StATE'. OF CA.llFO~NIA~TH~ Gov.:mcir · 4/15/1990 · StATE'. OF CA.llFO~NIA~TH~ RESOURCES AGENCY...

StATE'. OF CA.llFO~NIA~TH~ RESOURCES AGENCY

DOPMTMENT OF CONSERVATION

DIVISION OF MINES AND GEOLOGY 8A Y AREA REGIONAL OFFICE 380 CIVIC DRIVE, su1rs 100 PLEASANl HILL, CA 9...t$'23-1997 PHONE, (415) 646-'920

A TSS 599-'920

Mr. J. w. Cobarrubias city of Los Angeles Building and Safety Room 460-A City Hall Los Angeles, CA 90012-4869

Dear Mr. Cobarrubias:

GfOR:Gf: DEUKMEJIAN. Gov.:mcir

August a, 1990

We are placing on open file the following report, reviewed and approved by the City of Los Angeles in compliance with the Alquist-Priolo Special Studies Zones Act:

Geologic-seismic study for portion of sec. 11, T2N., R.14E., located at 11402 Riverwood Drive, Sunland, CA; by Keene Associates; 4/15/90.

EWH:hk / cc: A-P file!-"

Sincerely,

EARL W. HART Senior Geologist &

Program Manager

COMff'llSSIONE'.RS

MAACIA MARCUS PRE510~NT

TOM WOO VICE-PRESIDENT

AEVC:LACION P. A6RACOSA

RICHARD W. HARTZLER

BENITO A. SINCLAIR

July 27, 1990

Mr. Earl Hart

CtTY OF Los ANGELES CALIFORNIA

TOM BRADLEY MAYCR

Calif. Division of Mines and Geology 380 Civic Drive, Suite 100 Pleasant Hill, CA 94523-1997

~EPAFITME:l'>IT OF'

BUILDING AND s.-.FETY

411, CITY HALL. LOS ANGELES, CA 900 l 2·4869

WARREN V, 0'6AIE:N GENERAL MANAGER

E'.ARL SCHWARIZ EXECUTIVE Oil'F'lCER

SUBJECT: Geologic-Seismic Study for a portion of section 11,T2N, R14W located at 11402 Riverwood Drive.

Transmitted herewith is a copy of the Geologic-Seismic Report dated April 15, 1990 prepared by Keene Associates.

The City of Los Angeles has reviewed the report and finds it to be acceptable and in general conformance with the minimum requirements of the Special Studies Zones Act. A copy of the Department letter in review of the report, has been enclosed for your files.

GERALD TAKAKI Chief of Grading Division

;J,!.h-1fa-J. W. COBARRUBIAS Staff Geologist, Building and Safety (213) 485-2160

TDN:ge TGRMG072790A/6GR

Attachments: Geologic-Seismic Report Department Review Letter

AN SQUAL EMPLOYMENT OPPORTUNliY - AFFIRMATIVIC ACTION l;MPLOYE.A o~;c~l+l~mm.:ioel1omrr:qcled'll'd~!~ @

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Art Keene Associates 2601 E. Victoria, #308

... - ' I .-~4--+:.

Rancho Dominguez, California 90220

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May 17 1 1990 Work Order #90302

Subject: Soils Engineering Investigation for Proposed singleFamily Residence, 11402 Riverwood Drive, Sunland, California.

Reference: Keene Associates, 15 April 1990 1 Geologic Investigation for Proposed Single-Family Residence, 11402 Riverwood Drive, Sunland, California .

Dear Mr. Keene:

In accordance with your request, our firm has undertaken a

study of the soil conditions which occur on the subject site.

Our purpose was to evaluate the distribution and characteristics

of the earth materials which occur at the site so that we might

assess their impact upon the proposed single-family residence.

The scope of work for this project included 1) review of

readily available files and reports, 2) mapping of the building

area, 3) sampling of earth materials from three borings,

4) laboratory testing of recovered materials, 5) engineering

analyses, and 6) preparation of this report .

This study was conducted on 9 March 1990 in conjunction with

a geologic investigation by Keene Associates (Appendix A) . The

19201 PARTHENIA STREET SUITE F NORTH RIDGE. CALIFORNIA 91324

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Keene Associates May 17, 1990 Work Order #90302

locations of our exploratory borings are shown on the attached 1-

inch to 20-foot scale Plot Plan (Plate 1). Site location, site

description, geologic interpretations, and geologic structure

sections are included in the attached report .

Proposed Site Development

Development plans are not available to us at this time.

However, it is our understanding that a single-family residence

is proposed as indicated on the Plot Plan (Plate 1).

FINDINGS

Lithology

As observed on the site and encountered in our exploratory

excavations, earth materials consist of artificial fill, natural

soil, and alluvium.

Artificial Fill CAf l

Two generations of artificial fill were encountered in the

three borings.

The upper 4.0 feet (Af2 ) of fill consists of a loose

admixture of silty sand which is light brown in color and moist

in nature. Numerous subrounded pebbles and a few cobbles up to

4.0-inches in diameter are also present.

From 4.0 to about 8.0 feet the fill (Af1 ) consists of

moderately dense clayey sand with silt which is mottled light and

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dark brown in color. This deposit is moist, and contains

numerous subrounded pebbles and cobbles.

Natural Soil

Natural soil is present on the ascending slope immediately

superjacent to the proposed building area and was observed to be

about 1.0 foot thick.

It consists of sandy silt with minor amounts of clay and is

brown in color. The soil is slightly moist and firm in nature.

Alluvium roall

Alluvium consists of poorly stratified sands and gravels

with rounded cobbles and boulders.

LABORATORY TESTING

Undisturbed and bulk samples of earth materials encountered

at the site were collected during the course of our field

exploration. Selected laboratory tests completed on the

retrieved samples are described below.

Moisture-Density Test

The field moisture content and dry unit weight were

determined for each undisturbed sample recovered. Dry unit

weight is expressed in pounds per cubic foot and the moisture

content represents a percentage of the dry unit weight. The test

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Keene Associates

results are presented in Table 1 .

Compaction Test

May 17, 1990 Work Order #90302

To determine the compaction characteristics of the onsite

materials, a compaction test was performed in accordance with

ASTM Test D 1557-78. The maximum dry density is reported in

pounds per cubic foot and the optimum moisture content as a

percentage of the maximum dry density. The test results are

presented in Table 1.

Sample Location and Description

B-1 @ 2.0 Feet Artificial Fill (Af2 )

B-1 @ 5.0 Feet Artificial Fill (Af1 )

TABLE 1

Field Dry

Density Cpcfl

96.2

103.4

Moisture Content

(%)

s.o

11.9

Compaction: Artificial Fill (Af2 Maximum Dry Density Optimum Moisture

and Af1 l Admixture 129.5 pcf

9.0 %

Shear Strength Tests

Shear strength tests were performed in a Direct Shear

Machine of the strain control type. The rate of deformation is

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approximately 0.050 inches per minute. Shearing occurred under a

variety of normal loads in order to determine the residual shear

strength parameters. The tests were performed on undisturbed

samples that were repeatedly sheared in an artificially saturated

condition. The test results are presented on Plates D.l and D.2.

SLOPE STABILITY

Engineering calculations have been performed to determine

the stability of the existing slopes. Residual shear strength

parameters for the materials were determined by laboratory

testing. The material type, cohesion, internal angle of

friction, and soil/bedrock unit weight parameters utilized in the

slope stability analyses are presented in Table 2. Permanent

slopes are considered stable by the City of Los Angeles if they

possess a static factor of safety equal to or greater than 1.50.

TABLE 2

Friction Unit Material Cohesion Angle Weight

Type (psfl (degree) <pc fl

Bedrock 300 26 120 Shale Parallel to Bedding

Soil 200 26 120

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Engineering analysis of the existing slopes were performed

utilizing Singh's Charts (based on Taylor's Charts with balanced

factor of safety) for uniform slope conditions, homogeneous and

isotropic soil, without water seepage forces .

The gross stability analysis indicates that the bedrock

slopes have a static factor of safety greater than 1.50 and are

considered to be stable in their present configuration. The

results of the gross stability analysis is presented on

Plate 3.

The surficial slope stability analysis indicates that the

natural soil has a static factor of safety greater than 1.50 .

The soil is considered to be stable in its present configuration.

The results of the analysis is presented on Plate 4 .

DISCUSSION AND RECOMMENDATIONS

Data from our research and field exploration coupled with

inferred conditions between exploratory excavations are the basis

for the following discussion. Recommendations for design and

construction of the foundation system, based upon the presently

available data, are presented below for your consideration .

DISCUSSION

The existing artificial fill is not considered suitable for

foundation support due to a high potential for settlement. Fill,

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to a minimum depth of 8.0 feet, should be removed from the

proposed building area and recompacted to a minimum of 90%

maximum density. All foundations then may be placed into

certified compacted fill .

The ascending bedrock slope is considered to be grossly

stable in its present configuration.

RECOMMENDATIONS

1) The proposed structure may be placed at the existing

grade and footings should be founded in the certified compacted

fill .

2) The existing fill, on the proposed building area, should

be removed and replaced as certified compacted fill for

foundation support .

3) A slough wall should be constructed at the toe of the

ascending slope to intercept potential slough material.

4) A 9:"$J.~n wall should be constructed along the western

toe of the existing stream bank to protect the building area from

erosion .

Grading

The following recommendations should be used in preparation

of the grading plan and job specifications:

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Keene Associates May 17, 1990 Work order #90302

Compacted Fill

1. The areas to receive compacted fill should be stripped

of all vegetation, debris, existing fill, and loose

alluvial soils. The estimated removal depth is 8.0

feet except in the area of the abandoned seismic trench

where removals may be deeper than ± 10.0 feet. The

removed area should extend a minimum of 5.0 feet,

measured horizontally, out from the perimeter footings .

2. The exposed grade should then be scarified to a minimum

of 6 inches, adjusted to optimum moisture content, and

reworked to achieve a minimum of 90 percent of the

maximum dry density.

3. Compacted fill, consisting of soil approved by the

soils engineer, should be placed in lifts not exceeding

6 inches in uncompacted thickness. The excavated

onsite materials are considered satisfactory for reuse

in the fill provided all organic material and debris is

removed. Any imported fill should be observed, tested,

and approved by the soils engineer prior to use as

fill. Rocks larger than 6 inches in diameter should

not be used in the fill.

4. The fill should be compacted to at least 90 percent of

the maximum dry density for the material. The maximum

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Keene Associates May 17 1 1990 Work order #90302

density should be determined by ASTM Test Designation D

1557-78.

5. Field observation and testing should be performed by a

representative of Salus Geotechnical Corporation during

the grading to assist the contractor in obtaining the

required degree of compaction and the proper moisture

content. Where compaction is less than required,

additional compactive effort should be made with

adjustment of the moisture content, as necessary, until

a minimum of 90 percent relative compaction is

obtained.

Foundations

The following recommendations may be used in preparation of

the design and construction of the foundation system. The

building may be supported by conventional spread footings bearing

in certified compacted fill .

Spread Footing

Continuous and isolated spread footings bearing in certified

compacted fill may be used to support the proposed apartment

building and garage. The footings should be founded entirely

within certified compacted fill with an expansion index of less

than 50. The following design criteria for spread footing

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foundations are considered appropriate:

Certified Compacted Fill

Allowable Bearing Capacity. 1500 psf (a) Lateral Resistance. . . . . 250 psf/ft Maximum Lateral Resistance. 2500 psf (b) Coefficient of Friction . . 0.30 Minimum Embedment Below Lowest Adjacent Grade

One-story Construction . . . . . 12 inches Two-story Construction ...... 18 inches

Minimum Reinforcement (c) .... two #4 bars, one near top, one near bottom

(a) May be increased by 1/3 for short duration loading such as by wind or seismic forces.

(b) Decrease by 1/3 when combined with friction.

(c) Isolated pad footing should be at least 2 feet square ..

Foundation Settlement

Based upon anticipated structural loads, the maximum total

settlement is not expected to exceed \ inch. Differential

settlement between adjacent footings is not expected to exceed \

inch.

Concrete Slabs-on-Grade

Concrete slabs-on-grade should be placed on certified

compacted fill. Slabs utilized for vehicular parking and traffic

do not require granular bedding, provided the expansion index is

less than 50.

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Keene Associates

Minimum Thickness . . Minimum Reinforcement

Bedding

May 17 1 1990 Work Order #90302

Full 4 inches #3 @ 24 11 each way on center (a) 3 inches of clean sand (b)

(a) The reinforcement should be properly supported to ensure proper positioning within the slab .

(b) Place vapor barrier 1 inch below top of sand layer beneath all enclosed areas.

The bearing soils for slabs-on-grade should be pre-moistened

to a depth of at least 12 inches and proof rolled prior to

placing forms, steel or concrete.

Walls

The following recommendations may be used in preparation o~

the design and construction of retaining walls. The walls should

be supported by footings bearing in the certified compacted fill .

The fill area beneath proposed walls should be removed for a

minimum depth of 4.0 feet. The removal should be extended

horizontally for 4.0 feet, in both directions, out from the edge

of the footings.

Retaining Wall

e Retaining walls may be utilized in the development of the

site. The foundation design recommendations are as stated in the

Foundation section of this report .

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Keene Associates

Surcharge Loads

Slope Behind Wall

Level

1.5:1


(evaluated individually)

Equivalent Fluid Density (pcfl

30

55

Any additional surcharge due to the building, traffic, or

other loading should be included in the design of the walls.

All retaining walls should have an adequate pipe back

drainage system installed. Where living spaces adjoin retaining

walls, a moisture barrier should be installed on the back of the

wall to mitigate against efflorescence. All retaining wall soil

backfill should be compacted to at least 90 percent of the

maximum dry density.

Free-draining material consisting of at least 1 cubic foot

of 3/4-inch crusher-run gravel should be utilized around pipe

drains. If an open space greater than 1 foot exists between the

back of the wall and the soil face, gravel backfill should be

compacted by vibration. An impervious cap should be provided at

the top of the wall backfill to prevent infiltration of water

into the backdrain system. The cap may be a combination of

concrete and compacted soil. The compacted backfill soil cap

should be at least 1 foot thick when used in conjunction with a

concrete cap and at least 2 feet thick when used exclusively.

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Keene Associates

Slough Walls


In order to protect the proposed structure from erosion and

potential ravelling of the ascending road slope, a 3.0 foot high

(minimum) slough wall should be constructed at the toe of the

ascending slope. The wall should have a concrete swale placed

between the slope and the wall for control of runoff drainage.

water should be directed to the stream area .

Gabion Wall

In order to protect the building area from flood damage

caused by stream bank erosion a gabion wall should be constructed

at the toe of the west stream bank. See Plate 5 for a typical

detail of a gabion wall. The gabion wall should extend the full

length of the building pad area. The gabions should be keyed a

minimum of 6.0-inches into bedrock (± 2.0 feet below existing

stream grade) and extend at least 5.0 feet above the alluvium

fill contact .

Temporary Excavations

Temporary excavations in fill and natural materials may be

made. The maximum safe vertical height for these cuts is 5 feet .

All excavations over 5 feet in height should be shored, braced,

and/or laid back to a 1:1 gradient.

All shoring and bracing should be in accordance with current

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Keene Associates May 17, 1990 Work order #90302

requirements of the State of California Division of Industrial

Safety and other public agencies having jurisdiction.

Temporary shoring should be designed for an activo

equivalent fluid pressure of 30 pounds per cubic foot. All

temporary excavations should be stabilized within 30 days of

excavation.

Drainage

Positive drainage should be established on the site.

Ponding of water adjacent to foundations should be prevented. A

minimum of a 2% grade toward the street should suffice .

Plan Review

Development plans were not available at the time of this

writing. Formal plans should be reviewed by SOLUS GEOTECHNICAL

CORPORATION prior to their implementation. Additional

recommendations may be made at that time .

Site Observation

It is recommended that all temporary and permanent

excavations be observed by a representative of SOLUS GEOTECHNICAL

CORPORATION. Should the observation reveal any unforseen

conditions, additional recommendations may be made.

Placement of all fill and backfill should be monitored by a

representative of SOLUS GEOTECHNICAL CORPORATION. This includes

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observation of prepared bottoms prior to placing compacted fill .

Foundation excavations should be observed by a

representative of SOLUS GEOTECHNICAL CORPORATION to determine if

the recommended penetration of the proper supporting material has

been achieved. Such observations should be made prior to placing

forms, steel, or concrete.

This off ice should be notified at least 48 hours prior to

requiring observations for excavations or pouring concrete.

All work and materials should comply with the latest

applicable specifications of the city of Los Angeles .

Limitations

The soils engineer has prepared this report using that

degree of care and skill ordinarily exercised, under similar

circumstances, by reputable geotechnical consultants practicing

in this or similar localities. No other warranty, express or

implied, is made as to the professional advice provided under the

terms of the agreement and included in this report.

The subsurface conditions, excavations, and characteristics

described herein have been projected from individual test borings

placed on the subject property. The subsurface conditions and

excavation characteristics discussed should in no way be

construed to reflect any variations which may occur between these

test borings.

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Thank you for this opportunity to be of service to you .

Should you have any questions, please feel free to contact our

office.

Respectfully submitted,

SOLUS GEOTECHN!CAL CORPORATION

Tony s.c. Lee, PE Senior Project Engineer R.C.E. 44045

Michael R. Rampton staff Engineer

TSCL/DDG/MRR/rc

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Reveiwed By Dale D. Glenn President

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Keene Associates

Enclosures: Plot Plan . . . . . . . . . . .

Xe: ( 6)

Boring Logs . . . . . . . . . . Gross Slope Stability Analysis surficial Slope stability Analysis Gabion Wall . . . . . Shear Strength Tests Geologic Report . . .

17


Plate 1 Plates 2.1-2.3 Plate 3 Plate 4 Plate 5 Plates D.1-D.2 Appendix A

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PLOT PLAN

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EXPLANATION

Ex'PLo RA-roR Y B 0R1Nc;

Ou-rcROP SAl'IPLE. - 8€DRoCK

SoiL SAMPLt

/l?!'fi. ox. ""'- NoR IH )...

,, 2 / SCALE I : 0

EOTECHNICAL

5-l?-90

Work order f </0302. PLATE j_

·~~~--~~~--~~~~~~~--~~~~~~~~~--~~--1~~~~~ ·~...:::;_~~~~~

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J<ELLY W'E1(;H7'S:

2<.oo //:,s. o- '1. 3' I (,OO /b5. 2. 3

1- f.3

1 BORING LOG: 1

-:<f Artificial Fill: (Af4) Silty sand, light brown, ,~).~ medium grained, loose, moist. '.'Q."'. Numerous subrounded pebbles, :--,0~ few cobbles up to 4-inches

--~~~:·:r---------.:i~n~d.:i:ameter . ~:'iJ (Af1 ) Clayey Sand w/ Silt,

mottled light and dark ::).~- brown, moderately dense,

moist. Numerous subrounded pebbles and cobbles .

Alluvium: Sands and Gravels, brown, dense, moist. Contains some rounded cobbles and boulders.

e It)

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THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC LOCATION AND THE DATE INDICATED. IT IS NOT WARRANTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES .

70r?9L DEPIH /0. 5' rl~r

!Vo t..!AreR

No CAVING

GEOTECHNICAL

DATE · -~:..../ 7-11' WORK ORDER If ~.....:!..."'<jo-3-i-.0::-:2.:----

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.w ,...,, Q 0 ;J (]) ~ <fl

0 H .w .. :>-. "' u ;J c .w (])

.w (]) ·rl '1J c :< <fl .w <fl ,_. '1J 0 •.-1 c :>-. i:: OJ 1-1 ,_. 00 1-1 <\l ·rl <ti

l"1 ::t: u 0 Cl "'" ::c

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..c: ,_. .w .w "'" "'"OJ s (]) (]) <ti

0 "'" ell

SOR! NG LOG: 2

- . . . .

5' -. • . .

10-

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. • -. . • . -. • . • -• . • •

-• . . .

Artificial Fill: (Af~) Silty Sand, light brown, medium grained, loose, moist . Numerous subrounded pebbles, few cobbles up to 4-inches

I

THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC LOCATION AND THE DATE INDICATED. IT IS NOT WARRENTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES.

in diameter.

(Af1 ) Clayey sand w/ Silt, mottled light and dark brown, moderately dense, moist. Numerous subrounded pebbles and cobbles .

Tor111... DEPT/I 6. a rc£T /V'o WA/eR

;Vo CAv1NG

~~~ ~0 ~~EOTECHNICAL

~~ATE WORK ORDER ff __ 29.!<'.0.=.3!!.o:Z..:..__ __

PLATE Z.2

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,_, ~

c ~ c ;:I (!) '-'

•rl 0 l-< ,_, (!) u ;:I c

.a ...... ,_, (!) ,_, ,_, p,

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p, (!) f.i 0 .... c (!) <IJ OS rl 0 0 Q "" Cl) "" ::SU -

"' ~ "' ,_, (!) .... '"O c "' ...... '"O

~c (!) l-< l-< <IJ ·..< OS QQ ~:r::

0 -"' 4. q: "' "' 0 \!I .J

BORING LOG: 3

. Artificial Fill: (Af~) Silty sand, light brown, medium grained, loose, moist. Numerous subrounded pebbles, few cobbles up to 4-inches

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. 5' -.

--•

10-. . . --• • ---. . . --. ----. . •

-....

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THE LOG OF SUBSURFACE CONDITIONS SHOWN HEREON APPLIES ONLY AT THE SPECIFIC LOCATION AND THE DATE INDICATED. IT IS NOT WARRENTED TO BE REPRESENTATIVE OF SUBSURFACE CONDITIONS AT OTHER LOCATIONS AND TIMES .

in diameter .

(Af1

) Clayey Sand w/ silt, mottled light and dark brown, moderately dense, moist. Numerous subrounded pebbles and cobbles .

/orA L DEPTH 6. 0 r&€."1

;Vo /Jti T € R.

No C f/lllNG

t#w ~~O~EOTECHNICAL

)!\IV DATE · · s--~17-fo WORK ORDER # 903oz

PLATE 2.3

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SLOPE STABILITY ANAl_YS IS (liA5£D oii TAYLOR'S METHOD lo/ITH lVJ..AUC!:D FACTOR Of s;.n:rn

. ~ OH lAY1..0R."S C:hAAl~ -'-----1 . . . .

ci lo 20 ~o •(I ~o

~, DEt;l<Lt.;;,

FIG.11.- F-CONTOURS FOR SLOPE 15=1

l. Horoogenous Soil 2. No Seepage force> ~- Circular failure 4. Simple Slope S~ccion 5. St-tic Conditions Only

fROU: Singh Awto.r, "She02r Strcn;;th .:md St«bility of 11.>n•H:idc Slopes'', Journal of th~

c - -300 psf

~ - 6( "2 •

y - /~0 pd

g£IT

CALCULATIOr<

C/fH 0, 08 FACTOR Of SAFETY # /.'7{)

C • Cohc~ion

Intern"l Angl~ of r~i-iciion

r - Unic Soil lo/eight

Soil ticcb .... nic:.: /JnJ l'-tur,d.;..rion Div l ~ ic.r,. Al:·sn.;.::;:-s1:i.Lo. fiav~mL.r, 1910, pp. 1879·1852. Work Order i 90302...

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.Plate 3

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L=:J C~:=:J LJ [::=J C~JL=:J

SURFACE SLOPE STABILITY

J.O. 90302 DATE 05/16/90

COHESION 200 PSF GAMA ~ 120 PCF PHI ~ 26 DEGREES

SLOPE ANGLE ~ 34 DEGREES

VERTICAL SATURATION ~ 3 FEET

1·-·-···----·-·' ·--···· FORMULA

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SAF!:T¥ f"ACTCR •Ct (GA - 82.4) It H ff COS'~C[ZJ * TANIPHlJ • i.55

S4 • H It SINIZJ ~ COS{Z)

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SINCE THE SAFETY FACTOR OF 1.55 IS GREATER THAN THE

REQUIRED 1.50, Wf CONSIDER THE SLOPE TD BE SURFICIALLY

STABLE. ALL RECOMMENDATIONS OF OUR REPORT SHOULD BE

INCORPORATED INTO THE PLANS .

Sol us Work Order

PLATE

GEOTECHN!CAL

# '10302

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Cfi'OS.S SECT/O!V - TYPJCl9L GAB/ON' WIJLL

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BEDROCK 611

• Gabion (rock-filled wire mesh boxe~! _____ J

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Date 5'-17- fo

• Work Order j 90302 PLATE S

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SHEAR TEST DIAGRAM

J,O, 90302 PATE 05/16/90

Shale, Undisturbed, SaturatP<l, Sheared Parallel to Bedding

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NORMAL PRESSURE KSF

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Sol us GEOTECHNICAL

Work Order # </0302 PLATE D. I

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SHEAR TEST DIAGRAM

J.0. 90302 DATE 05/15/90

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Samp J e #1 0.5 tt. SOIL

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Sol us GEOTECHNICf\L

Work Order # 90302-

PLATE J),2

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CIVIL ENGINEERING AND GEOTECHNICAL CONSl,JL TING

ASSOCIATES

GEOLOGIC INVESTIGATION FOR PROPOSED SINGLE FAMILY RESIDENCE -

11402 Riverwood Drive, Sunland ca.

For Fred Fleck, Owner April, 15, 1990

-Prologue-

At your request, a geologic investigation was initiated on

March 4, 1990 to evaluate the feasibility of constructing a

single family structure on your lot, consisting of 2 acres of

previously graded land with irregular lot boundaries. The site

lies within the California State Special Studies Zones, a

legislative act to control development in active fault zones.

Your lot is located in one of these zones in Ebey Canyon,

Sunland. The scope of the work involves : (1) one boring to

determine the adequacy of fill materials on site to support the

structure and possible slope stability analysis of the

slope behind the existing structure; (2) a seismic trench to

show an active fault related to the Lakewood fault segment of

the San Fernando Earthquake of February 9, 1971 does or does

not underlie the location of your proposed structure; and (3)

geologic mapping of the site to determine if adverse geologic

conditions affect the site, such as ground failure potential.

-Introduction-

Site Location and Description

The site is located in the San Gabriel Mts., north of

Sunland and the Big Tujunga Canyon drainage. Access to

the area is by Oro Vista Ave. (Figure 1 Site Location Map)

Access to the specific site is from Riverwood Drive, via a

A. G. Keene, C.E.G. # 16, 2601 E. Victoria, # 308, Rancho Dominguez, Ca. 90220

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LEGEND

fo11ult !race or ground crack showing amount of 11ertic<;1J displatement, in centimUer~. 45 ball on down!hrown side_

MAP OF SURFACE BREAKS

SAN FERNANDO, CALIFORNIA

PRELMINARY REPORT 11, PLATE I * SITE LOCATION MAP --------.J· -- GI!_

FIGURE 1 0•53• -f

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private road and a concrete apron crossing the creek

drainage.

The site is located within the Ebey Canyon Creek Drainage .

It occupies a portion of a broad flat bench on the west

side of the stream. The bench has been covered with

compacted fill to a height of about 12 feet above the

stream's invert .

The site is bordered by a l~:l 30-foot high slope above

the bench. The private drive providing access

to 11402 Riverwood Drive is built on the crest of this

slope and thus over-looks the site toward the east. Pico

formation shales appear to underlie the slope (See Geologic

Cross-Section A-A', Figure 2, and Geologic Map Figure 3) .

A minor trace of the Lakewood fault segment of lg71,

based on the 197g Alquist-Priolo Special Studies Zone Map,

crosses Riverwood Drive north of the property as

mapped by James Kahle, Bull.196. The access road off

Riverwood Drive does not appear to have been affected.

Also, the trace, though shown to be cutting across River

wood Drive, does not extend westward as far as the Ebey

Canyon Creek. The site's north boundary line is thus not

affected by this trace.

Previous Earthwork Completed

Four generations of fill, under permit in 1958, (Figure

4) were placed over the stream alluvium and partially

over the Pico formation near the site's north boundary.

The stratigraphic relationships are revealed on Plate 1,

Seismic Trench.

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A. (;. KEENE, .CERTIFIED ENGINEERING GEOLOGIST, NO. 16. TEL: {213) 537-6615

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GEoLOG!c S;:cr10N A-A 1

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GEOLOGIC MAP

11402 RIVERWOOD DR.,SUNLAND, CA.

APSSZ MAP, 1979 fOR Fred Fleck

A.K••n•, Aprll, 1980

FIGURE 3

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~tu.~4,,........ ............ ~ -i" \~ 1 . ~·· ~':i!ll!ll• ,. •Ill -........ -·,..,.....:.·.:.:.=.r'-'_'"~·-·• .. c•.-..,.. •

APPLICATION FOR GRADING AND FILL PLACEMENT COMPLETED IN OCTOBER, 1959.

FIGURE 4

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GEOLOGY OF THE SITE

Four elements of a geologic nature affect the site:

A. Stratigraphic Relationships

B. Active Faulting

C. Slope Stability

D. Surface Hydrology

Stratigraphic Relationships

Alluvium and Terrace Materials

The canyon drainage appearto be an elevated hanging valley

above the Tujunga Wash. Drainage as a result of repeated

upward movements of the upper plate of the Lakewood fault

system. These upward movements are geologically very young.

Repeated downcutting of this and neighboring canyons has

revealed at least two generations of gravel/boulder

terrace deposits, the younger one of which appears to be

exposed on the west bank of the canyon drainage on the

subject site. Bulletin 196 describes the older unit as

Quarternary terrace (Qt). The younger unit labeled Qoa

appears to have been used as borrow material for the first

generation fill above the recent gravel/boulder stream

bed. These repeated movements may have been severe

enough to create temporary impoundment of stream flows,

resulting in ponding of considerable geologic time periods

until over-flow recurred with consequent downcutting

toward Big Tujunga Wash. This site in Ebey Canyon may have

experienced such temporary impoundment.

The site is presently underlain by recent alluvium

(Qal), which has locally cut its invert into the underlying

Pico formation (Ttp).

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A: G: KEENE, -CERTIFIED ENGINEERING GEOLOGIST, NO. 16. TEL': (213) 537---'6615

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Pico Formation

Reference to Bulletin 196 indicates the site is underlain

by the Pico formation, striking N 75E to E-W, with beds

of shale and conglomerate dipping generally 62 degrees to

the north .

Very good exposures of the Pico formation exists east of

the site, above the access road called Riverwood Ln., and

on Riverwood Dr., west of the site and stream drainage.

According to Kahle, bedding plane slip of 5 cm occurred

between shales and conglomerate on the east exposure

above and north of the subject site. This places the site

on the lower plate of the fault; the upper plate moved

upward and southward.

Active Faulting

C.D.M.G. Fault Trace, Feb. 9, 1971 Event

As noted on the Geologic Map, Figure 3, a trace of the 1971

event is located north of a private access road off

Riverwood Dr. which provides acc.ess to a mesa over-looking

Big Tujunga Wash. The private road is above and north of the

11402 Riverwood Drive pad. A second trace, not aligned with

the first, terminated east of Ebey Canyon Creek but cuts

across Riverwood Drive south of the intersection of Riverwood

Drive and the private access road serving the above

mentioned mesa and 11402 Riverwood Drive. This places

the trace almost adjacent to the south side of the. concrete

apron at the intersection of the two roads, and east of

the creek. The concrete apron basically paves the creek

bottom, and serves as the creek invert at the

intersection .

A seismic trench (Plate 1), was started 37 feet south of

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the concrete apron and extends 142 feet southward,

parallel to Ebey canyon Creek, and across the length of

the level pad. The trench was, on the average, about

9 feet deep, with maximum depth at about 12 feet in

certain portions to obtain needed contacts between the

base of the lower-most fill and-the underlying clean

alluvial deposits anticipated to be present .

As shown by the trench log, three generations of

compacted fill overlie historic clean coarse sands and

gravels deposited in Ebey Canyon. The lower-most fill in

contact with the alluvium was obtained locally from the

young stream terrace remnants west of the lot, under

permit in 1958. It consists of bouldery material in a

blackish-brown matrix of clayey silty sand. The second

generation fill, consisting of an olive-brown, and

grayish yellow-brown pebble/cobble fill in a clayey silty

clay matrix was placed over the first generation. The

contact was observed to have a straight line relationship

in the trench by sighting down the length of the trench,

verified by carefully scraping the contact with a rake,

whisk broom and bayonet. A third generation, a very

distinctive, well compacted light gray silty clay with

uniformly disseminated white blebs of lime throughout,

exists between stations 8 and 25, capping the second

generation do.wn to a depth of 2-3 feet and exhibiting a very

distinctive contrasting contact line exhibiting no

vertical shear displacements .

No distinctive vertical displacement shears could be

observed on the contacts between the alluvium and the

overlying fills or between the burnt orange Pico bedrock

shales and the over-lying charred colluvium, or between

the charred colluvium and the overlying fills. Most

significantly, no vertical shears were observed between

the second and first generation fills. The overall

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conclusion drawn from this seismic trench is: No

displacement due to the 1971 event disturbed the fills

placed in 1958. No displacements were detected in the

fills by C.D.M.G. (Kahle) in 1971. Shears between bedrock

(Pico) and fill were not evident. Junk fill, a recent

fourth generation fill, was placed after the 1978 flood.

lt was not compacted. Contacts of this material were

poorly developed and mixed with underlying fill materials,

alluvium and artifacts.

It must be emphasized that the 5 cm movement documented

by C.D.M.G. Bulletin 196 was observed on the bedding

contact between shales and coarse conglomeratic sandstones

of the Pico formation off-site from and north of 11402

Riverwood Drive.

The proposed structure, 22 feet wide, will be placed at

least 87 feet south of the recorded earthquake fault

trace as mapped by c.D.M.G.

Seismicity

Roger Greensfelder (C.D.M.G.) suggests the area may

experience a maximum credible rock acceleration from

future earthquakes in the Sunland area of about .Sg, with

a magnitude M=~5 •

The proposed structure, of wood frame and single story,

should be constructed to withstand at least 2/3 of the

maximum credible acceleration of .Sg.

Slope Stability

The east facing slope behind the proposed residence exhibits

a slope ratio of l~:l or greater. Bedding supporting the

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slope is neutral to the slope, dipping to the north. No

landslide exists, or slumping. Slope stability, based on

assumed strengths of the underlying Pico shales, (Geologic

Cross-Section A-A', Figure 2) may be performed by Salus

Geotechnical should the soils engineer determine its

necessity .

In this consultant's opinion, the slope is grossly

stable, and will not affect the proposed residence.

Surf ace Hydrology

Storm activity of Jan~Mac, 1978 appears to have eroded

the southern portion of the site and portions of the level

lot occupied by compacted fill near the intersection of

Riverwood Dr. Subsequent remedial work placed "dump" fill

on the eroded portion of the lot. This "dump" fill is

uncompacted and loosely placed. It will not support any

structures without excavation and recompaction using a clay

matrix.

Repeated flooding in the future may be expected, and

should be evaluated by a hydraulics engineer for

anticipated flood heights and debris flows .

The Ebey Canyon drainage east bank adjacent to the site

should be reinforced to mitigate against bank erosion,

using a gabion-wire revetment as a minimum design .

Eventually, a diversion flood wall may be desirable for

future security against maximum floods .

SEWAGE DISPOSAL

The area to be developed is underlain by several

generations of compacted fill. Fill materials were

derived from on-site and possibly imported fill from

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elsewhere. The irregular lot boundaries contain about 2 acres

of flat land, appropriate for a leach field design with more

than enough area available for expansion. The leach field

may be located north or south of the proposed new residence,

but as far to the west of the Ebey Canyon Creek drainage as

is possible to prevent potential flooding conditions from

affecting the leach field. Appropriate set-back distances

from the residence must be maintained .

seepage pits may not be appropriate in view of the

proximity of Ebey Canyon Creek, and possible shallow

groundwater below the creek's invert .

Conclusions

Based on the site investigation, it is concluded that:

1. The site is grossly stable. It is not underlain or

affected by landslide or slumping. Future ground

e failure is not anticipated.

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2. The site is not affected by active fault

displacement .

3. The potential for renewed active faulting in Ebey

Canyon cannot be discounted. The active fault

trace near your lot, which experienced 5 cm. of move

ment in 1971, may activate in the remote future .

4. At least four (4) generations of fill underlie the

site, placed over recent alluvial boulder, gravels,

• and sands in the Ebey Canyon drainage, and partially

on Pico formation bedrock.

5. Flooding potential exists, and should be evaluated by

3 a civil engineer experienced in surface water

hydraulics and debris flow potential from the

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A. G. KEENE, CERTIFIED ENGINEERING GEOLOGIST, NO. 16. TEL: (2l3) 537-6615

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Ebey Canyon drainage.

6. Sewage disposal should be accomplished using a leach

field system. Sufficient space is available.

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Shallow ground water teepage exists about 10 feet

below ground surface in the northern portion of the

lot.

Foundation support provided by the on-site graded

fills should be evaluated by a foundation engineeer

and a soils engineer.

9. The lot is basically suitable for development .

Reco1D1Dendations

1. The structure's proposed location en Plate 1, Geologic

Map, and Geologic Section A-A', Figure 2 , is more than

50 feet away from a known active trace of the Lakewood

fault segment. This location should be retained, but,

in any event, not shifted to the north portion of the

lot within 50 feet of the known active fault trace, and

no further than Station 0 of the Seismic Trench 1 Plate 1.

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3.

The proposed structure should be placed about 15-20 feet

away from the toe of the existing slope .

The graded fill's adequacy for foundation support must

be evaluated by a soils engineer .

4." The location of the structure must not be placed on the

uncompacted fill debris exposed in the Seismic Trench,

and designated Af4, without further evaluation by a

soils engineer .

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A. G. KEENE, CERTIFIED -ENGINEERING GEOLOGIST, NO:- 16. -TEL: (213) 537-6615

• 5. Sewage disposal in the uncompacted debris fill (Af4) is

feasible, since the proposed structure will not be

e adversely affected, if located as recommended. Use of

the fill for this. purpose must meet City regulations and

approval.

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6. A debris flow protective wall or similar device should

be constructed adjacent to Ebey Canyon Creek to protect

the proposed structure against flood damage in the event

flooding experienced in 1978 should occur in the future.

Rip-rap on the west stream bank should be placed to

prevent westward erosion of the bank.

Warranties

This evaluation was conducted in accordance with generally

accepted professional geologic procedures and within limits

proscribed by the client. No other warranty, expressed or

implied, is made as to the evaluations included in this

report.

Significant variations in bedrock or soil conditions are not

anticipated. If conditions are encountered during future

restoration work, and these conditions appear to be

different from those disclosed by this evaluation, this

office should be notified to consider the need for

documenting variations in geologic conditions at the site .

References:

1) SAN FERNANDO, CA. EARTHQUAKE OF FEB., 1971 Bulletin

196, C.D.M.G. - Art. 8, Surface effects and related

geology of the Lakeview fault segment of the San

Fernando fault zone, by James E. Kahle pgs 119-136 -

1975 - Editor: Gordon B. Oakeshott, C.D.M.G .

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A. G. KEE.NE, CERTIFIED ENGINEERING GEOLOGIST, NO. 16. TEL: (21-3) 537-6615

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2) San Fernando Quadrangle, Los Angeles County, Ca.

Bulletin 172, C.D.M.G., by Gordon B. Oakeshott -

1958 .

3) Geologic Map of the San Fernando Earthquake Area by

A. G. Barrows, eal, c.D.M.G. - 1974

4) Fault - Rupture Hazard Zones in California Special

Publication 42, Rev. 1988. Ref: Alquist-Priolo

Special Studies Zones Act of 1972, Dept of

Conservation, Div. of Mines and Geology.

5) Special Study Zone Map - Sunland Quadrangle APSSZ,

Jan. 1, 1979 7.5 minute series.

6) Map of surface Breaks Resulting from the San

Fernando, ca. Earthquake of Feb. 9, 1971 by Barrows,

Kahle, Weber, 1971, 1:24,000.

7) Recent Reverse Faulting in the Transverse Ranges,

U.S.G.S. Prof. Paper 1339, by Crook - 1987.

8) MAXIMUM CREDIBLE ROCK ACCELERATION FROM EARTHQUAKES

IN CALIFORNIA, Roger Greensfelder - California Div. of

Mines and Geology, 1972, revised Aug., 1974.

A. g. Keene

l\GK/bk

Di str: ( 9)

Salus Geotechnical (7)

Fred Fleck ( 2)

A. G- KEENE, CERTIFIED ENGINEERING GEOLOGIST, NO. 16. TEL: (213) 537-6615

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StATE'. OF CA.llFO~NIA~TH~ Gov.:mcir · 4/15/1990 · StATE'. OF CA.llFO~NIA~TH~ RESOURCES AGENCY...

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Transcript of StATE'. OF CA.llFO~NIA~TH~ Gov.:mcir · 4/15/1990 · StATE'. OF CA.llFO~NIA~TH~ RESOURCES AGENCY...