igmw.consrv.ca.gov/shp/apsi_siteinvestigationreports_ocr/apsi_0… · 22/05/1980 · i i i i i i i...

I I I I I I I I I I I I I I I I I I _I

HARDDIG·LAWSON ASSOCIATES

GEOLOGIC HAZARDS INVESTIGATION BISHOP RANCH

LOTS 1, 2, 5, AND 6 SAN RAMON VALLEY

CONTRA COSTA COUNTY, CALIFORNIA

HLA Job No. 8294,005.03

A Report Prepared for

Sunset Development Company 1819 Barcelona Street

Livermore, California 94550

by

E. C. Winterhalder, Engineering Geologist - 272

Ronald L. Soroos, Engineering Geologist - 1056

Harding-Lawson Associates

!':

7655 Redwood Boulevard, P.O. Box 578 Novato, California 94947

415/892-0821

May 22, 1980

I 'JT'r

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HARDING-LAWSON ASSOCIATES

INTRODUCTION

This report presents the results of our geologic hazards

investigation for the planned light industrial and residential

development of Lots 1, 2, 5, and 6, Bishop Ranch property, San

Ramon Valley, California. The small scale Geologic Map, Plate 1,

indicates the approximate boundaries of each lot within the

property which is within the level floor of San Ramon Valley.

With the exception of Lot 1, there are presently no specific

development plans for the property. Development will, however,

be typical of that in surrounding areas and will include low-

r ise light industrial, commerical and residential buildings.

There are presently no plans for unusually high-use public

buildings or critical facilities for which the acceptable geo

logic hazards risk would be unusually low.

Previous Work

we previously performed a preliminary geological study of

the entire property, the results of which were presented in our

report dated September 19, 1979. That study was based upon

reports of previous investigators including public agency geol

ogists and Woodward-Lundgren Associates who performed geophysi

cal surveys and test borings but no intensive subsurface explo

ration such as trenching. Our preliminary report summarized the

considerable new geologic information available since the

Woodward-Lundgren report and pointed out remaining areas of

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I I I I I I I I I I I I I I I I I I I


concern with emphasis on the risk of fault rupture. Subse

quently, we have performed an intensive investigation of Lot 1

and presented the results in our Soil and Geologic Hazards

Investigation report dated January 4, 1980. A copy of that

report is appended. This report, covering Lots 2, 5, and 6, is

based upon all of the earlier information plus new subsurface

geologic data which became available in reports of investiga

tions outside the property subsequent to the preliminary study.

Object and Scope of Work

The Bishop Ranch property is within the special study zone

encompassing the Calaveras and San Ramon Valley faults created

in accordance with the provisions of the Alquist-Priolo Special

Studies Zones Act of 1972. The object of our investigation was

directed towards satisfaction of the requirements of the act.

The primary purpose of the act is to preclude siting of struc

tures for human occupancy on the surface trace of an active

fault. Accordingly, our investigation has been directed pri

marily toward a resolution of the question of whether active

faults exist within the property. Other seismic hazards have

also been evaluated utilizing data developed in the course of

the fault investigation. Our investigation has been performed

within the State guidelines for geologic hazards investigations

involving surface fault rupture.

The scope of our investigation consisted of

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1. Review of all pertinent geologic reports and other data, including our preliminary report, and new information developed subsequently; a list of references is attached

2. Discussions with Mr. James Baker, Contra Costa County Geologist

3. Interpretation of aerial photographs taken during different seasons

4. Electromagnetic surveys

5. Geologic logging of trenches excavated across aerial photo lineaments and vegetation changes, and across geophysical anomalies

3



GENERAL GEOLOGIC SETTING

San Ramon Valley and the paralleling mountain ranges to the

east and west are part of the Coast Ranges geomorphic province

of northern California. The northwest-trending valley and

ranges are typical of that province and reflect the orientation

of the more recently active structure, in this case, the

Calaveras and San Ramon Valley faults which approximately bound

the valley floor.

Plate 1 presents the general geology of the property and

near vicinity and is a modification of the map by Brabb and

others, 1971. As shown, the valley is blanketed by Quaternary

alluvium which overlies bedrock of Pliocene and Miocene age

which is exposed in the nearby low hills and higher ridges.

Bedrock formations within the mapped area consist of the Orinda,

Cierbo sandstone, and Briones sandstone formations, all ranging

in age from middle Miocene through late Pliocene. These rocks

were strongly folded and faulted in at least two episodes during

the late Pliocene and Pleistocene epochs. Uplift which accom

panied these events exposed the rocks to erosion and large

volumes have been stripped away in the carving of San Ramon

Valley.

San Ramon Valley was once more deeply carved by a former

stream which flowed northward out of Livermore Valley. At some

time during the Pleistocene epoch, this drainage became blocked

by uplift north of the site. The flow was reversed and San

4


HARDING-LAWSON ASSOCIAllS

Ramon Valley, together with Livermore Valley, now drain to the

south and east into South San Francisco Bay. In the process,

alluvial sediments accumulated in San Ramon Valley, and near the

site, it ultimately filled with up to approximately 300 feet of

stream deposits. These are underlain by the bedrock formations

exposed on either side of the valley. The uplift may have been

due to fault displacements, to uplift related to the Diablo

antiform or to some combination thereof. In any event, it is

clear that differential movement on the Calaveras and San Ramon

Valley fault zones accompanied by uplift has continued up to the

present. This recent uplift in the vicinity is inferred by the

opposite direction of flow of San Ramon and South San Ramon

Creeks on the west and east sides of the valley, respectively.

5



ACTIVE FAULTING

Basis for Special Studies Zone

For various purposes, geologists over the past 50 years have

mapped a number of faults in the area on the basis of strat-

igraphic separation in bedrock, topographic inference, histori-

cal descriptions of surface rupture accompanying earthquakes,

differences in ground-water levels, aerial photo lineaments, and

finally, exposure of fault structures in trenches. All of the

fault lines so mapped which could conceivably indicate

Quaternary age faulting were utilized in the delineation of the

Special Studies Zone. The trenching and other more intensive

investigations required for development in the special studies

zone have resulted in significant modification of earlier

mapping conducted for purposes other than evaluation of geologic

hazards.

Plate 2, a map of the Bishop Ranch and adjacent properties,

shows the inferred faults and lineaments which have been mapped

in that area and have served as a basis for delineation of the r- .. : ~--)pecial dtudies·~one. The map also shows the locations of

trenching performed on Bishop Ranch and adjacent properties,

including that performed for this investigation. The trenching

was performed over several years and individual trenches were

located to intercept aerial photo lineaments, geophysical

anomalies, and fault prolongations. Not all of the trenches are ~

shown, only those which are significant with respect to faults

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which might occur within or could logically project into the

property.

Calaveras Fault

The active Calaveras fault, as approximately located on

Plate 1, generally follows the west edge of the valley floor

except where it cuts across the alluvial fan which has been

deposited by San Ramon and San Catania Creeks. Extensive

trenching in that area has clearly indicated the location of

this major active fault and confirms the evidence presented by

Radbruch (1968) concerning the location of surface rupture on

the Calaveras fault accompanying the 1861 earthquake.

Other locations of the Calaveras fault indicated by dotted

lines within the property on Plate 2 are based on topographic

inference for a northward prolongation of the Calaveras fault

into San Ramon Valley. There are no aerial photo lineaments

within the property parallel to the Calaveras fault zone.

Despite this lack of direct evidence for faulting, exploratory

work has been conducted and it has precluded active faults at

those inferred locations (Harding-Lawson Associates, 1980;

Merrill and Seeley, 1980).

San Ramon Valley Fault

Early evidence for a possible young fault on the east side

of San Ramon Valley included aerial photo lineaments trending

west of north and diagonal to the valley axis, differences in

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ground-water levels which might be due to fault-created aqua

cludes, and possible northwestward prolongation of the active

Pleasanton fault mapped by Radbruch in northern Livermore

Valley. Subsequent trenching outside the property on aerial

photo lineaments has confirmed the presence of young faulting -

near the base of the steeper slopes on the east side of Alcosta

Boulevard. There has been some reinterpretation of the earlier

investigation by Burkland (1973) with regard to the relative age

of faulting indicated by trench exposures. This reinterpreta

tion has not substantially modified the location and direction

of the San Ramon Valley fault although some minor eastward

* adjustment is indicated by presently ongoing work.

*James Baker, personal communication.

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ON-SITE EXPLORATION

General

As mentioned previously, the geology within the site has

been investigated before by surface methods including aerial

photo interpretation and geophysical surveys using shallow seis

mic refraction techniques. Prior subsurface investigation was

limited to scattered test borings and water level measurements

in existing wells. The result of this earlier work was the

designation of a geophysical anomaly zone within Lot 5 more or

less parallel or coinciding with two northwest trending aerial

photo lineaments. These have been explored by electromagnetic

(EM) surveys and by trenching oriented approximately normal to

the lineaments and geophysical anomalies. The locations of the

EM survey lines and trenches are indicated on the Site Plan,

Plate 3. Logs of the trenches are explained on Plate 4 and

presented on Plates 5 through 12. The EM profiles are presented

on Plate 14.

Trenches 1 through 3 were excavated about 10 feet deep

across aerial photo lineaments precisely plotted on the topo

graphic base map with reference to identifiable features such as

roads, farmhouses, and so forth. The different aerial photos

show lineaments at slightly different locations and orienta

tions; consequently, the trenches were extended sufficiently to

cover all of the lineaments.

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Surface examination of the ground surface at the time of

trenching revealed distinct vegetation changes coinciding

closely with the lineament at Trench 1. Vegetation changes at

Trenches 2 and 3 were less distinct and questionable. The vege

tation change at Trench 1 coincided with a distinctive change in

surface soil moisture content; higher moisture content being

associated with darker toned areas as viewed on the photos.

Trench Results

Trench 1 encountered moderately plastic clay surface soils

with lower moisture content in the lighter toned area northeast

of the lineament and highly plastic wet clay soils in the darker

toned area southwest of the lineament. The distinct change in

plasticity is confirmed by laboratory tests on two composite

samples; the plasticity test results are presented on Plate 13.

As indicated by the topographic contours on Plate 3, the

lineaments and darker toned soil zone approximately coincide

with a northwest trending topographic low or broad channel which

descends southeastward from near the head of an alluvial fan

generated by San Ramon and San Catanio Creeks. Probably, the

more plastic clays represent gradual filling of a broad,

channel-like depression in the fan following its active develop

ment.

As indicated by the log of Trench 1 on Plates 5 and 6, the

plastic clay surface soils are underlain by interlayered clayey,

silty, and sandy alluvium. With regard to the presence or

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HARDING-LAWSON ASSOCIATIS

absence of young faulting, the relatively thin but continuous

sand layers penetrated near the bottom of the trench provided

the best opportunity to detect even small fault offsets.

Trench 2 (Plates 7 and 8) which explored the southwest limit

of the darker toned zone, encountered generally similar condi

tions but with no distinct change in surface soil plasticity or

moisture content. Trench 3 (Plates 9 and 10) explored a dis

tinct narrow lineament oriented slightly divergent from the crop

rows visible on aerial photos. Trench 4 (Plates 11 and 12)

explored the seismic refraction anomaly. All of the trenches

encountered similar interlayered clays, silts, and sands which

apparently were all deposited in the aforementioned alluvial fan.

Age of Alluvium

The alluvial soils do not contain sufficient carbonaceous or

other materials which would permit reliable absolute dating by

radioisotope methods. However, the age of the alluvium pene

trated by the trenches can be estimated through correlation of

regional geomorphic events with the depositional environment

indicated by the various alluvial and soil types exposed in the

trenches. Merrill and Seeley (1980) citing Schlemon (1979),

developed a stratigraphic column for the upper alluvium exposed

in trenches immediately north of Lot 2. They point out a

paleosol immediately underlying younger alluvial fan deposits

and estimate its age in the range of 8,000 to 12,000 years. A

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similar dark brown paleosol was encountered beneath sandy

alluvial fan deposits in the trenches for Lot 1 (see appended

report). Trench 3 for the present investigation also encoun

tered a dark brown clay with a mottled and fissured texture

typical of paleosols beneath alluvial fan deposits at a depth of ,,

about eight feet. On this basis, it can reasonably be concluded

that all of the alluvial fan deposits penetrated by the trenches

within the property and adjoining areas are of a similar age.

Detailed logging, as indicated on the trench profiles, dis

closed no abrupt discontinuities in the alluvium which would be

attributable to faulting. All irregularities within the

alluvium are of a type most reasonably attributable to the ordi

nary fluvial processes.

Electromagnetic Surveys

Prior to trenching within Lot 5, we performed four electro

magnetic profiles at the locations indicated on Plate 3. Their

purpose was to measure the electrical conductivity of near

surface alluvium as an indication of anomalous discontinuities

which might then be explored by trenching. The surveys were

performed on December 4, 1979, by our geophysicist using a

Geonics Model EM-31 electromagnetic induction system. This

equipment incorporates a fixed coil spacing of 12 feet and

generates an alternating magnetic dipole field which induces a

current in the ground penetrating to depths of 15 to 20 feet.

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The equipment then measures the secondary magnetic field which

is set up by the current in the ground. The instrument provides

direct readout of the measured conductivity of the soil in

millimhos per meter. The profiles are plotted on Plate 14.

Profiles 1 and 2 detected no significant anomalies. The

minor fluctuations are due to soil grain size and moisture con

tent variations as revealed by the trenching within Lot 1 and

the trenching performed by others in the adjacent property to

the north. EM Profile Line 3 crossed the aerial photo lineament

near Trench 3 and the ranch road separating plowed ground on the

east from orchard on the west. A persistent change in conduc

tivity was noted at the roadway with higher readings in the

plowed ground and lower in the orchard. Repeated profiles

across the road at nearby locations disclosed the same change.

No variation or anomaly was noted at the lineament between this

road and the railway. We concluded that the conductivity change

is due to higher near-surface moisture in the plowed ground than

in the orchard.

EM Line 4 was performed in the area of Trenches 1 and 2 and

crossed several aerial photo lineaments. This line detected the

greatest anomaly of the four lines. A distinctively higher con

ductivity was encountered in the vicinity of the darker toned

soils and it coincided approximately with the more plastic soils

with higher moisture content encountered in Trench 1. A similar

increase in conductivity coincides with the lineament crossed by

13


HARDING-LAWSON ASSOCIATl!S

Trench 2. We believe the anomalous conductivity measured by

Line 4 is probably due to near-surface variations in soil mois

ture content as indicated by the trenches. The EM survey

results are believed to be supportive of the other data indicat

ing local variations in surface soil conditions and an absence

of anomalous discontinuities in the upper 15 to 20 feet of

alluvium.

Off-Site Trenching

In addition to the trenches within Lots 1 and 5, extensive

trenching has been performed near the north property line by

Peter Kaldveer (1978 and 1979) and by Merrill and Seeley

(1980). These trench locations are shown on Plate 2. They pro

vide an essentially continuous profile through the upper

alluvium across the northerly end of the property. Merrill and

Seeley state that, "Based on our evaluation of previously exist

ing information and subsurface data developed specifically for

this investigation, we have concluded that the subject property

is free from evidence of active faulting. It is our opinion

that the potential for future surface faulting is low and that

the property can be developed with noncritical structures for

human occupancy". This statement is in regard to the entire

property adjacent to the north boundary of Lots 1 and 2.

Together with the trenching performed in Lot 1, the investiga

tions effectively I:i::eslude active fau},ts within the property

parallel to the Calaveras fault and any northwest striking

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faults which might extend through the northeast portion of the

property from the San Ramon Valley fault.

One other northwest striking aerial photo lineament has been

mapped near the southwest corner of the property (Lot 6) as

indicated on Plate 2. Exploratory work was performed in that

area by United Soil Engineering, Incorporated (USE!) in reports

to Shapell Industries, developers of a subdivision property

immediately south of Lot 6. The investigation included exten

sive trenching along Ascot Drive extending approximately the

full width of Lot 6. It revealed no indications of faulting.

On this basis, we conclude that the aerial photo lineament in

that area is due to processes other than faulting and probably

is related to near-surface soil conditions as disclosed in our

trenches within the Bishop Ranch property. On the basis of the

USE! investigation, the subdivision was granted approval in

compliance with the requirements of the Alquist-Priolo Act.

To the east, Berlogar, Long & Associates (1978 and 1979) and

Berklund & Associates (1973) performed numerous trenches to

evaluate the San Ramon Valley fault zone, as inferred by aerial

photo lineaments. The results of their trenching indicate that

Holocene or post-alluvium faulting has occurred in an irregular

zone approximately indicated by the fault traces on Plate 1.

Trenches adjacent to the east side of Lot 5, as shown on

Plate 2, revealed no indications of faulting that would project

northwestward into Lot 5 or Lot 2.

15



SEISMICITY

Plate 15 presents, on a regional scale, the major known

active faults within the San Francisco Bay Region and the loca

tions of epicenters for earthquakes greater than magnitude 4

during the period from 1934 through 1976. As shown, the site

lies a short distance east of the Calaveras fault and within

about 15 and 45 kilometers, respectively, of the Hayward and

main San Andreas faults farther to the west. As shown, there

have been a number of historical earthquakes in the range of

magnitude 4 to 6 centered near the Calaveras fault. Nearly all

have occurred in the area to the south of San Jose and none

within the immediate vicinity of the site.

The more notable earthquakes in the Bay Region occurred

prior to 1934, including two major earthquakes on the Hayward

fault in 1836 and 1868, and the great earthquake of April 18,

1906, on the San Andreas fault. The star symbol on Plate 15

indicates the focal center for this event although it preceded

1934. Early records describe an earthquake on the Calaveras

fault in 1861. Due to lack of instrumental records and the

remote location relative to population centers at that time, the

event is poorly documented. However, based on reported inten

sities, it has been assigned a magnitude of about 6. Surface

rupture was reported in two areas, one a short distance north

west of San Ramon Village. The location, if correct, coincides

16



closely with the presently located surface trace of the

Calaveras fault.

There have been no significantly damaging earthquakes on the

San Ramon Valley {Pleasanton) fault during historical time. Lee

and others, 1971, suggest the possibility that a sequence of

small earthquakes which occurred near Danville in 1970 may have

been caused by movement on a possible northward continuation of

the Pleasanton fault. At that time, the Pleasanton fault had

been mapped only in the vicinity of Pleasanton in Livermore

Valley; there was no mapped northward continuation to the vicin

ity of the earthquake sequence. Present mapping of the fault

suggests it could have been responsible for the sequence

assuming that it has an eastward dip. This is consistent with

the eastward dip generally observed in the trenching at nearby

sites.

In summary, the historical earthquake records indicate a

potential for strong earthquake shaking at the site with maximum

magnitudes in the range of 6 to possibly 7 for local events on

the Calaveras fault, about 7 on the Hayward fault, and up to

8-1/4 on the San Andreas fault. Judging by the historical

record and considering the length of the San Ramon Valley -

Pleasanton fault, it would appear that its magnitude potential

is low in comparison to the other faults mentioned. Conse

quently, even though this fault is quite close to the site, the

Calaveras fault possesses the greater potential for damaging

earthquakes.

17



CONCLUSIONS AND RECOMMENDATIONS

Surface Rupture

Based on our investigation, we conclude that there are no

indications of active faults within the property. All of the

surface indications of faulting or inferred faults have been

shown not to exist or to be due to geological processes other

than faulting. Furthermore, there are no known active faults

which would logically project or propagate into the property

from outside.

Geologically young active faults are known to exist outside

the property both to the west and east. Old faults no longer

active undoubtedly exist in the bedrock nearby and beneath the

site. Conceivably, new displacements on the nearby active

faults might also be accompanied by small displacements on those

old faults beneath the site. However, it is generally agreed

that, from a probability standpoint, any significant new fault

displacements within the relatively brief span of 50 to 100

years would be far more likely to occur on known active faults

which have experienced repeated displacements in most recent

geologic time. Consequently, we conclude that the risk of ~.

on-site surface rupture is small and can be safely disregarded i in the siting of buildings as presently planned for the property. l

i Because of the inherent limitations in the evaluation of th~-·~

future behavior of geologic phenomena, we cannot preclude all

possibility of future faulting. This would be true for any

18

~ '1£.:'' .



seismically active region where faulting has occurred at various

times in the geologic past. This inherent uncertainty has been

incorporated in the concept of balanced acceptable risk adopted

by the State of California. This concept recognizes that

various types of building usage or activities involve widely

varying degrees of risk to occupants from seismic activity,

including faulting. The consequences of damage to a light one

or two-story residential structure are potentially much less

severe than damage to a hospital, for example. Critical struc-

tures such as large dams and nuclear power plants, if damaged,

represent a significant hazard well away from the structure

itself. For such structures, a highly intensive and often

costly investigation of seismic hazards is warranted.

Applying the concept of balanced acceptable risk to this

proposed development, we believe that the level of investigation

which has been accomplished is appropriate and sufficient with

regard to our present understanding of geologic structures in

the region. Supplemental investigation of seismic risks may . .,- .... ,_.,,,.-- .. ' ,. -·

become appropriate in the future for particular building types

or site usage. That decision must unavoidably be made when.-··i:.he

specific usage is proposed and in the light of any new geologi

cal information which may be significant to that particular

site. Such supplemental investigations might include further

evaluation of faulting but more probably would be directed

toward the earthquake shaking risk and response of the site and

building to strong earthquake shaking.

19

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Foundation Conditions

With regard to the general foundation conditions, probably

of greatest significance from a design planning and development

cost standpoint are the presence of expansive surface soils and

near-surface compressible alluvium. Plastic and expansive sur

face clays are widespread although as we have seen, they are not

everywhere highly expansive. Our previous investigation of

foundation conditions within Lot 2 indicates no unusual founda

tion problems from the standpoint of soil compressibility and/or

adverse response to earthquake shaking such as liquefaction and

densification. The requirement for modified foundations such as

piers to gain support below the zone subject to expansion or

consolidation should be based upon detailed investigation of the

conditions at specific building sites. Large or heavy struc

tures with high foundation loadings should be the subject of a

thorough soil investigation, possibly including site response

analysis where the structure, soil and ground-water conditions

so indicate.

Earthquake Resistant Design

Regardless of the particular site conditions, all structures

should be designed to resist strong earthquake shaking even

though no active faults have been found to exist within the

property. The close proximity of two active faults, in particu

lar the Calaveras fault, indicates the need for careful atten

tion to earthquake resistant design. Based on the earthquake

20


HARDING-LAWSON ASSOCIATl!S

history, at least one strong earthquake can be expected to

affect the site within the average building lifetime. The

earthquake, or earthquakes, could either be local events with

moderate magnitude and moderate to high intensity or they could

be from relatively distant sources such as the San Andreas

fault, but still with high intensity at the site. Development

of a design earthquake should consider the earthquake history of

the region as indicated on Plate 15.

21



PLATES

Plate 1 Geologic Map

Plate 2 Inferred Fault, Lineament and Trench Location Map

Plate 3 Site Plan

Plate 4 Explanation of Trench Logs

Plates 5 through 12 Trench Logs

Plate 13 Plasticity Chart

Plate 14 Electromagnetic Profiles

Plate 15 Active Faults and Earthquake

DISTRIBUTION

6 copies: Sunset Development Company 1819 Barcelona Street Livermore, California 94550

Attention: Mr. M. R. Mehran

ECW/RLS/jd

22

Epicenters



REFERENCES

1. Berlogar, Long & Associates, August 1978, Supplemental Investigation II, Vista San Ramon Subdivision 5204, San Ramon, California.

2. Berlogar, Long & Associates, November 1979, Geotechnical Investigation, Proposed Church Facilities, Alcosta Boulevard, San Ramon, California.

3. Bolt, B. A., and R. D. Miller, 1975, Catalogue of Earthquakes in Northern California and Adjoining Areas, 1 January 1910 - 31 December 1972, Seismographic Stations, University of California at Berkeley.

4. Borcherdt, R. D., 1975, Studies for Seismic Zonation of the San Francisco Bay Region, U.S. Geological Survey Professional Paper 941-A.

5. Brabb, E. E.; H. s. Soneman; and J. R. Switzer, Jr., 1971, Preliminary Geologic Map of the Mount Diablo-Byron Area, Contra Costa, Alameda and San Joaquin Counties, California, U.S. Geological Survey, Basic Data Contribution No. 28.

6. Brown, R. D., Jr., and w. H. K. Lee, 1971, Active Faults and Preliminary Earthquake Epicenters, 1969 through 1970, in the Southern Part of the San Francisco Bay Region, USGS Miscellaneous Field Studies Map MF-301.

7. Burkland and Associates, November 1973, Geologic and Seismic Hazards Investigation, Winston Valley, Contra Costa County, California.

8. California Department of Water Resources, 1964, Crustal Strain and Fault Movement Investigation, Bulletin 116-2.

9. California Department of Water Resources, 1966, Evaluation of Ground Water Resources, Livermore and Sunol Valleys, Bulletin 118-2, Appendix A.

10. California Department of Water Resources, August 1967, Evaluation of Ground water Resources, South Bay, Appendix A: Geology, Bulletin 118-1.

11. California Division of Mines and Geology, 1961, Geologic Map of California, San Jose Sheet.

12. California Division of Mines and Geology, 1972, Preliminary Earthquake Epicenter Map of California, 1934-1971 (June 30) , Seismic Safety Information 72-3.

23



13. Ford, Robert S., October 4, 1969, Ground-Water Geology of Livermore Valley - A Satellite Urban Area, in Urban Environmental Geology in the San Francisco Bay Region, Association of Engineering Geologists, Special Publication.

14. Gibson, w. M., and H. A. Wollenberg, 1968, Investigations for Ground Stability in the Vicinity of the Calaveras Fault, Livermore and Amador Valleys, Alameda County, California, Geological Society of America, Volume 79, pp. 627-638.

15. Harding-Lawson Associates, November 11, 1971, Seismic Risk Assessment, The Bishop Ranch Property, Contra Costa County, California.

16. Harding-Lawson Associates, October 22, 1973, Preliminary Soil and Geologic Investigation, Planned Danville Country Club, Danville, California.

17. Harding-Lawson Associates, September 19, 1979, Preliminary Geological Study, Bishop Ranch Property, San Ramon Valley, Contra Costa County, California.

18. Harding-Lawson Associates, November 10, 1979, Preliminary Soil Investigation, Bishop Ranch Lot 2, San Ramon, Contra Costa County, California.

19. Jennings, Charles w., 1975, Fault Map of California with Location of Volcanoes, Thermal Springs and Thermal Wells, California Division of Mines and Geology, California Data Map Series, Map No. 1.

20. Peter Kaldveer & Associates, September 1979, Fault Location Study, Proposed Commercial Development for Frank Henry Associates, San Ramon, California.

21. Peter Kaldveer & Associates, 1979, Geotechnical Investigation, Wells Fargo Bank, San Ramon, California.

22. Peter Kaldveer & Associates, October 1979, Fault Location Study, Proposed 13.25-acre Commercial Subdivision, San Ramon, California.

23. Lawson, Andrew C., 1908, The California Earthquake of April 18, 1906, Report of the State Earthquake Investigation Commission, in two volumes and atlas: Carnegie Inst. Washington, Publication 87.

24



24. Lee, w. H. K.; M. s. Eaton; and E. E. Brabb, 1971, The Earthquake Sequence Near Danville, California, 1970, Bulletin of the Seismological Society of America, Vol. 61, No. 6, pp. 1771-1794.

25. Radbruch, D. H., 1968, New Evidence of Historic Fault Activity in Alameda, Contra Costa, and Santa Clara Counties, California, Proceedings of Conference on Geologic Problems of San Andreas Fault System.

26. Saul, Richard B., March 1967, The Calaveras Fault Zone in Contra Costa County, California, California Division of Mines and Geology, Mineral Information Service, Vol. 20, No. 3,

27. Schlemon, J., 1979, Late Quaternary Soil Stratigraphy, General Electric Reactor Site, in ESA Geologic Investigations Phase II, GE Test Reactor Site, Appendix A, unpublished consultant's report.

28. Seismological Society of America, Bulletin, Volume 60, No. 6, December 1979, pp. 2094-2096 (Danville Earthquake).

29. Townley, Sidney D., and Maxwell w. Allen, January 1939, Descriptive Catalogue of Earthquakes of the Pacific Coast of the United States 1769 to 1928, Bulletin of the Seismological Society of America, Volume 29, No. 1.

30. United Soil Engineers, February 1976, Geologic and Geophysical Investigation, 120-acre parcel, Shapell Industries, Inc., San Ramon, California.

31. Woodward-Lundgren & Associates, October 1972, Active Fault Investigation and Preliminary Soil Investigation, Bishop Ranch, Contra Costa County, California.

32. Woodward-Lundgren & Associates, 1973, Environmental Geotechnical Input, Contra Costa County Assessment District 1973-3, San Ramon, California.

Aerial Photographs

AV-1056-020-5 to 07 AV-334-21-23 to 26 AV-353-23-32 to 39

5/24/72 7/2/59

5/23/57

25

1:12,000 1:8,500 1:12,000

I I

- I .

I I I I

: _, I ,• .

I / .. I -_ ___ . To

I EXPLANATION

I _,..._.. FouN -•• •

I Note' totodified Ir- 8ral>ll, elal, 1971.

.!&

°"""'-' "'-

-HAl'llDINO ·LAWSON ASSOCIAT•S

Couulting Engineers and Geologi•t•

Appr· t:;i:."'-' Date 5/22/80

:D:tot ll!lL. Qal

To

Tc Tb

...,

< ~ ! < ' ~

J.. ...

Scale• I in.=2000ft ~ FQ!!totAT!QH

lJnconlOftdatrrld Olknium, Clar', litt,sond,ond QrOVei st'90fft ........ .

Ortnda bfl'ldont l'IOft-marine mudltone, sdt;one, wdslu a -and C011tiqloi•• all. Cierto ................... ..

._ - bnoliun.

PL ATE GEOLOGIC MAP

Bishop Ranch Contra Costa County,Califo~nia 1

I I I I I I I I I I ~· ... ~·

I I

•' ,/"

./ . - , ·-I \. _____ ----r---• - 1 _

'

/i ~--

I /

I --·1 . -· E

I -,_.,_ __ _

~ . -" . -~--

I

I I I

' . . ~ ·--~.;:...-~, .. i£.~_:~:~-~-::: .~ :1,};.;:~~~~..:.r"'"""~--~•~i'6~i~,:.a- ;~" '· .,,, __ . :..:.;.;.;;;'~'.J:.';>~'.i-,;; .;,_,_:~.11~~1~-v-~~:_j..:..c.. __ ::,:~-~~~.:'t~~~,~~~8~i~:i~~~- ,,;;0;.~!;'.!!<!lv"it'-'i"c',1.bi,.,,;,u± . .:.;.:~ ~- -, .

Trench, lot and trench number in box

EXPLANATION

t-- EM ---l

r17f--

© ' j.-·

Electromagnetic induction profile

Aerial photo lineament

~

~ -·

r

! _)

I. ./

J

.... I

~ --------1--

·1 i !-i I

L

1

-~_j __ \ ..

\ -~L__

.................. ~ ,_ IO A••eOIAT••

lf•--G ... _

/

I 111'

~

'"""""'"'""'"'' 'm•• ''T> ,.,,..,, ,.,.,. • ..,.,.

j

'"" 3

I I I I I I I I I I I I I I

• ITTTIT:m llllilill

". "o •••• • 0 •

: o'· . . . . a .. Cl.. rl 0

EXPLANATION

Dark brown clay, high plasticity, organic surface soils

Dark brown clay, medium plasticity, silty, organic surface soils

Brown to light brown, silty clay to clayey silt, mottled and fissured with abundant fine root holes, abundant mottled light gray carbonate nodules and stringers

Brown to light brown sandy silt to sandy clay, with abundant mottled light gray carbonate nodules and stringers, abundant fine root holes

Brown silty to clean poorly graded sand, fine to coarse-grained

Brown sandy gravel to gravelly sand

HARDING• LAWSON ASSOCIATES Engineers 1 Geologists and Geopflys/Cists

5 22 80 Approved Date

EXPLANATION OF TRENCH LOGS

Bishop Ranch Contra Costa County, California

PL ATE

4

lr-~~~~~~~~~~~~~~-~-~~---==~--=---------------------·~~=-..::~-=-----"------'c_---__,·· u.

1°'

I I I I I I I I I I

\I I

465

15 460 H

It ~ w

455

465

... "' es 460 H

:;: ~ w

455

0 10 20 30 40 50 60 70

I I I

~JLLLL.._ ____________ 11~·1:! ffillTTT'" __________ :!:i./J.L,_,__ _________ 11m ITTiTITi I' 11i!i'1·1: I. : I

'1' : I I ' 'I I I ! ; 1 I I

! .. ! .1 i I

H+i-l-µ_J..U..µ.u.J../..J..U.J..J.JJ..J... ___ ---- ----------------------====:·3"::;::::=:::=:::=======~~~

4/29/80 4/29/80

70 80 90 100 110 120 130 140

~ '

0 5 lOft. See Explanation, Plate 4 Continued on Plate 6

HARDING• LAWSON ASSOCIATES

~ Consulting Engineers and Geologists

Job No .. ==8=2=9=4'::, o=o=5='.=0-=-3 __ Appr· t".'Zt-voate 5/22/80

LOG OF TRENCH 1 SHEET 1 of 2


PLATE

5

r--N.....LL

I I I I I I I I I I I

465

.µ .... 460

z 0 H

~ ~ "' 455

I

,J 465

.µ 44 460

15 H

;;: ~ "' 455

450

~ Continued from Plate 5

iff{n+{..P...,.------- - - -----------------------

.. : ... ·. ·. · ... ~·-· .··.::

r- ~--- ---,-140 150 160 170 180 190

l+A+H~'~-------------- ------------------- ------- --- - ---- -------

,-----------~-----------~ I --···--- --1

200 210 220 230 240 250

0 5 lOft.

HARDING - LAWSON ASSOCIATES


Job No. 8294, 005. 03 Appr· &k)Date 5/22/80

200


Bishop Ranch Contra Costa County, Cal i:·)rnia

PL ATE

6

~r----------------.-----------------------=~ .;_I----------------------------. 1

I I I I I I I I I I I

460

455 .µ 4-<

15 H

!;: :> ;s 450

"'

445

r~----------------_--------------------~-------~~ I,

11 I' I I! , : Ii ·::::: l ~------------------------------- - - ------------~·111:~:m1:1::1: 1 : ~:n1 • • • . ,. 1· • , •. .i

• • 1· ' 1' • I ....•. 1.:

... . · .. : .. : : . . . . . . : .

0 5 !Oft.

f

f i

Continued or. Plate 8

See Explanation, Plate 4 HARDING - LAWSON ASSOCIATES


LOG OF TRENCH 2 SHEET l of 2

Bishop Ranch

PL ATE

7 Job No. __ 8_29=4='=0=0=5=·=0=3==A~pp!::r'.;;::;:P:C='.::::b::::!-:'.a!'.te:.:;:;5;;:/=22:/=8:0::.JL_c_o_n_t_r_a_c_o_s_t_a_c_o_u_n_t_y_,_c_a_l_i_f_'.)_rc-'i_· a_..J ___ _J

-c-- -------------- ----------- -----------

' I I I I

I

I I

Continued from Plate 7

.., ""' ~ H E-< .0: :> el r.l

.., ""' z 0 H

~ el r.l

460

455

450

445

460

455

450

445

.... .... ... r::.: . : .. : . '"".. .. I . . . • .......

...

70

----------------------------..

' .. •I•'• ' • . ... ·. . ..

80 90 100 110 115

r 1t+f-------------______________ ...J......., ........ ~...l,-j

-----------------------------lY+H-t Ii: . ' : . : . .... r ..... ". r ..... · .. 1· ...... .

:::. : : : : : : : : . ,_ .......... :: .. r ... I·• • ..

. ..

115 120

0 5 !Oft.

130 140 150



Job No. 8294,005.03 Appr:EZWoate s;22;00

160



PL ATE

8

------------ ---------------------- --- --------------- -------- --- --------- ------------------------------------------------------ ------------- ---

IN--~~~~~~~~~~~~~~~~~~~~~~~~~~~---~~~~~~~-, II.

"' I I I I I I I I I I I

445

. 440 +-' ....

5 ,., ~ :> "1 ..< 435 "1

4/29/80

430

0

I I

__,..,.--------=::....-::.-:==..::-::.=---=--.--------- - ---- - - ----- .d I

10 20

0

See Explanation, Plate 4

. . . •' • ·:~ • .., 0

\------~------,-~-:--:--::--:--::--;,---:-::'::::;: . : .•• : ••• :·. . . ". 0. 0 • ()

4/29/80 ~ " 'o • • o · 'o • · 'o. r:> o ' " · · 0 ', o • " · :;;-.:..: · • • '""·'· " ·

'O,p,.O.C,O

. · .... · . . . . .

30 40 50

5 lOft.



i-'t:1. o · . .-......:.. . : : ·I

0 •• ·o: o; o ." ;;:--:::1

60

Continued on Plate 10


Bishop Ranch

PL ATE

9 Job No. 8294,005.03 Appr:e&...)oate 5122180 Contra Costa County, California

l--------u.

f I I I I I I

Continued fran Plate 9

. .µ ....

~ .... ;;: &i ..:!

"'

.µ

"' z 0 .... ;;: :>-~ "'

445

440

435

60

445

440

435 f• .......... .

105 110

0

r==r:r:=7·" • ... I ••

70 80 90 100

120 1°30 140

5 !Oft.



Job No._s_2_9_4_, _oo_s_._o_3 __ Appr:tu.J Date s;22;so

105

150

LOG OF TRENCH 3

SHEET 2 of 2

Bishop Ranch Contra Costa County, Califor~ia

PLATE

10

~ -~-------------( ,...-------------=-----_---=----_--_---=--------_---=------_-----_---_-----_----_--------_--_---=-----_-_----_-_ ____,---

' I I I I I I I I

..., "' ~ H 8 ..; :> ~ .., ~

445

440

435

445

435

0 10 20

50 60 70

See Explanation, Plate 4

30 40

80 90

0 5 lOft.


'9 Consulting Engineers and Geologists

Job No .. _8_2_9_4...:.,_o_o_s::.... o:..:3:___Appr: &,,Joate s;22/80

50

100

Continued on Plate 12

LOG OF TRENCH 4 SHEET l of 2


PL ATE

11

11..---------_----_---_-_----~-=-=------=._---~--_--_--~-----_--_------=-=--::-_---_---_-----_----_--_----_----_----_--_--_--_----_----_--_______ ---_-----_--_---_--_-----_---_---_---_--_-_----___ ----u.

1t Continued from Plate 11

II 445

., 4-<

rl z 0 H E-o 440 II ~ f'.l Ol II

435

I I I

445

., 4-<

1§ H 440

~ Ol >-1 Ol

435

l fn-p-·~~ ~==--==------rri1··· .. :~_-_=--:=_--_--__ -=--_--_--_-___ - __ =:-___ I_,,,~.. . .·;

1:·?· ..•. ,[__ - ---- I h·~;_;..,:,,. '--..---- --.----- ------- I .......... . £· c ~ . . . . • ------- --~ -- --~.-±:~::!= ..... •:·'. ·:,.· o.o, o·o· o .. : : .· : .. . . . .. ::;,...;..-~. o I

100

. . . . . . . ~-..:...!~'LL. 0 • "1 ·:· .. ·.. ' --,

110 120 130 140

I I I I

150

M,:...~-----------------------... r--·---------------j_ ·.·.· .. --------------ii· .. ,,......------ i --'Tf

I. . . w------------'Tlll· .. • ·w--------=:::.::::.===- -----t--.,,.-M .. +I ttli~ I' '1

1 I' ________ l ___ ... W#".'

--- ---- I . --=---- -- - - ---------- - L.J...l..'-''----. -.-. . . ------ ~ l·o· D· • , 0

• • ',a· o: •. ~ • 0 0: 0 ~"j·jj;:;:::":.I..~~;:is..,,...-10· •• o.' .· .. . o. -.-... .---_.,------ . ''o;,....~·.:··-·· -------..:.. • 0 • • • • • • •• • --~;,..;"" ••• •• 1. . • ----=- 0 ...... ~·~·'"""~·_,_~· ..... ______ :::.::._ ...... _.;'-'""..-

1. • • --=-..:..-.. 1 .. I . : : I,' .

150 160 170 180 190

0 5 lOft.

HARDING- LAWSON ASSOCIATES


Job No. 8294, 005. 03 Appr:&woate 5/22/80

200 205



PLATE

12

70

60

~ so t. x w Cl 40 z ~ 30 Ci i== "" ~ 20

CH / /

/ CL .A. /

/

/ A Line v I

"-

10

0

CL - MLJ v MH or OH

ML - CL, /

~v ML or OL M I I . I .

0 10 20 30 40 so 60 70 80 90 100

LIQUID LIMIT(%)

Symbol Classification and Source liquid Plastic Plasticity % Passing

• DARK BROWN SILTY CLAY (CL) (northeast of lineament)

DARK BROWN SILTY CLAY (CH) (southwest of lineament)


@ Consulting Engineers and Geologists

ob No. 8294 005 03 Appr: e?-t...l Date 5/22/SO

%

41 22 19

56 21 35

PLASTICITY CHART

Surface Soils - Trench 1 Bishop Ranch, Lots 1, 2, 5 and 6

112

PLATE

13

1-II. IX

I I I I I I I ii I 11

I

I I I I

----- - - ------ -

--40

--30

w --20

~ - 40

- .... 30

w - - 20

--50

--40

NE

--30

-- 50

- 40

·- 30 NE

- - 20

E Trench

/'- E . / '· - . '· ·-· \ ·-· ./ '----·" ........ -· ...... / \ LINE 2 ·-· / \ / ., . .-·-·-·.... _,.--/ . ....,

\. ./ \/ \. ,,./ ....... / ........ __ ................. ___ ./ ' / ....... ____ ....... . ........ " __ / ·-·-· ' ' ,, ' / _, \ . ..-./ -·,./ ...... _.-·-·

- Plowed Road Orchard-

t .......... /'-. / ..... /'\ ...... . ·-..... -, . ......__/ __ ,,,,..,_

I ·-· \ , '·-- .... . / -·\ LINE 3

\ ---·-· '·-·-·, .... ........ ./·-... ...... _ , ___ ..... -- . ............. ,,,--......... ___ ./ SW

Powerlii!.es

/., ..... '-...,,.._,

. ·--...'-/ ·-,

/. '·, . \ /-·,_

I . , /. \ . ' /'- . SW ~ '·-·-·-·-· ·-· ' ........ .-· "----· .,

-_____ _,,... . .._,, .......... --·-·-·..... w t z . ,,.

-- .-- e one '---·----· LINE 4

0 . 200ft. 400ft. .

' Horizontal Scale



ELECTROMAGNETIC PROFILES

Bishop Ranch San Ramon

Contra costa,County, California

'

PLATE

) ~- ~r-

--~ d"~"""' ·~.,- ,, "'--+~ _''i:'.

I )

Reference: ..:al1fornia Division of ~incs & Geology, 1975, Fault Map of California, and Bolt ~hllcr, 19"75, Catalogue -,f f:arthqu:.lkes in ~ortri.ern

\ .. ll1fornia, updated in June i'):'i, by R. Uhrhammer.

o~~,,;;IOiioiiiiiii2iii0~~~30ii;;;;;;_4_0~~"50 Km.

O 10 20 30 40 Miles ~~~~~"!""'5iiiiiiiiiiiiiiiiiiiii


Cons11lting F .. :ngi1ictrs nnd Geologists

ob No 8294,oos.~ __ Apprc.c:<J Date s;22;so

EXPLANATION

EARTHQUAKE EPICENTERS '

SYMBOL MJlGNITUDE

0 4.0 -4.4 '" © 6 ~

0 0 t?

<~ -.:._"'"

ACTIVE FAULTS 13 EARTHQUAKE

EPIC ENTERS, SAN FRANCISCO

BAY REGION 1934-1976

PLATE

15


Appendix

SOIL AND GEOLOGIC HAZARDS INVESTIGATION BISHOP RANCH BUSINESS PARK, LOT 1


HAl:'DING·LAWSON ASSOCIAT£S

SOIL AND GEOLOGIC HAZARDS INVESTIGATION BISHOP RANCH BUSINESS PARK, LOT 1

SAN RAMON, CALIFORNIA

HLA Job No. 8294,004.03

A Report Prepared for

Sunset Development Company 1819 Barcelona Street

Livermore, California 94550

by

E. C. Winterhalder, Engineering Geologist - 272

tJe41B. wtnnfl ~l'~ Cecil B. Wood,

Civil Engineer - 18671

Harding-Lawson Associates 2430 Stanwell Drive, Suite 110

Concord, California 94520 415/687-9660

January 4, 1980



lt;'l'RODUCT IQ:,

'l'nis report presents the results of our soil and geologic

hazards investigation for the planned Bishop Ranch Business

Park, Lot 1, San Ramon, Contra Costa County, California. As

shown on the Geologic Map, Plate 1, Lot 1 is situated in the

level floor of San Ramon Valley east of the I-80 freeway anc

north of Norris Canyon Road.

Two buildings about 50,000 square feet each are planned at

the locations indicated on the Site Plan, Plate 2. The build

ings will be two stories high and of steel and wood construc

tion. Maximum column loads will be on the order of 75 kips.

Other development will consist of paved access roadways and

parking, underground utilities and landscaping. 'l'he new eleva

tions will conform closely to the existing ground surface at

about 485 to 490 feet elevation.

Background

The property lies within a Special Studies Zone created by

the Alquist-Priolo Geologic Hazards Zones Act. The zone

encompasses all of San Ramon Valley and some of the adjacent

slopes. Mapping of faults in the area which serves to define

the zone included general geologic mapping, ground-water studies

and interpretation of aerial photo lineaments, all from a number

of sources. Many fault lines are only inferred and some con

siderable revision to fault locations ana the relative ase of

1


HA~OING-LAWSON ASSOCIATES

faults have resultea from subsecuent investigations. hear this

location, previously mapped faults are inferred faults in bec

rock based on a highly generalized interpretation of a northward

prolongation of the Calaveras fault through San Ramon Valley.

Up to the time of this investigation there has been no direct

evaluation of the geological conditions within the site and

there have been no direct indications of faulting within the

site. Previous investigation outside the site west of the I-80

freeway has shown the surf ace trace of the known active

Calaveras fault lies well to the west and would not logically

project into the site.

Object and Scope of Investigation

The object of our investigation was to confirm that there

are no geologically young active faults within the planned

building sites which would constitute a threat of surface

rupture within the expectable lifetime of the buildings. Also,

we have evaluated the general geology and seismicity with regard

to any other geologic hazards including earthquake shaking and

its possible secondary effects. In addition to the geologic

hazards evaluation, our scope of work included a soil investiga

tion to provide soil engineering criteria for the development.

The data obtained for this investigation were correlateci with

test data obtained for a soil investigation we perforrr.ea on the

adjacent site to the east for Beckman Instrurr.ents, Inc.

2


HA'2DING-LAWSON ASSOCIATES

In tor;Gulat1ng our scope of work we have considerec all of

tne results ot previous geologic investigation witn particular

regara to the strike and possible prolongation of any geolog

ically young faults in the area. The scope of work included

research of both published and unpublished geologic reports and

maps, interpretation of aerial photographs, and trenching. The

trenching consisted of two trenches located, as shown on Plate

2, so as to cover the two building sites with respect to the

predominant northwest direction of active faulting in the area.

The trenches were excavated continuously-with a backhoe to

depths ranging from 8 to 16 feet; they average about 12 feet.

The trenches were logged continuously by our geologist; the

results are presented on Plates 3 and 4.

Representative samples of the surface soils were obtained by

our engineer for a limited laboratory testing program. Test

results are presented later in this report. The seismicity is

indicated by Plate 5 showing major active faults and earthquakes

within the region. The general geology and seismicity are

discussed in succeeding paragraphs. Reference material and

aerial photos we utilized are listed at the end of this report.

GENERAL GEOLOGIC SETTING

The general geology in the vicinity of San Ramon Valley

surrounding the site is presented on the Geologic Map, ~late 1.

This map is a modified portion of the map by Brabb, et al.

3


HAIO'DING~lAWSON ASSOCIATES

(1971) to which has been adoeu the generalized locations of the

Calaveras and San Ramon Valley faults.

San Ramon Valley and the paralleling ranges to the east and

west all lie within the Coast Ranges Geomorphic Province. The

dominant structural and topographic trend is northwest. The

Calaveras fault, a part of the San Andreas fault system, approx

imately bounds the west side of the Valley and has haa obvious

influence on the structural development of the Valley. The San

Ramon Valley fault, which is less well defined by the work

accomplished to date, approximately bounps the east side as

indicated by the fault trace on Plate 1.

San Ramon Valley was once carved deeper by erosion and has

subsequently been filled by river and stream deposits to depths

up to several hundred feet. As shown on Plate 1, the site lies

centrally within the valley and is probably underlain by at

least 100 feet of alluvium.

Geologic formations exposed within the area of Plate 1 con

sist of Miocene and Pliocene age marine and nonmarine sedimen

tary rocks including the Briones, Cierbo and Orinda formations.

They crop out in the slopes surrounding the valley and extend

beneath the alluvium in the valley floor. The Quaternary age

alluvium consists of Pleistocene river and stream deposits and

overlying upper Pleistocene to Holocene age alluvial fan depos

its of north San Ramon Creek in the more immediate vicinity of

the site.

4



SI'l'E GEOLOC>:

Previous Work

Previous work in the immediate vicinity of. the site includes

test borings, trenching ana shallow refractive seismic profiling

in the adjoining property to the north (Peter Kaldveer Associ

ates, September 197~). The trenching was conducted in an area

well to the east of the north line of Lot 1 so that it has no

direct bearing on the possibility of faulting within Lot 1. The

trench was excavated across the possible surface trace of a

fault indicated by a dotted symbol to be covered by the alluvium

and to be of pre-Quaternary age. The trench, excavated to a

depth of about 10 feet found no evidence of faulting. The seis

mic profile which extended into the area north of Lot 1 detected

no anomalous changes in velocity which might be indicative of

faulting within the alluvium. Two test borings indicate the

water table is relatively constant at about 30 feet aeep.

Previous investigation by others in the area west of I-680

has confirmed that the surface trace of the active Calaveras

fault approximately parallels I-680, thus essentially ruling out

any prolongation of that fault into the site. Northwest trend-

ing aerial photo lineaments and geophysical anomalies in an area

to the south of Lot 1 have not yet been explored by trenching.

These features could be due either to faulting within the upper

layers of the alluvium or to linear changes in the original

5



sedimentation that deposited the alluvium. Our previous preli~

inary geological stuay (Haraing-Lawson Associates, 1979) which

incluaed review of trenching in an adjoining property to the

east (Burkland and Associates, November 1973) indicates that

these features are not due to faulting. Northwest prolongation

of the stronger lineaments and geophysical anomalies (Woodward-

Lundgren & Associates, October 1972) would cross I-680 at least

1000 feet south of Lot 1.

Trenching Results .

The trench logs presented on Plates 3 and 4 reveal that the

site is blanketed by dark colored, highly plastic adobe-type

clays and silts in a continuous two- to three-foot-thick surface

soil zone. These soils grade downward into generally lighter

colored clays, silts and sands with occasional gravelly lenses.

Fine-grained sandy silts to silty sands predominate although a

thick lens of coarse sand and gravel was encountered in Trench

1. Most conspicuous were continuous thin layers of light brown

colored, fine-grained sand. One or more of these layers were

found at depths ranging up to about 11 feet and represent the

most useful strata by which any offsetting structures might be

detected.

As shown by the logs, the stratification within the alluvium

to the depths explored is uninterrupted except by features which

are clearly a result of normal erosional and depositional

processes expectable within the stream deposited alluvium. A

6


HA~DING-lAWSON ASSOCIATES

thicker gravel lens exposed by Trench l is bounaea on the west

by a steeply inclined erosion surrace which represents the

bottom and bank of a channel eroded into the brown silty sand

layer. Eastwar6 the gravel interfingers and grades laterally

into finer-grained brown sandy silt.

Minor structures encountered consist of minute steeply

oriented narrow fissures within the finer grained soils. These

are believed to be shrinkage cracks formed immediately below an

exposed desiccated surface.

Laboratory tests were performed on soil samples obtained

from the central portion of Trench No. 2 and are summarized

below:

Sample

l

2

Depth (feet)

2.0

5. 0

Moisture Content

( % )

24.5

12.7

Dry Density

(pcf)

89

102

Liquid Limit

52

40

SEISMICITY

Plastic Limit

22

22

Plasticity Index

30

18

Plate 5 presents, on a regional scale, the major known

active faults within the San Francisco Bay Region and the loca-

tions of epicenters for earthquakes greater than magnitude 4

during 1934 through 1976. As shown, the site lies a short

distance east of the Calaveras fault anC within about 15 and 45

kilometers, respectively, of the Hayward and main San Andreas

7


HAs;iOING-lAWSON ASSOCIATES

faults farther to the west. As snown, there have been a number

of historical earthquakes in the range of magnitude 4 to 6

centered near the Calaveras fault. Nearly all have occurred in

the area to the south of San Jose and none within the immediate

vicinity of the site.

The more notable earthquakes in the Bay Region occurred

prior to 1934, including two major earthquakes on the Hayward

fault in 1836 and 1868, and the great earthquake of April 18,

1906 on the San Andreas fault. The star symbol on Plate 5 indi-

cates the focal center for this event al~hough it preceded

1934. Early records describe an earthquake on the Calaveras

fault in 1861. Due to lack of instrumental records and the

location remote from population centers at that time, the event

is poorly documented. However, based on reported intensities,

it has been assigned a magnitude of about 6. Surface rupture is

reported in two areas, one a short distance northwest of San

Ramon Village. The location, if correct, coincides closely with

the presently located surface trace of the Calaveras fault.

There have been no significant damaging earthquakes on the

San Ramon Valley (Pleasanton) fault during historical time. Lee

and others, 1971, suggest the possibility that a sequence of

small earthquakes which occurred near Danville in 1970 may have

been caused by movement on a possible northward continuation of

the Pleasanton fault. At that time, the Pleasanton fault had

been mapped only in the vicinity of Pleasanton in Livermore

B


HA'1DING~lAWSON ASSOCIATES

Valley; there was no mappea northwaro continuation to tne vicin

ity of the eartnGuake sequence. Present mapping oi the fault

suggests it could have been responsible for the sequence

assuming that it has an eastward dip. This is consistent with

the eastward dip generally observed in the off-site trenching.

In summary, the historical earthquake records indicate a

potential for strong earthquake shaking at the site with maximum

magnitudes in the range of 6 to possibly 7 for local events on

the Calaveras fault, about 7 on the Hayward fault, and up to

8-1/4 on the San Andreas fault. Judgin~ by the historical

record and considering the lengths of the Calaveras and the San

Ramon Valley - Pleasanton faults, it would appear that of these

two nearby faults, the Calaveras fault possesses the greater

potential.

CONCLUSIONS ;..ND RECOHMENDATIONS

Based on the results of the investigation, it is our opinion

that Lot 1 contains no geologically young active faulting.

Although faulting may occur in bedrock beneath the site and

conceivably might extend upwards into the deeper alluvium, none

occurs in the upper layers. We believe that the depths attainea

by the trenches represents a time span sufficient to preclude

persistently active Holocene age faulting. Consequently, the

probability of geologically young faulting which would present a

9


HA~OlNG·lAWSON ASSOCIATES

significant threat to the type of structures planned tnrougt,

surface rupture is sufticiently small that it can be safely

disregaraed.

The property lies within a seismically active region and

future displacements on nearby active faults can be expected to

produce at least one strong earthquake within the aeveloFment

lifetime. The maximum expectable earthquake is about magnituae

6 for the Calaveras fault and about 7 and 8, respectively for

the more distant Hayward and San Andreas faults. All could

produce strong shaking although the Calayeras probably repre

sents the greater potential for high ground accelerations.

Consequently, all buildings should be designed to resist strong

earthquake shaking.

The level site and absence of nearby large bodies of water

essentially precludes other geologic hazards, either seismically

or nonseismically related such as landsliding or flooding. Soil

liquefaction as a result of strong shaking is not known to have

occurred during historical earthquakes in San Ramon Valley

although it is conceivable that such might occur in areas of

high ground-water table underlain by sandy soils. Because the

soils are comparatively stiff or dense, are capped by relatively

impervious clayey soils and because the grouna-water table is

deep, the risk of soil liquefaction and any seismically induced

ground failure would appear to be small.

10


HAROING·LAWSON ASSOCIATES

Since the surface soils are potentially expansive (shrink

ana swell with changes in moisture content), precautions should

be taken to protect footings and slabs-on-grade from the detri-

mental effects of soil shrinking and swelling. In addition,

pavements will need to be thicker than normal to offset expan-

sive soil effects.

The upper expansive soils can be blanketed with select

* fill to support shallow building foundations and

slabs-on-grade or, alternatively, the building can be supported

on foundations that extend below the zon~ of significant

seasonal moisture change. In either case, a blanket of material

of low expansion potential (select fill) should be used beneath

interior slabs-on-grade. If supported wood floors are used,

pier and grade beam foundations would be suitable to provide

protection from the detrimental effects of the expansive soils.

Specific recommendations for site development are presented in

the following paragraphs.

Site Preparation and Grading

In areas to be graded, the upper two to three inches of soil

containing roots and organic matter should be stripped and

*select fill is material of low expansion potential conforming to the following: (1) free of organic debris; (2) free of hard rocks or lumps over six inches in maximum dimension; (3) plasticity index no greater than 15; and (4) liquid limit no greater than 40.

11

I I

HA~OING-LAWSON ASSOCIATES

stockpiled for later use as topsoil or removed from the site.

I The stripped materials should not be used in compacted fills.

I I I I I I I I I I I I I I I I

Prior to fill placement, the exposed surface should be

thoroughly moistened to close shrinkage cracks to their full

depth. This may require extended presoaking or sprinkling; it

grading is performed during or following the winter rains, pre-

soaking would not be required. The exposed surface then should

be scarified to a depth of at least six inches, moisture condi-

tioned to slightly in excess of optimum moisture content, and

* compacted to at least 90 percent relativ~ compaction. Fill

material, consisting of on-site soil or select fill, should be

placed in lifts eight inches or less in loose thickness,

moisture conditioned to slightly in excess of optimum, and

compacted to at least 90 percent relative compaction.

As outlined in the subsequent section, select fill should be

placed in building areas where interior floors are concrete

slabs-on-grade. This may require excavation of existing natural

soils to provide the required thickness.

*Relative compaction refers to the in-place dry density of soil expressed as a percentage of the maximum dry density of the same material, as determined by the ASTM Dl557-70(C) test method. Optimum moisture is the water content (percentage by weight) which corresponds to the maximum dry density.

12


HAJ:lOING-lAWSOO ASSOCIATES

Foundation Support

~orrnal wood and steel office buildings can be supported

satisfactorily on spread footings bottornea in either the stiff

natural soils or properly compacted fill. Because of the expan-

sive surface soils, a blanket of select fill should be provided

beneath interior concrete slabs-on-grade. The thickness and

extent of the select fill will depend upon the foundation

alternative chosen from the following table.

Select Material Thickness and Footing Depths

Alternative

Minimum Select Fill*

Thickness (inches)

Minimum Exterior Footing Depth**

(inches)

Minimum Interior Footing Depth**

(inches)

l 12 30 12

2 24 18 12

* Gravel or rock provided beneath slabs for a capillary moisture break is not included as part of the select fill thickness.

** Depth of footings measured from lowest adjacent grade.

The select fill blanket should extend at least five feet

beyond perimeter footings for Alternative 2. Wall and column

footings should be at least 12 and 18 inches wide, respec-

tively. Footing excavations should be cleaned of all loose soil

and be kept moist prior to placement of concrete.

13


HA~DING-LAWSON ASSOCIATES

F~otings can be ciesignea to impose dead load bearing pres

sures of 2000 psf ana total design loads of 3000 psf including

wind or seismic loads. We judge that postconstruction settle

ment of normally loaded footings, constructea as recommended,

will be less than 1/2 inch.

If structures have "conventional" wood floors with no

interior concrete slabs-on-grade, the structures can be

supported on drilled pier and grade beam foundations. We recom

mend that the piers extend below the zone of significant

seasonal moisture change and should be poured in contact with

firm natural soil or compacted fill. The piers should be a

minimum of 6 feet below pad grade. Piers drilled in groups

should be spaced no closer than 2-1/2 diameters, center to

center. The piers can be designed on the basis of an allowable

skin friction of 500 psf on the embedded area, neglecting

support in the upper two feet below final grade. End bearing of

the pier should also be neglected in design.

The grade beam between piers should be as narrow as practi

cal (about six inches wide) and poured on moist soil to minimize

uplift pressures caused by the swelling of the expansive soils.

The grade beams should be designed to resist uplift pressures of

about 1000 psf, reinforced with top and bottom steel and

anchored to the pier with reinforcing steel.

14


HAQDING-LAWSON ASSOCIATES

'l't1e equipment used to drill tne pier holes should proauce a

hole free from a surface film of weak disturbed material so that

the concrete will be in contact with undisturbed supporting

soi 1. Loose material should be removed from the bottom of the

pier hole. Soil in the pier holes and grade beam excavations

should not be allowed to dry and crack prior to pouring con

crete. Periodic sprinkling or watering may be required to keep

the soils moist.

Slab-on-Grade Floors

Interior concrete slab-on-grade floats should be underlain

by at least four inches of clean, free-draining gravel or

crushed rock to provide a capillary moisture break. Where

migration of vapor through the slab would be detrimental, a

vapor barrier should be provided.

As previously discussed, expansive soils beneath slabs may

cause heaving and cracking. The risk of damage can be reduced

by wetting the soils to a high moisture content to cause expan

sion before construction. The moisture content should be main

tained one to three percent above optimum. To help prevent

moisture change in the expansive clays, they should be blanketed

with at least 12 inches of select fill, as described previously.

For exterior decks and walks, the effects of subgrade

shrinking and swelling will be reduced by maintaining a high

moisture content. The best method of protection would be to

provide a blanket of select fill; however, the normal watering

15


HAJ<'OING·LAWSON ASSOCIATES

ot around vegetation arouna the decking may oe sutficient.

Intermittent watering is not the best method of edge protection,

but we believe that it is a practical and effective methoa ot

lessening the effects of the expansive soils as oppo9ea to the

high initial cost of providing a relatively maintenance free

section (select fill blanket}. As with all pavement construc

tion in expansive soil areas, there will be some maintenance

required especially at the edges.

In addition, exterior slabs-on-grade should be designed to

move vertically with respect to structur~s. ~eakened joints

should be provided to control cracking, and wire mesh incor

porated to help prevent separation.

Flexible Pavements

Pavement thicknesses for roadways and parking areas are

based on the quality of the final subgrade soil and the antic

ipated traffic (Traffic Index). We recommend that during con

struction, resistance value (R-value) determinations be made to

evaluate t.he soil quality at subgrade level. With estimated

traffic indexes and R-value test results, an economical pavement

thickness could be determined.

For preliminary design, considering the soil types present

at the site, we computed the following thicknesses.

16



Preliminary Asphalt Pavement Design

Thickness (inches)

Material

Asphalt Surfacing

Class 2 Aggregate Base

lJriveways and Truck Traffic

2-1/2

12

Automobile Parkino

2

8

Class 2 aggregate base should have an R-value of at least 78

and conform to the requirements of Section 26, State of

California "Caltrans" Standard Specifications dated January

1978. The aggregate base should be plac~d in thin lifts in a

manner to prevent segregation, uniformly moisture conditioned,

and compacted to at least 95 percent relative compaction to

provide a smooth, nonyielding surface.

Additional Soil Engineering Services

Prior to construction, we should review the final plans and

specifications for conformance with the intent of our recom-

mendations. Substantial changes in the nature or design should

be reviewed by us and our conclusions either verified or modi-

fied, as required.

17


HAIO'OING-lAWSON ASSOCIATES

RE.FERE.NC!:.S

1. Bolt, B. A., and R. D. Miller, 1975, Catalogue of Earthquakes in Northern California and Adjoining Areas, 1 January 1910 - 31 December 1972, Seismographic Stations, University of California at Berkeley.

2. Borcherdt, R. D., 1975, Studies for Seismic Zonation of the San Francisco Bay Region, U.S. Geological Survey Professional Paper 941-A.

3. Brabb, Earl E., et al., 1971, Prelirr,inary Geologic 1'1ap of the Mount Diablo - Byron Area, Contra Costa, Alameda, and San Joaquin Counties, California, Basic Data Contribution 28, USGS and HUD.

4. Brown, R. D., Jr., and W. H. K. Lee, 1971, Active Faults and Preliminary Earthquake Epicenters, 1969 through 1970, in the Southern Part of the San Francisco Bay Region, USGS Miscellaneous Field Studies Map MF-301.

5. Burkland and Associates, November 1973, Geologic and Seismic Hazards Investigation, Winston Valley, Contra Costa County, California.

6. California Department of water Resources, 1964, Crustal Strain and Fault Movement Investigation, Bulletin 116-2.

7. California Department of Water Resources, 1966, Evaluation of Ground Water Resources, Livermore and Sunol Valleys, Bulletin 118-2, Appendix A.

8. California Department of Water Resources, August 1967, Evaluation of Ground Water Resources, South Bay, Appendix A: Geology, Bulletin 118-1.

9. California Division of Mines and Geology, 1972, Preliminary Earthquake Epicenter Map of California, 1934-1971 (June 30), Seismic Safety Information 72-3.

10. Gibson, W. M., and H. A. Wollenberg, 1968, Investigations for Ground Stability in the Vicinity of the Calaveras Fault, Livermore and Amador Valleys, Alameda County, California, Geological Society of America, Volume 79, pp. 627-638.

18

I I I I I I I I I I I I I I I I I

HA~DING·LAWSON ASSOCIATES

11. Harding-Lawson Associates, November 11, 1971, Seismic Risk Assessment, The Bishop Ranch Property, Contra Costa County, California.

12. Harding-Lawson Associates, October 22, 1973, Preliminary Soil and Geologic Investigation, Planned Danville Country Club, Danville, California.

13. Jennings, Charles W., 1~75, Fault Map of California with Location of Volcanoes, Thermal Springs and Thermal ~ells, California Division of Mines and Geology, California Data Map Series, Map No. 1.

14. Peter Kaldveer & Associates, September 1979, Fault Location Study, Proposed Commercial Development for Frank Henry Associates, San Ramon, California.

15. Lee, W. H. K.; M. S. Eaton; and E. E. Brabb, 1971, The Earthquake Sequence Near Danville, California, 1970, Bulletin of the Seismological Society of America, Vol. 61, No. 6 , pp. 1771-179 4.

16. Radbruch, D. H., 1968, New Evidence of Historic Fault Activity in Alameda, Contra Costa, and Santa Clara Counties, California, Proceedings of Conference on Geologic Problems of San Andreas Fault System.

17. Saul, Richard B., March 1967, The Calaveras Fault Zone in Contra Costa County, California, California Division of Mines and Geology, Mineral Information Service, Vol. 20, No. 3.

18. Woodward-Lundgren & Associates, October 1972, Active Fault Investigation and Preliminary Soil Investigation, Bishop Ranch, Contra Costa County, California.

19. Woodward-Lundgren & Associates, 1973, Environmental Geotechnical Input, Contra Costa County Assessment District 1973-3, San Ramon, California.

Aerial Photographs

AV-1056-02-05 to 07 AV-334-21-23 to 26 AV-353-23-32 to 39

5/24/72 7/2/59

5/23/57

19

1:12,000 1:8,500 1:12,000


Plate l

Plate 2

Plate 3

Plate 4

Plate 5

6 copies:

ECW/CBW/jd

HAQDING·LAWSON ASSOCIATES

PLAT LS

Site Location and Geologic Map

Site Plan and Trench Location

Log of 'lrench l

Log of Trench 2

Active Fault and Earthquake Epicenters

• DISTRIBUTION

Sunset Development Company 1819 Barcelona Street Livermore, California 94550

Attention: Mr. M. R. Mehran

20

1~ Cot'lloci

I _,~.o• Fault

t.vff: Modified from Brr;:ibb, etol, 1971.

IARDING. LAWSON AS£0CIATES

@ CoMulting Engineers arni Geologist1

No. 8924,004.03 Appr· Ow Date 1 / 2/SJ

' ': IS' SITE '\ .,, . .., .....

..,, . :

FQRMATIQfi sYMBO'~

Oal Unconiolidoted allu..-ium, cloy, 1itt,MJnd,orid 9rovel stre-om ledtments.

To Orinda formation, non·rnorine muds!'one, sil1sfone 1

sandstone and ~lometote.

Tc Oerbo son<!>~ forn-oton.

Tb Sriooe1 sondstor.e i:imotlon.

GEOLOGIC MAP

Bishop Ranch Business Park San Ramon,

Contra Costa County, California

PL ATE

1

REQUEST FOR CEO LUCIC llliV I LW

To: Jim Baker

of:

~ ~itial Study ~eologic Report __ Soils Report (check both if combined report)

for:

Single Site File # _1...-Minor Subdivision File # M.S. S.-V - (,i':;,

Major Subdivision File# Sub. ------located in: (District)

Date:

On: 7-1/2 Min. Quadrange -------------- Parcel No.

Hearing Date: 6- 2 } -- '6 D

Pi ease comment by: 15 1 :j i!;O (Deadline Date)

Respond to: J)/7 ;':/ (Planner's Name) ----"--'-~-------

(Phone Extension) -------

File is: Attached _,At My Desk

==-z~-6 In Main File c.abinets

Note: (Special Requests)

I

I I I • ., erences:

·-. -.

o.

. .

Cfifornia Division of 0 es & Geology, C"

5, Fault MqJ of ~

C(iforni a, ond Bolt & ""'Z-' ler, 1975, Catalogue

' . .. l

. earthquakes in Northern C ~ornia, updated in June 17, by R. Uhrhammer.

~-------~~

I o 10 20 30 40 50 Km.

0 10 20 30 40 Miles

kROING- LAWSON ASSOCIATES

@ Consulting Engineers and Geologists

8294,004.03 ~ 1/2/80 ..;b No _______ Appr· Date

EXPLAN.4TICN

SYM9CL

4 0 -4 4

4 5- 4 9 50-54 55-59

~~ oi~··'.:'J¢::'{j:~~~ .. - '

f ...

ACTIVE FAULTS 8 EARTHQUAKE

EPICENTERS, SAN FRANCISCO

BAY REGION 1934-1976

Bi shop Ranch Business Park

. - ·•.'. I • ·~ ,.

PLATE

igmw.consrv.ca.gov/shp/apsi_siteinvestigationreports_ocr/apsi_0… · 22/05/1980 · i i i i i i i...

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