age.~cy department of cohservation fax (415) 904-7715 · 3/8/1991 · state of california - the...

STATE OF CALIFORNIA - THE RESOURCES AGE.~CY

DEPARTMENT OF COHSERVATION DIVISION OF MINES AND GEOLOGY BAY AREA REGIONAL OFFICE 185 Berry Street, Suite 3600 San Francisco, CA 94107 Phone (415) 904-7707

ATSS 539-7707 Fax (415) 904-7715

c

November 3, 1993

James.O. Berkland, County Geologist Santa Clara County Planning Dept. Government Center, East Wing, 7th Floor 70 West Hedding Street San Jose, CA 95110

Dear Jim:

PETE WILSON, Governor

This is to acknowledge receipt of the reports submitted to us for file a month or so ago. Eleven of the reports (list enclosed) are for projects in Special Studies Zones and are accepted for the AP-file. An additional 34 reports (list enclosed) are fault or fissure investigations for sites outside the sszs and will be added to our C-file collection.

Also, receipt is acknowledged for the 6 geologic and geotechnical reports prepared by consultants for the Planning Department following the Loma Prieta earthquake for the Mary Alice Way landslide (Assoc. Terra Consultants), Redwood Drive landslide (Assoc. Terra Consultants), Alder Heights Rd. - Laurel Rd. (Wm. Cotton), Helen Way area, Redwood Estates (Assoc. Terra Consultants), and Goebel Court Landslide (Assoc. Terra Consultants). These reports will be placed in our C-file.

The remaining geologic and soils reports (perhaps 100 or more) are for sites outside. sszs and do not provide significant information on faults or fissures. It is our intention to discard these or give them away to a consultant. rf you want these reports returned to your file or object to our giving them away, please let me or Perry Wong know by November 17.

Thanks for your help and cooperation.

EWH:ra Enclosures cc: Perry Wong/A-P/'

Sincerely,

EARL W. HART, Senior Geologist &

Program Manager

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I I I I I I I I I I I I I \ I I I I I I

SOIL AND GEOLOGIC STUDY

Proposed 18-Lot Residential Development Hecker Pass Road at Watsonville Road

Santa Clara County, California

MARCH 1991

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

Applied Soil Mechanics, Inc.

File No. A9-2085-Sl

Mr. Andy D'Arrigo P.O. Box 850 Salinas, CA 93901

SOIL AND FOUNDATION ENGINEERS • GEOLOGISTS 835 Blossom Hill Road, Suite 215 • San Jose, California 95123

(408) 365-8100 • FAX (408) 365-8362

October 17, 1989 Revised March 8, 1991

Subject: Proposed 18-Lot Residential Development Hecker Pass Road at Watsonville Road

on 283 +/- acres

Santa Clara County, California REVISED SOIL AND GEOLOGIC STUDY

Dear Mr. D'Arrigo:

As requested by the Santa Clara County Geologist, Jim Berkland, we have revised our Soil and Geologic Investigation dated October 17, 1989 for the proposed development (Berkland, 1990). Mr. Berkland requested that our original geologic map be revised to show topography and locations of proposed improvements. In addition, we were asked to evaluate the effects of the October 17, 1989 Loma Prieta earthquake on the D'Arrigo propeny. The project will involve constructing 18 new single family residences off Hecker Pass Road. The following repon presents the results of our study for the proposed development and supersedes our earlier repon.

Based on the results of our study, the site is suitable from an engineering geology and soil engineering viewpoint for the proposed new residences, provided that the recommendations presented herein are incorporated into all appropriate construction plans and specifications. We should review preliminary grading plans, prior to construction bidding, to verify conformance with our recommendations. We should also provide the on-site soil services during grading and foundation construction, as specified in our recommendations.

The scope of our services did not include any environmental assessment or study for the presence of hazardous or toxic materials in the soil, surface water, groundwater or air; on or below or around this site.

Sincerely,

APPLIED SOIL MECHANICS, INC.

Written by:

L-~.

Lewis Rosenberg Project Geologist

Copies: 6 to Addressee

Reviewed by:

&f~~ Carl W. Greenlee Geotechnical Engineer #355

i

Reviewed by:

~z ff.~~----Richard T. Gorman, C.E.G. #1325 Consulting Geologist


File No. A9-2085-Sl

TABLE OF CONTENTS

INTRODUCTION


Pai:e Nos.

Purpose and Scope....................................................................................... 1 Site and Project Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Literature and Map Review .............................................................................. 3 Aerial Photograph Interpretation........................................................................ 4 Field Exploration Program........................................................................ . . . . . . 5 Laboratory Test Program................................................................................ 5

GEOLOGY

Regional Geologic Setting ............................................................................... 6 Site Geology.............................................................................................. 7 Groundwater. ............................................................................................. 8

SEISMIC HAZARDS

Seismicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Primary Earthquake Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Secondary Earthquake Effects .......................................................................... 10

GEOTECHNICAL EVALUATION AND DISCUSSION

Expansive Soils ........................................................................................... 12 Slope Stability ............................................................................................ 12

CONCLUSIONS ......................................................................................... 13

RECOMMENDATIONS

Site Development and Grading ......................................................................... 15 House Foundation Design ............................................................................... 18 Concrete Slab-On-Grade Construction ................................................................ 19 Utility Trench Backfill ................................................................................... 21 Surface Drainage ......................................................................................... 22 Asphalt Pavement Design ............................................................................... 23

LIMITATIONS AND UNIFORMITY OF CONDffiONS ......................................... 24

REFERENCES CITED .................................................................................. 25

APPENDIX A

APPENDIXB

APPENDIXC

Field Drilling Procedures ..................................................... A2

Laboratory Testing Program ................................................. B2

General Grading Specifications .............................................. C2

ii


File No. A9-2085-Sl

TABLE OF CONTENTS (continued)


Page Nos. LIST OF FIGURES

Figure l Figure 2 Figure 2a Figure 3 Figure 4 Figure 5 Figures Al-AS Figure Bl

LIST OF TABLES

Table I

Table II

Location Map .................................................................. 27 Regional Geologic Map ....................... , ............................... 28 Explanaiton to Geologic Map ................................................ 29 Site Plan and Geologic Map .................................................. 30 Cross Section .................................................................. 31 Epicenter Map ....................................•............................. 32 Logs of Test Borings & Trench ......................................... A3-Al0 Laboratory Compaction Test Results ....................................... B5

Summary of Moisture, Density, ............................................ B3 and Direct Shear Testing

Summary of Atterberg Limit Testing ........................................ B4

Ill


File No. A9-2085-S l

INTRODUCTION


This report presents the results of our soil and geologic evaluation for the proposed new

subdivision. The property is located near the city of Gilroy, California in an unincorporated

portion of Santa Clara County. The irregularly shaped property encompasses approximately 283

acres in area, as shown on Figure 1. Hecker Pass Road (Highway 152) is the north boundary;

steep foothills form the south boundary, and agricultural land borders the east and west sides.

Purpose and Scope of Investigation

The purpose of this investigation is to detennine the soil and geologic conditions at the site; assess

the feasibility of the proposed 18-lot residential development; and develop recommendations for

site preparation, grading, pavements, and general foundation design criteria. This report covers

local and regional geologic conditions, and the constraints that they impose on the development as

well as local soil and foundation conditions. The findings and recommendations in this report

should be included in the development plans for the site.

In order to fulfill the above objectives, the investigation included the following:

1 . Literature review of available reports and maps.

2. Study of stereo pairs of aerial photographs to aid in evaluating the distribution of

surface and subsurface materials, slope stability, and evidence of faulting.

3. Site reconnaissance and mapping of soil and geologic features by our project

geologist.

4. Excavation of exploratory borings and one trench, along with sampling materials

encountered.

5. Laboratory testing of selected samples to determine pertinent physical and

engineering characteristics.

1

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

File No. A9-2085-Sl October 17, 1989 Revised March 8, 1991

6. Analysis of field and laboratory data to aid in developing geotechnical

recommendations and design criteria; and,

7. Preparation of this report, including supporting graphics.

Site and Project Description

The D' Arrigo property is situated on an alluvial plain along the foothills of the Santa Cruz

Mountain Range. Bodfish Creek runs roughly east-west across the site, a short distance north of

the south property line. The planned development is north of Bodfish Creek and is referred to as

"the site". South of the creek, the land is steep and mountainous. Elevations range from about

280 feet near the southeast corner to about 350 feet at the northwest corner. The present use of the

property is agricultural, with prickly pear cactus under cultivation. The soil has recently been

disced and irrigated. Several unimproved dirt roads cross the site and provide access to the cactus

fields.

Preliminary plans entitled "Vesting, Tentative map for Lands of D'Arrigo" (M.H. Engineering

Co., 1989) show the development will consist of subdividing 101 acres of the 283 acre parcel into

eighteen (18) individual lots. 182 acres will remain as open space. This investigation addresses

I conditions on the 101 acre parcel.

I Access to the site will be from a new street off Hecker Pass Road. One and/or two-story detached,

single-family residences will be constructed on each Jot. The structures will have elevated-wood

I I I I I

floors and concrete slab-on-grade garage floors. Sewage from each lot will be disposed into

individual septic tanks and leach fields. No basements or depressed parking areas are anticipated.

Grading plans were not available at the time of the investigation, however, it appears the amount of

grading will be minimal. Figure 3 shows the approximate locations of the planned improvements.

2


File No. A9-2085-S 1

FINDINGS

Literature and Map Review


As part of our study, we reviewed reports and maps pertaining to the site and vicinity. This

included examining files contained in the offices of the Santa Clara County Geologist, in addition

to available published literature. Most of the published geologic information on this area is

preliminary in nature, and is based on reconnaissance techniques and extrapolation of data.

The regional geology was first mapped in detail by Allen (1946) as a stratigraphically and

structurally complex area of plutonic, metamorphic, and sedimentary rocks ranging in age from

Jurassic-Cretaceous to Holocene (150 million years before present to historic time). More recent

studies by Dibblee (1973) and Dibblee and Brabb (1978) show the structure and stratigraphy in the

southern Santa Cruz Mountains. These maps and local studies by Terratech, Inc. (1981, 1989)

show a trace of the northwest-striking Camadero fault across the foothills in the southern portion

of the site. Soil units and erosion hazards are mapped by the U.S. Soil Conservation Service

(Lindsey, 1974).

Reports discussing regional seismic hazards show that the parcel is within an area of potential

seismic hazards. Rogers and Williams (1974) show that the nearly level portion of the property is

within a zone of high potential (Dl-2) for liquefaction, lurching, and soil spreading. The hillside

portion of the property in Zone Fs, which represents areas of low potential for earthquake-induced

landslides. Information on the effects of earthquakes in the area is discussed in reports by Lawson

(1908), Griggs (1973), and Plafker and Galloway (1989). These reports document that the

vicinity has been strongly shaken by several moderate to large earthquakes during the past century.

3



Aerial Photo~h Interpretation


We studied aerial photographic stereo pairs taken of the subject property from 1939 to 1985. The

following aerial photographs of the site and vicinity were used in this study:

October 1949

April 1950

April 1985

Approximate Scale

1:20,000

1:20,000

1:31,680

black and white

black and white

black and white

Source

USDA

USDA

WAC

These photographs were studied for geomorphic evidence of faults and landslides. Faults typically

appear on aerial photographs as a linear features with tonal differences on either side. These

differences could be related to changes in soil and rock type, vegetation, groundwater levels, or

bedding characteristics. Lineaments are sometimes associated with topographic features

characteristic of fault zones such as linear and shutter ridges, sag ponds, springs, and offset

drainages.

A northwest-southeast trending lineament with topographic and tonal differences on either side is

visible approximately 2,000 feet south of the site. This lineament roughly corresponds to the

Carnadero fault as shown on published mapping (Dibblee, 1973).

Landslides often appear on aerial photographs as semi-circular scarp areas, closed depressions,

disturbed vegetation, hummocky terrain, offset drainages, and spring woes. Examination of the

aerial photographs taken before and after the severe 1982-83 rainfall storms indicates that the

surface conditions at the subject site were relatively unaffected by the heavy precipitation

encountered during those years. No indication of landsliding that would affect the planned

development area is visible in the aerial photographs used in this study.

4


File No. A9-2085-Sl

Field Exploration Program


A reconnaissance of the site and vicinity was conducted on September 26, 1989, to field check the

geology as mapped by Dibblee (1973). No evidence of rupture or offset was seen along the trace

of the Carnadero fault as mapped by Dibblee (1973). The area was also examined for evidence of

slope instability along the banks of Bodfish Creek. No signs of slumping or major instability were

apparent The geologic conditions are described in detail in following sections of this report.

Since the original version of this report was issued on the day of the 7 .1 M Loma Prieta earthquake

(October 17, 1989), we visited the property on October 20, 1989 to determine the effects of the

Loma Prieta earthquake on the site. No signs of earthquake-induced damage such as ground

rupture, sand blows, lateral spreading, or lurch cracking were observed.

The approximate locations of the exploratory borings and trench are illustrated on Figure 1, Site

Plan. The drilling was accomplished on September 22 and 26, 1989 and the trenching on October

2, 1989, under the supervision of our staff geologist. A total of seven exploratory borings were

drilled and one exploratory trench was excavated within the subject site. The exploratory borings

were drilled to depths of approximately to 16-1(2 to 23-1/2 feet below the existing ground surface.

A detailed description of the field exploration program along with the exploration logs are included

as Appendix A.

Laboratorv Testing Program

Subsequent to the field drilling program,.selected soil samples were tested in the laboratory, in

order to determine their engineering properties. Details and results of the laboratory testing

program are contained in Appendix B.

5


File No. A9-2085-Sl

GEOLOGY

Regional Geologic Setting


The site is located in the foothills of the southern end of the Santa Cruz Mountains Range and is

pan of the Coast Ranges geomorphic province of central California. In this pan of the Coast

Ranges, the mountains trend roughly northwest-southeast. The structural grain is dominated by

the San Andreas fault and subsidiary faults such as the Sargent-Berrocal and the Zayante-Vergeles.

The Sargent fault is a northwest-southeast striking, steeply southwest-dipping shear zone

separating Miocene sedimentary rocks from Cretaceous Franciscan basement rocks. The fault is

not a single trace, rather a zone of discontinuous, imbricate traces (McLaughlin, 1973). Most of

the displacement is vertical, with some right-lateral strike-slip component of motion (Allen, 1946;

McLaughlin, 1973; Bryant, 1980). Allen (1946) estimated at least 3,000 feet of vertical throw and

at least 250-300 feet of right-lateral slip along the fault trace.

The Carnadero fault was first described by Allen (1946) as a high-angle, southwest-dipping

reverse fault separating Jurassic age Franciscan Complex on the southwest from Tertiary age

Temblor Formation on the northeast. This fault is believed to be inactive and is classified as

"Quaternary--activity unknown" by Buchanan-Banks and others (1978).

Regional mapping by Allen (1946) and Dibblee (1973) shows the site is mantled by recent

alluvium derived from the foothills and Bodfish Creek. Underlying the alluvium are Jurassic

Cretaceous age sandstone, greenstone, and chert of the Franciscan Complex on the south side of

the Carnadero fault; and Tertiary age Temblor Formation sandstone on the north side. No

landslides impacting the site are shown on this map. The regional geology is shown on Figure 2.

6


File No. A9-2085-Sl

Site Geology


·The property is underlain by Temblor sandstone north of the Cam<idero fault and Franciscan chert,

sandstone, and greenstone south of the Carnadero fault. Bedrock was encountered in Boring 5

and consists of pale yellowish orange, well-cemented, medium- to coarse-grained sandstone which

is very moist and very dense. Surficial materials in the planned development area consist of light

brown, non-plastic sandy silt with gravel; which is damp and medium dense. This layer is

underlain by a unit of dark yellowish-brown cobbles and boulders with silty sand and gravel. The

upper material is approximately two to four feet thick and is interpreted as a soil horizon overlying

the gravels. The lower material is at least fifteen feet in thickness and represents unconsolidated

alluvial deposits derived from Bodfish Creek. The distribution of geologic units is shown on the

Site Plan and Geologic Map, Figure 3. A schematic cross-section through the site is included as

Figure 4.

One exploratory trench was excavated across the proposed house site closest to the mapped trace of

the Carnadero fault. A detailed description of the field exploration program and the logs of the

exploratory trenches are included in Appendix A. Two units were visible in the trench excavation.

The uppermost unit extending from the ground surface to a depth of approximately 2 to 4 feet is a

well-drained, light brown, non-plastic sandy silt with traces of fine gravel and abundant roots up to

1/4-inch-diameter. This layer is underlain by a unit of dark yellowish-brown cobbles and boulders

with silty sand and gravel. This material is interpreted as terrace deposits (older alluvium) and is

probably Pleistocene age (Dibblee, 1973).

No offset or shearing of the alluvial materials was observed in the exploratory trench excavation.

This suggests that the trace of the Carnadero fault crossing the site has not moved since the older

alluvial sediments were deposited. Since the older alluvial material is probably Pleistocene in age,

the Carnadero fault has been inactive for at least the past 11,000 years.

7


File No. A9-2085-Sl

Groundwater


Free groundwater was not encountered in the exploratory trenches excavated on the site.

However, slow seepage was encountered in Boring 4 at a depth of approximately 17 feet below the

ground surface during our investigation. Rogers and Williams (1974) show depth of first

groundwater to be 18 feet below the surface at a point approximately 0.3 miles northwest of the

site, and at 84 feet approximately 0.6 miles southeast of the site, based on private well data.

8



SEISMIC HAZARDS

Seismicity


In assessing the seismic hazards for a given area, it is useful to examine historic records of local

earthquake intensities. This information is useful for predicting the recurrence of severe shaking in

an area. Within the last 200 years, significant earthquakes have severely damaged man-made

structures over a large part of southern Santa Clara County. These include the 1865 M 6.5 San

Francisco (Lawson, 1908), 1906 M 8.3 San Francisco (Lawson, 1908), 1984 M 6.2 Morgan Hill

(Stover, 1984), and the 1989 M 7.1 Loma Prieta earthquakes (Plafker and Galloway, 1989). The

locations of significant earthquake epicenters and faults is shown on Figure 5.

Primary EarthQJ!alce Effects

Fault-Related Ground Rupture - Recently active fault zones are defined by the State of

California (Hart, 1988) as displaying sufficient and well-defined evidence of movement within the

Holocene Epoch (about the last 11,000 years). No structures for human occupancy are permitted

on the trace of an active fault. Unless proven otherwise, the area within 50 feet of an active fault is

presumed to be underlain by an active fault. The definitions of "potentially active" vary widely.

The most widely accepted definition of potentially active is a fault showing evidence of

displacement older than 11,000 years and younger than 2,000,000 years (Pleistocene Epoch).

"Inactive" faults are classified as not having been active for at least two million years. The site is

not located within, nor is it immediately adjacent to any of the published Alquist-Priolo Special

Studies Zones (CDMG, 1976; Hart, 1988)

The Carnadero fault is believed inactive and is classified as "Quaternary--activity unknown" by

Buchanan-Banks and others (1978). No offset of the alluvial or terrace materials was observed at

the site. This suggests that movement along the trace of the Carnadero fault mapped by Dibblee

9



(1973) as crossing the site has not occurred since the alluvial sediments were deposited. Since the

planned house site nearest the Carnadero fault is approximately 175 feet north of the mapped trace,

the possibility of fault-related ground rupture is considered to be low.

Secondazy Earthquake Effects

Ground Shaking - The primary seismic hazard that will have the greatest impact on the

proposed development within its design life span will be ground shaking from a seismic event.

Ground shaking can trigger other secondary seismic hazards that are discussed in following

sections. The active San Andreas fault and Calaveras fault zones are mapped approximately 6

miles west and 8 miles east of the site, respectively (Rogers and Williams, 197 4). The trace of the

potentially active Sargent fault is approximately 1-1/2 miles southwest of the site.

In the lifetime of the proposed development, the most significant event would be a maximum

probable 7.5 magnitude earthquake occurring on the San Andreas fault. Although higher

accelerations may be experienced on the site from closer active faults, such as the Sargent-Berrocal

fault system, the recurrence interval for such events may be much longer than an event on the San

Andreas fault.

Recent earthquakes in the vicinity also provide data on ground acceleration response. The nearest

strong-motion seismograph stations to the site are approximately 4 miles to the southeast in Gilroy.

The maximum recorded ground accelerations at Gilroy stations situated on alluvium were 0.38 g

vertical acceleration, and 0.55 g horizontal acceleration (Shakal and others, 1989). A strong

motion station situated on Franciscan sandstone in Gilroy recorded maximum ground accelerations

of 0.22 g vertical acceleration, and 0.50 g horizontal acceleration (Shakal and others, 1989).

10


File No. A9-2085-S 1 October 17, 1989 Revised March 8, 1991

The estimated shaking intensity in the vicinity of the site during the 1989 Loma Prieta event was

VII on the Modified Mercalli (MM) scale (Plafker and Galloway, 1989). During the 1984 M 6.2

Morgan Hill earthquake, shaking intensity was estimated at MM VI (Stover, 1984).

Ground Failure and Liquefaction . Associated seismic hazards include ground failure due to

fissuring, liquefaction, and seismically-induced landsliding. The site and vicinity appears to have

suffered no damage as a result of the October 17, 1989 earthquake. We did not observe any

features on-site suggesting that ground rupture or fissuring had occurred as a result of the 1989

Loma Prieta earthquake.

Soil liquefaction is the loss of soil strength during a significant seismic event. Liquefaction occurs

during rearrangement of the soil particles into a denser condition, resulting in localized areas of

settlement. It occurs primarily in saturated loose- to medium-dense, fine to medium-grained sands

and sandy silts. The topographically lower portion of the site is mapped as an area of high

liquefaction potential (Dl-2) by Williams and Rogers (1974). The presence of probable Pleistocene

age older alluvium and younger dense sands and gravels indicates that there is a low liquefaction

potential on the portion of the site planned for development.

11



GEOTECHNICAL EVALUATION AND DISCUSSION

Expansive Soils ·


The soils at the site are low in plasticity, with Plasticity Indices ranging from 3 to 8. The potential

for differential movement due to changes in soil moisture is judged low.

Slope Stability

As the planned development area is nearly level to gently sloping, the potential for landsliding is

low under seismic and non-seismic conditions. The southern stream bank of Bodfish Creek is

composed of nearly vertical-standing cobbles and gravels. These are stable when dry, however,

high flow in the creek could undercut the banks and contribute to instability. Houses should be set

back at least a distance equal to the intersection with the ground surface of an imaginary line

projected up at a 2H: 1 V (horizontal to vertical) distance from the bottom of the creek bank. The

alluvium is well-drained and sewage effluent is most likely to percolate downward, rather than

laterally toward the creek. The risk of the septic systems destabilizing the creek bank is low.

12


File No. A9-2085-Sl

CONCLUSIONS


The following conclusions are drawn from the data acquired and evaluated during this investigation

for the proposed project

1. The site is suitable for the proposed residential development (see Project Description), from

a geotechnical viewpoint, provided the recommendations presented in this report are closely

followed.

2. The near-surface native soils exhibit a low shrink-swell potential when subjected to

variations in water content.

3. It is anticipated that total, differential, long and short term static settlements of the proposed

residential buildings will be less than 1/2 of an inch. These predicted settlements assume the site

has been properly prepared per our recommendations, prior to the construction of the foundation

system.

4. The study of geologic literature, examination of a time-series of aerial photographs, and

field reconnaissance all indicate that the proposed building site is entirely underlain by Quaternary

old alluvial deposits. The nearest active fault is the active San Andreas Fault, located

approximately 6 miles west of the site. The trace of the potentially active Sargent fault is

approximately 1-1/2 miles southwest of the site (Rogers and Williams, 1974).

5. There are no known active or potentially active faults, active landslides or ancient landslide

deposits that directly affect this site.

6. There are no known geologic or seismic hazards present that would preclude use of this site

as planned.

13



7. A moderate earthquake could cause severe ground shaking at this site. Utility service as

well as access to the site, depending on the location of underground utilities and above ground

lines, could be disrupted in the event of a moderate to severe earthquake generated on any of these

earthquake faults.

8. The potentials for secondary seismic effects of lateral spreading, liquefaction or lurch

cracking to occur at this site are considered to be low.

9. The potential for seismically induced landsliding to occur on-site is considered to be low.

14



RECOMMENDATIONS


The following paragraphs present recommendations for the general design and construction of the

building pads and foundations for the proposed wood frame, single-family, one and two story,

homes plus related site improvements. These recommendations are based on the results and

conclusions reached during our engineering analysis and evaluation of the field and laboratory data

for this investigation.

Site Development and Grading

1. Development of the property as proposed will require moderate amounts of cut and fill

operations. All of the grading should be done under the direct observation of, and testing by a

representative of our firm.

2. Any existing utility lines, where known, should be located on the grading plans to assist

the Soil Engineer during the grading operations. The necessity to remove abandoned underground

utility lines should be determined by the soil engineer during site grading.

3. All debris should be removed from the site. All surface organics and uncompacted fill

should be stripped from all proposed structural areas and areas to receive structural fill, buildings,

patios, and pavements. It is expected that organic stripping will involve the removal of at least the

upper two to six inches of surface soil over most of the proposed building area. The exact amount

of stripping should be determined by the Soil Engineer in the field during grading operations.

Organically contaminated soil may either be stockpiled for later use as topsoil in landscaped areas,

or be hauled from the site. Noncontaminated soils may be reused as structural fill for areas

designated for building structures and under pavement sections.

15

I I I

File No. A9-2085-SI October 17, 1989 Revised March 8, 1991

4. Structural fill is defined herein as a native or imponed fill soil material which, when

I properly compacted, will suppon foundations, pavements, concrete slabs-on-grade or other fills

without detrimental settlement

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

5. All abandoned septic tanks located in the proposed grading area shall be removed prior to

any grading or fill operations. The connecting line between the septic tank and the leach field shall

be removed or plugged. The drain pipes and the top two (2) feet of soil over the old leach field

shall be subexcavated. The noncontaminated soil, previously subexcavated, may be reused as

compacted structural fill. The old drain gravel in the leach field trenches may remain in place

below the top (2) feet of soil cover.

6. Al_I abandoned underground utility or irrigation lines shall be plugged, removed or

demolished. The appropriate final disposition of such lines shall depend upon their depth and

location, and the method of removal or demolition shall be determined by field observation by the

Soil Engineer. One of the following methods will be used:

7.

A.

B.

c.

Excavate and totally remove the pipeline from the trench.

Expose and subsequently crush the pipeline in the trench before filling the trench

with compacted native soil.

Cap the ends of the utility line with concrete to prevent entrance of water. The

locations at which the utility line shall be capped will be determined by the Soil

Engineer. The length of the cap shall not be less than five feet, and the concrete

mix employed shall have minimum shrinkage.

Any ruts or depressions resulting from the removal of uncontrolled fill, septic tanks,

foliage, and abandoned or buried structures should be cleaned down to firm engineered fill or

native soils. Unless otherwise approved by the Soil Engineer, all excavations and depressions

created during site clearing and demolition operations, such as for the septic tank, shall be

16



temporarily left open in preparation to being filled by the grading contractor. For safety purposes,

sidewalls may be ramped outward from the temporary excavations. The depression(s) should then

be backfilled with compacted structural fill as described in Paragraphs 8 through 12 inclusive. All

tree roots encountered in grading, which are larger than one-inch in diameter, should also be

removed from the fills. Clearing and backfilling operations should be performed under the

observation of the Soil Engineer.

8. The properly cleared and stripped native ground in areas to receive fill or pavement sections

should be scarified to a depth of 8 inches, moisture conditioned over optimum and recompacted to

not less than 90% relative compaction prior to receiving compacted fill or pavement sections.

9. All fills placed on sloping ground greater than 10: I (horizontal to vertical), must be

properly keyed at their base and continuously benched into the underlying natural slope. Once the

keys have been approved by our firm, filling may proceed. Each layer of fill must be compacted to

at least 90% relative compaction and at optimum moisture (or above) before the subsequent layer is

placed.

10. Constructed slopes, either cut or fill should not exceed 2:1, horizontal to vertical, in

finished slope. Fill slopes should be constructed slightly oversize laterally so that they can be

trimmed back to a clean finished surface at the completion of grading. All constructed slopes

should be protected against over-the-slope runoff of rain or surplus irrigation water by some

appropriate drainage control facility. All new slopes should receive some type of erosion control

planting soon after completion of grading and prior to winter rains.

11. Any proposed imported fill soil material for this project should:

a. have a plasticity index ofless than 13;

b. be free of deleterious organics, debris or other deleterious material;

17



c. have a maximum particle size of three (3) inches; and


d. contain sufficient clay binder to allow for stable foundation and utility trench

excavations.

12. Compaction of all structural fills should be to at least 90 percent relative compaction except

as specifically stated in other paragraphs in this report. Compaction of import aggregate baserock

materials under proposed asphalt pavements should be to at least 95 percent relative compaction.

Compaction criteria is based on the laboratory procedure ASTM D1557-70(C).

13. The Soil Engineer should be notified at least 48 hours prior to commencement of any

grading operations so that he may coordinate the work in the field with the contractors.

House Foundation Desiw

14. We recommend that a continuous spread footing system be used to support the proposed

one or two story houses constructed on near level cut and fill pads, unless otherwise designated by

the Soil Engineer.

15. An allowable bearing pressure value of 2,500 pounds per square foot should be used to

design the footings.

16. Both interior and exterior drilled footings should be a minimum of twelve (12) inches in

width and should extend a minimum of eighteen (18) inches below the firm soil building pad.

17. All footings should contain horizontal reinforcing bars which extend the length of the

footing and contain at least one #4 steel reinforcing bar near the top and one near the bottom of the

beam.

18



18. Concrete fireplace foundations should be extended at least 18 inches below the compacted

soil building pad. The fireplace base footings should contain horizontal steel reinforcing bars in

both directions and should be structurally tied to the adjacent house foundation.

19. The above recommended footing dimensions and reinforcement are minimums based on

geotechnical considerations. The project structural engineer should verify that these values are

sufficient from a structural engineering viewpoint. The final design of the footings, including

depth, reinforcement and spacing, will depend on the actual building loads and should be

determined by the project structural engineer. The proposed foundation plans should be reviewed

and approved by our office prior to being submitted to the County of Santa Clara for final

approval.

20. The dimensions of the footings should be measured immediately upon completion of

excavating by our representative to insure adequate penetration into the bearing stratum, and to

determine the actual final depth. Immediately prior to concrete placement, the depth and width of

the footings should be remeasured to see that the dimensions have been maintained and that no

sloughing has occurred. If sloughing has occurred, the hole should be re-excavated and

remeasured prior to concrete placement. Our office should be contacted at least 48 hours prior to

the commencement of foundation excavation so that we may be present to periodically observe the

foundation construction.

Concrete Slab-On-Grade Construction

21. Exterior, non-traffic bearing concrete miscellaneous slabs-on-grade, such as sidewalks and

patios, may be founded directly on firm, properly moisture conditioned native soil or on compacted

structural fill, if so desired.

19



22. Concrete slab-on-grade garage floors and driveways should be founded on a minimum of

four ( 4) inches of compacted, import granular base.

23. In living areas, where dampness of floor slabs cannot be tolerated, two alternative moisture

protection methods are recommended:

Alternate I

The concrete floor slab-on-grade should be founded on two inches of clean sand over a plastic

membrane at least six (6) mils thick over a minimum of two inches of imported pea gravel,

bringing the total thickness of imported granular base material under the slab to four inches.

Alterpate II

The concrete floor slab-on-grade should be founded on at least four inches of clean 1/2-inch

maximum diameter washed gravel. No plastic membrane or sand is required for this alternative.

24. Interior concrete slabs-on-grade in Jiving areas should contain as minimum reinforcement:

a.

b.

c.

Structural reinforcing steel bars; or

12 x 12-w2.8 welded wire fabric; or

6 x 6-10/10 wire mesh.

All interior floor slabs in living areas should be structurally tied to adjacent perimeter foundations.

Reinforcement of driveway and garage slabs-on-grade is considered optional. Slabs-on-grade

adjacent to door openings, in the garage area, should be structurally tied to the adjacent foundation.

All construction and expansion joints in all concrete slab-on-grade units should be doweled.

25. Both driveway and garage slabs-on-grade should be divided into four at least (4) to six (6)

approximately equal size sections in order to reduce the potential for shrinkage cracking. This

sectioning may be accomplished by deep scoring, emplacement of expansion joints or other

20



standard techniques. The divisions should be in two directions perpendicular to the edges of the

slabs.

Utilitv Trench Backfill

26. Appropriate procedures for backfilling trenches on-site will vary, depending on the type of

utility line, the depth and location of the trench and the type of material used for backfill. As a

general guideline, trench backfill should be compacted to at least 90 percent relative compaction in

all building and pavement areas and to at least 85 percent compaction in all non-structural areas

such as landscaped areas. All pipes 18 inches or less in diameter should be bedded and shaded

with an approved import sand or gravel to a height of at least six inches over the top of the pipe.

For pipes larger than 18 inches in diameter, the import shading material should extend to at least

the spring line of the pipe. Utility trenches may be backfilled with on-site soils, select granular

import material as defined below, or a combination thereof.

a. On-Sjte Materjals: The on-site native soils are not ideally suited to compaction by

jetting and will therefore require mechanical compaction. If jetting is to be considered, we

should be contacted for specific recommendations related to a jetting procedure. The

backfill should be compacted in lifts, with the appropriate lift thickness being primarily

contingent on the type of compaction equipment used. If hand-compaction equipment is

used, the lifts will likely need to be approximately six inches or less in thickness in order to

achieve adequate compaction.

b. Select Granular Import Material: As an alternative to on-site materials, a relatively

free-draining uniform sand or pea gravel (rounded, washed of fines, 3/8-inch maximum

grain size) may be used for backfilling trenches. These imported granular materials will

likely require significantly less compactive effort than the native soils.

21

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


27. In landscaped areas, granular backfill should be capped by at least two feet of compacted

on-site soil in order to prevent rapid infiltration of irrigation water into the trench. In proposed

asphalt or concrete paved areas, the top 12 inches of trench backfill should be native soil or other

approved soil compacted to not less than 90% relative compaction.

28. In order to prevent ponding or channeling of water, the final grade of all compacted soil

backfill should not be depressed below the surrounding soil grades. A relatively impermeable full

depth cutoff of compacted on-site material should be placed in trenches which pass beneath the

perimeter footings of the buildings to reduce the migration of outside rain or irrigation water

beneath the structures. The cutoff should be approximately four feet long and centered on the

building perimeter. Where underground utility lines pass through the perimeter footings, a

plumbers mastic-type sealant should be placed around the lines.

Surface Drainage

29. In areas where exterior pavements do not abut the buildings, soil should be backfilled

against the exterior foundations in such a manner as to provide a positive gradient away from the

building. This will provide rapid removal of surface water and prevent ponding of such water

adjacent to the foundations. Rain water downspouts should discharge the collected water onto

splash blocks, adjacent paved areas, or be tied into a water-tight drain pipe which carries the water

away from the building areas and towards the street frontage.

30. Panning out of the soil pad to create crawl space under the houses is not recommended

I since this may create a catchment for the accumulation of water beneath the houses.

I I I 22


File No. A9-2085-Sl

Asphalt Pavement Design <City Streets and Private Driveways)


31. Laboratory tests performed on samples of near surface native subgrade soil indicated ail R

Value equal to 52. Due to possible variations in near surface native soils across the site, we have

utilized an R-Value of 35 in the designs presented below:

Aggregate Base Asphaltic

Iraffis;: Ind~ii; Mi;ltroal (in.l CQn~ti; (in)

4.0 4.5 2.0

4.5 4.5 2.5

5.0 4.5 3.0

5.5 6.0 3.0

6.0 7.5 3.0

NOTE: If minimum Santa Clara County regulations require thicker pavement sections than

calculated above, the Santa Clara County minimum thicknesses would govern.

The final 6 inches of soil subgrade should be compacted to not less than 90% relative compaction.

Compaction of aggregate baserock materials under proposed asphalt pavements should be to at

least 95 percent relative compaction. Compaction criteria is based on the laboratory procedure

ASTMD1557-70(C).

23



LIMIT A TIO NS AND UNIFORMITY OF CONDITIONS


1. The recommendations of this report are based upon the assumption that the subsurface conditions do not deviate substantially from those disclosed in the borings. If any variations or undesirable conditions are encountered during construction, or if the proposed construction will differ from that planned at the present time, Applied Soil Mechanics, Inc. should be notified so that supplemental recommendations can be given.

2. This report is issued with the understanding that it is the responsibility of the owner or of his representative to ensure that the information and recommendations presented herein are called to the attention of the project architect and engineers for the project and incorporated into the project plans and specifications, and that the necessary steps are taken to see that the contractor and subcontractors carry out such recommendations in the field.

3. The findings of this report are valid as of the present date. Changes in the conditions of a property can occur with the passage of time, however, whether they be due to natural processes or the works of man, on this or adjacent properties. In addition, changes in applicable or appropriate standards occur, whether they result from legislation or the broadening of knowledge. Accordingly, the findings of this report may be invalidated, wholly or partially, by changes outside of our control. Therefore, this report should not be relied upon after a period of three (3) years without being reviewed by an engineering geologist.

4. This report was prepared upon your request for our services, and in accordance with currently accepted standards of professional engineering geology practice. No warranty as to the contents of this report is intended, and none shall be inferred from the statements or opinions expressed.

5. The scope of our services did not include any environmental assessment or study for the presence or absence of wetlands or hazardous or toxic materials in the soil, surface water, groundwater or air, on or below or around this site. Any statements in this report regarding odors noted or unusual or suspicious items or conditions observed are strictly for the information of our client.

24



REFERENCES CITED


Allen, J.E., 1946, Geology of the San Juan Bautista quadrangle, California: California Division of Mines Bulletin 133, 75 p., 3 plates, 1:62,500 scale.

Berkland, J.O., 1990, Memo to the file 1960-89Z-89S-(D'Arrigo), dated 12-19-90: Santa Clara County Planning Department, 2 p.

Buchanan-Banks, J.M., Pampeyan, E.H., Wagner, H.C., and McCulloch, D.S., 1978, Preliminary map showing recency of faulting in coastal south-central California: U.S. Geological Survey Miscellaneous Field Studies Map MF-910, 5 p., 3 maps, 1:250,000 scale.

Bryant, W.A., 1980, Fault evaluation repon: SE segments of Sargent and Castro faults: California Division of Mines and Geology Fault Evaluation Repon FER-96, 21 p., 11 plates, 1 :24,000 scale.

California Division of Mines and Geology, 1975, Recommended guidelines for determining the maximum credible and the maximum probable earthquakes: California Division of Mines and Geology Note 43, 1 p.

__ 1976, Special studies zones: Mount Madonna quadrangle: 1:24,000 scale.

Dibblee, T.W, Jr., 1973, Preliminary geologic map of the Mt. Madonna quadrangle, Santa Clara and Santa Cruz Counties, California: U.S. Geological Survey Open-File Repon OF 73-59, 1 :24,000 scale.

Dibblee, T.W, Jr., and Brabb, E.E., 1978, Preliminary geologic map of the Watsonville East quadrangle, Santa Cruz, Santa Clara and Monterey Counties, California: U.S. Geological Survey Open-File Repon OF 78-453, 1:24,000 scale.

Hart, E.W., 1988, Fault-rupture hazard zones in California: California Division of Mines and Geology Special Publication 42, 24 p.

Lindsey, W.C., 1974, Soil survey of the eastern Santa Clara area, California: U.S. Depanment of Agriculture, Soil Conservation Service, 90 p.

McLaughlin, R.J., 1971, Geologic map of the Sargent fault zone in the vicinity of Mount Madonna, Santa Clara County, California: U.S. Geological Survey Open-File Report 71-196, 2 sheets, 1: 12,000 scale.

__ , 1973, Geology of the Sargent fault zone in the vicinity of Mount Madonna, Santa Clara and Santa Cruz Counties, California (unpublished M.S. thesis): San Jose State University, San Jose, California, 131 p.

Oppenheimer, D.H., Bakun, W.H., and Lindh, A.G., 1990, Slip partitioning of the Calaveras fault, California, and prospects for future earthquakes: Journal of Geophysical Research, v. 95, no. B6, p. 8483-8498.

25



REFERENCES CITED (continued)


Plafker, George., and Galloway, J.P., eds., 1989, Lessons learned from the Loma Prieta, California earthquake of October 17, 1989: U.S. Geological Survey Circular 1045, 42 p.

Rogers, T. H., and Williams, J.W., 1974, Potential seismic hazards in Santa Clara County, California: California Division of Mines and Geology Special Report 107, 39 p., 6 maps, 1 :62,500 scale.

Shakal, A., Huang, M., Reichle, M., Ventura, C., Cao, R., Sherburne, R., Savage, M., Darragh, R., and Petersen C., 1989, CSMIP strong motion records from the Santa Cruz Mountains (Loma Prieta), California: California Division of Mines and Geology, Office of Strong Motion Studies Report No. OSMS 89-06, 196 p.

Stover, C.W., 1984, Intensity distribution and isoseismal map for the Morgan Hill, California, earthquake of April 24, 1984 in Bennett, J.H., and Sherburne, R.W., eds., The 1984 Morgan Hill, California earthquake: California Division of Mines and Geology Special Publication 68, p. 1-4.

Terratech, Inc., 1989, Preliminary geologic evaluation, Proposed residence, Lands of Bonfante, Santa Clara County, California: unpublished report prepared for Mr. Michael Bonfante, 8 p., 1 plate.

__ , 1987, Preliminary geologic feasibility evaluation, 16 lots, Lands of D'Arrigo, Santa Clara County, California: unpublished report prepared for Mr. Andy D'Arrigo, 5 p.

__ , 1981, Geologic investigation, Tree Haven Restaurant, Santa Clara County, California: unpublished report prepared for Mr. Skip Kover, 8 p., 3 plates.

Williams J.W., and Rogers, T.H. 1973, Environmental geological analysis of the South County Study Area, Santa Clara County, California: California Division of Mines and Geology Preliminary Report 18, 41 p., 2 plates, 1 :24,000 scale.

AERIAL PHOTOGRAPH REFERENCES

U.S. Agricultural Adjustment Administration, 1939, Flight No. CIV, B & W, 1:20,000 scale, flown 10-20, 10-21, 10-22, 10-26-39.

U.S. Department of Agriculture, 1950, Flight No. 8, B & W, 1:20,000 scale, flown 4-18-50.

W. A. C. Corp., 1985, Flight No. WAC-85A, B & W, 1:31,680 scale, flown 4-2, 4-3, 4-12, 4-13-85.

26


• • ' I

File No. A9-2085-Sl

\_. Auams ~n \ . .

October 17. 1989 Revised March 8. 1991

.'·0 / I,. . 'fi. t ,'

Uuas ..

~--·

Contour Interval 20 feet

Base: U.S.G.S. topographic maps of the Mt. Madonna & Watsonville East. California 7.5' Quadrangles

Figure 1 - Location Map 27


File No •. A9.,-2085,.,Sl

1000 0 1000 2000 3000

October 17. 1989 Revised March 8, 1991

, " --. ·~ -·-

6000 7000 FEET

E=E3=a'==<==3::=0E:o:=:o:=:==:==:==:==:==~I KILOMETER

Contour Interval = 20 feet

Figure 2 - Regional Geologic Map

28

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

File No. A9-2085-Sl October 17. 1989

Revised March 8, 1991

Qg

Qal/Qa

Qoa

Qla

Tm

Tm

Tma

Tsh

sp

fag

lg

fa

le

./." . ~ \.•

Q

~70°

~d' /

x / /

x /

/

IBXJ?JLANA TION

Geologic Units

Gravel and sand of stream channels (Holocene)

Alluvium (Holocene)

Older alluvium (Pleistocene)

Landslide dapostts (Quaternary)

Monterey Shale, semi-siliceous (Miocene)

Monterey Shala, clayey to semi-siliceous (Miocene)

Temblor(?) Sandstone (Miocene)

Marine Shale (Paleocene-Eocene)

Sepentinite (Jurassic and Cretaceous)

Franciscan greenstona altered from basaltic agglomerate (Jurassic and Cretaceous)

Franciscan greenstone altered from basalt (Jurassic and Cretaceous)

Franciscan graywacke sandstone, minor micaceous shale or argillite (Jurassic and Cretaceous)

Franciscan varicolored chert (Jurassic and Cretaceous)

Symbols

Contact, dashed where app1oximately located or gradational

Fault, dashed where inferred, dotted where concealed; U is relatively upthrown block, D is relatively downthrown block.

Strike and dip of inclined bedding

Strike and dip of overturned bedding

Strike and dip of vertical bedding

Anticlinal axis, showing direction of dip of limbs and direction of plunge

Synclinal axis, showing direction of dip of limbs and direction of plunge

I Figure 2a- Explanation for Figure 2, Geologic Map 29

October 17, 1989 1 . .,. __ F_i_l_e_N_o_._A_9_-_2_oa_s_-_s_1 ____________________________________________________________________________________ ~--------~--------------R_e_v_1_se_d_Ma __ rc __ h_a_._1_99 __ 1..,

>.

" I Propo~d 3:

.f,0 ~--L-~~~~~%ment --- ~ ~

, ~I

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

. 0 ~o/1' '.'( I

r----') \ .

/ 1" f'!'

CARNADERO FAULT ---APPROXIMATE SCALE IN FEET

AS MAPPED BY DIBBLEE (1973) 0 100 250 500

/.,,-.. ~ ~

Base: MH Engineers, 1990 BO (Original Scale: 1 in =150 It)

Geologic symbols

Contact; dashed where approximately located or gradational

Fault; dashed where inferred, dotted where concealed

Srike and dip of inclined bedding

Strike and dip of overturned bedding

Geology modified from Dibblee (1973) by fieldwork by Applied Soil Mechanics, 1989.

\if'

IEXlPl..ANA 'fKON 1000

' Geologic 1Units

Qa Stream aii!Jvium I

Qt Terrace; depostts

' Tma Temblor(?) Sandstone

I Sp Serpent,inite

lg F . I ranc1scan greenstone I I

le Francisca:i chert

Is FrancisCan sandstone I

~

Proposed Roadway (Typical)

~ecker Pass

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

Symbols '

Approximate location of expiorato4 boring

Approximate location of bulk soil jmple

I ' Approximate location of explorator}' trench ,I

CJ Approximate location of proposed touse

A MW Approximate location of proposed leachfield -, "ff• '4 I ~ Line of Cross-Section I,

)llJ

-N-

Figure 3 - Site Plan and Geologic Map

w ....

- - - - -- - - -' - - - - --1 - - - - - -.,, -· IQ c: ., ID .. ("')

a "' "' V> ID .., ~ -· 0

"'

A z 0 I-

~ 600 UJ _J

UJ~ w ... I- " <(~ 400

l: c x= 0 a: 200 a.. a.. <(

0 (Meah

Sea Level)

Carnadero Fault

? ?

-N 8° w..-

I I J

-2001 .............................. ..,,_ ............................................................................... ....,. .... ... 0 500

Note: Bedding is sch~matic only. Geology from Dibblee (1973), and Applied Soil Mechanics (1989)

1000 1500

Horizon ta I Distance (In Feet) No Vertical Exagg<?ration

IEXJPILANA 'll'ION

2000

Qa Stream alluvium /'~

,,,- Contact; dashed where approximately located or gradational

Qt Terrace depos~s _.,,,, Fault; dashed where inferred, dotted Tms Temblor(?) Sandstone ..,,,,,, where concealed

sp Serpentinite

fc Franciscan chert

.,, -~ ID

:z 0 •

~ I

g .,, I

"' ....

if < -· "' ID 0 Q...,

~i .., ., :::r .... co .... • •


File No. A9-2085-Sl

l.Z l'

SAN ANDREAS· .. FAULT

. .

SAN GREGORIO· .. FAULT~"·.

EXPLANATION • - MAGNITUDE 5.0-5.9

·-MAGNITUDE 6.0 6.9 ·-MAGNITUDE 7.0 7.9 A-MAGNITUDE ? 8.0

.

. .

NTRA COSTA

\ i L

. HAYWAli. D . _:FAV L fi

I

.'-

. ' . . .

"

;d


.. -... _,,/

SAN JOAQUIN

/

r ~·I _; f.

//,-STAN 1lsLAU s

MERCED

/ /

/ FRESNO

" "

'\. '

SAN ANDREA FAULt

J•" ------"',,..._ ____ __JH------"<-~ )£_ CONADA AULT.

Base: From California Division of Mines and Geology Seismic Safety Information (1972). Additional epicenter information from D.H. Oppenheimer, et al, 1990, Toppozada et al, 1981, Real et al, 1978, Bolt and Miller 1975, and Plafker et al 1989

Figure 5 - Epicenter Map

32

SCALE IN MILES

0 8 16

I I I I I I I I I APPENDIX A

I Field Exploration Promm

I Logs ofExploratozy Borings

Log ofExp!oratozy Trench

I I I I I I I I


File No. A9-2085-Sl

FIELD EXPLORATION PROGRAM


The approximate locations of the exploratory borings are illustrated in Figure 3, Site Plan and

Geologic Map. The drilling was accomplished on September 25 and 26, 1989, under the

supervision of the Project Geologist, Lewis Rosenberg. A total of seven exploratory borings were

drilled to depths between 14.5 and 16.0 feet below the existing ground surface.

The borings were drilled with a truck-mounted Mobile B-53 drill rig, using eight-inch diameter

hollow stem auger. As the borings were advanced, relatively undisturbed samples were obtained

at various depths by hammering a standard three-inch diameter (0.D.) split-tube sampler into the

undisturbed soil mass. The hammering system consisted of a 130-pound hammer with a 30-inch

free fall, in order to obtain a blow-count value. A relatively undisturbed soil sample was obtained

from the standard three-inch diameter sampler. Three bulk samples of surficial soils were also

obtained. The borings were left open during the drilling operation to allow groundwater levels to

stabilize. After completion of the drilling, the borings were backfilled with compacted native

materials.

The Logs of the Test Borings, showing the vertical distribution of the soil units, the locations of

the samples, blowcount values and selected laboratory test results are presented in Figures Al

through A7.

As part of the geologic investigation, one exploratory trench was excavated at the location shown

on Figure 3. The trenching was accomplished on October 2, 1989, under the supervision of the

Project Geologist, Lewis Rosenberg. The trench was excavated using a rubber tire John Deere

310 backhoe, with a 30-inch wide bucket to a maximum depth of 18 feet below the existing ground

surface. Materials exposed in the trench walls and floor were logged and are depicted on Figure

A8. After the trench logging was completed, the excavation was backfilled with native materials

and compacted by wheel-rolling the upper few feet

A2


File No. A9-2085-Sl

figure Al - Log of Test Boring No. I

A3


I I I I I I I

Ffle No. A9-2085-Sl

""'" ....... .• ... -flET -•

2 • 2-1 75+

4 • 2-2 60

6 • 2-3 90+

• I . 8.

I I I I I I I I I

IO •

2-4 80+

.12 •

14 •

16 80+


Drilled 9-25 & 9-26-89 by JES & LR

Very fine Sandy SILT with fine angular gravels, Light brown, damp, hard

Silty SAND with angular fragments of weathered muds tone, approx. 111

• Dark yellowish brown, damp, dense

Increasing gravel content and size (!")

Clayey SANO with angular fragments of weathered mudstone (!") Wet at 11.5 feet

Mudstone is smaller (1/4"), more weathered

Boring terminated at 16.5 feet

No groundwater encountered

Pl-PL.&Cf

... Dl:•SITl'

O&l

115

113

122

125

117

... ..... -WIT .........

7.5

10.2

10.4

11.7

13.1

I Figure AZ - Log of Test Boring No. 2

I A4


file No. A9-2085-Sl

IV'TH

IN

m:r

SAMPLE LOG 8 P.,.~ NO. UXA TION "nil._

"' .........

" 0

.... - .... N,;• ,,, 3-1 '- .".\/ 35

2 • g ~;~ ~t~~ }ii·

October 17. 1989 Revised March 8, 1991

DDCltlPT IC*

Drilled 9-25 & 9-26-89 by JEB & LR

Elevation 335'

Very fine Sandy SILT with fine (3/4") gravel Moderate brown, slightly damp, very stiff

IN- PLACE

lllY DENSITY ... ..

105 10.1

-------------Drills hard in gravels

6 •

3-3 8 •

I. 10 • 3-4

• 12 •

• 14 •

• 16 •

'

• 18 •

• 20

80+ Silty SANDY with angular weathered mudstone fragments (1-'>"). Moderate brown, moist very dense

feet. Drills near

Gravel ls finer (i,"), subrounded

Wet at 12 feet

Clayey matrix

Boring terminated at 20 feet


figure A3 - Log of Test Soring No. 3

AS

122 11.1

83 8.8

122 9.8


file No. A9-2085-Sl

ll!J'T H SAMPLE LOG a •• NO. l.OCATION ....-..

•UT ....... "'-'"

0 •

2 • 4-1 24

4 •

• 6 • 4-2 75+

8 •

IO 4-3 50

• 12 •

• 14 •

• 4-4 0/SJ," • 16 •

• 18 •


IN- PL ACE

CDatlPTIOfll ... y MOISTUM

O[lllSIT't' C<»tTl!:WT

Drilled 9·25 & 9-26-89 by JEB & LR ~·· '%.*Y wt

Elevation 342'

Fine sandy SILT, moderate brown, damp, very 102 12.2 stiff

--------- -Silty fine-medium SAND with angular mudstone fragments (!"). Moderate yellowish-brown, damp, dense

112 8.5

-------- ---Mudstone, grades finer ('4"), matrix is clayey, 112 8.3 wet

Gravel

Subrounded, coarse (3/4 11 -l-~") GRAVEL with clay. Moderate yellowish-brown, wet, dense

82 10.0

Groundwater stabi.l ized at 17 feet .5L

Coarse, well-cemented SANDSTONE • Pale yellowish orange, moist, very dense. Drills very hard


figure A4 - Log of Test Boring No. 4

A6


File No. A9-2085-Sl

"""" SMIPLE LOO • '" NO. -·- ....-

"'"'' "" ..-.. "-'"

0 :m

2 5-1 60

4

•

6 5-2 80+

8

10 • 5-3

• 12 •

• 14 •

5-4 • 16 •

• 18.

• 20 • 5-5

• 22 •

• 24 •


Drilled 9-25 & 9-26-89 by JEB & LR

Elevation 348'

Fine Sandy SILT, moderate brown, damp, hard

with fine I," muds tone fragments

Sub rounded coarse GRAVEL { 1-Y,"), average (3/4"-3") with Sand. Dark yellowish-brown, fresh surface, moist, very dense Hard drilling from llY,-13

Elongate, subrounded Sandstone { 2-4") COBBLES with Sand

Medium-coarse grained, with cemented, moderately weathered SANDSTONE. Pale yellowish-orange, very moist

Drill met refusal on dense SANDSTONE



IN- PLACE

DllY MOISTUM:

MNllTY ....

98

114

CONTENT "',,., ...

7.4

8.4

No Reco ry 92 15.8

No Reco ry

119 14.9

Figure AS - Log of Test Boring No. 5

A7


File No. A9-2085-Sl

"""" SMllPLE LOG I .... •• NO . 1.DCATION ...._ .... "' ........ ..._,tt

0 •

~~\\ ;:f; ''" ::i~ .;::: <·=·

• .:·.'.-:

2 •

6-1 0/5'>"

4 •

6-2 50/6" 6 •

8 •

IO.

6-3 75

• 12.

• 14.

• 16 • 6-4 50/6"

• 18.

• 20.


IH- PLACE

ouatl''''* .. , MOIST UC

O(JllSITY CONT£11fT

Drilled 9-25 & 9-26-89 by JES & LR lt-C.I. %*' ...

Elevation 328'

Fine Sandy SILT. Light brown, slightly damp, very stiff

Silty SAND with angular Sandstone fragments. 90 7.7 Moderate brown, damp, very dense

----------Sandstone COBBLES & coarse GRAVEL with clay binder 105 10.3 Moderate yellowish-brown, moist, very dense

Fine gravelly CLAY. Moderate yellowish-brown, very moist, hard 120 10.3

Gravel grades moister Silty fine SANO - - -Moderate yellowish-brown, wet, dense

119 15.1

----------Silty coarse GRAVEL with well-sorted SAND. Moderate yellowish-brown, moist, dense



Figure A6 - Log of Test Boring No. 6

A8


File No. A9-2085-Sl October 17, 1989


EEPTH

•• •UT

0.

- • . 2 •

• • . 4 •

. .

. 6 •

I. . . 8 •

I. . lo 10 •

I. . • 12 •

. . • 14 •

. . • 16 . . . • 18 . . . • 20 . . . . . . . . . . . . . . . . .

SIMPLE LOG a NO. 1.DCATION .... ..._

"" MWU ...._,ft Drilled 9-25 & 9-26-89 by JEB & LR

Elevation 320 '

Fine Sandy SILT. Light brown, damp, very stiff

~----------Silty fine to coarse (3/4") GRAVEL with fine Sand • Moderate yellowish-brown, damp, dense

Clayey SILT with fine (!.'') gravel

·,-;,-A,-

. rt::·~~ 7-3 68

7-4

~~ft-- '------------.~~~· Silty coarse subrounded GRAVEL (l") and Sandstone .~i~ L- _. ~ _CQ.Bfil.ES._ Mo~ra~ _.lell£wish-brown, moist, dense

;{:/,.:•,; Fine Sandy coarse GRAVEL (l") with Silt ii;·:':::\ Moderate yellowish-brown, moist, dense

LJ[~·'.:'

i;ff&t ,. .. · ..... ·'·. ~ If- -1 Me\ljum grainea 01muo1unt, well-cemented, pale

yel owish-oranoe ffresh surfacel



Figure A7 - Log of Test Boring No. 7

A9

IN- PLACE

DOT

MNSITY p.c.t.

103

102

103

117

lllOISTUllC

CONTlJfT .,...., ...

8.0

15.9

8.0

13

I File No. A9-2085-Sl

0 I

EXPLORATORY TRENCH ET-1 ~ N1'SW

25 50 75 I I I

345- . -~~~~~·~~~·~::~:~·2~~-~-~:~:~~;;,;:;-~ ~~.)~.:·_i;:~~·~·L·~;_-.~~:.~~.;~··:·~ .. ~:;~}/:·.:.\:;·: : :.·:~ ·_.·: :·.: .... : ; ... ~: :.:·::· .. ::· .. ··::- ~: :_@:<:_:_.-.·:·::·~i;.;~. · · .. ~ :··.· . . • •. 0 · 0 ·a·"-.)· O· •. ··· · ·. OO•_o·.·.·o··,.'·-~.· ~ 0_ •• -:--": ·•.:.-:----------.-:;~- ..... _:.:.,,,:.;...'( - • .-.-:..+--

O~ -.~o · . . &>_._.¢,0·. ·t:J····o.':---/. o ~-O·..,. ··.t:::::J ~o-· ....... · •..•. o .. •.· , O '" O . •, · 0 • · ~ e . · c::;IO 0 . .· 0 ~ " • G , ' . . 0 '0 0 . · · . . · · 0 O . • ' . 'Qll. · ,. • • 04' 00

. . . , . . . '--.I.. . o·. . ""--J"' . .. o C>• • · .. - • • • o ... o• •: ··." ... ·. c::>'. . ·. ~o ... · ·1 .O• "'· o ~.: " . . .,. - - - • - • -- . t:J . • • • • • "° - - o • - • • • • . . ~ . c tS\ . . . : . I . . . <.__I. •. 340-

"°''°e>.-_G18°oo 00_ o:····· .. o · ·o,. · .• ·.· .. ·· · t1> •• 0 -c-~~~-·: .. ··.. · \Ql 0 • .. c:::.· o .. · ·.·.

~ _oo .. b @··. ·.·. • a· ,oo~·-@ ~ .. :-0· ·a ·"'-.,...-> ... o c::>.... • . . I· . ~-.o . . · •. . o •. ·. O .· . . o,o : # . . 00 . . o , . 0 . . . .. O . ~ . . . . . • .. er • •O: • · .... ~. "'o •o.o ..

. . . . . . 0 . . . . . 6 0 . 0 '(II • . .•

, ~ • 0 . ' • •. - o • - Ac:::::=.• - ... 0 ·- • ·.' • .0 .I

335-o .. • c;;:> • C:I. • • o,. • ·o •. - o . . . . _,o,.· .;::"':_:o:..:,• ..;,;; ·~I _·_:.,_.;...;.-'---• o .. , . O.o o , ·

· .. · •o oo ·

I' I

330-

EXPIAllATIOll OF mns

A Sandy SILT: About 65S non-plastic fines, about 35S very fine Sancl.

B

Low dry strength, .,ist, light brown. Rootlets present, excavates easily. Geologic Interpretation: Topsoil

COBBLES ancl BOULDERS with SILTY GRAVEL and SAllD Total sa,,.,le (by vol.-): about 30S 3-5 inch hard, subrounded cobbles; about 20S 5-12 inch, hard subrounded cobbles; about 51 hard, subrounded boulders, llilXi- dimension 24 inches; about 451 minus 3 Inch fraction; about 501 hard, subrounded, coarse to fine gravel; about 30S coaese to fine, hard, subangular sand; about 20S non-plastic fines. Crude bedding of gravels. Gravels show moderate llll!athering with clay filllS. In-place conditions: Moist to very .,!st, dark yellowish-brown, excavates with little difficulty. Geologic interpretation: Old Alluvi•

SCALE: 1"=14'

345-

340-

335 -

330-

100 I

Ir

I \.

125 I

October 17. 1989 Revised March s. 1991

-345

-340

-335

-330

ooo

O• 00 0 .. . . ...

!, Figure A8 - Log of Exploratory Trench 1 ,


APPENDIXB

Descriptions of Laboratory Test Procedures

Laboratory Test Results



DESCRIPTION OF TEST PROCEDURES

The following laboratory tests were performed on selected samples of the various soil strata

encountered in the exploratory borings, to determine pertinent physical and index properties. The

testing program was selected on the basis of the probable final design requirements, and correlated

to the site subsoil profile, as determined by the logs of the borings and the site geology. A short

general description of the tests performed, including a brief discussion of the purpose of each test,

is given as follows:

A.

B.

c.

D.

Moisture-Density CASTM D2937l: Conducted on undisturbed soil samples, to determine their in-situ moisture contents and dry unit weights. These tests aids in determining general soil conditions and properties. See the Logs of the Test Borings (Appendix A), and Table I (Appendix B).

Direct Shear CASTM D308Q): Conducted on a undisturbed soil sample, and a disturbed, bag soil sample, remolded to approximately 90% relative compaction at approximately optimum water content, to determine the sample's in-situ and remolded unit cohesion and angle of internal friction. This test provides soil shear strength values, which aid in determining such design criteria as bearing capacities and lateral earth pressures. See Table I (Appendix B).

Atterber~ Limits CASTM D424-7D: Conducted on a undisturbed soil sample, to determine its in-situ liquid limit and plastic index values. This test provides water content values for the sample's liquid and plastic phases. The test aids in determining the expansive characteristics of the soil tested. See Table II (Appendix B).

Compaction Curve CASTM D 1557-70 CA)): Conducted on a disturbed, bag soil sample, to determine its maximum dry density and optimum water content, based upon a standard compactive effort. See Figure Bl (Appendix B).

B2

I File No. A9-2085-S 1 October 17, 1989

I Revised March 8, 1991

I TABLE I

I Summazy of Moisture-Density & Direct Shear Results

Sample l&pth In-Place Condjtions Direct Shear Testini:

I Moisture Dry Internal Content Density Friction Cohesion

No. feet (%dry wt.) (p.c.f.) (degrees) (p.s.f.)

I 1-1 2.5 8.7 105

I 1-2 4.0 13.9 113 1-3 5.5 17.0 112 1-4 11.0 15.8 115 1-5 16.0 16.5 115

I 2-1 2.0 7.5 115 2-2 4.0 10.2 113

I 2-3 6.0 10.4 122 2-4 11.0 11.7 125 2-5 16.0 13.1 117

I 3-1 1.5 10.1 105 3-2 4.0 11.1 122 3-3 7.0 8.8 83

I 3-4 11.0 9.8 122

100 4-1 2.0 12.2 102 30

I 4-2 6.0 8.5 112 4-3 10.5 8.3 112 4-4 15.0 10.0 82

I 5-1 2.0 7.4 98 5-2 6.0 8.4 114 5-3 10.0 15.8 92

I 5-5 20.5 14.9 119

6-1 2.5 90 7.7

I 6-2 5.5 10.3 105 6-3 11.5 10.3 120 6-4 15.5 15.1 119

I 7-1 1.5 8.0 103 33 700 7-2 6.0 15.9 102 7-3 11.0 8.0 103

I 7-4 16.0 13.0 117

I I B3


File No. A9-2085-Sl

Sample No.

2-1

5-1

Depth ft.

2.0

2.0

TABLE II


Summazy of Laboratozy Atterber~ Ljmjts Test Results

Description of Soil

Native: Brown silty SAND with gravel

Natiye: Brown sandy SILT with gravel

B4

Anerber~ Limits Liquid Plasticity Limit Index

% CP.I.l

21

25

3

8


File No. A9-2085-Sl

" •, --October 17, 1989


130 __ _

.....

...: 125 u ci ...... >. -"in 120 c ., 0

>. ... 0 115

8 9 10 11 12 13 14

Moisture Content - (% of Dry Weight)

Sample : B, (1 foot depth)

Description : Medium brown sandy silt with gravel

Laboratory Test Procedure ASTM D1557-70(C)

Maximum Dry Density : 124.2 pcf

Optimum Moisture Content 10. 9%

Figure Bl - Laboratory Compaction Test Results -85

I I I I I I I I I APPENDIXC

I Genera] Grad.in g Specifications

I I I I I I I I I

I I


I GENERAL GRADING SPECIFICATIONS

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

FOR:

1.

Proposed Lands of D'Arrigo 18-Lot Residential Development on 283 Acres Hecker Pass Road at Watsonville Road Santa Clara County, California

Limitations

1.1 The following information is of a general nature and is intended for use only in conjunction with the site-specific information contained within the main body of the soil investigation of which it is a part. The report should be reviewed in its entirety prior to implementation of these specifications.

1.2 These specifications concern clearing, grubbing and general soil preparations; spreading, compaction and control of fill operations; and subsidiary work necessary to complete grading to conform within the lines, grades and slopes as shown on the accepted plans.

1.3 In the event that any conditions not covered in this report are encountered during grading operations, the Soil Engineer (see Item 2.1) shall be immediately notified for directions.

2. Field Observation and Testing

2.1 Applied Soil Mechanics, Inc., hereafter referred to as the Soil Engineer, should be consulted prior to commencement of any work involving these specifications. Verification of compliance by the Soil Engineer requires observation and testing services which must be conducted contemporaneously with the associated construction operations. The Soil Engineer shall be notified at least forty-eight ( 48) hours in advance of any clearing or grading operations on the site.

3. Laboratory Tests

3 .1 Compaction specifications contained in this report are based upon the maximum density and optimum moisture content of the material. The laboratory test used to define these soil properties is ASTM Test Procedure No. D1557-70. Minimum densities allowable during compaction control are expressed as a percentage of the maximum density value ("% relative compaction").

4. Site Clearing and Demolition

4.1 All abandoned buildings and foundations, trees (except those specified to remain for landscaping purposes), fences, weeds and miscellaneous surface debris shall be removed, piled or otherwise disposed of to an extent that the areas proposed for development have a neat appearance and are suitable for grading.

C2



4.2 All abandoned septic tanks, and any other subsurface structures existing in proposed development areas, shall be removed prior to any grading or fill operations. All appurtenant drain fields and other connecting lines must also be totally removed.

4. 3 All abandoned underground irrigation or pipeline shall be removed or demolished. The appropriate final disposition of such lines shall depend upon their depth and location, and the method of removal or demolition shall be determined by field observation by the Soil Engineer. One of the following methods will be used.

4. 3.1 Excavate and totally remove the pipeline from the trench.

4. 3.2 Excavate and crush the pipeline in the trench.

4.3.3 Cap the ends of the line with concrete to prevent entrance of water. The locations at which the utility line shall be capped will be determined by the Soil Engineer. The length of the cap shall not be Jess than five feet, and the concrete mix employed shall have a minimum shrinkage.

4.4 All abandoned water wells shall be capped and sealed in accordance with the requirements of the appropriate government agency. The strength of the cap shall be at least equal to the adjacent soil. The final elevation of the top of the well casing must be a minimum of 36-inches below the lowest adjacent grade existing after grading or fill operations. In no case shall building foundations be placed over the capped well.

4.5 Unless otherwise approved by the Soil Engineer, all excavations and depressions created during site clearing and demolition operations shall be left open with bottoms consisting of undisturbed native soil. For safety purposes, sidewalls may be ramped outward from the excavations. During grading operations, all such excavations or depressions will be backfilled according to specifications determined as appropriate by the Soil Engineer for their location and depth.

5. Rough Grading

5.1 All organically contaminated soil shall be stripped and removed from the ground surface upon which foundations, structural fill or pavement sections are to be placed.

5. 2 The undisturbed natural ground surface exposed by the organic stripping, shall be plowed or scarified until the surface is free of ruts, hummocks or other uneven features which may inhibit uniform soil compaction. The ground surface should then be disced or bladed until it is uniform in texture and free from large clods.

5.3 Upon completion of Items 5.1 and 5.2, the ground surface shall be ready for moisture conditioning and compaction.

5 .4 Reference should be made to the Recommendations section of this report for the required depths of organic stripping and scarification, proper moisture conditioning, and allowable values of relative compaction.

C3



6. Fill Materials


6.1 The materials for engineered fill shall be approved by the Soil Engineer before commencement of grading operations. Any imported material must be approved for use before being brought to the site. The materials used shall be free from vegetable matter and other deleterious material. Refer to the Recommendations section of this report for minimum quality standards for fill material.

7. Fill Construction

7 .1 The approved fill materials shall be placed in layers no thicker than will permit adequate bonding and compaction. Each layer shall be spread evenly and shall be thoroughly blade mixed during the spreading to insure uniformity of material in each layer.

7.2 Fill material approved for certain purposes may include rock. No rocks will be allowed to nest, and all voids shall be filled and properly compacted. No rocks larger than three inches in diameter will be permitted in the fill unless approved in writing by the Soil Engineer

7 .3 When the moisture content of the fill is .b:!llillY. that specified by the Soil Engineer, water shall be added until the moisture content is as specified to assure thorough bonding during the compaction process.

7.4 When the moisture content of the fill is ~ that specified by the Soil Engineer, the fill material shall be aerated by blading or other satisfactory methods until the moisture content is as specified.

7 .5 After each layer has been placed, mixed, and spread evenly, it shall be thoroughly compacted to the specified density.

7. 6 Compaction shall be by sheepsfoot roller or other types of acceptable compacting rollers. Rollers shall be of such design that they will be able to compact the fill to the specified relative compaction within the specified moisture content range. Rolling of each layer shall be continuous over its entire area until the required minimum density has been obtained.

7. 7 Field density tests shall be made by the Soil Engineer during compaction operations. Where sheepsfoot-type rollers are used, the soil may be disturbed to a depth of several inches. Density tests shall be taken in compacted material below the disturbed surface. When these tests indicate that the density of any layer of fill or portion thereof is below the required relative compaction, the particular layer or portion thereof shall be reworked until the relative density has been obtained.

7. 8 The fill operation shall be continued in compacted layers as specified above until the fill has been brought to the finished slopes and grades as shown on the accepted plans.

7. 9 All earth moving and working operations shall be controlled to prevent water from running into excavated areas. All excess water shall be promptly removed and the site kept dry.

7 .10 Observations by the Soil Engineer shall be made during the fill and compaction operations to an extent sufficient to determined that the fill was constructed in accordance with the specifications of this report.

C4


File No. A9-2085-Sl

8. Seasonal Llmjts


8.1 Fill material shall not be placed, spread or rolled while it is at an unsuitably high moisture content or during unfavorable weather conditions. When the work is interrupted by heavy rain, fill operations shall not be resumed until field tests performed by the Soil Engineer indicate that the moisture conditions in areas to be filled are as previously specified.

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age.~cy department of cohservation fax (415) 904-7715 · 3/8/1991 · state of california - the...

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