567 El Camino Real Crestwood Drive...Jul 31, 1978 · Orinda, California 94563 Re: Engineering...

!ATE OF CALIFORNIA-THE RESOURCES AGENCY

DEPARTMENT OF CONSERVATION

DIVISION OF MINES AND GEOLOGY DIVISION HEADQUARTERS RESOURCES BUILDING, ROOM 1341

1416 NINTH STREET SACRAMENTO, CA 95814

District Offices: LOS ANGELES SACRAMENTO

Junipero Serra Bldg., Rm. 1065 107 South Broadwoy

Resources Bldg,, Rm. 118 1416 Ninth Street

90012 9581.4

February 16, 1979

Hr. Kenneth Niemczyk City of San Bruno Planning Division 567 EL CAMINO REAL San Bruno, CA 94066

Dear Hr. Niemczyk:

SAN FRANCISCO

Ferry Building 94111

RONALD REAGAN, Governor

We are placing on open file the following report, reviewed and approved by the City of San Bruno In compliance with the AlqulstPrlolo Special Studies Zones Act:

Engineering geologic study for proposed restaurant on Crestwood Drive, San Bruno, CA; by J.C. Prendergast; July 31, 1978; with supplement of December 12, 1978.

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cc: A-P file~

Sincerely yours,

c;;/ ,;f ,;:/~vff-

EARL W. HART Office of the State Geologist CEG 935

~ttp of ~an J/iruno

DEPARTMENT OF PLANNING ANO BUILDING

State Geologist Division of Mines and Geology Department of Conservation Resources Building, Room 1341 1416 Ninth Street Sacramento, California 95814

To the State Geologist:

567 EL CAMINO REAL, SAN BRUNO, CALIFORNIA 94066

(415) 583-3083 {415) 589-8357

February 13, 1979

Pursuant to the Alquist-Priolo Special Studies Zones Act, please find the following enclosed materials for your open files:

v 1. Engineering Geologic Study for Proposed Restaurant on Crestwood Drive, San Bruno, California dated July 31, 1978.

v' 2. Preliminary Geotechnical Report for a New Restaurant, Assessor's Parcel 017-245-090, Crestwood Drive, San Bruno, California dated December 12, 1978.

3- Review of Engineering Geologic Study by Earth Systems Consultants for the City of San Bruno, dated September 8, 1978.

4. Review of Preliminary Geotechnical Report by Earth Systems Consultants for the City of San Bruno dated January 26, 1979-

Regards, CITY OF SAN BRUNO Juan A. Garcia Director of Planning and Building

~~ Kenneth Niemczyk, Associate Planner Planning Division

KN: jan

enc ls.

RECEIVED BY

GEOTECHNICAL ENGINEERING • ENGINEERING GEOLOGY o ENVIRONMENTAL GEOLOGY

File No. C8-0758-Cl January 26, 1979

City of San Bruno 567 El Camino Real San Bruno, California 94066

Attention: Mr. Kenneth Niemczyk, Associate Planner

Subject: Proposed Restaurant Building Site Crestwood Drive San Bruno, California REVIEW DF PRELIMINARY GEOTECHNICAL REPORT

Gentlemen:

In response to your letter of December 29, 1978, and your verbal authorization of January 16, 1979, we have reviewed the "Preliminary Geotechnical Report for a New Restaurant," by Diablo Soil Engineers, dated December 12, 1978. This review supplements our earlier review of September 8, 1978, of the "Engineering Geologic Stu~y" by JCP - GEOLOGISTS, dated July 31, 1978.

The Preliminary Geotechnical Report by Diablo Soil Engineers has provided sufficient clarification of the items listed in our initial review letter, so that in our opinion, the tworeporj:s together comply with the guidelines of the Alquist-Priolo Act of 1972. - - ------

In reviewing the report by Diablo Soil Engineers, we contacted discuss certain statements and recommendations in his report. that the following items be brought to your attention:

Mr. Volin to He suggested

- On page 4, the reference to Figure 2 should read Figure 2a. The statement that " ... the gully appears to have eroded because of uncontrolled runoff which will need to be corrected" should be re-emphasized as a recommendation dealing with site grading and drainage.

- On page 7, item 3d. is intended to apply only to foundation elements on the slope; and item 3e. applies only to foundation elements on level ground.

1900 Embarcadero Road • Suite 200 • Palo Alto • California • 94303 • (415) 321"6750

File No. C8-0758-C1 January 26, 1979

To assure implementation of the recommendations contained in the "Preliminary Geotechnical Report," it is suggested that the Soil Engineer be retained to review the site grading and drainage plan, and the building foundation plans. In addition, the Soi1 Engineer should observe the site grading, foundation installation, and the final site drainage facilities.

We trust the foregoing provides the necessary information requested by the City. Shou1d you have any additional questions, please contact our office.

Very truly yours,

EARJH SYSTEMS CONSULTANTS "'.··7 / /> 1 /y/ .. ·;/ 7,/

v fV",L, ,,< i».!Jf./._;_ Phili;~ Burkland, E.G. 513

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Copies: 3 to City of San Bruno 1 to Diablo Soil Engineers

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File No. C8-0758-Cl September 8, 1978

City of San Bruno 567 El Camino Real San Bruno, California 94066

Attention: Mr. Kenneth Niemczyk Associate Planner

SPECIALISTS IN THE APPLIED EARTH SCIENCES

Subject: Proposed Restaurant Building Site Crestwood Drive San Bruno, California REVIEW OF ENGINEERING GEOLOGIC STUDY

Gentlemen:

In response to your letter dated August 24, 1978, we have completed our review of the "Engineering Geologic Study for Proposed Restaurant on Crestwood Drive, San Bruno, California" by JCP-GEOLOGISTS, dated July 31 ' 1978.

The purpose of the review is to determine general consistency with the guidelines and requirements for engineering geologic studies for projects located within a special studies zone as determined by the California Division of Mines and Geology, pursuant to the requirements of the Alquist-Priolo Geologic Hazard Zones Act of 1972. As part of our review, we have made a brief inspection of the property, discussed the geologic report with Mr. Prendergast, and reviewed the basic references listed in the Bibliography (Appendix A) of his report.

In our opinion, the JCP-GEOLOGISTS report is generally consistent with the guidelines established by the California Division of Mines and Geology for Geologic/Seismic reports for projects located within the special studies zones (reference: CDMG Notes 37 and 49). The report appears to be consistent with current standards of geologic practice. We concur with the principal findings of the JCP report: namely that the site is suitable for the planned development; that the probability of fault rupture at the site is low; that minor lurch cracking and/or localized landsliding or sloughing

1900 Embarcadero Road • Suite 200 • Palo Alto • California • 94303 • (415) 321-6750

File No. C8-0758-Cl September 8, 1978 Page 2

may occur in the surface soils (and/or fills) on the steep slopes; and that the site will be subjected to strong seismic shaking in the event of a future Bay Area earthquake. There are, however, some items in the report which should be clarified either now or as part of a subsequent soil and foundation investigation.

1. Paragraph 3, page 2 of the JCP report states that the proposed restaurant building location is shown on Figure 4. Figure 4 of the report, however, shows only the property lines and does not indicate the location of the proposed restaurant structure. ·

2. On page 8 of the report, the second paragraph under the heading of Conclusions and Recommendations ends with the statement "however, such movements are not expected to have an effect on the planned development". Without specific information regarding the location of the proposed building, there is no way to determine the basis for that statement. It should be clarified.

3 •. At the bottom of page 8, the report recommends the use of "seismic criteria contained in the currently adopted Uniform Building Code (Pseudo-static Forces equal to l.2g)". It is assumed that the recommendation implies the use of the 1976 Building Code with respect to lateral force requirements. The reference to 1.2g is unclear and perhaps refers to a lateral force equal to 1.2 x the vertical weight of the building. This item should also be clarified.

4. Figures 4 and 5 of the report, the site plan and cross-section, respectively, indicate the presence of fill along the easterly slope, but the contact between the fill and the natural ground is shown as approximate and questionable. In our opinion, the distribution, thickness, and characteristics of the fill materials are essential to determining the stability of the fills, and hence their influence on the proposed project.

It is recommended that further investigation at the site be conducted to more precisely define the limits of fill, its thickness and engineering characteristics; its possible influence on the proposed foundation conditions; and its performance characteristics under seismic shaking. These items can all be determined as part of a soil and foundation investigation which is recommended in the JCP report and which we also recommend.

It is. suggested that, at the time of the soil investigation, the engineering geologist review the subsurface conditions as determined from test borings, backhoe pits or trenches, and submit a supplementary report which accurately defines the limits of fill. An analvsis or evaluation of the stability of the fill, particularly during seismic shaking, should be made by either the engineering geologist or the soil engineer, prior to construction at the site. The possible

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• File No. C8-0758-Cl September 8, 1978 Page 3

adverse effect of surface erosion and lurching within the fills should also be discussed.

We trust the foregoing review provides the necessary information requested by the City. If you have any questions, please contact our office.

Very truly yours,

EA~ SYSTEMS CONSULTANTS

~J~ (J 4-~~/0 PhilipN. Burkland, E.G. 513

sfr

Copies: 3 to City of San Bruno 1 to JCP-GEOLOGISTS

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• ENGINEERING GEOLOGIC STUDY

• FOR PROPOSED RESTAURANT

ON CRESTWOOD DRIVE,

SAN BRUNO, CALIFORNIA

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JCP - GEOLOGISTS CONSULTING ENGINEERING GEOLOGISTS

7246 SHARON PR., SUITE lOS SAN JOSE, CA 9S12'l

(408) 446-4400

July 31, 1978

e Project No. JCP-359

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Mr. Herb Volin Diablo Soils 122 Camino Pablo Orinda, California 94563

Re: Engineering Geologic Study for proposed Restaurant, San Bruno, California. APN: 17-245-9

e Dear Mr. Volin:

As requested by you, we have conducted an engineering geologic study for the above referenced site. The accompanying report presents the results of our field and office studies and related analyses. The geologic and seismic conditions are discussed and appropriate

e conclusions and recommendations are presented.

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Based on our studies, we conclude that from an engineering geologic standpoint, the site is suitable for the proposed development.

We refer you to the text of the report for a detailed discussion of our findings. If you have any questions concerning our findings, please call.

JCP:cs Copies: Addressee (6)

Very truly yours,

~ James C. Prend~t President

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ENGINEERING GEOLOGIC STUDY

For:

PROPOSED RESTAURANT BUILDING, SAN BRUNO, CALIFORNIA

To:

MR. HERB VOLIN DIABLO SOILS 122 CAMINO PABLO ORINDA, CALIFORNIA 94563

JULY 1978

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TABLE OF CONTENTS

Letter of Transmittal

TITLE PAGE

TABLE OF CONTENTS

INTRODUCTION

PROPOSED CONSTRUCTION

SCOPE

SITE INVESTIGATION

A. - SITE DESCRIPTION

B. - GEOLOGY

C. - SEISMICITY

EARTHQUAKE RISK

CONCLUSIONS AND RECOMMENDATIONS

LIMITATIONS

Figure 1 - Location Map Figure 2 - Regional Geologic Map Figure 3 - Area Geologic Map Figure 4 - Site Plan and Geologic Map Figure 5 - Geologic Cross Section

APPENDIX A - BIBLIOGRAPHY

APPENDIX B - DRAINAGE AND MAINTENANCE GUIDELINES

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ENGINEERING GEOLOGIC STUDY

FOR PROPOSED

RESTAURANT BUILDING,

SAN BRUNO, CALIFORNIA

INTRODUCTION

In this report we present the results of our engineering geologic studies performed for the referenced site on Crestwood Drive, San Bruno, California, as shown on the attached Location Map, Figure 1.

The purpose of this study was to evaluate the geologic conditions and to analyze the effect of these conditions on the site and the proposed development. More specifically, the study was directed toward evaluating any potential geologic hazards, including the location of possible fault traces (Sierra Fault) or landslides in the vicinity of the studied property •

PROPOSED CONSTRUCTION

It is our understanding that the proposed restaurant building will be a one or two story, wood-frame structure located as indicated in Figure 4. Portions of the studied site have been developed in the past as evidenced by the existing level parking area and the existance of fills on the east facing slope. Minor grading will be performed to clear and regrade the site for the planned development.

SCOPE

The scope of work consisted of a detailed site reconnaissance by the engineering geologist; the performance of geologic interpretation of aerial photographs; a geotechnical literature search, interpretation of the geologic and seismic conditions and the preparation of this report. A bibliography is inoluded herein; it cites the geologic reference materials used in this report.

SITE INVESTIGATION

A detailed geologic reconnaissance was performed at the site on July 25, 1978 by James C. Prendergast (E.G. 955) and a geologic map was developed. Due to the topography of the site area, the soil exposures just northwest of the site and existing geologic information, it is in our opinion, unnecessary to perform subsurface exploration in an effort to locate fault traces .

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A. - SITE DESCRIPTION

The irregularly shaped, partially developed site is located between Crestwood Drive and Junipero Serra Blvd. (Route 280) as shown on Figures l and 4. Structures do not exist on the studied property.

The studied property encompasses part of the nose, and northeastern and western flanks of a small, north-trending ridge. The top of the ridge on the property has been leveled in the past, and is presently paved with asphalt concrete, and is used as a parking area. From the paved area, the property slopes down to interstate highway 280 at an inclination of approximately 1.8:1 (horizontal to vertical), and down to Crestwood Drive at an inclination of about 2:1. The nose of the ridge steepens north of the property and continues downward toward highway 280 at an inclination of 3:1. All slopes are covered with tall, dry grass.

An erosion gully, incised t6 a maximum depth of 8 feet, is located along the northern property on the slope adjacent to Highway 280. This gully was apparently caused by water overflowing the paved area due to a plugged drain (See Figure 4).

B. - GEOLOGY

The area studied lies within the San Francisco Bay Region which is bounded by mountain ranges of the Coast Range Geomorphic Province as shown on the attached Regional Geologic Map, Figure 2. The subject site is located within an Alquist-Priolo Special Study Zone in the eastern-most foothills of the Central Santa Cruz Mountains approximately 2300 feet northwest of the intersection of Freeway 380 and Freeway 280. Bedrock formations mapped on and in the immediate vicinity of the site are the Merced Formation (QTm) and artificial fill (Qaf).

The Merced Formation materials were observed on the slopes immediately northeast of the site and in an erosional gully cut into the east-facing slope of the subject site. The Merced Formation consists of sandstone, siltstone, and claystone with minor amounts of conglomerate and volcanic ash. The materials observed in the erosional gully were sands, silts and gravels in the form of fill overlying dense silty sands with gravel identified as the Merced Formation. ·

The erosional gully was apparently caused by water overflow due to a plugged drain on the paved area (See Figure 4). This drain has since been unplugged. However, the drain empties onto the adjacent property to the north, and the owner of the adjacent property has voiced concern over an erosion problem on his property caused by the drained water .

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• The level parking area of the site that is located on the top portion of the hill apparently was graded in the past in conjunction with the

• commercial development south of the studied property. Apparently, the fills generated by the excavation were pushed over the eastfacing slopes, including that of the subject site.

No landslides were observed on the subject site and none have been mapped on the site or on the adjoining properties. A creep and

e erosion condition was observed on the steeper slopes especially on the east slope. In addition, the aerial photographic studies did not reveal any lineations that might be interpreted as fault traces across the site.

The questionably active Serra Fault has been mapped by Brabb approx-• imately 500+ feet southwest of the site. The cited mapped location

of the Serra Fault is the northern-most mapped extent of the fault. No indications of fault traces were observed in our studies. we

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should note that the Serra Fault is considered (by U.S.G.S. and C.D.M.G. Geologists) to be only potentially active as no known evidence of activity has been established .

C. - SEISMICITY

California is one of the most seismically active areas in the world. Historical records show that large earthquakes have occurred more frequently in the San Francisco Bay Region than in any other part of California.

An earthquake occurs when the rocks deep within the earth suddenly release stored energy by rupturing. The zone of rupture is termed a fault and rupture of the ground surface along the fault trace usually accompanies large earthquakes. Shaking of the ground surface in the gneneral area of the fault occurs during large earthquakes, and gives rise to the term 'earth-quake'.

Historically, most earthquakes in the greater San Francisco Bay Area have occurred on the major fault zones. The San Andreas, Hayward and Calaveras fault zones are the longest of the major earthquakeproducing faults mapped through the Bay Area (See Figure 2). There are also many other, smaller faults in the Bay Area which are capable of producing major earthquakes.

The subject site is located approximately 3800 ~eet northeast of the 1906 trace of the active San Andreas Fault,? k'6 miles southwest of the active Calaveras Fault and approximately~.211 miles southwest of.I.the active Hayward Fault. In addition, a trace of the questionably active Serra Fault is located about 500 feet southwest of the subject site .

The San Andreas Fault is one of the longest and most active faults in the world and extends from the Gulf of California to north of Cape

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Mendocino. It has ruptured and produced at least four large damaging earthquakes during recorded history (1808, 1838, 1865, and 1906) • Geologic evidence suggests that such movements and the resulting earthquakes have been occurring for at least 30 million years averaging 5 to 10 feet of offset every 100 years. The 1906 San Andreas Fault rupture extended 270 miles along the fault and offsets of up to 21 feet were measured. The 1906 earthquake was felt in California, Nevada, and Oregon and caused damage to buildings more than 70 miles from the fault.

The Hayward Fault is a branch of the San Andreas Fault and is located on the east side of San Francisco Bay. At least two major earthquakes, with surface rupturing, on the Hayward Fault were experienced by residents of the Bay Area (1836 and 1968) . Both earthquakes caused extensive damage, and offsets of several feet were recorded near the City of Hayward .. In addition, tectonic creep of the fault has bben documented at several locations since 1960.

The Calaveras Fault branches from the San Andreas Fault south of the town of Hollister. A major earthquake (1861) is attributed to the Calaveras Fault and another earthquake (1868) was probably located on this fault. In addition, tectonic creep has recently been detected at the Cochran Bridge where the fault crosses Anderson Reservoir in Santa Clara County.

Many other fault traces, subsidiary to the major fault zones, exist and may be the source of damaging earthquakes in the future. The historic record clearly shows that damaging earthquakes have occurred a number of tiems in the past. A simple understanding of the nature of fault mechanisms indicates that large earthquakes and associated phenomenon will continue to occur •

In summary, surface rupture, strong ground shaking, and other secondary effects from earthquakes can damage structures. As discussed above, there are many active and potentially.active faults in the San Francisco Bay Area, and earthquakes have occurred on them in the past and will continue to occur again in the future. Earthquake effects constitute a significant geologic hazard. The degree of hazard depends on a number of factors.

The presence of an active fault trace on a property indicates that there has been fault offset (surface rupture) in the past. Offset occurs when the ground on one side of a fault moves relative to the other side. Active faults are expected to move again at some time in the future. The movement can be vertical or horizontal or a combination of both. The offset can occur either in fractions of an inch over many years (tectonic creep) and/or in relative movement of several feet in just a few seconds (rupture) . The degree of offset hazard imposed by a fault on a given site is deter-mined by (1) the proximity of the fault to the site; (2) the amount of fault offset anticipated; and ·(3) the frequency of fault related movement.

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• When a fault ruptures, large amounts of energy are released which causes the ground in the surrounding areas to shake. The intensity

e of shaking is dependent upon: (1) the amount of energy released (Richter Magnitude scale is commonly used), (2) the distance the site is away from the source fault; as shaking generally decreases over distance, and (3) the types of subsurface materials underlying the site as well as their densities and strengths .

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In general, (1) the of energy released; ground shaking; and the more severe the

longer the fault rupture, the larger the amount (2) the closer to the fault the more severe the (3) the thicker and weaker the subsurface soils, ground shaking.

Certain types of subsurface deposits are more adversely affected by earthquake vibrations. Loose, partially consolidated deposits can densify causing the ground surface to settle unevenly. Landsliding can be triggered by vibrations causing dowslope movements. Loose, saturated, granular deposits can liquify. These and other effects may produce distortion of the ground surface. There are also several other secondary effects including tsunami, seiche, and lateral spreading.

The chances of a large earthquake occurring in the future is a major factor in assessing the degree of earthquake hazard. Recurrence relationships have been calculated for several major faults based upon the historic record. However, the several-hundred-year period of existing records is relatively short compared to the millions of years involved in the evolution of fault systems. A precise understanding of how often faults cause earthquakes has not yet been developed. Some researchers have worked out relatively crude, statistically-based relationships. Forcasting based upon calculated probabilities can give a general idea of possible future events . Techniques for accurately forcasting earthquakes are currently being researched, but at present no reliable methods are available. Another approach to the assessment of earthquake probability is to recognize that the relatively high seismicity of the San Francisco Bay Region means that the site will most likely be subjected to strong ground shaking some time during the economic life of the proposed development.

EARTHQUAKE RISK

The actual risk at a site can be evaluated by defining the hazards present and considering the effects of economical mitigating measures .

Because of the traumatic and inescapable nature of earthquakes, there is a very strong and natural tendency for prople to take an emotional rather than a rational approach to the subject of earthquake risk. While we do not wish to downgrade the risks involved in development in areas of high seismic activity, we believe that the risks should be assessed in relation to other risks that the public accepts. In other words, judgments of earthquake risk should be approached in the same manner as judgments of other risks, where the factor of safety against failure is weighed against the consequences of failure .

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The following four general categories of earthquake phenomenon can be used to evaluate the earthquake risk at a site:

1. Fault Creep

Buildings that straddle an active fault trace can be slowly distorted by relative ground displacement along a fault trace due to tectonic creep .

Tectonic creep is a rare phenomenon that has been documented in only a few locations in California (i.e. the Hayward Fault in Berkeley and Fremont and the Calaveras Fault in Hollister) •

2. Surface Rupture

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Buildings that straddle an active fault trace can be distorted along the fault trace during an earthquake.

If a major earthquake of Richter Magnitude of 6 or greater were to occur along any of the major fault systems in the San Francisco Bay Area, there would probably be ground breakage along at least one of the main fault traces. However, it does not necessarily follow that there would be ground breakage on all fault traces or even other fault traces within that system causing such an earthquake. In other words, if the San Andreas Fault ruptured, there is little likelihood that the Serra Fault would also rupture.

Ground Shaking

Buildings can be damaged by ground shaking caused by earthquakes. The arrival of energy due to an earthquake causes the ground surface to shake, and vibrations are transmitted to the structure founded in the ground.

It has been fairly well established taht the magnitude of the accelerations and intensity of the shaking caused by earthquakes is not totally dependent upon the proximity of an area to the fault which releases the earthquake energy. The magnitude of shaking effects are, to a large degree, depentent upon the types of bedrock and character of materials overlying the bedrock at a particular site. In general, the most severe shaking and worst damage will occur on sites underlain by thick deposits of weaker or softer materials.

Secondary Effects

Buildings can be damaged by landsliding, lurch cracking, tsunami, liquefaction or other secondary seismic hazards.

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Secondary earthquake effects are extremely varied. The most common and damaging secondary effect is that of landslides which are triggered by the shaking. Other secondary effects are relatively rare and occur only where 'special' geotechnical conditions exist. Applicable secondary earthquake effects for the subject site are discussed in the GEOLOGY and CONCLUSIONS Sections of this report .

The risk of damage or failure which might result from an earthquake should be analyzed on an individual site basis. The analysis should generally consider the type of structure, the potential seismic hazards, the probability of occurrence, the consequences of failure, possible mitigating measures, and the costs of mitigating measures.

e These analyses should be appropriately tempered considering the concept of risk acceptance.

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CONCLUSIONS AND RECOMMENDATIONS

Based on our studies, we conclude that from an engineering geologic standpoint, the site is suitable for the planned development. The nearest active or potentially active fault trace is mapped about 500 feet southwest of the site. Evidences or indications of fault traces were not observed on the studied site and therefore, it is our opinion that the probability of fault rupture under the proposed structure (primary effect from major earthquake) is low .

Secondary seismi9 effects such as lateral spreading, liquefaction and tsunami are unlikely to occur due to the location and the nature of the materials under the site. It is our opinion that during a strong earthquake there is a small possibility that minor lurch cracking and/or localized landsliding or sloughing may occur in the surficial soils on-the steep slopes. However, such movements are not expected to have an affect on the planned development.

Slope stability analyses to evaluate the possibility for major landsliding that would involve the entire site vicinity was beyond the scope of this report. Major landsliding is intended to mean very large landslides that totally encompass several acres. However, we believe that the possibility of such major landsliding is very low.

We recommend that a soil and foundation engineer study the subject property and make appropriate recommendations and make an inspec-tion of the site during foundation construction. If any unanticipated materials are encountered this geologist should be promptly informed.

The site is expected to be subjected to strong seismic shaking at least once during the design life of the proposed structure. This seismic shaking hazard is one that is shared by all structures in the San Francisco Bay Area and is normally considered in the local building codes regulating the design of the structures. In our opinion, design according to the seismic criteria contained in the currently adopted Uniform Building Code (Pseudostatic Forces equal to l.2g) are sufficient for the planned structure .

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LIMITATIONS

Our services consist of professional opinions and recommendations made in accordance with generally accepted engineering geology principles and practices. This warranty is in lieu of all other warranties either expressed or implied.

If you have any questions concerning our report, please call • Figures and appendices are attached and complete this report.

JCP:cs

Very truly yours,

JCP-ENGINEERS & GEOLOGISTS, INC .

James c. E.G. 955

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• BASE: Thomas Bros.

SCALE

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ft"" 1 I I I I I : ·o 14 IS !ii

• JCP - GEOLOGISTS

CONSULTING ENGINEERING GEOLOGISTS

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LOCATION MAP

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~ PROPOSED RESTAURANT ON CRESTWOOD DRIVE

PROJECT NO. DATE Figure 1

JCP-359 AUG. 1978

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EXPLANATION

1CJ Mud

21 91' i Unconsolidated sediments

1 11 1 1, 1 3, I r.1 I I f. I ,

~ 4~

AGE >-0:: <(

z 0:: w I<(

=> 0

>-0:: <(

lo::

Moderately consolidated to well-consolidated sedimentary rocks

Volcanic rocks ~

5~ Franciscan assemblage

KJf-sandstone and shale chert, metamorphic r6cks, limestone, sheared rocks (melange)

KJv - volcanic rocks

6g Sandstone, shale, and conglomerate; locally in oldest part basaltic volcanic rock and chert

Serpentine and peridotite

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8 ~~~~,(~~-: Granitic rocks

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Cl U)

z => <lo uw _(J U) <( en 1-<l w 0:: 0:: =>u ...,

Contact Das/Jed where approximately located .

Faull known to be active Dotted where concealed

Fault not known to be active Dotted where concealed Only selected faults shown. Query indicates uncertainty as to existence of fault

Geology compiled by J.Schlocker and Kenneth C.Crowther 1967, mostly from Geoloaic map of California, Olaf P. Jenkins Edition, San Francisco, Santa Rosa, Sacramento. San Jose, and Santa Cruz sheets pub I ished by the California Div. of Mines and Geology, 1958 to 1966; and from U.S.Coast and Geodetic Survey maps and fie Id sheets of surveys of San Francisco Bay of I 850 and later

SCALE 1:500 000 0 IO 20 30 MILES

BY J. SCHLOCKER USGS - HUD BOC NO. B

JCP - GEOLOGISTS CONSULTING ENGINEERING GEOLOGISTS

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REGIONAL GEOLOGIC MAP

PROPOSED RESTAURANT ON CRESTWOOD DRIVE

PROJECT NO DATE !--------+--------~ Figure 2

JCP-359 AUG. 1978

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-N- APPROXIMATE SCALE

~ CONTOUR INTERVAL 200 FEET

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;:j.~:.:.::,'=:;e:; r:!i!.'=4!.:'~::..~;-11=~~=:~::.."":"""'• 1"<1 U"fl-nt.I

Tpl, t•lt.t -•r tf C-!11 1"'4 """"' l\tUl1-~ 1.,,, »• &.-o11>rl1 -• ol -1-.• 1"11 ot~ .. , \HU; ,...,.1.,., 1,., '-"'" -· ,, c.-1"'' '"" , .... ,.,.. 11nz : ttlluo.,. TJI, '""°"" -·II,_,..,, '"" tU..ro (lH!): un6ito ... '""onto-

B s .. 11 '"''""""',..or Chi'\ !IHfi)

UIC(llFOllMITT

EJ l-ln hM1t.w of Chi'\ (ltq)

n., 1-.. 1 s~.1. I~, .......... l1M11M1t '""· ••-,. hult .. d otlo•r "luolt ""''

::; ' :~:~•;:.:;:~.!:':~~· .~~;:::;:; ,:::~;-:: :;4 ,::'::1 (ltU)

hi• ,_,. !.h1h - .. o! ta• hr"Ona fo,.,..I\.., of lr1t>t> (ltU) 111: l-••I ••d 1., lu•••• ro,..u-. ~NlhU•': _,,,_,.. '"' 1~111

1\, '"''"" s....i1u ... , 1-.dlrtUd; •'""-h'"•t11 .. _.,_, ,....,, ollolo

~'.".~:;r-..... Source:

I{

EXPLANATION

llUT Ill" JM UUDUO , ....... 1

El

lfTVl.IO "° Ullil:WtlO Mtl rlLUCITOS•µio -.0.S fAIU1

1111.1, ..... 1. ''•'"• •ut '""1-. ·...... h ni • .,,. •• ,.., Hrhlln. ,.,...,n. ""' .,11,. ••••• ·-

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...... t,,.t.17 huW

,..u._ __ ... . D ,..,,

IMM<I """"' --• .. t1l1 1-t.41 •11-4-.,, -·h•., i.1 .... ,, '· ,.u......,, '"" •• -Ill- oltlo. 0...'7 h1(!<Hn thol ,,,,._ ••- ~ IHll lo --...

"""11 1 .. 11

FMlt - -11 t.o •"-'.,.""'Wt 11.,tncnt Mu ... ""'""-·' ._ .... 11, .... ......i lfll:lll• .....,, '"' hn 11111,0CI) ,.."

J' - "'"" • l•H"" h"'hal ~ •r1o .. u1

lt>-lq ... .,, 9f -

*tlol nlal!""' ....:orl.11• kt *--· 1ro:11 ..

t•,. ... ,....,lit "rH" Pol•I , • ._11 ......... , ....... ,, .. Cret.<HUS

lASl Of SM M-.0.S r~t

'"" Mt 11 lualt

] .. l~ » • • •• ~i

,.,. ,,,..., .. ,

ltrlh '"' (t1 of j1tot1

10~. hrlkt 1"4 iffJ ti .. 111110 Jelol ttt"- ....

flo1ht1 .. 1....i - ..... ~.)

·~ ... •tl7 •ut .. I•-- oM oh,.._ •IU ·- tlltHoM, 1..i ..-11 .. __ lw_

Sl>tlo ,..,. loloJ.ltoo ~

~ ~

i ""''"" o...i rolluoll H-•th10

• ... h•"4 ., .. ~, •• ,,_,.1 ... '" o ,,,.,"4,..trh. l1><l~M1

... 11 ...... , •llo.c• ... ,,. nd •M otltu-<o-Nt.o -·

'"><1u~~~.!~,!~'.! ::},:: !.:.~ :1 :t~ tit«) ~ Uf. -ITl<IH rn .. hcu ... -,,,., ... u1., ...... .._ .... •Mh, - ~ h~'";~~.::;-:~-: .. :.. ... ,;::;! ... ,J, •\Mir 1Ml1 s 1,. ,. ..... i. ... (•l\o..., ~ .. n. 1111>1111 ,.,. ..... ..,1 ... t. ""<hi "· ·~··t f<t, -•h •• uMlh _,,_,.,. n, 11-u~ .. ""· -"'-'""'' -1.J of 11 ... ,.ht.1 rutn ":;t!:;~;.i,~< '."':.~I.::: .~~I"";: I: .:;1::-::;~ •-~ft ::;t::;.:.1;

Brabb and Pampeyan, 1972

AREA GEOLOGIC MAP

JCP - GEOLOGISTS PROPOSED RESTAURANT ON CRESTWOOD DRIVE CONSUL TING ENGINEERING GEOLOGISTS

P"OJECT NO DATE

JCP-359 AUG. 1978 Figure 3

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•

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•

•

•

•

• 40

•

JUN I PERO SERRA

_____ Drain outlet

-i_tO'

/

/~

APPROXIMATE SCALE 0 40 80

feet

FREEWAY (ROUTE 280 l,. ~

----?- __ , __

.... - , -

PARK G AREA

area

I

2. 3'5.-,/

FILL

QTm

Note 1 Thi• -P i• a schi!:lllatic .illuz.tration of observed geoloqic data and ahould not be used for any other purpose. Con~s are approximate .

EXPLANATION

Man-plac~d soil material

MERCED FORMATION

Erosion of surface material

Line of GEOLOGIC CROSS SECTION

BASE: Sketch by JCP GEOLOGISTS

SITE PLAN AND GEOLOGIC MAP

JCP - GEOLOGISTS PROPOSED RESTAURANT ON CRESTWOOD DRIVE CONSUL TINC ENGINEERING GEOLOGISTS

PROJECT NO DATE Figure 4

JCP-359 AUG. 1978

• • • • • • • • • • • N 65° E

x x 280 Q) 280 i::

·.-i .....

>< .µ Q)

~ i:: Q) . .; p.. ..... 240

0 paved area 240 ~ >< CRESTWOOD p.. ......._ f/LL- .µ

DRIVE ~

~/ ......... Q) / . / °' 8 ,QT~ .. /

. / ' .·... ......... .......... 0 8 /

~ / .

~ µi µi . QTn-i ...._,. p.. µi µi /

./

~ '• ' ' • "' "' 200 •. ., . ..

// 200 z z ' ........ H H

' / / z //

/ z 0 0

.. / H H /

E-< E-< / :;; . / ,:i; . > µi /

160 µi ..:I 160 \ ..:I

/ µi µi / .

// ' / /

/ /

~ / ·,, . /

/ . 120 APPROXIMATE SCALE 120

40 0 40 80

feet

VERTICAL AND HORIZONTAL See figure 4 for EXPLANATION

NOTE: This cross section is a.-'------------------,..----------------:---------1 schematic illustration of general geologic relationships and should not be used for any other purpose. JCP - GEOLOGISTS

CONSULTING ENGINEERING GEOLOGISTS

GEOLOGIC CROSS SECTION

PROPOSED RESTAURANT ON CRESTWOOD DRIVE

PROJECT NO DATE

JCP-359 AUG. 1978 Figure 5

•

•

APPENDIX A

BIBLIOGRAPHY

California Division of Mines and Geology, 1966, Geologic Map of California, San Francisco Sheet.

Greensfelder, R.W., 1974, "Maximum Credible Rock Acceleration e from Earthquakes in California", California Division of Mines

and Geology (M.S. 23).

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•

•

•

•

•

•

HUD Basic Data Contributions 6, 7, 30, 41, 42, 43, & 44.

San Mateo County, Seismic Safety Element, 1976 •

United States Geological survey, Aerial Photographs, (6/25/74), from Keith Cole, Redwood City, California.

Wallace, RlF., 1970, "Earthquake Recurrence Intervals on the San Andreas Fault", Bulletin, Geologic Society of America, V. Bl, No. 10 •

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•

•

APPENDIX B

DRAINAGE AND MAINTENANCE GUIDELINES

As engineers and geologists, we have observed over the years that most foundation and hillside problems are either caused by water or aggrevated by water. In general, (1) water will cause most clays to expand, (2) running water will erode slopes, (3) saturation of the subsurface materials makes soil and rock materials heavier and thereby affects the stability of slopes, (4) water decreases the strength of clays and some bedrock materials and (5) water flowing through soil and bedrock materials exerts seepage forces and therefore can contribute to a failure.

Water is an instrument of nature and it erodes gullies, swales, valleys, and even eroded the Grand Canyon. Landslides are caused by water as are soil or mud flows and obviously floods, all of which are natural on-going geologic processes. The above mentioned natural processes can adversely affect man-made structures and, therefore, geologists and engineers must consider them and design to minimize their effects •

The following recommendations and suggestions, when utilized, constitute proper maintenance procedures that will improve drainage conditions and increase slope stability:

• Maintain positive drainage at all times. All water should have a cleared flow route away from buildings •

• Water should be drained into lined ditches or closed pipes that discharge into appropriate facilities.

•

•

Check roof drains, gutters and down spouts to be sure that they are clear. Depending on their location, roofs can shed tremendous quantities of water during a rainstorm. Without gutters or other adequate drainage facilities., water falling from the eaves may collect against the foundation and/or basement walls.

Erosion on slopes should be corrected immediately and any flowing water should be directed away from eroding area.

• Water should not be allowed to flow over slopes. Large concentrations can be particularly harmful.

• Water should not be permitted to pond or flow adjacent to a building's foundation.

• Periodically check to verify that subsurface drains are not clogged .

• Correct any damage to the drainage system as soon as possible . Prompt attention to minor problems may prevent them from growing into major problems .

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•

•

•

•

•

• Remove any obstructions from surface drains. Make certain that all elements are in good repair •

• Check for loose fill materials above and below your property since they can erode or slide during the rainy season.

• Do not over-irregate landscaped areas. Sprinklers or water hoses should not be left on longer than necessary and never overnight.

• Never connect roof drains to subs'urface drains.

• Do not modify or obstruct any part of the existing drainage system without professional advise from a registered civil engineer.

• Do not allow water to flow into or accumulate on areas above .septic tanks or leach fields .

• Do. not compact earth behind walls or in trenches by flooding with water.

• Do not place loose soils or fills on a slope.· .

In general, common sense and normal awareness is to prevent costly and sometimes serious damage. observed contact our office as soon as possible •

\

all that is needed If distress is

•

l 2 3 4

• • • • • • • • • TYPICAL CROSS SECTION OF HILLSIDE BUILDING SITE

Showing Locations of Typical Design Features 19

6

7 9 8

s

,.

6 _,.

.,.

'· 20 10 f"':"~ - -

- - ,:".".. ::-__ .. ::: . .:::..;=-- -7'-~,..-~·- 21 - ..... .. /-- ... •'

-"-~-------"

Original Ground Surface Typical cut Slope Typical Fill Slope Engineered Fill (Compacted · to Specifications -

Keyed and Benched into Firm Ground)

5 Typical Building 6 Roof Gutters 7 Drain Pipe 8 Drain Spout outlet onto

Paved Surf ace or extend at least 10 feet from building.

9 · Curb to prevent downslope 10 Typical Subdrain 11 Typical French Drain 12 Typical Drainage Swale

, _,. .,.

II

erosion

13 Typical Retaining Wall 14 Typical Surface Drainage Ditch 15 Typical Subsurface Drain with

perforated or slotted pipe. 16 Typical Weep Holes 17 Typical Drainage Terrace 18 Typical Lined Drain and/or Ditch 19 Typical Brow Ditch 20 Typical Footing Foundation 21 Typical Pier Foundation

NOTE: The features described'above are for illustration purposes only; detailed design recommendations for a specific building should be made by a licensed Civil Engineer.

NOT TO SCALE TYPICAL CROSS SECTION

JCP - GEOLOGISTS PROPOSED RESTAURANT ON CRESTWOOD DRIVE CONSULTING ENGINEERING GEOLOGISTS

~AOJECT NO DATE

JCP-359 AUG. 1978 Figure B-1

•

necember 12, 1978 File 3040 Page i

lll.\.l~J,() ~()II .. l•::'I (_~I~ l•:l•:I { ~

Preliminary Geotechnical Report for a New Restaurant Assessor's Parcel 017-245-090 Crestwood Drive, San Bruno, California

This report is ~ased on a detailed engineering examination by the undersigned of the above lot that is proposed to be graded and built upon. We conclude that the property is suitable for a wood framed build'ng to be placed wit~in the area shown on the attached site plan.

Jur special concer;1s 'or this-project involve the hazards of ground scis~ic shaking, differential settlement, and slope failure. Therefore, we ask that this report be studied and that care be taken to implement the recommendations and to use good building practices to assure adequate stability. Furthermore, this report should be provided to thr building manaqer for his information.

J~on request, we will inspect and test the earthwork construction and foundation installation on a regular basis whi 1 e the work is being do1e. Then we will discuss the construction procedures, field changes (if any) and test results in a Final Report.

Please contact us at any time in the future if there are questions or whenever we may be of further service.

I

122 CAMINCJ PABLO ORINDA, CALlFOR~ilA 94563 • 1 415) 254·5922

r ~-• ,.

December 12, 1978 Fi le 3040 Page i i

Preliminary Geotechnical Report for a ~ew Restaurant Assessor's Parcel 017-245-090 Crestwood Drive, San Bruno, California

TABLE OF CONTENTS

TITLE PAGE

A. INTRODUCTION

Scope Location ~d Description of Project Field Investigation Laboratory Testing

S. FINDINGS

Topography Vegetation Rainfall and Drainage Soi 1 s

C. CONCLUSIONS

General Slope Stability Design Values

D. RECOMMENDATIONS

General Building Location Grading Drainage Foundations Trenching Concrete Slabs on Grade Asphalt Retaining Walls Planting Maintenance

E. LIMITATIONS AND UNIFORMITY OF CONDITIONS

F. REFERENCES

FIGURES

PAGE

1

1 . 1 2 3

3

3 4 4 4

5

5 6 7

8

8 8 8 9

10 10 11 11 11 11 12

12

12

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December 12, 1978 File 3040 Page 1


A. INTRODUCTION

1. Scope

This report presents our findings, conclusions, and recommendations which are based on an extensive surface and subsurface soil investigation, and a review of publications prepared for the site and nearby areas. The findings describe the results of our research and field and laboratory testing that was done to evaluate the soil conditions at the site. Conclusions in this report describe our interpretations of the findings, and the recommendations .section suggests requirements for grading, foundations, and building locations. Surface and subsurface drainage recommendations are also presented as are planting and maintenance instructions.

This report also supplements the Engineering Geologic Study (l)* prepared last July and the subsequent critique (2) which was prepared by the City of San Bruno's independent consultant. Our specific responses to items in reference 2 are to be found in Section C of this report. These geologic reports were prepared as required by the terms of the Alquist-Priolo geologic hazards "Special Studies Zone Act".

Our work included:

a. Drilling three borings to evaluate the surface and subsurface materials that may be influenced significantly by water, existing fi 11 and fUture structural loads,

b. Laboratory tests to determine soil characteristics,

c. Engineering analyses to evaluate parameters for use in the design of foundations, grading, etc.,

d. Research into previously published reports, and

e. Preparation of this report.

2. Location and Description of Project

The project is located west of the business district of San Bruno as shown on figures 1 and Z in the appendix. The area is in the foothills below Sweeney Ridge at an elevation of approximately 230' above sea level. The

*Numbers in parentheses refer to publications listed in Section F



site is quite near a potentially active branch of the San Andreas Earthquake Fault as discussed further in Reference 1.

It is proposed to build a restaurant that is to be custom-designed by an experienced architect, Ted C. Jeong. The structure will be a wood frame building that rests partially on very deep foundations which bear on undisturbed native bedrock, as described in Section 05. Earthmoving on the site will be limited to whatever is necessary to provide proper parking lot grades, drainage, and building elevations.

Foundation loadings from the structure will be relatively light, but provisions will be necessary to prevent movement from pressures within the clayey soil. Slopes will be kept as flat as possible, or they will be supported with retaining walls. Drainage will be positively controlled.

The publications that we reviewed for this project are listed in Section F. Of particular interest is the engineering geology report which was prepared last summer for the project. This report supplements the earlier study with additional information that was requested by The City of San Bruno.

3. Field Investigation

The field portion of our study was performed during November, 1978. This included examinations of the site by our staff geologist and engineers, drilling three test borings and collecting representative disturbed and undisturbed soil samples for various laboratory tests. The borings were drilled with portable 4" augers on the slope at the locations indicated on Figure 2 of this report. The test borings were drilled 4 to 6 feet below existing grade and core-sampled at selected elevations. The soils encountered were visually examined and logged in the field, and verified in the lab as shown on the boring logs.

Undisturbed core samples were obtained from the test borings at selected depths by driving a 2.5'' ID California Sampler into the soil with a 35 pound hammer falling 30 inches per blow. Samples were field-tested with a small, hand held penetrometer and then capped to retain moisture before they were brought to the laboratory for further testing.

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December 12, 1978 Fi le 3040 Page 3


4. Laboratory Testing

Laboratory testing was done to determine representative densities and natural moisture contents of the soil, and an Atterberg Limits test was performed. The Atterberg Limits test is useful in classifying siltclay relationships, the expansiveness potential, and the moisture contents at the standard liquid limit and the plastic limit. Standard ASTM test procedures were used including D 423, 424, and 2487.

A compaction test was made in the laboratory in order to determine the standard 100% density and optimum moisture content for a soil sample obtained from drill cuttings in the existing fill near boring #2. The "Modified Proctor" compaction test was done according to ASTM D 1557 test procedures. The test shown in the Appendix will also be useful as the standard against which to compare densities of future field compaction tests when grading at the site begins. Other lab compaction tests on imported soil should be n1ade as necessary when earthwork construction begins.

To evaluate the strength characteristics of the soil for foundation design, direct shear tests were performed on native soil and remolded fill according to ASTM D 3080 test procedures. The samples for direct shear were placed in water and consolidated for a minimum of 24 hours prior to testing and were single-sheared under undrained conditions.

Unconfined compressive strength tests were made at field moisture contents to supersede field penetrometer tests. The lab tests were done according to ASTM Test D 2166 to obtain cohesive strength and bearing capacity data.

B. FINDINGS

1. Topography

The site has been extensively modified in the past by earthmoving. The lot is generally on two levels that have been excavated out of an apparently continuous hillside that sloped up to the west.

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Freeway construction beyond the eastern property line is responsible for excavation and levelling for the lower terrace. The upper terrace was established when a number of adjacent lots were graded and developed. Crestwood Drive forms a third terrace beyond the western boundary.

Most of the lot is cut into native bedrock except for a relatively thin veneer of dumped fill which was pushed over the edge of the upper level. The fill is 5' deep on the average, and will need to be disregarded for foundation support.

2. Vegetation

Only scattered weeds grow around the asphalt on the upper levrl. Vegetation on the slope consists of native grasses, but there are no signs of lush, water-tolerant growth indicative of seepage areas.

3. Rainfall and Drainage

Rainfall at the site is 22 inches per year, with about 80% of the rain falling between the months of November and April. This amount of rainfall is moderate for the Peninsula .which receives from 14 inches per year in Foster City to 43 inches west of Woodside (3). About 60% of the rain runs off of the site due to shallow bedrock and asphalt cover when the ground has been pre-saturated by earlier rains.

Site drainage collects on the upper level and is discharged through a storm drain. Slope drainage is overland to the east. There is a gully on the slope at the northeastern property line as shown on Figure 2. The gully appears to have eroded because of uncontrolled runoff which will need to be corrected.

4. Soils

The natural soils on the site, before grading was done, were a few inches of slightly clayey silt topsoil unrlerlain by dense, well-graded sand and lightly cemented sandstone.

The topsoil is a residual product of leaching and evaporation where clay minerals have accumulated. It is· organically permeated from plant growth which gives the soil its dark color. Clayey topsoils in the Bay Area nearly always are moderately to highly expansive; that is they have a significant capacity to shrink and swell with seasonal moisture changes. When



such soils are on slopes, they tend to creep downhill, resulting in tipped trees, fences and other obstructions.

Slopewash is very similar to topsoil, but it is generally lighter in color, and more nearly like its parent bedrock below. Slopewash also moves down hillsides, but at a slower rate until it becomes exposed at the surface and becomes topsoil also. Such processes normally occur quite slowly.

The bedrock at the site as more ·fully described and lightly fractured. excellent.

is a sandstone member of the in Reference 1. The rock is Strength characteristics for

Merced Formation generally massive foundation bearing are

Characteristics of the project's soils relative to others in the area are:

moderate shrink-swell potential with moisture changes low compressibility easy compactibility with optimum moisture moderate permeability moderate shear strength in dense sand, high in rock severe erosion hazard on bare, exposea slopes

C. CONCLUSIONS

1. General

This section describes our conclusions which are based upon field and laboratory testing, research, calculations and judgment. We present here our criteria for grading and structural design as well as other parameters to be used in developing the project. Construction methods and performance requirements are suggested in the following Recommendations section.

The engineering geologic study was prepared under subcontract to evaluate the potentially active Serra Fault which is located 500' southwest of the project (1). The engineering geologist concluded that there is a low probability of fault rupture at the site. Seismic shaking, however, is a factor that must be evaluated in studying slope and structural stability.

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The City of San Bruno retained an independent consultant to review the initial study (2). Clarification of some items was requested, and we respond to the consultant's remarks below.

2. Slope Stability

The fill slope east of the upper pad is loose but stable. According to our calculations on the profiles shown as Figures 2a and 2b, the slope has a safety factor well in excess of 1, even if the slope is saturated and pseudostatic lateral forces of 0.2 g are applied (the lateral force factor of 1.2 g is a ti~ographical error in Reference 1).

Safety of the slope is greater, of course, if the soil is never saturated. We believe that this will be the case because the building will cover a large part of the slope, and drainage from~he parking lot will never be allowed to flow over the edge. Also, there does not appear to be any subsurface seepage coming from within the bedrock.

Even if the fill does move in the future because of changed conditions or unforeseen factors, we believe that there will be no damage to the building if its foundations penetrate to bedrock. Such a procedure will be necessary to prevent foundation movement prim2rily because the fill is too variable to provide sufficient bearing capacity.

The fill slope is currently lY, : 1 or flatter. It is safe from massive landsliding or lurching on the bedrock or native soil interface in the event of saturation and/or seismic shaking, and it will become more stable in the future as it densities and as it is kept relatively dry by being covered. It is quite susceptible to erosion (as is evident in the gully) and should be protected from further uncontrolled runoff.

We conclude that the project is suitable for installation of a conventional framed restaurant with fn11ndations bearing on clean, unweathered bedrock. There are hazards of soil instabili:y because of its natural tendency to shrink and swell and creep downhill from season to season. Such a hazard can be provided for, however, with prudent building practices and implementation of measures similar to those described in the Recommendations section below.

The structure is expected to be safe from massive movement within the soil as it will be well anchored into firm bedrock and much of the subsurface drainage will be intercepted by uphill underdrains. Building pad and driveway cuts should be supported with properly installed walls and/or drained fills.

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Earthwork for the driveway and building pad will probably consist of balanced cutting and filling. Because of the clay content of the soil, fill wedges will probably creep slowly on hillsides regardless of their slope. Sudden failure of slopes as steep as 2 horizontal : 1 vertical will not occur.

Because the site is not in an active fault zone, the building will be outside of the area of predicted possible ground breakage, and there is little likelihood of direct fault offset beneath the structure. However, seismically induced shaking should be expected to occur within the economic life of the project with possible minor structural damage. Nevertheless, damage should be no more severe in the project area than elsewhere in the region.

3. Design Values

a. For structural design purposes, the product CS in the Section 2312 1976 Building Code formula V=ZIKCSW may be taken as 0.14. The seismic zone factor, Z, may be taken as 1. V should not be less than 0.2.

b. Piers should be designed for end-bearing in dense, unweathered bedrock which will support 5000 pounds per square foot of end area plus 20% per foot of bedrock penetration to an aggregate maximum of 15,000 psf. All piers must be drilled to near-refusal in order to gain this kind of support.

c. Piers may or may not be installed deeply enough to gain fixity at their bottoms in order to act as vertical cantilever beams. Depth to fixity will depend on length of embedment into passively acting soil or bedrock. It may be more efficient to design as if the piers are pin-connected at their bottoms.

d. Creep pressures may be estimated as being with the highest pressure at the surface. to be in the form of a triangular loading foot at the top and zero at·5' depth.

in the top 5 feet of topsoil We estimate such pressures

with 250 pounds per square

e. Passive pressures for soil and weathered bedrock may be estimated at 200 pcf equivalent fluid weight for footing sliding or seismic reaction, and/or use sliding friction of 0.25 times dead load when footings are truly on level ground.



f. Passive pressures for dense, unweathered bedrock may be taken at 400 pcf-efw for footing sliding or seismic reaction, and/or use sliding friction of 0.35 times dead load when footings are on level ground.

D. RECOMMENDATIONS

1. General

Following are recommendations for the proper completion and maintenance of the project. The recommendations are of a general nature and should be discussed with an experienced soil engineer if there are any questions about their implementation. It may be of benefit to retain a soil engineer to provide:

a. Approval of the foundation, grading and drainage plans, b. Updating this report if necessary because of changes or delays, c. Inspection of the work in order to determine construction adequacy

and to make field changes as necessary, d. Preparation of a Final Soil Engineer's Report that indicates how

construction was done according to generally accepted engineering practices and our recommendations.

2. Building Location

This report is written as if the building is to be located as shown on Figure 2a. If the building is to be located wholly on the upper pad, the project will be simplified considerably.

3. Grading

Grading should be kept to a minimum. Cuts in soil and all fills should be no steeper than l~ horizontal : 1 vertical. Where steeper slopes are desired, we recommend the installation of retaining walls unless steep cuts in sound bedrock are made. Stability of steep cuts should be discussed with a soil engineer.

All trash and heavy growth should be cleared from the locations of ~tructural cuts, fills and building areas, and removed from the site. Existing grades to be filled .should then be thoroughly scarified and recompacted in order to prepare for further filling.

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December 12, 1978 Fi 1 e 3040 Page 9


If any further earthwork construction is to be done to the east of the upper pad, then the fill should be removed and replaced after benching into native bedrock. Underdrainage beneath structural fills should be provided as recommened in the field by an experienced soil engineer. See Figure 5a. The fills should then be raised in 8-inch layers that are properly moisture-conditioned to within 2% of optimum moisture content and compacted to 90% relative compaction (ASTM Test Dl557), also as determined by the soil engineer. If fill material contains rock or rubble, no rocks larger than 6 inches in greatest dimension should be allowed.

All finish grades should slope at least 2% in such a manner that surface water will not run over bare slopes or collect against obstructions.

Non-structural, un-engineered fills such as presently exist may be installed, but settlement and/or creep must be expected within the soil if moisture fl~ctuates. If the restaurant is placed on the fill as proposed, it will be important to assure that foundations penetrate to dense sand or bedrock below.

4. Drainage

Foundation underdrainage at the site will be necessary to assure soil stability. The underdrains will work by draining running water and by drying the soil from internal air circulation and evaporation.

Four-inch perforated PVC pipe should be placed behind uphill foundations, retaining walls, and in fill benches as directed by the engineer. Oo not use thin corrugated plastic pipe. Perforated pipe should be surrounded with at least one cubic foot per linear foot of CalTrans class 2 permeable material according to the detail shown in the appendix. Underdrains should outfall on natural ground below the building or on pavement. Do not introduce surface runoff into perforated underdrains. Cleanouts should also be placed on the uphill ends of the pipes so that they can be flushed out annually during dry weather.

Yards should slope at least 2% away from the foundations or they should drain to catch basins. Parking lot runoff should be collected in catch basins at low points and piped to adequate disposal points. Slope runoff should be intercepted behind retaining walls and other structures by installing gutters that empty into small catch basins for proper disposal. Drainage must not be allowed to collect and pond anywhere on the site. Roof runoff should also be directed away from foundations. Do not allow downspouts to deposit.runoff where it can saturate foundation soil. Do not use rock-filled sumps ("French drains").



Landscape watering on the slope should be kept that are self-sustaining should be encouraged. sprinkler systems is not recommended.

5. Foundations

to a minimum. Native plants Installation of timer-operated

Building foundations should be end-bearing piers or piles that are tied together in downhill fashion to provide anchorage tension to each of the members. See the details in the appendix of this report. The piers should all be reinforced with steel bars that are stuck a few inches into the hole bottoms before filling with concrete in order to assure that the reinforcing remains properly spaced during the concreting. Piers should be filled in one continous pour in order to prevent cold joints below grade. Grade beams should be poured separately after the piers have been installed.

Standard reinforced concrete spread footings are not recommended unless they bear on rock. Hybrid foundation systems utilizing stepped, spread footings cut into rock beneath shallow soil, and piers elsewhere are acceptable if all elements bear on rock. Retaining wall footings may bear on soil if necessary, but if so, they should be spudded with piers drilled to rock. Because of the lower strength of the topsoil, we recommend that care be taken to assure foundation bearing on clean unweathered bedrock.

6. Trenching

The Occupational Safety and Health Act of 1970 requires that trenches 5 feet deep or more either be shored or that the trench walls be sloped back in order to improve worker safety. If sloping is done, it should vary with soil type varying from ~: 1 (horizontal : vertical) for very stable soils like hard clay, to 2 : 1 or flatter for loose or sensitive soils. When doubt concerning the stability arises, the underground contractor should seek an opinion from a soil engineer, or he should shore his trenches.

Some utility lines are normally placed on sand bedding, which inadvertently can serve as underdrains and/or underground moisture conduits. Furthermore, trenches can become weak planes in tension at the tops of slopes, or they can remove buttressing support at bottoms of slopes. Consultation with a soil engineer is recommended if such problems can be foreseen.



Trench backfill should proceed in accordance with our suggestions for earthwork compaction, or they should follow normal utility or governmental specifications for backfilling and street subgrade preparation. Trench backfill flooding or "jetting" is not recommended in clayey soil, but it may be acceptable in permeable, non-cohesive material.

7. Concrete Slabs on Grade

Framed wood flooring is anticipated for the building; concrete slabs are not recommended.

Around the exterior of the restaurant where slabs are to be used, a minimum of 4'' of crushed rock should be pl~ced between compacted cut subgrade and concrete slabs. Filled subgrade should be made with densely compacted crushed rock or other nonexpansive fill material. Concrete slabs should be at least 4" thick and reinforced--preferably with bar reinforcement. Wire mesh is acceptable if layout and concrete clearance is carefully controlled. Expansion joints should separate slabs from foundations.

8. Asphalt

The recommended driveway section is 3" of plant-mixed asphalt over 6" of crushed aggregate base. In the parking lot 2" of asphalt over 4" of crushed aggregate base may be utilized. Four inch reinforced concrete pads should be installed over 4'' base in areas where trucks or garbage boxes are likely to be parked. Subgrades should be thoroughly moistened after compaction of the base to prevent heaving from swelling soil.

9. Retaining Walls

Retaining walls should be designed to resist active pressure of 30 pounds per cubic foot of equivalent fluid weight. Normal consideration to slope surcharge must be given. Otherwise, we recommend spudding the footings to rock with reinforced concrete piers designed to take bending stress. All impervious. retaining walls should be underdrained; see the detail in the Appendix.

10. Planting

We recommend landscape installation of plants that require minimum watering. Pines, bays and oaks may be encouraged to grow on the property in order to kn't t1e surface soil together with roots. However, do not plant shallow-rooted trPes so close to structures or pavement that root heave can occur. Use of automatic timer-operated sprinkler systems is not recommended.

Fresh cut slopes should be seeded and maintained to prevent erosion which can easily occur in the silty soils.



11. Maintenance

Annual flushing with a garden hose of all underdrains, catch basins and downspout piping is recommended. If any pipes become clogged, they should be cleared so that hydrostatic water pressures do not lessen the shear strength of the soils. Ground surfaces should be maintained to promote good drainage and to prevent saturation.

E. LIMITATIONS AND UNIFORMITY OF CONDITIONS

The recommendations presented herein are based on the soil conditions revealed by our test borings and evaluated for the existing conditions and proposed construction. If any unusual situations are encountered during construction, or if the actual construction will differ from that planned at the present time, we should be notified for supplemental recommendations. The conclusions and recommendations in this report should not be assumed to apply to properties beyond the project area.

This report is issued with the understanding that the owner chooses the risk he wishes to bear by the expenditures and savings involved with the construction alternatives and scheduling that is chosen. For this report to be valid, the owner should ensure that necessary steps are taken to carry out the recommendations of the report in the field.

The items in the report are valid as of the present time. However, the future may change conditions due to natural processes, works of man, legislation and the broadening of knowledge. Therefore, this report is subject to review and should be relied upon less with the passage of time in the event that delayed construction is coctemplated.

F. REFERENCES

1. JGP Geologists; July 31, 1978; Engineering Geologic Study for Proposed Restaurant; File JCP359.

2. Earth Systems Consultants; September 8, 1978; Review of Engineering Geologic Study; File C8-0758-Cl.

3. U .. S. Geological Survey; 1971; Mean Annual Precipitation Data for S.F. Bay Region; BDC 32.

File 3040

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SCALE 124000 0

LOCATION MAP

1 MILE :c:cc:cc:c.c=::c""···~"':~=aa

showing San Andreas Fault Zone and known or suspected breaks as shown by heavy lines, according to the State Geologist

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Logged By: HRV

Date Ori I led: 11-26-78 ..... .,

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103.4 12.5 85 10+ 11'.h 1ll h qn in+

100. 7 13. 7 70 10+

107 .4 13.6 66 10+ 113.6 14.2 96 10+

14 .7

Remarks: Holes were Califa.rnia sampler and

Direct Shear Test

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10 20 30 Moisture Content {% of dry weight)

SAMPLE:

DESCRIPTION:

LABORATORY TEST METHOD:

MAXIMUM DRY DENSITY:

A (from cut bank at southwest corner of site)

Medium brown well graded silt, sand & fine gravel

ASTM D 1557 c

120~ pounds per cubic foot

OPTIMUM MOISTURE CONTENT: 12% by weight

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567 El Camino Real Crestwood Drive...Jul 31, 1978 · Orinda, California 94563 Re: Engineering...

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Transcript of 567 El Camino Real Crestwood Drive...Jul 31, 1978 · Orinda, California 94563 Re: Engineering...