division of mines and geology - california€¦ · 30/09/1976 · terrasearch, inc. soil,...

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SlATe OF CAl1FORNIA.-THE RESOURCl;S AGt;NCY

DEPARTMl:NT OF CONSERVAllON

DIVISION OF MINES AND GEOLOGY DIVISION l-IEADQUARTERS. R.E$OURC.£$ RUILblNG, itOOM 1341

1416 NlN'rH STR.i;.l.:'r

SA.CRAMEN'J"O, CA 9S814

Didri1;t Offi1;eJ; LOS A.NGl:lES SA.CRAM~MTO

EDMUND G. &ROWN JR •• Gov1trnor

Ju11ip~ro SqrrQ Bldg., Rm. 106!1 107 Soulh B1ot1d0¥QY

Reao1..1r1;e& Bldg., Rm. 1 l8 1416 Ninth Street

SAN FRANCISCO Ferry Building 94111

90012

Darwin Myers Contra Costa County Planning Department P.O. Box 951

95814

Martinez, California 94553

Dear Darwin:

(!115) 557-0413

January 31, 1977

We are placing on open file the fo11""1ing reports, reviewed and approved by Contra Costa County in compliance with the AlquistPriolo Special Studies Zones Act:

1. Geologic investigation on fault location study, Larwin property (Subdivision 4656), Contra Costa County; by Terrasearch, Inc.; July 1, 1974.

~2. Geologic investigation and soils update on proposed J.7 l acre residential development (Subdivision 4931), San Ramon,

CA; by Terrasearch, Inc.; September JO, 1976.

It ls noted that the first report is approved conditionally.

EWH/mkr

cc: A-P file (2)~

Sincerely yours,

EARL W. HART Office of the State Geologist CEG 935

TO: Subdivision 4931

FROM: Darwin Myers Planning Geologist RG 3164, EG 91;6

CONTRA COSTA.COUNTY PLANNING DEPARTMENT

DATE: January 27, 1977

SUBJECT: Compliance with the Requi reme.nts of the Alquist-Priolo Act

r l have reviewed the geologic report prepa~ed by the applicant for Subdivision 4931. The report was prepai-ed by Terrasearch and Titled "Geologic Investigation and Soils Update on Proposed 7,7 acre Residential Development, San Ramon, California" (report dated Septemb.,r, 1976), The inves.tigation was conducted under the supervision of a registered geologist and the resulting report generally fol lows the "Guide] ines for Evflluating the Hazard of Fault Rupture" promulg·ated by the California Division of Mines and Geol"gy (C.D.M.G. Note //119).

The primary conclusion of the resulting report is that the project site is free of evidence of active faulting. This conclusion is largely based on results of on-site trenching. However, the investigation also included a thorough review of previous maps and reports; analysis of aerial photographs and a magnetometer sur-vey. The report was well documented and the gnlphics were detailed and legible (the report should contain the registration of the responsible geologist).

It is my opinion that the report satisfies the requirements of the Al~uist-Priolo Act.

WDM/mb

cc: Di ck C r;;ine Curtis Messinger Earl W. Hart Jim SeMfus

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GEOLOGIC INVESTIGATION and

SOILS UPDATE on

PROPOSED 7.7-ACRE RESIDENTIAL DEVELOPMENT

San Ramon, California

for

L. B. NELSON

By

TERRASEARCH, INC. Project No. 1569-G

September 1976

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TERRASEARCH, INC.

SOIL, FOUNDATION AND GEOLOGICAL ENGINEERS

1580 NORTH FOURTH STREET SAN JOSE, CALIFORNIA 95112 (408) 287-9460

L. B. Nelson 64 Willow Place Menlo Park, CA 94025

Attention: Mr. Dick Crane

Project No. 1569-G 30 September 1976

Subject: Proposed 7.7-Acre Residential Development Northeast corner of Montevideo Drive

and Broadmoor Road San Ramon, California GEOLOGIC INVESTIGATION & SOILS UPDATE

Gentlemen:

In response to your authorization, TERRASEARCH, INC., has completed a geologic investigation of your property in the San Ramon area of Contra Costa county, California. In addition to the geologic investigation, the soil conditions on the site were evaluated ~n order to update earlier reports of soil investigation for the subject site .

It is our opinion, based on the available data, that there are no geologic or soil conditions which would preclude development of the site. Those conclusions are based on the assumption that design and construction will be conducted in accordance with the provisions of this report.

Should you have any questions or desire additional information, please contact our office at your convenience.

Reviewed by: .

~&.--7<2-Hassan Amer, P.E. Principal Engineer

HA:CM:EP:mor Copies: 6 to L.B. Nelson

SAN JOSE

Edward Porter Staff Geologist

SACRAMENTO

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TABLE OF CONTENTS

Page NO.

LETTER OF TRANSMITTAL

GEOLOGIC INVESTIGATION & SOILS UPDATE

Purpose and Scope Site Location and Description Regional Geology Regional Seismicity Field Investigation Subsurface Conditions Conclusions (Geology)

SOIT.13 UPDATE

Laboratory Testing Soil Conditions

RECOMMENDATIONS

General Suitability of the Site Grading Foundations Pier and Grade Beam Foundations Structural Slab Foundation Systems General Construction Requirements

REFERENCES

LIMITATIONS AND UNIFORMITY OF CONDITIONS

AI?PENOIX A

l 2 2 - 4 5 - 6 6 - 10

10 - 11 11 - 12

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15 15 - 17 17 18 18 - 19 19 - 21

22 - 23

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Regional Geology and location Map (Figure 1) 26 Site Plan (Figure 2) 27 Magnetic Traverse (Figure 3) 28 Air Photograph (Figure 4) 29 Map of Recent Investigation Data Points (Figure 5) 30 Log of Test Trench (Figure 6) 31 Summary of Laboratory Test Results (Table I) 32

APPENDIX B

Recommended Grading Specifications 34 - 40

(ii)

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Project No. 1569-G .30 September 1976

GEOLOGIC INVESTIGATION & SOILS UPDATE

Purpose and Scope

The purposes of this investigation were to:

a) determine if any seismic hazards, especially

active faulting, exist on the site;

bl determine if the recommendations of an earlier

report of soil investigation prepared by

Gribaldo, Jones ans Associates is applicable

to current development concepts.

Our investigation consisted of the following.

a) A review of literature including reports of

all soil investigations and geologic maps.

b) A compilation of recent geologic data points

within the area.

These various methods of data collection are described in detail

in this report.

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Site Location and Description


The proposed building site is located on the northeastern corner

of the intersection of Montevideo Drive and Broadmoor Road in

the unincorporated area of southern Contra Costa county known as

San Ramon (refer to Figure 1). Topographically, the site is

nearly flat with a maxiTinlm relief of approximately 7 feet between

the southeastern and the northestern corners of the parcel. Slopes

within the parcel are less than 2% .

The boundaries of the site were generally delineated by the Southern

Pacific Railroad tracks to the east with Montevideo and Broadmoor

roadways to the south and west,' respectively. A drainage channel

forms the northern boundary (see Figuare 2). Vegetation on the

site at the time of our investigation consisted of a sparse growth

of grass and weeds.

Regional Geology

The site is located near the center of the San Ramon Valley, which

is an alluviated valley located between two highlands. The valley

--~-is bound by (~~_)rrampas Ridge to the west, which is composed of a

series of Cretaceous to Lower Cenozoic rocks. The eastern side of the

valley, in the area studied, is bound by the Dougherty Hills. 'l'his

southern end of the Dougharty Hills is the western foothills of

the Diablo Range. This range is a member of the coast Range complex

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and is basically underlain by a series of northwest-striking

Cenozoic and Mesozoic rocks. Eight miles to the north of the

site, Brabb and others (1971) have mapped the Mt. Diablo Peak

as a Mesozoic diabase piercement which penetrates overlying

Cenozoic strata •

Just east of the site are found the Dougherty Hills, which are

formed by the western limb of a north to northwest trending

synclinal form within the Diablo Range. Brabb has mapped the

eastern dipping sediments in this area as belonging to the

Orinda Formation (Middle to Lower Pliocene) . This formation

consists of poorly to moderately consolidated non-marine con-

glomerates, sandstones and claystones.

Within the site boundaries, the bedrock is overlain by Quaternary

Fluvial sediments. These sediments occur as flood plain or over-

bank deposits associated with Coyote Creek, an intermittent stream

which flows to the east of the site. The fluvial sediments inter-

finger with basin deposits as were found to the southeast by Terra-

search (1976) in their investigation of Subdivision 4892. The

dentritic stream pattern, as seen in the Aerial Photograph {Figure 4)

is associated with the basin deposits. The total depth of these

late Cenozoic deposits is uncertain.

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The site is located within the State of California Special

Studies Zone. The inferred trace of the Calaveras Fault has

been reported and mapped by Hall (1957) and Brabb (1971) along

the west side of San Ramon Valley approximately 2,000 feet to

the west (see Figure 1). More recent investigations by Purcell

Rhoades (1976) placed an active ?Plinter of the Calaveras across

the Bishop Ranch 1-1/2 miles to the northwest in the foothills

of Los Trampas Ridge .

An aerial lineament, mapped by Ford (1973), follows the trend

of the Pleasanton Fault as mapped by Radbruch (1968). This

lineament follows an inferred active fault at the base of the

Dougherty Hills along the eastern edge of the site approximately

2,500 feet to the east.

Terrasearch, Inc. (1976) located a discontinuous fault in the

hills to the west of the site which correlated with the series of

J (~~~elon shears located by Burkland (1973). These faults were

aligned along the generally accepted location of the Pleasanton

Fault in the San Ramon area.

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Regional Seismicity


The site is located within the seismically active San Francisco

Bay Region. Within the ironiediate vicinity of the site, the

location and existence of the Pleasanton and Calaveras Faults

is in ques.tion. The nearest proven location of active movement

along the Calaveras Fault is in Dublin on the west side of the

San Ramon Valley, where Holocene movement is evident in recent

alluvial sediments. Historical accounts show local surface

rupture along the Calaveras Fault north of Crow Canyon in 1861

as a result of a severe earthquake in the San Ramon Valley.

Radbruch (1968) cites evidence for active lateral creep along

the Pleasanton Fault in the Camp Parks area. Gibson and Wollenberg

considered the Pleasanton fault as active and, on this basis, the

Atomic Energy Commission did not use Camp Parks as the site of

a linear accelerator.

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The Danville earthquake of 1970 was consider/9''to be generated by

movement along the Pleasanton Fault (Lee, et al, 1970). Burkland

(1973) investigated this area rather thoroughly and implied that

a reactivation of the Mt. Diablo piercement caused these earth

tremors of 1970 and is essentially the underlying cause for the

phenomena associated with the location of the Pleasanton Fault or

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faults. The most recent seismic activity to occur in this area,

an earthquake swarm in Green Valley on 15 August 1976, seems to

be associated with this same mechanism.

Terrasearch, Inc. (1974) crossed what is presumably an active

shear during an investigation conducted along Old Ranch Road

to the east of the subject site. In this case, the movement

along the fault was primarily vertical with an implication of

localized uplift similar to that noted in the later (1975) inves

tigation. This configuration would tend to confirm the hypothesis

that the faulting, and possibly the more recent earthquakes in the

Green Valley, are due to uplift forces associated with the Mount

Diablo piercement .

Field Investigation

General: The surface conditions of the site were investiga-

ted by airphoto interpretation, both black and white and infra-red

photographs,, and field observation. The subsurface conditions at

the site were investigated by the interpretation of available geo-

physical surveying data, either on or near the site, utilizing

. geomagnetic, resistivity and refraction seismic techniques.

Exploratory trenching and soil sampling was also accomplished.

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Geophysical investigations and interpretation were prepared by

Gasch and Associates for Terrasearch earlier. The applicable

portions of the magnetic studies are delineated in Figure 3 .•

Aerial Photograph Study: The aerial photographs used in

this study were a set of false-color infra-red photographs flown

in 1972 at a scale of approximately l inch equal to 600 feet.

A set of black and white infra-reds flown in 1971 at a higher

altitude were also used. Conventional black and white photographs

(see Figure 4) flown in 1957 prior to extensive development were

studied. These photos were reproduced at a scale of approximately

1 inch equal to 1,000 feet and were most useful for identification

of geomorphic land forms. All of these photographs provided

stereographic coverage of the site area .

These photographs were studied under the reflecting stereoscope

for lineations, seepage, spring areas, soil contrast and any other

indications of soil and/or geologic conditions. Since many faults

are represented by linear surface features, an aerial survey of

the site is an important part of the geological investigation .

Several "unnamed faults" have been included in the California

Division of Mines and Geology Special Studies Zone Map of the

Diablo Quadrangle (1974). These faults, as shown on Figure 1,

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are based on air photo lineations and have not been field checked

by the State. These lineaments cross the San Ramon Valley in a

northwest to southeast trend.

The nearest of these lineaments, as observed in our airphotos,

crosses just off the site near the southwest corner. This linea-

ment and several other lineaments within this area have been

studied by United Soil Engineering in their 1975 and 1976

geological investigations. Through geophysical exploration

and trenching, they state "anomalies ... in this area have gen-

erally been interpretated to be buried stream channels."

The only lineation we found within this site trends from north-

east to southwest (see Figure 4, "Air Photograph"). This lineament

is a weak stream channel as is shown in the "Log of Test Trenches,"

Figure 6, and is not due to faulting.

Geomorphic evidence was noted that indicates the hills to the

east of the site have undergone recent uplift. Existing drainages

reflect incisement along the base of the hills. A changing base

level and the rather low relief of the valley floor may explain

the meandering and migratory paths that streams have taken in the

vicinity.

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Due to the agricultural use of the site at the time photographed,

the infra-red photos did not reflect any vegetation or moisture

contrast. The stream chanrtel observed in the black and white

photos within the site did appear to the south of the site on

the infra-'reds .

Geophysical Study: Within the site boundary, magnetic

properties of the subsurface soils were investigated by Gasch

and Associates (1974) in their investigations for San Ramon Village.

The location of this magnetic line and other geophysical measure-

ments in this area have been plotted in Figure 5, "Map of Recent

Investigation Data Points.''

United Soil Engineering (1976) have investigated most of the area

to the northeast and west of this site. The location of their

investigation is also plotted in Figure 3.

Gasch and Associates has shown no natural magnetic anomalies on

lines M-3 and M-4 (Figure 5) which cross the site.

Seismic profiles made by Gasch to the south of the site (Figure 3)

are "relatively smooth" and eliminate the possibility of any

northeast-trending faults through the western half of the site.

United Soils Engineering finds as a result of their surface seis-

mic and.subsurface investigation no "indication that faulting has

disturbed the alluvial materials."

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Project No. 1569-G 30 Septetnber 1976

The location of all recent geophysical investigations essentially

"bracketed" the site, as shown in Figure 5, and have no magnetic,

resistivity or seismic anomalies which characterize fault displace-

ment or alluvial sediments within recent times .

Subsurface Conditions

A total of 660 feet of trench was excavated to a minimum depth

of 8 feet in a single trench trending east-west across the site / (see Figure 2). This trench provided information regarding strati-

graphy and geologic structure of the site and a record of soil

depth and composition. A field log of this test trench was prepared

and is shown in Figure 6, "Log of Test Trench."

As many as six lithologic units were observed in one section of

the trench, with at least three of these units forming sharp

contacts. A light brown clayey sand was logged throughout the

entire length of this trench at a depth of 5 to 6 feet below the

natural ground surface. This unit dips gently to the west at 2°.

As much as 3 feet of fill was identified at both the west and east

end of this trench. The trench log provided information on the

depositional history of this site,

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Underlying a 2-1/2 to 5 foot thick brown silty clay topsoil were

alternating sands and clays. This alternating pattern is the

product of stream channel and flood plain deposition of sands

and gravels followed by the generating of overlying clayey soils.

In most cases, the granular sediment forms a sharp contact with

the next generation soil. As many as two paleosoils were recog-

nized near the 350-foot mark of the trench .

A near-surface channel was recognized between the 150 and 180-foot

mark of the trench. This channel, found at elevation 408, is near

the topographic low for the site and most likely represents its

most recent position.

All stratigraphic units were found laterally continuous with on

indications of vertical discontinuities. 'l'his implies no post-

depositional faulting has occurred within this unit, within the

limits of this trench. In summary, there was no evidence of active

faulting apparent to the depth excavated in the trench .

conclusions (Geology)

Surface and subsurface investigations of the site and surrounding

area do not indicate the lineaments as mapped by the State are

fault related. On the basis of this investigation and other avail-

able data, there is no evidence that active faulting within the site

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has disturbed Late Cenozoic sediments. It is our opinion that

little risk due to seismic ground rupture exists. Due to the

close proximity of the site to active or potentially active,

faults, seismic shaking should be expected. However, the typical

type of structure proposed for this site should be able to

sufficiently withstand the reasonable consequences of a moderate

earthquake if it is designed and constructed according to conser-

vative Unified Building Code recommendations.

SOILS UPDATE

The soil investigation phase of this study consisted of a review

of a previous report of Soil Investigation prepared by Gribaldo,

Jones and Associates, reports for surrounding subdivisions, and a

sampling and testing program carried out using the test trench as

a sampling medium. Three soil samples were obtained by driving a

sampling device into the walls of the trench. These samples were

tested. The sample locations and depths are noted on Figure 6, "Log

of Test Tr~nch."

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Laboratory Testing

Project No. 1569-G 30; ·September 1976

The following laboratory tests were performed and the results

utilized for this project:

1. Moisture~density Determinations

2. Atterberg Limits

3. The Unconfined Compression test.

The purpose of these tests was to determine the allowable bearing

capacity and to evaluate the expansion potential .

All results of the laboratory testing are given on Table I,

Appendix A.

Soil Conditions

The characteristics of the soils encountered during our exploration

are described under "Subsurface Conditions". From an engineering

standpoint, two areas of uncompacted fill were noted: one near the

eastern boundary, which is essentially an overlap of the railroad

fill and one near Broadmoor which was evidently placed during the

construction of the street or the neighboring subdivision.

Below the fill in these areas and on unfilled surfaces, the upper

soil consists of a dark gray-brown silty clay of an extremely high

plasticity. The plastic index of this material (54) indicates a

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very high potential for shrink-swell with moisture variation.

In general, the alternating alluvium clays, silts and sands

found beneath the topsoil are firm to hard .

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RECOMMENDATIONS

General Suitability of the Site

1. The site may be developed for the proposed light-frame, one

or two-story residential structures provided the recommendations

included in this report are carefully incorporated into th.e

design considerations and project plans and specifications .

2. The site soils are capable of supporting the proposed light-

frame residential structures without detrimental settlements .

3. The Soil Engineer should be notified at least two working

days prior to any site clearing or grading operations on the prop-

erty in order to ensure proper stripping of surface contaminated

material and to coordinate the work with the Grading Contractor

in the field .

Grading

4. All vegetation, debris, rubble, existing fills and any contami-

nated or organic topsoil should be removed from all areas to receive

fill or structures. The rubble should be disposed of before commenc-

ing the grading operations. The existing fills may be stockpiled

for use as engineered fill. Contaminated soils may be stockpiled for

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later use as landscaping material. If any import fill materials

are required, such material must be approved by the Soil Engineer

prior to transporting the material to the subject property.

5. All grading requirements, in addition to those specifically

described herein, must be performed in accordance with the appli-

cable ·sections of the "Recommended Grading Specifications,"

which will hereafter be referred to as the "Specifications."

The Specifications are presented in Appendix B and set forth the

minimum standards necessary to satisfy the other requirements of

this report. Without compliance with these Specifications, the

de.sign criteria presented in this report will be invalid.

6. General rough grading is to be carried out in accordance with

the provisions set forth in the Specifications. Special require-

ments for grading operations requiring emphasis are described in

the following paragraphs.

7. Any irrigation lines should be handled as outlined in Paragraph

7.1 of the Specifications. The top 3 to 4 inches of contaminated

soil shall be removed from areas to receive engineered fill or

structural improvements. After the proposed streets and building

pad areas are stripped, the exposed ground surface should be scari-

fied a minimum depth of 8 inches and compacted to not less than

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90% relative compaction based on laboratory·compaction test

procedure ASTM Dl557-70 or, in the case of the highly expansive

upper soils, 85% of the maximum density. The above procedure

should also include cut areas if deemed necessary by the Soil

Engineer depending on the field conditions, as well as areas to

be filled. Special care is to be taken that the loose areas

resulting from the removal of trees or underground structures

are adequately compacted to the above relative compaction require-

ments.

8. All fill placed within the building pads should be compacted

to a minimum of 85% or 90% r.elative compaction as determined by

soil conditions in the field.

9. Minimal fill and cut slopes should both have inclinations no

steeper than 2:1 (horizontal to vertical),

Foundations

10. Due to the highly.expansive nature of the surface soils, the

proposed structures may be supported by either a friction pier and

grade beam foundation or a structural slab foundation .

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Pier and Grade Beam Foundations


11. Friction piers should have a minimum 10-inch diameter and

should have a minimum depth of 60 inches below the lowest adja-

cent pad grade .

12. Friction piers should be designed for a maximum friction

design loading of 500 p.s.f. for dead plus live load. This value

may be increased by one-third to include the effect of seismic

loading. No design friction value should be assigned to the

upper 18 inches of embedment. The actual spacing, depth and

diameter of friction piers will be determined by the design

loading of tho structure.

13. Grade beams should extend a minimum of six inches below the

exterior final grade and should be reinforced on top and bottom.

The friction piers should be reinforced for their full length,

with the reinforcement tied to the top reinforcement in the grade

beam.

Structural Slab Foundation Systems

14. The structural slabs should be thickened at the edges so as to

penetrate a minimum of 8 inches beneath final grade .

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15. The slabs should be underlain by a minimum 2-inch thick

layer of sand acting as a cushion and by a moisture-proof

membrane. In addition, it 1s suggested that 4 inches of free-

draining gravel or crushed rock should be placed between the

subgrade and the membrane .

16. The slab should be designed for a cantilever of 3 feet along

the outer edge of the slab. The outer edge should also be de-

signed for a·deflection of 1 inch in both directions.

17. Any exterior concrete flatwork such as steps, patios or

sidewalks may be designed either as part of the slab or completely

independent of the slab. If the flatwork is designed independently

of the slab, waterproof joints should be provided between the flat-

work and the structural slab unit .

18. The soil should be moisture conditioned prior to the pouring

of the slab. Proper moisture content should be verified by the

Soil Engineer prior to the pouring of the concrete.

General Construction Requirements

19. Six inches of soil shall be backfilled against the exterior

of the foundation and/or provided with sufficient slope to create

a positive drainage away from the structures. Water must not be

permitted to pond on the lot.

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20. The surface soils on the site are classified as highly

expansive, therefore, continuous roof gutters are recommended.

Splash plates should be provided below each downspout and

should be sloped away from the buildings to direct water away

from the sturctures. Where downspouts terminate in planting

areas adjacent to the building, precautions must be taken to

see that the drainage water from the downspouts flows away from

the buildings.

21. Trench backfill should be compacted to the same relative

compaction as the fill and should comply with the Grading Speci

fications set froth in Appendix c.

22. Where any opening is made under the perimeter grade beam

foundations for such items as utility lines and trenches, the

openings must be resealed so that they are water tight to minimi-ze

the possibility of seepage under the foundations .

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Project No, 1569-G 30 September 1976

23. During the planning stage, the location of test trenches

on the site should be plotted exactly so that it does not inter-

fere with foundation construction.

24. All grading and foundation plans should be reviewed by the

Soil Engineer prior to construction .

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REFERENCES


l. Brabb, E.E., Sonneman, H.S., and Switzer, J.R., Jr., "Preliminary Geologic Map of the Mt. Diahlo-Byron Area, Contra Costa, Alameda and San Joaquin Counties," U.S.G.S.-H.U.D. San Francisco Bay Region Environmental and Resources Planning Study, Basic Contribution 28.

2. Burkland and Associates, "Geologic and Seismic Hazard Investigation, Winston Valley," 1973 .

3. California Division of Mines and Geology, "Alquist-Priolo Special Studies Zones Map - Diablo Quadrangle," 1974.

4. Ford, R.S. et al, "Livermore and Sunol Valleys, Evaluation of Groundwater Resources through 1968," California Department of water Resources Memorandum Report, 1970.

5. Hall, C.A., "Geology and Paleontology of the Pleasanton Area, Alameda and Contra Costa Counties, California," University of California Publications in Geological Sciences, Volume 34, No. 1, 1957.

6. Purcell, Rhoades <:lnd Associates, "Bishop Ranch," 15 July 1976.

7. Radbruch, D.H., "New Evidence of Illstoric Fault Activity in Alameda, Contra Costa and Santa Clara Counties, California in Proceedings of Conference of Geologic Problems of San Andreas Fault System," Stanford University Publications in Geologic Sciences, Volume 11, p. 46-65, 1968.

8. Terrasearch, Inc., "Soil and Geologic Investigation, Subdivision 4650," Project No. 1090-E, 1974.

9. , "Geologic Investigation 2md Soils Update on Proposed Residential Development," l?roject No. 1484-G, 1976.

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10. , "Soil and Geologic Investigation, 192.-Acre Site, Alcosta Boulevard," Project No, 1417-E, 1976,

11. , "Fault Location Study, Subdivision 3843, 3844, 3845, 4171, 4517 and 4656, Contra Costa County," Project No. 1078-E, 1974.

12. , "Geologic and Soil Investigation on subdi-vision 4650," Project No. 1090-E, 1974 .

13, United Soil Engineering, Inc.~ "Geological and Geophysical Investigation for Tract 4487,'' Project No. 4-782A-Rl, 1974.

14. , "Geological and Geophysical Investigation for 120± A.ere Parcel," Project No. 6-968-Sl, 1976 .

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LIMITATIONS AND UNIFORMITY OF CONDITIONS

1. The recomrnendatlons of this report are based upon the

assumption that the soil cdnditions do not deviate from those

disclose"d in the borings and from a reconnaissance of the site.

If any variations or undesirable conditions are encountered

during the development of the site, TERRASEAR_Cll, INC., should

be notified so that supplemental recommendations mµy be given .

2. This report is issued with the understanding that it is the

responsibility of the owner, or his representative, to ensure

that the information and recommendations contained herein are

brought to the attention of the Architect and Engineer for the

project and incorporated into the plans, and that the necessary

steps are taken to see that the Contractor and Subcontractors

carry out such recommendations in the field .

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APPENDIX A

Regional Geology and Location Map

Site Plan

Magnetic Traverse

Air Photograph

Map of Recent Investigation Data Points

Log of Test Trench

Summary of Laboratory Test Results

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• Scale:

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ProJect No. 1569-G 30 SepteIBber 1976

REGIONAL GEOLOGY AS COMPILED FROM LITERATURE

1"""2,000' ----·-

FAULT CALAVERAS CALAVEil/..S

Ft1U t.:r (er.: A 38 i Ff.Ul:r (: li\LL l

......... Po:;siblo Ti·at;e o'i PLE:'\SAlHOi·i i~t.'Ji...T

t::-::,= 0 ri li~ D /\ F 0 :\ :.1ATI0 i-l ( Tor )

FIGURE NO. l, Regional Geology and Loe at ion---'-M"'a'-'p'-------

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PrOJect Uo. 1569-!': 30 September 1976

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ProJect No. 1569-G 3 0 Secot-.<>mber l 'l 7 6

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.fl I!:! ot <t 0 z 0 co \JJ I:: U1

rre~a~~~L\ ~a~f..iD'-Q~Cj INt:. F'IGURE NO, 3 - MAGNETIC TRAVERSE

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TiltRA SEAltt~H ••~.

Project No. ] 569-·G

FIGURE NO. 4 l\ir Photograph

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. OVER IZED <~·. .

DOCUME ·. T HAS ' '

BEENP LLED\ ANDSC NNED WITHT EMAP

FI E ..

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;· ! '

,·· '('

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• Sample Depth Dry

No. Density (ft.) (p.c.f.)

• 1 1 85.8

2 3 94.2

• 3 6 97.5

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TAllLE I

ProJect No. 1569-G 30 September 1976

.surnwary of Laboratory Test Results

}!oisture Conti=nt

(% Dry wt.)

24.l

21.8

19.5

At terberg J,imi ts Liq11i<l Plasticity Limit Index

(%)

78 24.3

32

Unconfined Compressive

Strength (p.s.f.)

10,000

9,900

Dire.ct Shear Cohes1on Ang.le of (p.s.f.) Internal

Friction (de!1;r<=e)

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• APPENDIX B

• RecoJIUl\ended Grading Specifications

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RECOMMENDED GRADING SPECIFICl\TIONS for

PROPOSED RESIDENTil\J, DEVELOPMENT San Ramon, California

1.1 General Description

1.11 These specifications have been prepared for the grading and

site development of the proposed residential development located in

:San Ramon, California. TERRASEARCH, INC., hereinafter described as

the Soil Engineer, should be consulted prior to any site work con

nected with site development to ensure compliance .with these

specific<1tions .

1.12 The Soil Engineer should be notified at least two. (2) working

days prior to any site clearing or grading operations on the prop

erty in order to observe the stripping of surface contaminated

material and to coordinate the work with the Grading Contractor

in the field.

1.13 This item shall consist of all clearing or grubbing, prepara

tion of land to be filled, filling of the land, spreading, compaction

and control of the filled areas to conform with tho lines, grades

and slopes as shown on the accepted plans. The soil engineer is

not responsible for determining lino, grade, elevations or slope

gradients. The property owner, or his representative, shall

designate the person or organizations that will be responsible for

these items of work .

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1.14 Contents of these specifications shall be integrated with

the Soil Report of which they are a part; therefore, they shall

not be used as a self-co~tained document.

2 .1 Tests

2.11 The standard test used to define maximum densities of all

compaction work shall be the ASTM Test Procedure No. Dl557-70.

All densities sh<lll be expressed as a relative compaction in terms

of the maximum dry density obtained in the laboratory by the

foregoing standard procedure.

3.1 Clearing, Grubbinq and Preparing Areas to be Filled

3.11 All trees, roots, debris, vegetable matter, and organic

topsoil shall be removed from all structural areas. The depth

of organic topsoil to be removed will be determined in the field

by the Soil Engineer but in general will vary from 3 to 6 inches .

3.12 All soil deemed soft or unsuitable by the Soil Engineer

sha,11 be removed. Old fills shull also be excavated, such as

in old drain channels .

3.13 All underground structures shall be removed from the site

such as old foundations, abandoned pipe lines, septic tanks, and

leach fields •

3.14 The final stripping and excavation shall be approved by

the Soil Engineer during construction before further grading is

started •

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3.15 After the areas to receive fill have been cleared, stripped

and scarified, they shall be disked or bladed u·ntil they are

uniform and free from large clods. Native subgrade soils to

receive fill shall be compacted to a minimum degree of compaction

of 85%, but not more than 90%, and at a moisture content of 1 to

3% above the optimum moisture content as determined in the labora

tory. Fill can then be placed to provide the desired finished

grades. The Contractor shall obtain the Soils Engineer's approval

of subgrade compaction before any fill is placed •

4.1 Materials Used for Fill

4.11 All fill material shall be approved by the Soil Engineer.

The material shall be a soil or soil-rock mixture which is free

- from organic matter or other deleterious substances. The fill

material shall not contain rocks or lumps over six inches in

greatest dimension, and not more than 15% larger than 2-1/2 inches.

Materials from the site are not suitable for use in fills. The

Soil Engineer shall determine the suitability of materials for use

as engineered fill.

4.12 Should import material be required, it must be approved by

the Soil Engineer prior to transporting it to the project and_

must meet the following requirements:

1. Plasticity Xndex not to exceed 12.

2. R-Value not lesS than 25 •

3. Should not contain rocks lai:ger than

six inches maximum size.

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4. Not more than 15%. passing the No. 200

sieve •

Import material meeting the above requirements should be

compacted to 90% of the maximum dry density obtained as

determined by ASTM Test Procedure Dl557-70 .

5.1 Placing, Spreading and Compacting Fill Material

5.11 ·The fill materials sh;:ill be placed in uniform lifts of

not more than eight inches in uncompacted thickness. Each

layer s.hall be spread evenly and shall be thoroughly blade mixed

during the spreading to obtain uniformity of material in each

layei:. Before compaction bc:gins, the fill shall be brought to

a water content that will permit proper compaction by eithei:

l) aerating the material if it is too wet; oi: 2) spraying the

material with water if it is too dry.

5.12 After each layer has been placed, mixed and spread evenly,

it shall be compacted to a relative compaction depending on the

soil's expansive characteristics as determined by the Soil Engi

neer in the field. Degree of compaction is the ratio of the

dry density of the constructed fill to the maximum determined by

ASTM '1'est Procedure Dl557-70.

5.13 Compaction shall be by sheepsfoot rollers, multiple

pneumatic-tired rollers or other types of acceptable compacting

rollers. Rollers shall be of such design that they will be

able to comp;:ict the fill to the specified density. Rolling sh<J.11

be·accomplished while the fill material is within the specified

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moisture content range. Rolling of each layer shall be con

tinuous over its entire area and the roller shall make suffi

cient trips to ensure thaJ: the required density has been

obtained. No ponding or jetting shall be permitted.

5.14 Field density tests shall be made in each compacted layer

by the Soil Engineer in accordance with ASTM Test Procedure

01556-64 or ASTM Test Procedure D2922-71. When sheepsfoot

rollers are used for compaction, the density tests shall be

taken in the compacted material below the surface disturbed by

the roller. - When these tests indicate that the density of any

layer of fill, or portion thereof, is below the required compac

tion, the particular layer, or portion thereof, shall be rewo~ked

until the required compaction has been obtained •

5.15 No soil shall be placed or compacted during periods of ra~n

nor on ground which is not drained of all free water. Soil which

has been soaked and wetted by rain or any other cause, shall not

be compacted until completely drained and until the moisture con

tent is within the limits hereinbefore described by the Soil

Engineer. Prior approval by the Soil Engineer shall be obtained

before continuing the grading operations •

6.1 Pavement

6.11 The proposed subgrade under pavement sections, native

soil and/or fill, shall be compacted to 95% relative compaction

for a depth of six inches and at a moisture content of 1 to 3%

above optimum moisture content as determined in the laboratory .

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6.12 All pavement construction and materials used shall conform

with the applicabl"e sections of the latest edition of the Cal

Trans Specifications for pavements, State of California, Depart

ment of Transportation, except as noted above.

7.1 Utility Backfill

7.11 Where any opening is made under or through the perimeter .

foundations for such items as utility lines Jnd trenches, the

openings must be resealed so that they are watertight to prevent

the possibl.e entrance of outside irrigation or rain water into

the underneath portion of the structures. The utility trenches

extending under the perimeter foundations and concrete slabs-on

grade floors shall be backfilled with engineered fill and compacted

. to 90% relative compaction. No ponding or jetting will be per

mitted.

B.l Subsurface Line Removal (if encountered in the field)

B.11 'l'he methods of removal will be designated by the Soil Engi-

neer in the field depending upon the depth and location of the

line. One of the following methods will be used.

B.12 Remove the pipe and fill and compact the soil in the trench

according to the applicable portions of Sections 5.1 and 7.1.

B.13 The pipe shall be crushed in the trench. The trench shall

then be filled and compacted according to the applicable portions

of Sections 5.1 and 7.1 .

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8.14 Cap the ends of the line with concrete to prevent entrance

of water. The length of cap shall not be less than five feet .

The concrete mix shall ha·ve a minimum shrinkage.

9.1 Unusual Conditions

9.11 In the event that any unusual conditions, not covered by the

special provisions, are encountered during the grading operations,

the Soil Engineer shall be immediately notified for directions .

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division of mines and geology - california€¦ · 30/09/1976 · terrasearch, inc. soil,...

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