GEOTECHNICAL ENGINEERING AND GEOLOGIC HAZARDS
GEOTECHNICAL ENGINEERING
AND
GEOLOGIC HAZARDS STUDY
Ygnacio Valley High School
Chemistry Laboratory Classroom Building
Concord, California
Prepared for:
Mt. Diablo Unified School District
3333 Ronald Way
Concord, California 94519
Prepared by:
GEOSPHERE CONSULTANTS, INC.
2001 Crow Canyon Road, Suite 100
San Ramon, California 94583
Geosphere Project No. 91-02968-A
TABLE OF CONTENTS
TABLE OF CONTENTS (continued)
FIGURES
Figure 1 - Site Vicinity
Figure 2 - Site Plan
Figure 3 - Site Vicinity Geology Map
Figure 4 - Schematic Geologic Cross-Section A-A’
Figure 5 - Site Geologic Map
Figure 6 - Liquefaction Susceptibility Map
Figure 7 - Flood Hazard Map
Figure 8 - Regional Geologic Map
APPENDIX A
Boring Logs
APPENDIX B
LABORATORY TEST RESULTS
Atterberg Limits
Direct Shear
Sieve Analysis
Corrosion
APPENDIX C
Liquefaction Analysis
GEOTECHNICAL ENGINEERING AND GEOLOGIC HAZARDS STUDY
Project: Ygnacio Valley High School –Chemistry Laboratory Classroom Project
Concord, California
Client: Mt. Diablo Unified School District
Concord, California
1.0 INTRODUCTION
1.1 Purpose and Scope
The purposes of this study were to evaluate the subsurface conditions at the site of the proposed chemistry lab structure and prepare geotechnical recommendations for the design and construction. This study provides recommendations for foundations, site preparation, grading, drainage and guideline specifications for grading. This study was performed in accordance with the scope of work outlined in our revised proposal dated December 6, 2012.
The scope of this study included the review of pertinent published and unpublished documents related to the site, the drilling of two subsurface borings, laboratory testing of selected samples retrieved from the borings, engineering analysis of the accumulated data, and preparation of this report. The conclusions and recommendations presented in this report are based on the data acquired and analyzed during this study, and on prudent engineering judgment and experience. This study did not include an assessment of potentially toxic or hazardous materials that may be present on or beneath the site.
1.2 Site Description
Ygnacio Valley High School is located at 755 Oak Grove Road in Concord, California, as shown on Figure 1. The proposed site improvement will be located at the west corner of the high school campus at the very western edge of the main driveway and parking lot to the school. The site is relatively flat, with the general site vicinity topography sloping gently to the northeast. The campus is bounded on the north and south by developed commercial and retail properties and to the east and west by residential development. The site is located at approximately 37.934815
° north latitude and 122.027017
° west longitude, and approximately 96 feet above mean sea level.
1.3 Proposed Development
It is our understanding that the proposed site improvement is to consist of the installation of a modular chemistry laboratory classroom building. Other minor improvements may consist of utility upgrades, exterior concrete hardscapes, and landscaping. The proposed improvements are shown on the attached Site Plan, Figure 2.
1.4 Validity of Report
This report is valid for three years after publication. If construction begins after this time period, Geosphere should be contacted to confirm that the site conditions have not changed significantly. If the proposed development differs considerably from that described above, Geosphere should be notified to determine if additional recommendations are required. Additionally, if Geosphere is not involved during the geotechnical aspects of construction, this report may become wholly or in part invalid; Geosphere’s geotechnical personnel should be retained to verify that the subsurface conditions anticipated when preparing this report are similar to the subsurface conditions revealed during construction. Geosphere’s involvement should include grading and foundation plan review, grading observation and testing, foundation excavation observation, and utility trench backfill testing.
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2.0 PROCEDURES AND RESULTS
2.1 Literature Review
Pertinent geologic and geotechnical literature pertaining to the site area were reviewed. These included various
USGS, CGS and other agency publications and maps.
2.2 Drilling and Sampling
A subsurface exploration program was undertaken to evaluate the soil conditions at the site. Two borings were drilled on January 3, 2013. The locations of the borings in relation to the proposed improvements are shown on the attached Figure 2. The borings were drilled using a Mobile D-53 drill rig equipped with eight-inch hollow stem augers.
A Geosphere representative visually classified the materials encountered in the borings according to the Unified Soil
Classification System as the borings were advanced. Relatively undisturbed soil samples were recovered at selected intervals using a three-inch outside diameter Modified California split spoon sampler containing six-inch long brass liners. A two-inch outside diameter Standard Penetration Test (SPT) sampler was used to obtain SPT blow counts and obtain disturbed soil samples. The samplers were driven by using a mechanical-trip, 140-pound hammer with an approximate 30-inch fall utilizing N-rods as necessary. Resistance to penetration was recorded as the number of hammer blows required to drive the sampler the final foot of an 18-inch drive. All of the blow counts recorded using
Modified California split spoon sampler in the field was converted to equivalent SPT blow counts using appropriate modification factors suggested by Burmister (1948), i.e. a factor of 0.65 with inner diameter of 2.5 inches. Therefore, the boring logs reported in this report are all equivalent SPT blow counts. Bulk samples were obtained in the upper few feet of the borings from the auger cuttings as needed.
The boring logs with descriptions of the various materials encountered in each boring, the penetration resistance values, and some of the laboratory test results are presented in Appendix A. The ground surface elevations indicated on the soil boring logs are approximate (rounded to the nearest ½ foot) and were estimated from Google Earth. True surface elevations at the boring locations could differ. The locations and elevations of the borings should only be considered accurate to the degree implied by the means and methods used to define them. The approximate locations of the borings are shown on the Site Plan, Figure 2.
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2.3 Laboratory Testing
Laboratory tests were performed on selected samples to determine some of the physical and engineering properties of the subsurface soils. The results of the laboratory testing are presented on the boring logs and are included in
Appendix B. The following soil tests were performed for this study:
Dry Density and Moisture Content (ASTM D2216 and ASTM 2937) – In-situ density and moisture tests were conducted to determine the in-place dry density and moisture content of the subsurface materials. These properties provide information for evaluating the physical characteristics of the subsurface soils.
Atterberg Limits (ASTM D4318 and CT204) - Liquid Limit, Plastic Limit, and Plasticity Index are useful in the classification and characterization of the engineering properties of soil, helps evaluate expansive characteristics of the soil, and aids in determining the soil type according to the USCS.
Direct Shear (modified ASTM D3080) - Direct shear testing is performed on samples to determine the angle of internal friction and cohesion of soil or rock materials. This data can be utilized in determining allowable bearing capacity, retaining wall design parameters, and strength characteristics of the materials. Direct shear specimens are saturated under a 100-psf surcharge for a period of 24 hours prior to testing.
Particle Size Analysis (Wet and Dry Sieve) - Sieve analysis testing is conducted on selected samples to determine the soil particle size distribution. This information is useful for the evaluation of liquefaction potential and characterizing the soil type according to USCS.
Soil Corrosivity, Redox (ASTM D1498), pH (ASTM D4972), Resistivity (ASTM G57), Chloride (ASTM D4327), and Sulfate
(ASTM D4327) - Soil corrosivity testing is performed to determine the effects of constituents in the soil on buried steel and concrete. Water-soluble sulfate testing is required by the UBC, CBC, and IBC.
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3.0 FINDINGS
3.1 Regional and Local Geologic Conditions
The site is located within the central portion of the Coast Ranges Geomorphic Province. The Coast Ranges are characterized by northwest –southeast trending regional faults and mountain ranges. The site is located east of San
Francisco Bay and northwest of Mt. Diablo, which is the northern peak of the Diablo mountain range. The site is mapped as being underlain by Pleistocene-aged alluvium. According to the Natural Resources Conservation Service,
Web Soil Survey, the site soil is part of the Zamora Clay Loam and Silty Clay Loam unit, which generally has a low to moderate expansive potential. Regional geology is shown on Figure 3, Site Vicinity Geology Map.
3.2 Subsurface Soil Conditions
The subsurface soil encountered in the borings consisted predominately of three to four feet of stiff to very stiff orange-brown lean clay fill with gravel, overlying three feet of stiff to very stiff brown lean clay (possible fill). The underlying soils were generally silty to sandy clays to the depths explored, with the exception of a four-foot layer of granular soil (loose to medium dense gravelly sand to sandy gravel) extending between approximately 12 and 16 feet below existing ground surface (bgs). We have included the boring logs performed for this study in Appendix A.
A near surface soil sample had a Plasticity Index of 21, and corresponding Liquid Limit of 47. This soil has a moderately high plasticity. Direct shear testing of sandy clay samples from two feet in Boring B-1 and from 4 ½ feet in boring B-2 resulted in an angles of internal friction of 35 and 29, with unit cohesions of 200psf and 280psf, respectively. Details of materials encountered in the exploratory borings, including laboratory test results, are included in the boring logs in Appendix A.
3.3 Groundwater
Groundwater was encountered in the two borings drilled for this study at 12 feet below existing ground surface.
Historically, wells in the vicinity show the groundwater level as high as seven feet. Groundwater levels can vary in response to time of year, variations in seasonal rainfall, well pumping, irrigation, and alterations to site drainage. A detailed investigation of local groundwater conditions was not performed and is beyond the scope of this study.
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3.4 Expansive Soils
Samples of the clayey soil obtained from the near surface of the site were found to be moderately highly plastic.
These plastic soils will exhibit a moderate to high expansion potential with moisture variation. Recommendations for the mitigation of the effect of these soils are contained in the earthwork and foundation section of this report.
3.5 Corrosion
Corrosion test results of soil samples obtained from the site were evaluated based on ASTM A888 methods. Table 1,
Soil-Test Evaluation, from the ASTM procedure is presented below. If the summed points are equal to 10, the soil should be considered corrosive to cast iron pipe. If sulfides are present and low or negative redox potential results are obtained, three points shall be given for this range.
Table 1:
Soil Test Evaluation Criteria (ASTM A888 Methods)
Soil Characteristics
Resistivity, ohm-cm, based on single probe or water-saturated soil box.
<700
700-1,000
1,000-1,200
1,200-1,500
1,500-2,000
>2,000
PH
0-2
2-4
4-6.5
6.5-7.5
7.5-8.5
>8.5
Points Soil Characteristics
Redox Potential, mV
10
8
5
2
1
0
5
3
0
0
0
5
>+100
+50 to +100
0 to 50
Negative
Sulfides
Positive
Trace
Negative
Moisture
Poor drainage, continuously wet
Fair drainage, generally moist
Good drainage, generally dry
Points
0
2
1
0
0
3.5
4
5
3.5
2
A bulk sample collected from the near surface had a pH of 6.5, a resistivity of 1,378 ohm-cm, negative sulfide, a redox of 532mV, and 8 ppm chloride. The sum of the points is 1, and the soil is considered not to be corrosive to buried metal.
These results are preliminary, and provide information on the specific soils sampled and tested. Other soil at the site may be more or less corrosive. Providing a detailed assessment of the corrosion potential of the site soils is not
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within our scope of work. A more detailed explanation of the test results is included in the ETS lab data sheet located in Appendix B. Appropriate corrosion specialists should be contacted if a detailed evaluation is required.
Water-soluble sulfate can affect the concrete mix design for concrete in contact with the ground, such as shallow foundations, piles, piers, and concrete slabs. The UBC, CBC, and IBC provide the following evaluation criteria.
Table 2:
Soluble Sulfate Evaluation Criteria
Sulfate
Exposure
Negligible
Moderate
Severe
Water-Soluble
Sulfate in Soil,
Percentage by
Weight or (mg/kg)
0.00-0.10
(0-1,000)
0.10-0.20
(1,000-2,000)
0.20-2.00
(2,000-20,000)
Sulfate in
Water, ppm
0-150
150-1,500
1,500-10,000
Cement Type Max. Water
NA
II, IP (MS), IS
(MS)
V
Very Severe Over 2.00 (20,000) Over 10,000 V plus pozzolan
Cementitious
Ratio by
Weight
NA
0.50
0.45
0.45
Min.
Unconfined
Compressive
Strength, psi
NA
4,000
4,500
4,500
The test results show that the onsite soil contains approximately 252 ppm of water-soluble sulfate. Hence, the watersoluble sulfate content in the site soil is considered to have a moderate impact on buried concrete at the site.
However, it should be pointed out that the water-soluble sulfate concentrations can vary due to the addition of fertilizer, irrigation, and other possible development activities. An appropriate expert should be contacted if a detailed evaluation is required.
3.6 Faults and Seismicity
Regional transpression has caused uplift and folding of the bedrock units within the Coast Ranges. This structural deformation occurred during periods of tectonic activity that began in the Pliocene and continues today. This seismic activity appears to be largely controlled by displacement between the Pacific and North American crustal plates, separated by the San Andreas Fault zone, and located approximately 30 miles (49 kilometers) southwest of the site.
This plate displacement produced regional strain that is concentrated along major faults of the San Andreas Fault
System including the San Andreas, Rodgers Creek, and Hayward faults in this area.
The site is located in a seismically active region dominated by major faults of the San Andreas Fault System. Major faults include the San Andreas Fault, located approximately 30 miles (49 km) southwest of the site; Hayward Fault,
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located approximately 12.6 miles (20.2 km) southwest of the site; the Calaveras Fault, located approximately 8.2 miles (13.2 km) southwest of the site; the Concord-Green Valley Fault, located approximately 0.7 miles (1.2 km) east of the site; the Mt. Diablo Thrust Fault, located approximately 2.1 miles (3.4 km) southeast of the site.
San Andreas Fault
The northwest-trending San Andreas Fault runs along the western coast of California extending approximately 625 miles from the north near Point Arena to the Salton Sea area in Southern California (Jennings, 1994). The fault zone has been divided into 11 segments. The site is located approximately 30 miles (49 km) to the east of the Peninsula segment. The slip rate on the nearest segment of the San Andreas Fault is estimated to be about 17 mm/year and has been assigned a moment magnitude (Mmax) of 6.9 (CGS, 2003). The Working Group on California Earthquake
Probabilities (WG07) has estimated that there is a 21 percent probability of at least one magnitude 6.7 or greater earthquake before 2036 along the San Andreas Fault (USGS, 2008).
Concord/Green Valley Fault
The north to northwest trending Concord Fault extends from the approximate central, Walnut Creek and Concord border, northward into the Green Valley Fault. The Green Valley Fault extends northward from Suisun Bay up to just west of Lake Curry, northeast of Napa. The site is located approximately 0.7 miles (1.2 km) southwest of the Concord
Fault. The slip rate of the Concord Fault is estimated to be about four mm/year and has been assigned a moment magnitude (Mmax) of 6.6 (CGS, 2002). The Working Group on California Earthquake Probabilities (WG07) has estimated that there is a four percent probability of at least one magnitude 6.7 or greater earthquake before 2036 along the Concord Fault (USGS, 2008).
Calaveras Fault
The Calaveras Fault trends northwesterly approximately 77 miles (88 km) from near Hollister to the San
Ramon/Dublin area. The Calaveras Fault has been divided into three segments, the Northern, Central, and Southern segments. The site is located approximately 8.2 miles (13.2 km) from the Northern segment of the Calaveras Fault.
The slip rate on the Northern segment of the Calaveras Fault is estimated to be about six mm/year and has been assigned a moment magnitude (Mmax) of 6.9 (CGS, 2002). The Working Group on California Earthquake Probabilities
(WG99) has estimated that there is a 7 percent probability of at least one magnitude 6.7 or greater earthquake before 2036 along the Calaveras Fault (USGS, 2008).
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Mt. Diablo Thrust Fault
The northwest trending Mt. Diablo Fault extends from near the Alamo and Walnut Creek border along Highway 680, extending southward to Cottonwood Canyon, in northern Dublin. The Mt. Diablo Fault is not currently mapped by
CGS, but fault coordinates have been published. The fault is different from the majority of Bay Area faults in that it is not a strike-slip fault exhibiting horizontal plate motion, but rather a “blind thrust” fault. A blind thrust fault is a compressional fault without apparent surface expression. In the case of the Mt. Diablo Fault, the compression is caused by the differential; horizontal motions of the Concord and Greenville faults which abut Mt. Diablo. The fault locations for this blind thrust fault are inferred. The 1994 Northridge earthquake is a recent example of faulting on a blind thrust fault. The site is located approximately 2.1 miles (3.4 km) north of the Mt. Diablo Fault. The slip rate of the Mt. Diablo Thrust Fault is estimated to be about two mm/year and has been assigned a moment magnitude
(Mmax) of 6.7 (CGS, 2002). The Working Group on California Earthquake Probabilities (WG07) has estimated that there is a three percent probability of at least one magnitude 6.7 or greater earthquake on the Mt. Diablo thrust fault before 2036 (USGS, 2008).
Hayward Fault
The Hayward Fault trends northwesterly approximately 55 miles (88 km) from the Milpitas area to San Pablo Bay.
The Hayward Fault has been divided into two segments, the Northern and Southern segments. The site is located approximately 13 miles (21 km) from the Northern segment of the Hayward Fault, and more distant from the
Southern segment. The slip rate on the Northern segment of the Hayward Fault is estimated to be about nine mm/year and has been assigned a moment magnitude (Mmax) of 6.9 (CGS, 2002). The Working Group on California
Earthquake Probabilities (WG07) has estimated that there is a 31 percent probability of at least one magnitude 6.7 or greater earthquake before 2036 along the Hayward Fault (USGS, 2008).
3.7 Surface Fault Rupture
According to DMG Special Publications 42 (Hart, 1994), the site does not lie within an Earthquake Fault Zone, as defined by the Alquist-Priolo Act of 1972. According to published mapping by DMG, no known fault traces cross the site, and no evidence of surface ground rupture was noted during our site reconnaissance. Therefore, it is our opinion that the likelihood of surface fault rupture at the site is low.
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3.8 Settlement Due to Collapsible Soils
Collapsible soils are fine sandy and silty soils that have been laid down by the action of flowing water, usually in alluvial fan deposits. Terrace deposits and fluvial deposits can also contain collapsible soil deposits. The soil particles are usually bound together with a mineral precipitate. The loose structure is maintained in the soil until a load is imposed on the soil and water is introduced. The water breaks down the inter-particle bonds and the newly imposed loading densifies the soil. Based on the soil classification and visual observation in the field, the site soils are considered to have a low collapse potential.
3.9 Settlement Due to Consolidation
Consolidation is the densification of soil into a more dense arrangement from additional loading, such as new fills or foundations. Consolidation of clayey soils is usually a long-term process, whereby the water is squeezed out of the soil matrix with time. Sandy soils consolidate relatively rapidly with an introduction of a load. Consolidation of soft and loose soil layers and lenses can cause settlement of the ground surface or buildings. Based on visual observation in the field and laboratory testing, the soils at this site are generally stiff to very stiff lean clays with a low potential to consolidate under the anticipated loads and consolidation settlement should be minimal.
3.10 Liquefaction Induced Phenomena
Research and historical data indicate that soil liquefaction generally occurs in saturated, loose granular soil (primarily fine to medium-grained, clean sand deposits) during or after strong seismic ground shaking and is typified by a loss of shear strength in the affected soil layer, thereby causing the soil to flow as a liquid. However, because of the higher inter-granular pressure of the soil at greater depths, the potential for liquefaction is generally limited to the upper 40 feet of the soil. Potential hazards associated with soil liquefaction below or near a structure include loss of foundation support, lateral spreading, sand boils, and areal and differential settlement.
Lateral spreading is lateral ground movement, with some vertical component, as a result of liquefaction. The soil literally rides on top of the liquefied layer. Lateral spreading can occur on relatively flat sites with slopes less than two percent under certain circumstances. Lateral spreading can cause ground cracking and settlement.
The site is mapped by the USGS and William Lettis & Associates as being located within a zone of low liquefaction potential (see attached Figure 5). Groundwater was encountered at approximately 12 feet below ground surface in a boring drilled at the site. The site was predominantly underlain with medium stiff to very stiff medium plastic clay
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(CL) with a layer of sandy clay (CL). Boring B-2 encountered a gravelly sand layer from a depth of 12 feet to 16 feet below ground surface. This soil had a field blow count (modified California Sampler) of 23 which is corrected to an
SPT blow count of 14. We ran Liquefy-Pro software to analyze a potential for the liquefaction settlement. For this analysis we considered water table as seven feet below ground surface, seismic coefficient of 0.50g (Sds/2.5), and earthquake magnitude of 7.0. The results of the liquefaction analysis are attached as Appendix C. Based on the information collected during the field investigation, laboratory test results, types of soils encountered in the borings within the project site and liquefaction analysis, we determined the maximum settlement of 1 ½ inches with a safety factor of 1.3 and with a differential settlement of about ¾ inch. This settlement should be taken into account by the
Structural Engineer during the design of the building foundations. We evaluated the potential for bearing capacity failure in accordance with SCES 1999 and determined that there is sufficient capping in non-liquefiable soils to preclude bearing capacity failure.
Based on the consistency of the soil, we judge this isolated layer to have a moderately high liquefaction potential. In the event this layer did liquefy, surface manifestation of liquefaction would not be observed as there are 12 feet of stiff to very stiff non-liquefiable soil overlying a four-foot layer of potentially liquefiable soil. Due to the soils type and their stiffness, the potential for liquefaction in this project site is low, except for the isolated layer encountered in
Boring B-2.
3.11 Dynamic Compaction (Seismically Induced Settlement)
Dynamic compaction is a phenomenon where loose, sandy soil located above the water table densifies from vibratory loading, typically from seismic shaking or vibratory equipment. The site is generally underlain by medium stiff to very stiff clay above the water table. Thus, the site should not be susceptible to dynamic compaction phenomena.
3.12 Flooding
The site is not subject to flooding, primarily because of its topographic position. FIRM (2009) has mapped the site vicinity as Zone X, “areas determined to be outside the 0.2% annual chance floodplain”. Because of the fact that there are no creeks crossing or in the immediate vicinity of the site, we conclude that the hazard of flooding at the site is low. Determining the flood potential of the site is beyond the scope of this study or our expertise, and a flood specialist should be contacted if a more in-depth flooding analysis is desired.
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3.13 Soil Erosion
Present construction techniques and agency requirements have provisions to limit soil erosion and resultant siltation during construction. These measures will reduce the potential for soil erosion at the site during the various construction phases. Long-term erosion at the site will be reduced by landscaping and hardscape areas, such as parking lots and walkways, designed with appropriate surface drainage facilities.
3.14 Other Geologic Hazards
The site is not subject to the potential geologic hazards of landsliding, loss of mineral resources, presence of naturally occurring asbestos, volcanism, tsunamis, seiches, or loss of unique geologic features, due to the sites location, subsurface soil conditions, groundwater levels and land use factors.
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4.0 CONCLUSIONS AND RECOMMENDATIONS
The following conclusions and recommendations are based upon the analysis of the information gathered during the course of this study and our understanding of the proposed improvements.
4.1 General
The site is considered geotechnically suitable for the proposed improvements provided the recommendations of this report are incorporated into the design and implemented during construction. The predominant geotechnical and geological issues that will need to be addressed at this site are summarized below.
Liquefaction – The site is mapped as being located within a zone of low liquefaction, with the exception of a localized four-foot-thick sand lens at a depth of 12 feet in Boring B-2. The Structural Engineer should take the potential 1 ½ inch total settlement and ¾ inch differential settlement into account in the design of the structure.
Corrosive Soil – The site soils are considered to have a relatively low corrosion potential in regard to buried metal and a moderate corrosion potential relative to concrete.
Expansive Soils – The site is underlain by highly expansive soils and some mitigation will be required during grading, including placement of a 24-inch section of non-expansive fill.
Existing Fill - During subexcavation of the pad for placement of the 24-inch section of Select Non-expansive Fill, the exposed existing fill should be evaluated by the Geotechnical Engineer relative to whether more over-excavation of the fill will be needed. The maximum depth of over-excavation for fill removal is unlikely to be more than three to four feet from pad grade, if necessary. Excavated fill soil may be placed back as compacted fill below the upper 24inch section of Select Fill.
Seismic Considerations – The site is located within a seismically active region. As a minimum, the building design should consider the effects of seismic activity in accordance with the latest edition of the CBC.
4.1.1 Seismic Considerations
The site is located within a seismically active region and should be designed to account for earthquake ground motions as described in this report. For seismic analysis of the proposed site in accordance with the seismic provisions of the CBC 2010, we recommend the following parameters and summary is attached in Appendix C.
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Table 3:
Seismic Design Parameters Based on 2010 CBC (2009 IBC)
Item
Site Class
Mapped Spectral Response Accelerations
Short Period, Ss
1-second Period, S1
Site Coefficient, Fa
Site Coefficient, Fv
MCE (S
MCE (S
MS
M1
)
)
Design Spectral Response Acceleration
Value
D
1.885g
0.671 g
1.0
1.5
1.885 g
1.007g
1.256g
0.671g
Table 1613.5.2
USGS R2
Location
R1
Table 1613.5.3(1)
Table 1613.5.3(2)
R1
R1
Short Period, S
DS
1-second Period, S
D1
R1 California Building Standards Commission (CBSC), “California Building Code,” 2010 Edition.
R2 U.S. Seismic “Design Maps” Web Application, https://geohazards.usgs.gov/secure/designmaps/us/application.php
4.2 Site Grading and Drainage
The grading section of this report is divided into several sections. The first section provides the compaction criteria for the project. The remaining sections discuss grading in general for building pads and concrete hardscape areas, and drainage.
4.2.1 Project Compaction Recommendations
The following table provides the recommended compaction requirements for this project. Not all soils, aggregates and scenarios listed below may be applicable for this project. Specific grading recommendations will be discussed individually within applicable sections of this report.
PROJECT COMPACTION REQUIREMENTS
Description
Fill Areas, Engineered Fill, Onsite Soil
Fill Areas, Engineered Fill, Select Fill
Building Pads, Onsite Soil
Building Pads, Class 2 AB or Select Fill
Concrete Flatwork, Subgrade Soil
Concrete Flatwork, Class 2 AB
Min. Percent Relative
Compaction
90
90
90
90
90
90
Min. Percent Above
Optimum Moisture Content
3
2
3
2
3
2
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PROJECT COMPACTION REQUIREMENTS (cont’d.)
Description
Underground Utility Backfill, Upper five feet
Underground Utility Backfill, Deeper than five feet
Pavement section, Class 2 AB
Min. Percent Relative
Compaction
95
90
95
4.2.2 Site Preparation and Demolition
Min. Percent Above
Optimum Moisture Content
3
2
2
Site grading should be performed in accordance with these recommendations. A pre-construction conference should be held at the jobsite with representatives from the owner, general contractor, grading contractor, and Geosphere prior to starting the clearing and demolition operations at the site.
Prior to commencement of grading activities, areas to receive fill, structures, or pavements should be cleared of existing surface vegetation, organic-laden soils, building materials including foundations if present, existing loose soil,
AC and AB pavement section, and debris. Debris resulting from site stripping operations should be removed from the site, unless otherwise permitted by the Geotechnical Engineer.
Excavations resulting from the removal of abandoned underground utilities, or deleterious materials should be cleaned down to firm soil, processed as necessary, and backfilled with engineered fill in accordance with the grading sections of this report. The Geotechnical Engineer’s representative should verify the adequacy of site clearing operations during construction, prior to placement of engineered fill.
Existing underground utilities proposed to be abandoned, if present, should be properly grouted, closed, or removed as needed. If the utilities are removed, the excavations should be backfilled with properly compacted fill or other material approved by the Geotechnical Engineer. The extent of removal/abandonment depends on the diameter of the pipe, depth of the pipe, and proximity to buildings and pavement.
4.2.3 General Grading
Onsite soil generated from cut areas following clearing and grubbing that is free of excess organic material (three percent or less by weight) or debris may be suitable for use as structural fill at the site. Imported fill should be nonexpansive, having a Plasticity Index of 12 or less, an R-Value greater than 40, and enough fines so the soil can bind
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together. Imported soil should be free of organic materials and debris, and should not contain rocks or lumps greater than three inches in maximum size. The Geotechnical Engineer should approve imported fill prior to delivery onsite.
If grading occurs in the winter rainy season, unstable subgrade conditions may be present. These conditions may require stabilizing the subgrade with admixtures, such as lime. Isolated areas may be stabilized using one foot of
Class 2 baserock over the geogrid. Additional recommendations can be provided, if required, during construction.
4.2.4 Building Pad Grading
Because the near surface consists of expansive soil, the building pads should be over-excavated at least 24-inches from finish subgrade. The bottom of the over excavation should then be scarified at least 10-inches, moisture conditioned and compacted. Engineered Fill can then be placed in eight-inch, uncompacted lifts, moisture conditioned and compacted. For expansive soil mitigation, the upper 24 inches of the building pad should be underlain by Select, non-expansive fill. The Select Fill should extend at least five-feet outside the building perimeter.
4.2.5 Grading Flatwork Areas
Flatwork areas can be scarified eight-inches, uniformly moisture conditioned, and compacted. Onsite soil can then be placed in eight-inch thick loose lifts and compacted to construct the flatwork up to finish subgrade elevation.
4.2.6 Drainage
Final grading should be designed to provide drainage away from the structure. Soil areas within 10 feet of proposed structures should slope at a minimum of five percent away from the building. Adjacent concrete hardscape should slope a minimum two percent away from the building. Roof leaders and downspouts should not discharge into landscape areas adjacent to buildings.
4.3 Utility Trench Construction
4.3.1 Trench Backfilling
Utility trenches may be backfilled with onsite soil above the utility bedding and shading materials. If rocks or concrete larger than four inches in maximum size are encountered, they should be removed from the fill material prior to placement in the utility trenches. Backfill more than five feet should have a higher compaction requirement than the soil in the upper five feet. The subgrade soil in building pads and pavement areas may also have different compaction requirements (see Section 4.3.1, Project Compaction Requirements).
16
Pea gravel, rod mill, or other similar self-compacting material should not be utilized for trench backfill since this material will transmit the shallow groundwater to other locations within the site and potentially beneath the building. Additionally, fines may migrate into the voids in the pea gravel or rod mill, which could cause settlement of the ground surface above the trench.
4.3.2 Utility Penetrations at Building Perimeter
Flexible connections at building perimeters should be considered for utility lines going through perimeter foundations. This would provide flexibility during a seismic event. This could be provided by special flexible connections, pipe sleeving with appropriate waterproofing, or other methods.
Utility trenches should be sealed with concrete, clayey soil, sand-cement slurry, or controlled density fill (CDF) where the utility enters the building under the perimeter foundation. This would reduce the potential for migration of water beneath the building through the shading material in the utility trench.
4.3.3 Pipe Bedding and Shading
Pipe bedding material is placed in the utility trench bottom to provide a uniform surface, a cushion, and protection for the utility pipe. Shading material is placed around the utility pipe after installation and testing to protect the pipe.
Bedding and shading material and placement are typically specified by the pipe manufacturer, agency, or project designer. Agency and pipe manufacturer recommendations may supersede our suggestions. These suggestions are intended as guidelines and our opinions based on our experience to provide the most cost-effective method for protecting the utility pipe and surrounding structures. Other geotechnical engineers, agency personnel, contractors, and civil engineers may have different opinions regarding this matter.
Bedding and Shading Material - The bedding and shading material should be the same material to simplify construction. The material should be clean, uniformly graded, fine to medium grained sand. It is suggested that bedding and shading material contain less than three percent fines with 100 percent passing the No. 8 sieve. Coarse sand, angular gravel, or baserock should be avoided since this type of shading material may bridge when backfilling around the pipe, possibly creating voids, and may be too stiff as bedding material. Open graded gravel should be avoided for shading since this material contains voids, and the surrounding soil could wash into the voids, potentially causing future ground settlement. However, open graded gravel may be required for bedding material when water is entering the trench. This would provide a stable working surface and a drainage path to a sump pit in the trench for water in the trench. The maximum size for bedding material should be limited to about ¾ -inch.
17
Bedding Material Placement - The thickness of the bedding material should be minimized to reduce the amount of trench excavation, soil export, and imported bedding material. Two to three inches for pipes less than eight-inches in diameter and about four to six inches for larger pipes are suggested. Bedding for very large diameter pipes are typically controlled by the pipe manufacturer. Compaction is not required for thin layers of bedding material. The pipe needs to be able to set into the bedding, and walking on a thin layer of bedding material should sufficiently compact the sand. Rounded gravel may be unstable during construction, but once the pipe and shading material is in place, the rounded gravel will be confined and stable.
Shading Material Placement – Jetting is not typically recommended since the type of shading material is unknown when preparing the geotechnical report and agencies typically do not permit jetting. If the sand contains fines or if the sand is well graded, jetting will not work. Additionally, if too much water is used during jetting, this could create a wet and unstable condition. However, clean, uniformly graded and fine to medium sand can be placed by jetting. The shading material should be able to flow around and under the utility pipe during placement. Some compactive effort along the sides of the pipe should be made by the contractor to consolidate the shading material around the pipe. A minimum thickness of about six-inches of shading material should be placed over the pipe to protect the pipe from compaction of the soil above the shading material. The contractor should provide some compactive effort to densify the shading material above the pipe. Relative compaction testing is not usually performed on the shading material.
However, the contractor is ultimately responsible for the integrity of the utility pipe.
4.4 Temporary Excavations
The contractor should utilize proper Cal OSHA methods during construction. Excavations in soil more than five feet deep for utility trenches and the basement should have side slopes constructed at 1H:1V (horizontal to vertical). If excavations are more than eight feet deep, the Geotechnical Engineer should be advised to review the impacts. The contractors should make selection of temporary side slopes based upon the materials encountered during the excavation. Maximum slope ratios provided above are assumed to be uniform from top to toe of the slope. Adequate provisions should be made to prevent water from ponding on top of the slope and from flowing over the slope face.
Surcharge loads should not be permitted within 10 feet of the top of the slope. Desiccation or excessive moisture in the excavation could reduce stability and require shoring or laying backside slopes.
18
4.5 Building Foundations
The proposed building can be constructed on shallow foundations founded at least 24 inches below the lowest adjacent finished grade. The Structural Engineer should determine foundation reinforcement requirements. The spread footings may be designed using an allowable bearing pressure of 3,000 psf for dead plus live loads at the recommended minimum depth. A one-third increase in allowable dead plus live load bearing pressure may be used when considering the effects of temporary wind or seismic forces.
For resistance to lateral loads, an allowable coefficient of friction of 0.30 between the base of the foundation elements and underlying material is recommended. In addition, an allowable passive resistance equal to an equivalent fluid weighing 300 pounds per cubic foot (pcf) acting against the foundation may be used to resist lateral forces. The top foot of passive resistance at foundations should be neglected unless the ground surface around the footing is covered by concrete or pavement.
Footing excavations should have firm bottoms and be free from excessive slough prior to concrete or reinforcing steel placement. If construction occurs during the winter months, it is suggested that a thin layer of concrete be placed at the bottom of the footings at the time of excavation. This will protect the bearing soil and facilitate removal of water and slough if rainwater fills the excavations.
Where utility trenches are to be located adjacent to foundations, the bottom of the footing should be located below an imaginary 1:1 (horizontal to vertical) plane projected upward from the nearest bottom edge of the utility trench.
Total and differential settlement should be approximately on the order of one-inch and a half-inch or less, respectively. Approximately half of the total settlement should occur during construction. A representative of
Geosphere Consultants, Inc., prior to placement of reinforcing steel or concrete, should observe the foundation excavations to evaluate the exposed soil conditions.
4.6 Concrete Slabs-on-Grade
4.6.1 Interior Floor Slabs
It is recommended that the floor slab be at least five-inches thick. The floor slab should be tied to the perimeter footings. The floor slab should be placed on a 24-inch thick layer of Select Fill or Class 2 baserock, per Section 4.3 of this report. Floors with moisture sensitive floor coverings should be underlain by a high quality vapor retarder meeting ASTM E1745 Class C requirements, such as StegoWrap, Griffolyn Type 65, Moistop Ultra C, or equivalent.
19
The vapor retarder can be placed directly on the prepared subgrade soil. If the floor slab will have very highly moisture sensitive floor coverings, such as wood floors or special vinyl floors, ASTM Class B requirements should be met (Griffolyn Type 85, Moistop Ultra B, or equivalent). ASTM E1643 should be utilized as a guideline for the installation of the vapor retarder. A capillary rock layer or rock cushion is not required beneath the floor slab and a sand layer is not required over the vapor retarder. If the design engineers require sand on top of the vapor retarder, the thickness should be minimized to less than one-inch. If construction occurs in the winter months, water may pond within the sand layer since the vapor retarder may prevent the vertical percolation of rainwater.
4.6.2 Exterior Concrete Flatwork
Exterior concrete flatwork with pedestrian traffic should be at least five-inches thick and should be underlain by at least four-inches of Class II AB. The flatwork should be reinforced to reduce potential tripping hazards; welded wire mesh should not be utilized. The flatwork should be doweled into the building foundation adjacent to doorways and into curbs to prevent possible tripping hazards.
If possible, the building should have a concrete apron around the building to reduce the potential for surface water percolating down through the soil adjacent to the buildings. Landscaping adjacent to the building should be avoided if possible. Typically, landscape areas adjacent to buildings are surrounded by concrete flatwork, which prevents irrigation and rainwater from flowing away from the building. The ponded water trapped by the surrounding flatwork could percolate down, or possibly laterally through perimeter foundation construction joints or pipe sleeves and travel beneath the floor slab. Drainage can be provided in these landscape areas, but the top of the drains should be located below the building pad subgrade elevation.
4.7 Plan Review
It is recommended that Geosphere be provided the opportunity to review the final project plans prior to construction. The purpose of this review is to assess the general compliance of the plans with the recommendations provided in this report and the incorporation of these recommendations into the project plans and specifications.
4.8 Observation and Testing During Construction
It is recommended that Geosphere be retained to provide observation and testing services during site preparation, mass grading, underground utility construction, foundation excavation, and to observe final site drainage. This is to
20
observe compliance with the design concepts, specifications and recommendations, and to allow for possible changes in the event that subsurface conditions differ from those anticipated prior to the start of construction.
21
REFERENCES
Abrahamson, Norman A., Effects of Rupture Directivity on Probabilistic Seismic Hazard Analysis, Proceedings GICSZ,
Palm Springs, California, November 2000.
Abrahamson, Norman A., State of the Practice of Seismic Hazard Evaluation, Proceedings of Geotechnical
Engineering, 2000, Melbourne, Australia, November 2000.
Abrahamson, N., and Shedlock, K., editors, Ground Motion Attenuation Relationships, Seismological Research Letters, v. 68, no. 1, January 1997 special issue, 256 pp.
American Society for Testing and Materials, West Conshohocken, Pennsylvania.
Association of Bay Area Governments (ABAG), April 2003, “On Shaky Ground”, website: http://www.abag.ca.gov/
Blake, Thomas F., EQSearch version 3.00, EQFault1 version 3.00, FriskSP version 4.00, software and manuals with
2004 CGS fault model updates.
California Building Code, 2010, California Code of Regulations, Title 24, Chapter 16.
California Geological Survey, Seismic Hazard Mapping Program, 2003 website http://gmw.consrv.ca.gov/shmp
California Geological Survey, 1996, Probabilistic seismic hazard assessment for the state of California, DMG Open-File report 96-08 (USGS Open-File Report 96-706), and updated Appendix A, Appendix A – 2002 California Fault
Parameters.
California Geological Survey, 2008, Guidelines for evaluating and mitigating seismic hazards in California: California
Geological Survey Special Publication 117, 60 p.
Campbell, Kenneth W., and Bozorgnia, Yousef, Updated Near-Source Ground-Motion (Attenuation) Relations for
Horizontal and Vertical Components of Peak Ground AcGeosphereeration and AcGeosphereeration Response
Spectra, Bulletin of the Seismological Society of America, Volume 93, No. 1, pp. 314-331, February 2003.
Cao, Tianquing, Bryant, William A., Rowshandel, Badie, Branum, Dave, and Wills, Christopher J., The Revised 2002
California Probabilities Seismic Hazard Maps, June 2003.
Division of Mines and Geology, 1990. Geologic Map of the San Francisco-San Jose Quadrangle compiled by D. L.
Wagner and E. J. Bortugno. Scale 1:250,000.
FIRM, Flood Insurance Rate Map, Contra Costa County, California, Panel 292 of 602, Map Number 06013C0292F, June
16, 2009.
Association of Bay Area Governments (ABAG), 1995, “Bay Area Dam Failure Maps for Contra Costa County”, http://www.abag.ca.gov/cgi-bin/pickdamx.pl
22
Hart, E. W., 1983, Summary Report: Fault Evaluation Program, 1981 – 1982, Area-Northern Coast Ranges region,
California, California Department of Conservation, Division of Mines and Geology, Open-File Report 83-10.
Jennings, C.W., compiler, 1994, Fault activity map of California and adjacent areas with locations and ages of recent volcanic eruptions: California Geological Survey, Geologic Data Map No. 6, scale 1:750,000, with 92-page booklet.
Lawson, A. C. (ed.), 1908, The California Earthquake of April 18, 1906, State Earthquake Investigation Commission, reprinted 1969 by the Carnegie Institution of Washington.
Malhotra, Praveen K., Earthquake Induced Ground Motions, American Society of Civil Engineers Continuing Education
Seminar, 2011.
Checklist for the review of engineering geology and seismology reports for California Public Schools, Hospitals, and
Essential Services Buildings: California Geological Survey – Note 48, (dated January 1, 2011).
California Geological Survey, 2008 “Guidelines for Evaluating and Mitigating Seismic Hazards In California” Special
Publication 117.
U. S. Geological Survey, Earthquake Hazards Program website eqhazmaps.usgs.gov.
U.S. Geological Survey, Geologic Map of Contra Costa County, USGS Scientific Investigation Map
American Society for Testing and Materials, West Conshohocken, Pennsylvania.
23
LIMITATIONS AND UNIFORMITY OF CONDITIONS
The recommendations of this report are based upon the soil and conditions encountered in the borings. If variations or undesirable conditions are encountered during construction, Geosphere should be contacted so that supplemental recommendations may be provided.
This report is issued with the understanding that it is the responsibility of the owner or his representatives to see that the information and recommendations contained herein are called to the attention of the other members of the design team and incorporated into the plans and specifications, and that the necessary steps are taken to see that the recommendations are implemented during construction.
The findings and recommendations presented in this report are valid as of the present time for the development as currently proposed. However, changes in the conditions of the property or adjacent properties may occur with the passage of time, whether by natural processes or the acts of other persons. In addition, changes in applicable or appropriate standards may occur through legislation or the broadening of knowledge. Accordingly the findings and recommendations presented in this report may be invalidated, wholly or in part, by changes outside our control.
Therefore, this report is subject to review by Geosphere after a period of three (3) years has elapsed from the date of issuance of this report. In addition, if the currently proposed design scheme as noted in this report is altered
GEOSPHERE should be provided the opportunity to review the changed design and provide supplemental recommendations as needed.
Recommendations are presented in this report which specifically request that Geosphere be provided the opportunity to review the project plans prior to construction and that we be retained to provide observation and testing services during construction. The validity of the recommendations of this report assumes that GEOSPHERE will be retained to provide these services.
This report was prepared upon your request for our services, and in accordance with currently accepted geotechnical engineering practice. No warranty based on the contents of this report is intended, and none shall be inferred from the statements or opinions expressed herein.
The scope of our services for this report did not include an environmental assessment or investigation for the presence or absence of wetlands or hazardous or toxic materials in the soil, surface water, groundwater or air, on,
24
below or around this site. Any statements within this report or on the attached figures, logs or records regarding odors noted or other items or conditions observed are for the information of our client only.
25
FIGURES
Figure 1 – Site Vicinity
Figure 2 – Site Plan
Figure 3 – Site Vicinity Geology Map
Figure 4 – Schematic Geologic Cross-Section A-A’
Figure 5 – Site Geologic Map
Figure 6 – Liquefaction Susceptibility Map
Figure 7 – Flood Hazard Map
Figure 8 - Regional Geologic Map
N
Site
Ygnacio Valley High School - Chemistry Lab
755 Oak Grove Road
Concord, California
91-02968-A
Site Vicinity Map
January 2013
Figure 1
N
- Proposed Building
- Geologic Cross Section
Qpa
- Alluvium, Pleistocene
- Approximate Boring Location
100 ft
- Approximate Scale
0
Base Map Reference: Google Earth
Ygnacio Valley High School - Chemistry Lab
Concord, California
91-02968-A
Site Plan and Site
Geology Map
January 2013
Figure 2
Source: United States
Geologic Survey, Geologic
Map of Contra Costa County, USGS
Scientific Map Investigations
2918
Site
Geologic contacts Geologic faults af - Artificial Fill Qha - Alluvium, Holocene
Ygnacio Valley High School - Chemistry Lab
Concord, California
K s - Great Valley complex sedimentary rocks , Cretaceous Qpa - Alluvium, Pleistocene
91-02968-A
Site Vicinity Geologic
Map
January 2013
Figure 3
CLIENT Mt Diablo Unified School District
PROJECT NUMBER 91-02968-A
100
A
0
95
90
85
80
75
70
65
10 20
2-4-5
(9)
5-8-8
(16)
5-7-8
(15)
5-6-6
(12)
4-8-9
(17)
8-10-10
(20)
B-2
CL
CL
CL
GP
CL
30
60
55
50
45
0 10 20
CL - Unified Soil Classification System (USCS)
30
14 - Blows Per Six Inches, Standard Penetration Test
(21) - N Value
2001 Crow Canyon Road, Suite 100
San Ramon, CA 94583
Telephone: 925-314-7100
Fax: 925-855-7140
40
40
SUBSURFACE DIAGRAM
PROJECT NAME Ygancio Valley High School - Chemistry Lab
PROJECT LOCATION 755 Oak Grove Road, Concord, CA
Projected
Proposed
Building
50 60 70
50 60 70
Distance Along Baseline (ft)
80
Projected
90
80 90
100 110 120 130
100
95
2-1-3
(4)
2-2-3
(5)
3-5-8
(13)
3-5-9
(14)
5-8-10
(18)
4-5-6
(11)
4-5-6
(11)
5-8-12
(20)
B-1
CL
CL
6-8-12
(20) CL
CL
90
85
80
75
70
65
60
55
50
6-12-18
(30)
100 110 120
Schematic Geologic Cross-Section A-A'
130
45
Figure 4
Liquefaction Susceptibility
Map
Sus c eptib ility Lev el
Very High
High
Moderat e
Low
Very Low
Major Roads
Local Roads
Scale: 1 inch = 0.41 miles
This map is intended for planning use only and is not intended to be site-specific. Rather, it depicts the general hazard level of a neighborhood and the relative hazard levels from community to community. Hazard levels are less likely to be accurate if your neighborhood is on or near the border between two zones. This information is not a substitute for a site-specific investigation by a licensed professional.
This map is available at http://quake.abag.ca.gov
Sources:
This map is based on work by William
Lettis & Associates, Inc. and USGS.
USGS Open-File Report 00-444, Knudsen
& others, 2000 and
USGS Open-File Report 2006-1037, Witter
& others, 2006
For more information visit: http://pubs.usgs.gov/of/2000/of00-444/ http://pubs.usgs.gov/of/2006/1037/
680
Jo n s e
R d
M rc a ia
D r
R a m n o a
D r e
P rs
D g in h r g g in o
C
D
W a ln u t
B lv d
C h rr e y
L n
M
R ae
A nn e
D r o h
S ti m e l
D r
A ld e rw
M on um
P ea ch r Ln
T ra u d
D o o d
R d r
Dias Dr
Dupre Ct
Ca nd el e ro
D r
K in ro ss
D r
Y en t B
P l lv d
Nu al
W hi tm an
R d
G e to u a
St n
D
M in er t R d
G ill
P or
B a n c ro ft
R
V ia
A
P e r a
D
Da vi d
Av e d t L n p pia
Walnut Creek g n ac io
V al le y
R d
S ierra R d
A rk e ll R d
P ar is h
D r
Ba nb
S an
C a rl o s
D r
La
C as a V ia r
W
S h a h
Sm ith
Tr ea t B lv d
W in to ur y
Rd ra tto n
R d
St ry Ci r it m an
R d
R oc kn e
D r
Oa k
L n
G ro v e
R n D r d
L e n n o n
L n
Site
W aln ut
Av e
Sa n A nto nio
D r
Fy ne
D r
L a ne
D r
S a n
M ig u e l R d
L y o n
C
M a d ig ir
R ya n
R d a n
A ve lv d
En tra nc e
Tr ea
Sa t B
C
D r nta
Pa ul a be rr y
Ln ug ar itr us
A v
S
Pe ac hw ill ow
Ln
M itc he ll
D r ela nd s D r
Sh ad
Yg naci o Val ley
R d e
C
Via
Verd ly d e
D
W
D o r v e r D r ig e t
L n
E b a n o
D r
Yg na
Quiet Pla ce Dr
Comistas D r
N av a ro n n e
W a y
K a s k i
L n k c o
R
O k a
R
T ill ey
C ir
L y n n
D r
Concord cio
Va lley
Rd ado w D r
Dia blo
Sh
Ced ro L n a
N n ra ja
D r e
De erpark Dr
B o w lin
P e ra d a
D r
Kirby Ln
W h i g G re e n
D r
C o we
Valle y Vis ta R d
Arbola do Dr ll
R
Indian Hill Dr tehaven Dr
North Gate R d d
Ygnacio Valley High School - Chemistry Lab
Concord, California
91-02968-A
Liquefaction
Susceptibility Map
January 2013
Figure 5
Alquist-Priolo Earthquake
Fault Zones
Earthquake Fault Zones
San Andreas-North Golden Gate
San Andreas -- Peninsula
San Andreas -- Santa Cruz
Rodgers Creek
North Hayward
South Hayward
Northern Calaveras
Central Calaveras
Sargent
Maacama
West Napa
Concord/Green Valley
Greenville
Northern San Gregorio
Major Roads
Local Roads
Water
Sonoma
County
Marin
County
580
Napa
County
780
780
680
80
Solano
County
680
Site
Contra Costa
County
Scale: 1 inch = 6.65 miles
Reproduced with permission, California Geological
Survey from CD-ROM 2001-04 (2001), Official Map of Alquist-Priolo Earthquake Fault Zones
This interactive map was created using digital files of AP
EFZ quadrangles and is considered an electronic facsimile of the Official Alquist-Priolo Earthquake Fault
Zone map. If there is any doubt or conflict with respect to the location of EFZ boundaries, the original clear-film overlay compiled by and on file with CGS is the official version of the map. Fault information in these digital files is not sufficient to serve as a substitute for the geological site studies required under Chapter 7.5 of Division 2 of the California Public Resources Code.
For more information visit: http://www.consrv.ca.gov/CGS/rghm/ap/
This map is available at: http://quake.abag.ca.gov/
Map Prepared by the ABAG Earthquake Program. April 2004.
101
San Francisco
San Mateo
County
101
80
580
880
580
Alameda
County
Ygnacio Valley High School - Chemistry Lab
Concord, California
Sacramento
County
91-02968-A
Regional Fault
Map
January 2013
Figure 6
Summary Distribution of
Slides and Earth Flows in the San Francisco
Bay Region
Mostly L an dslid es
Many La nd slide s
Fla tl and
Fe w Lan dsli des
Very Fe w Lan dsli des
Scale: 1 inch = 0.82 miles
This map is intended for planning use only, and is not intended to be site-specific.
Rather, it depicts the general risk within neighborhoods and the relative risk from community to community.
This map is available at http://quake.abag.ca.gov
For more detailed informtion regarding this map, please visit the USGS website at http://wrgis.wr.usgs.gov/open-file/of97-745/
Source:
USGS Open File Report 97-745 E, 1997
Martinez
C hilpa ncingo Pkwy
Viking Dr
Taylor Blvd
Concord Ave
C a s o tr n o
C d lv
B ta
D ia m o n d
B lv d
W ill ow
P as s R d
M e a d o w
L n
Sa lv io
S t
D e tr o it
A v e
Cow ell R d
Concord Blvd e b a
B n l L
242
B
Concord
Pleasant Hill
Gregory Ln
Boyd Rd
Oak Park Blvd u
B s k ir k
A v e
M oh r Ln
Geary Rd k ir
A k s u
B e v n e u
B a
V is ta
A v e a
M in
S t
D ic iv
C r
Yg na cio
V al le y
R d
Lafayette
Diab lo d lv
B d k a n la
O
O ly m p ic
B lv d
B ro a d w a y
O a k
G ro v
Site e
R d
Da vi d
Av e
Tr ea t B lv d
B a n c ro ft
R d
W aln ut A ve
Tr ea t B lv d
Walnut Creek
Ygnacio Valley High School - Chemistry Lab
Concord, California
W es t
S t
D e n k in g e r
R d
Cla yto n R d
B ai le y
R d
A y e rs
R d
Yg na cio
Valley
Rd Ygnac io Valle y R d
N or th
G a te
R d
M o u n t D ia b lo
S c e n ic
B lv d
91-02968-A
Existing Landslide
Map
January 2013
Figure 7
Site
Site
Zone X Areas determined to be outside the 0.2% annual chance floodplain.
Ygnacio Valley High School - Chemistry Lab
Concord, California
91-02969-A
Flood Hazard Map
January 2013
Figure 8
APPENDIX A
Boring Logs
CLIENT Mt Diablo Unified School District
PROJECT NUMBER 91-02968-A
DATE STARTED 1/3/13
LOGGED BY RJW
NOTES
COMPLETED 1/3/13
DRILLING CONTRACTOR Exploration Geoservices Inc.
DRILLING METHOD Hollow Stem Auger 8"
CHECKED BY GH
0
5
BORING NUMBER B-1
PAGE 1 OF 2
PROJECT NAME Ygancio Valley High School - Chemistry Lab
PROJECT LOCATION 755 Oak Grove Road, Concord, CA
GROUND ELEVATION 95 ft
GROUND WATER LEVELS:
HOLE SIZE 8"
AT TIME OF DRILLING 12.00 ft / Elev 83.00 ft
AT END OF DRILLING ---
AFTER DRILLING ---
ATTERBERG
LIMITS
MATERIAL DESCRIPTION
(CL) SANDY CLAY/CLAYEY SAND : Orange/Brown, moist, very stiff, medium plasticity, w/ gravels and traces of organics. Fill.
MC
1-1
(CL) SANDY CLAY : Gray/Brown, moist, very stiff, medium plasticity, with some gravels. Possible fill.
MC
1-2
(CL) LEAN CLAY : Gray/Brown, moist, very stiff, low plasticity.
4-5-6
(11)
5-8-12
(20)
105 20 47 26 21
115 14
MC
1-3
6-8-12
(20) 110 18
10
(CL) SANDY CLAY : Brown, wet, soft to medium stiff.
MC
1-4
2-1-3
(4) 95 31 51
15
SPT
1-5
2-2-3
(5)
20
SPT
1-6
3-5-8
(13)
25
(Continued Next Page)
CLIENT Mt Diablo Unified School District
PROJECT NUMBER 91-02968-A
25
MATERIAL DESCRIPTION
(CL) SANDY CLAY : Brown, wet, soft to medium stiff.
(continued) gravelly sand lense approximately 0.5 feet
BORING NUMBER B-1
PAGE 2 OF 2
PROJECT NAME Ygancio Valley High School - Chemistry Lab
PROJECT LOCATION 755 Oak Grove Road, Concord, CA
ATTERBERG
LIMITS
SPT
1-7
3-5-9
(14) 94 21 59
30
SPT
1-8
5-8-10
(18)
35
SPT
1-9
4-5-6
(11)
40
45
50 becomes very stiff to hard.
Bottom of borehole at 50.0 feet.
SPT
1-10
6-12-18
(30)
CLIENT Mt Diablo Unified School District
PROJECT NUMBER 91-02968-A
DATE STARTED 1/3/13
LOGGED BY RJW
NOTES
COMPLETED 1/3/13
DRILLING CONTRACTOR Exploration Geoservices Inc.
DRILLING METHOD Hollow Stem Auger 8"
CHECKED BY GH
0
BORING NUMBER B-2
PAGE 1 OF 2
PROJECT NAME Ygancio Valley High School - Chemistry Lab
PROJECT LOCATION 755 Oak Grove Road, Concord, CA
GROUND ELEVATION 95 ft
GROUND WATER LEVELS:
HOLE SIZE 8"
AT TIME OF DRILLING 12.00 ft / Elev 83.00 ft
AT END OF DRILLING ---
AFTER DRILLING ---
ATTERBERG
LIMITS
MATERIAL DESCRIPTION
(CL) LEAN CLAY : Orange/Brown, moist, stiff, low plasticity, w/ lots of gravels and traces of organics. Fill.
5
10
(CL) SANDY CLAY : Brown, moist, stiff, low plasticity, w/ some gravels and roots. Possible fill.
MC
2-1
2-4-5
(9) 106 19
(CL) LEAN CLAY : Gray/Brown, moist, very stiff, low plasticity.
MC
2-2
5-8-8
(16) 111 17
(GP) FINE GRAVELLY SAND/SANDY FINE GRAVEL : wet, dense.
MC
2-3
5-7-8
(15) 106 10
15
(CL) LEAN CLAY : Brown, wet, stiff, low plasticity, w/ some fine sand.
SPT
2-4
5-6-6
(12)
20
4
SPT
2-5
4-8-9
(17)
25
(Continued Next Page)
CLIENT Mt Diablo Unified School District
PROJECT NUMBER 91-02968-A
25
MATERIAL DESCRIPTION
(CL) LEAN CLAY : Brown, wet, stiff, low plasticity, w/ some fine sand. (continued)
BORING NUMBER B-2
PAGE 2 OF 2
PROJECT NAME Ygancio Valley High School - Chemistry Lab
PROJECT LOCATION 755 Oak Grove Road, Concord, CA
ATTERBERG
LIMITS
SPT
2-6
8-10-10
(20)
30
Bottom of borehole at 30.0 feet.
APPENDIX B
LABORATORY TEST RESULTS
Atterberg Limits
Direct Shear
Sieve Analysis
Corrosion
APPENDIX C
Liquefaction Analysis
