to moist, fine sand, few medium sand, moderate to high plasticity fines
...mottled red-brown and yellow-brown w/ trace blue- gray, moist CLAYEY SAND:mottled red- brown, yellow-brown and blue- gray, very dense, moist, fine to medium sand, traceto few coarse sand, moderate plasticity fines
@6" AC
JOB NAME: Vortex Tube Rehabilitation Project JOB NO.: BKFEN-42-00 CLIENT: BKF Engineers DATE DRILLED: 8/26/19 LOCATION: S. shoulder of eastbound Montgomery Drive, Santa Rosa, CA ELEVATION: 317± feet DRILLER: Clear Heart Drilling, Inc. LOGGED BY: EW DRILL METHOD: DR8K track-mounted drilling rig w/ 4-inch solid stem augers
T yp
SANDY MODERATE PLASTICITY CLAY: red- brown w/ yellow-brown mottling,hard, moist, fine to medium sand, trace coarse sand, moderate to high plasticity fines
SANDY FAT CLAY/CLAYEY SAND: red-brown w/ yellow- to orange-brown oxidation and off-white specks, hard/very dense, moist, fine to medium sand ...apparent near vertical layering observed in unoriented sample
BASALTIC ANDESITE: dark gray w/ yellow- to red-brown oxidation staining, moderately weathered, moderately soft, closely fractured
% Fines=57 LL=47, PI=26
Completely Weathered Bedrock (Basaltic Andesite)
% Fines=48 LL=55, PI=26
T yp
The boring was terminated at approximately 26½ feet bgs.
Groundwater was encountered in the boring at approximately 22 feet bgs.
The borehole was left open overnight and groundwater was subsequently measured at 7½ feet bgs on August 27, 2019.
The borehole was backfilled with neat cement grout on August 27, 2019.
T yp
20
Note: Elevations derived from Exhibit, Vortex Tube Rehabilitation Project, Santa Rosa Creek, Sonoma Water, by BKF Engineers, Job no. 20180695, dated July, 2019.
15 Distance (Feet)
0 30 45 60 9075 105 120 150135 165 180 195 225210 240 255 270 285
El ev
at io
Groundwater Elevation: as encountered (queried where uncertain)
Artificial Fill
Sonoma Volcanics: Andesitic to Dacitic Tuff, Breccia & Minor Flows (Pliocene & Miocene)
Boring Locations - Approximate
MW-1 Monitoring Well Location - Approximate
??
ATTERBERG LIMITS TEST DATA
4
7
10 20 30 40 50 60 70 80 90 100 110 0
10
20
30
40
50
60
0
Boring B-1 12½ 32.8 74 28 46 Fat Clay w/ Sand (CH)
Boring B-2 9½ 29.0 55 26 29
Sandy Fat Clay (CH)
Sandy Moderate Plasticity Clay (CL/CH)
GEOTECHNICAL ENGINEERING INVESTIGATION VORTEX TUBE REHABILITATION PROJECT
DATE: October, 2019
Sandy Fat Clay/Clayey Sand (CH/SC)
GRADATION TEST DATA
0
10
20
30
40
50
60
70
80
90
100
0.010.1110100
P e rc e n t F in e r b y W e ig h t
Grain Size (mm)
C O
B B
LE S
COARSE FINE
GRAVEL SAND
P e rc
DATE: October, 2019
(CH/SC)
B-1-5B
13
(CH/SC)
B-2-2B
10
0
10
20
30
40
50
60
70
80
90
100
0.010.1110100
P e rc e n t F in e r b y W e ig h t
Grain Size (mm)
C O
B B
LE S
COARSE FINE
GRAVEL SAND
LEGEND
GEOTECHNICAL ENGINEERING INVESTIGATION VORTEX TUBE REHABILITATION PROJECT
DATE: October, 2019
Geotechnical-Engineering Report Important Information about This
Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.
While you cannot eliminate all such risks, you can manage them. The following information is provided to help.
The Geoprofessional Business Association (GBA) has prepared this advisory to help you – assumedly a client representative – interpret and apply this geotechnical-engineering report as effectively as possible. In that way, clients can benefit from a lowered exposure to the subsurface problems that, for decades, have been a principal cause of construction delays, cost overruns, claims, and disputes. If you have questions or want more information about any of the issues discussed below, contact your GBA-member geotechnical engineer. Active involvement in the Geoprofessional Business Association exposes geotechnical engineers to a wide array of risk-confrontation techniques that can be of genuine benefit for everyone involved with a construction project.
Geotechnical-Engineering Services Are Performed for Specific Purposes, Persons, and Projects Geotechnical engineers structure their services to meet the specific needs of their clients. A geotechnical-engineering study conducted for a given civil engineer will not likely meet the needs of a civil- works constructor or even a different civil engineer. Because each geotechnical-engineering study is unique, each geotechnical- engineering report is unique, prepared solely for the client. Those who rely on a geotechnical-engineering report prepared for a different client can be seriously misled. No one except authorized client representatives should rely on this geotechnical-engineering report without first conferring with the geotechnical engineer who prepared it. And no one – not even you – should apply this report for any purpose or project except the one originally contemplated.
Read this Report in Full Costly problems have occurred because those relying on a geotechnical- engineering report did not read it in its entirety. Do not rely on an executive summary. Do not read selected elements only. Read this report in full.
You Need to Inform Your Geotechnical Engineer about Change Your geotechnical engineer considered unique, project-specific factors when designing the study behind this report and developing the confirmation-dependent recommendations the report conveys. A few typical factors include: • the client’s goals, objectives, budget, schedule, and risk-management preferences; • the general nature of the structure involved, its size, configuration, and performance criteria; • the structure’s location and orientation on the site; and • other planned or existing site improvements, such as retaining walls, access roads, parking lots, and underground utilities.
Typical changes that could erode the reliability of this report include those that affect: • the site’s size or shape; • the function of the proposed structure, as when it’s changed from a parking garage to an office building, or from a light-industrial plant to a refrigerated warehouse; • the elevation, configuration, location, orientation, or weight of the proposed structure; • the composition of the design team; or • project ownership.
As a general rule, always inform your geotechnical engineer of project changes – even minor ones – and request an assessment of their impact. The geotechnical engineer who prepared this report cannot accept responsibility or liability for problems that arise because the geotechnical engineer was not informed about developments the engineer otherwise would have considered.
This Report May Not Be Reliable Do not rely on this report if your geotechnical engineer prepared it: • for a different client; • for a different project; • for a different site (that may or may not include all or a portion of the original site); or • before important events occurred at the site or adjacent to it; e.g., man-made events like construction or environmental remediation, or natural events like floods, droughts, earthquakes, or groundwater fluctuations.
Note, too, that it could be unwise to rely on a geotechnical-engineering report whose reliability may have been affected by the passage of time, because of factors like changed subsurface conditions; new or modified codes, standards, or regulations; or new techniques or tools. If your geotechnical engineer has not indicated an “apply-by” date on the report, ask what it should be, and, in general, if you are the least bit uncertain about the continued reliability of this report, contact your geotechnical engineer before applying it. A minor amount of additional testing or analysis – if any is required at all – could prevent major problems.
Most of the “Findings” Related in This Report Are Professional Opinions Before construction begins, geotechnical engineers explore a site’s subsurface through various sampling and testing procedures. Geotechnical engineers can observe actual subsurface conditions only at those specific locations where sampling and testing were performed. The data derived from that sampling and testing were reviewed by your geotechnical engineer, who then applied professional judgment to form opinions about subsurface conditions throughout the site. Actual sitewide-subsurface conditions may differ – maybe significantly – from those indicated in this report. Confront that risk by retaining your geotechnical engineer to serve on the design team from project start to project finish, so the individual can provide informed guidance quickly, whenever needed.
This Report’s Recommendations Are Confirmation-Dependent The recommendations included in this report – including any options or alternatives – are confirmation-dependent. In other words, they are not final, because the geotechnical engineer who developed them relied heavily on judgment and opinion to do so. Your geotechnical engineer can finalize the recommendations only after observing actual subsurface conditions revealed during construction. If through observation your geotechnical engineer confirms that the conditions assumed to exist actually do exist, the recommendations can be relied upon, assuming no other changes have occurred. The geotechnical engineer who prepared this report cannot assume responsibility or liability for confirmation- dependent recommendations if you fail to retain that engineer to perform construction observation.
This Report Could Be Misinterpreted Other design professionals’ misinterpretation of geotechnical- engineering reports has resulted in costly problems. Confront that risk by having your geotechnical engineer serve as a full-time member of the design team, to: • confer with other design-team members, • help develop specifications, • review pertinent elements of other design professionals’ plans and specifications, and • be on hand quickly whenever geotechnical-engineering guidance is needed. You should also confront the risk of constructors misinterpreting this report. Do so by retaining your geotechnical engineer to participate in prebid and preconstruction conferences and to perform construction observation.
Give Constructors a Complete Report and Guidance Some owners and design professionals mistakenly believe they can shift unanticipated-subsurface-conditions liability to constructors by limiting the information they provide for bid preparation. To help prevent the costly, contentious problems this practice has caused, include the complete geotechnical-engineering report, along with any attachments or appendices, with your contract documents, but be certain to note conspicuously that you’ve included the material for informational purposes only. To avoid misunderstanding, you may also want to note that “informational purposes” means constructors have no right to rely on the interpretations, opinions, conclusions, or recommendations in the report, but they may rely on the factual data relative to the specific times, locations, and depths/elevations referenced. Be certain that constructors know they may learn about specific project requirements, including options selected from the report, only from the design drawings and specifications. Remind constructors that they may
perform their own studies if they want to, and be sure to allow enough time to permit them to do so. Only then might you be in a position to give constructors the information available to you, while requiring them to at least share some of the financial responsibilities stemming from unanticipated conditions. Conducting prebid and preconstruction conferences can also be valuable in this respect.
Read Responsibility Provisions Closely Some client representatives, design professionals, and constructors do not realize that geotechnical engineering is far less exact than other engineering disciplines. That lack of understanding has nurtured unrealistic expectations that have resulted in disappointments, delays, cost overruns, claims, and disputes. To confront that risk, geotechnical engineers commonly include explanatory provisions in their reports. Sometimes labeled “limitations,” many of these provisions indicate where geotechnical engineers’ responsibilities begin and end, to help others recognize their own responsibilities and risks. Read these provisions closely. Ask questions. Your geotechnical engineer should respond fully and frankly.
Geoenvironmental Concerns Are Not Covered The personnel, equipment, and techniques used to perform an environmental study – e.g., a “phase-one” or “phase-two” environmental site assessment – differ significantly from those used to perform a geotechnical-engineering study. For that reason, a geotechnical- engineering report does not usually relate any environmental findings, conclusions, or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Unanticipated subsurface environmental problems have led to project failures. If you have not yet obtained your own environmental information, ask your geotechnical consultant for risk-management guidance. As a general rule, do not rely on an environmental report prepared for a different client, site, or project, or that is more than six months old.
Obtain Professional Assistance to Deal with Moisture Infiltration and Mold While your geotechnical engineer may have addressed groundwater, water infiltration, or similar issues in this report, none of the engineer’s services were designed, conducted, or intended to prevent uncontrolled migration of moisture – including water vapor – from the soil through building slabs and walls and into the building interior, where it can cause mold growth and material-performance deficiencies. Accordingly, proper implementation of the geotechnical engineer’s recommendations will not of itself be sufficient to prevent moisture infiltration. Confront the risk of moisture infiltration by including building-envelope or mold specialists on the design team. Geotechnical engineers are not building- envelope or mold specialists.
Copyright 2016 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly prohibited, except with GBA’s specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission of GBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document or its wording as a complement to or as an element of a report of any
kind. Any other firm, individual, or other entity that so uses this document without being a GBA member could be committing negligent
Telephone: 301/565-2733 e-mail: [email protected] www.geoprofessional.org
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