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144, Construct pool in the front ya, Studies & ReportsR. BRUCE LOCKWOOD, R.E.G. AWTAR SINGH, C.E. • Lockwood -Singh & Associates A CORPORATION Consulting Foundation Engineers and Geologists 997.7 Jefferson Boulevard • Culver City, California 90230 Telephone: (213) 870-7335. May 13, 1975 Proj. Ref. 390-52 Mr. & Mrs. Harry M. Fieger 8004 El Manor Avenue Los Angeles, California 90045 SUBJECT: GEOLOGY AND SOIL ENGINEERING INVESTIGATION PARCEL 55 OF R.S. 59, PGS 8-10, INCL. 55 CREST ROAD EAST ROLLING HILLS, CALIFORNIA Dear Mr. & Mrs. Fieger: In accordance with your request, we are pleased to sub- mit a report of a geology and foundation investigation for proposed residential construction at the address referenced above. The accompanying report has been substantiated by sur face and subsurface exploration, geologic investiga- tion, and mathematical analysis made in accordance with generally accepted engineering practice, includ- ing those field and laboratory tests considered neces- sary in the circumstances. It is the professional opinion of the undersigned that this report presents fairly the information requested by you. Respectfully submitte4, LOCKWOOD-SINGH & SOCIATES R. Bruce Lockwood REG 204 RBL/HAT/AS/WLN:ml Awtar Singh CE 17727 INTRODUCTION This report presents the findings and conclusions of a soil and geology investigation on Parcel 55,R.S. 59, pp 8-10,located. at 55 Crest Road East, Rolling Hills, California. The investigation was undertaken to evalu- ate conditions pertinent to future site grading and single family residential development. At the time of this report no grading or development plan had been pre- pared. However, it is understood that development con- templates creating a flat cut pad area along the ridge top and construction of a relatively narrow elongated structure in this area. Since prior geologic instiga- tion on the adjacent parcel indicated the likely presence of adversely dipping structure below elevation 500 on the southwest facing slope this investigation has been limited to the area upslope from location cf the fold axis that marks the lower boundary of bedding planes favorably oriented from the standpoint of geologic slope stability. ,It 1 1 • • • Proj. Ref. 390-52 Fieger 2 May 13, 1975 FIELD INVESTIGATION Field investigation included geologic reconnaissance of the subject property together with the examination, logging, and mapping of three exploratory test pits excavated with a Case 1000 tractor loader to obtain data to implement geological assessment in areas of the property that lack natural exposures. The test pits ranged in depth from 4 to 5 feet. No undisturbed sub- surface samples could be obtained owing to the nature and relative hardness of bedrock strata. All test pits were backfilled subsequent to examination, logging, and mapping. Logs of the test pits are included as Plates B-1 through B-3, inclusive. SITE CONDITIONS The subject property is located along the crest of the eastern portion of the Palos_ Verdes hills-: -The north- east boundary of the lot adjoins Flying Mane Road a cul- de-sac street that connects to Crest Road East on the north. The subject site at the time of this investigation was covered with indigeneous grasses,•wild oats, and other low growing vegetation. ,:I I • • Proj. Ref. 390-52 Fieger Topography -3- May 13, 1975 The upper portion of the ridge slopes gently to the south- east at a gradient ranging from about 8° on the north- west to 3° on the southeast. The southwest facing slope has• a relatively uniform slope ratio slightly flatter than 2 horizontal to one vertical for a vertical distance of approximately 200 feet to existing residences below along Ring Bit Road East. Drainage Essentially all drainage comprises sheet flow runoff of rainfall incident within site boundaries. In the past surface runoff has been minimal and has created no adverse erosional conditions. Most of the precipi- tation is apparently absorbed into the clayey soil. Ground Water No ground water was encountered in the test pits, and none is anticipated within depths pertinent to future residential development owing to the elevated position of the site in 'relation to the adj acent topography. Proj. Ref. 390-52 Fieger GEOLOGIC CONDITIONS Earth Materials Fill -4- May 13, 1975 No fill soils were observed at the site during the course of this investigation. Topsoil The soil. profile is characterized by a, relatively thin layer of medium brown silty clay ranging from 1.5 to 2.0 feet in thickness. The topsoil contains fragments and chunks of residual bedrock along with an occasional residual calcargillete boulder, often larger than 2 feet in the longest dimension. Dessication cracks on the surface of the topsoil indi- cate sitesoils to be expansive and not suitable for the support of footings or concrete slabs. Bedrock The subject site is underlain by marine sediments of the Altamira member of the Monterey formation of Miocene geologic age. The predominent rock types are bentonitic shale, clayey sandstone, diatomaceous,siltstone, and calcargillete (argillaceous_limestone): The__bedrock is anticipated to offer no significant resistance to grading with standard earth moving -equipment. Proj. Ref. 390-52 Fieger 5 May 13, 1975 GEOLOGIC STRUCTURE The geologic structure at the site is reflected to a degree by the topography. The southwest -facing slope is underlain by strata that dip westerly at angles ranging from 15° to 23° whereas on the northeast the strata dip gently in an easterly direction. Minor un- dulation in the bedding result in isolated anamolous strikes and dips that do not coincide with the overall structural pattern. This condition is common throughout the Palos Verdes area and results from the general in- competence of the Altamira strata when subject to the geologic forces present during periods of uplift and folding. GEOLOGIC STABILITY No evidences of surficial or gross instability were ob- served during the course of this investigation. How- ever, small creep movements within the topsoil horizon may be anticipated owing to relatively steep southwest slopes. In spite of the evidence of longtime stability of the subject property, the. -southwest portion of the lot below elevation 500 is undeiain by strata which exhibitn. adverse unsupported out -of -slope component of dip. The stability of this slope could _b ady_ersely affected if the slope were to be surcharged by the addition of .fill or if the strata were permitted to become saturated, eg. by seepage pit effluent. • • Proj. Ref. 390-52 Fieger LABORATORY INVESTIGATION -6- , May 13, 1975 No laboratory work was undertaken, or considered necessary) during the course of this investigation since proposed development considered a pad cut into firm bedrock strata obviously capable of supporting any loads that might be anticipated for residential construction. CONCLUSIONS AND RECOMMENDATIONS General Residential development of Lot 55 is considered feasible from a geologic standpoint subject to the specific con- clusions and recommendations presented herein. Since the nature or extent of any future grading is unknown at this time, no specific recommendations covering this phase of development are included herewith. Such data can•be provided when plans have been prepared. Grading Hazards. It is extremely important to recognize that site grading will be hazardous since large residual boulders of bedrock are present in the upper soils. These boulders can be easily dislodged and roll down slope onto res.i- dences below. A protective fence capable of stopping Proj. Ref. 390-52 Fieger -7- May 13, 1975 and retaining boulders with a diameter of 2 feet shall be maintained during all grading operations. The extent of the fence shall be sufficient to protect all down - slope properties. Fill Owing to adversely dipping strata throughout the south- westerly portion of the lot no fill shall be placed below elevation 500 on the southwest slope of the lot. If fill should be contemplated elsewhere, in the future' specific recommendations can be provided at that time. Cut Slopes Cut slopes with a maximum slope ratio 1.5 horizontal to 1 vertical to a maximum verticalleight of 20 feet are considered satisfactory for all slopes where the bedding planes do not project unsupported from the proposed slopes at angles in excess of 10°. The geo- rlogic conditions shall be reviewed during grading to verify the -absence of potentially unstable conditions. Sewage Disposal, Since sanitary sewers are unavailable, a private sewage disposal system will be required: The seepage pit shall be designed to minimize the likelihood of saturation of any future fill placed on the site and to minimize. Proj; Ref. 390-52 Fieger -8- May 13, 1975 the possibility of effluent escaping on the westerly slope which, in part is underlain by adversely dipping strata. A desirable location for the seepage pit would be in the vicinity of Flying Mane Road. The final decision as to exact location and specific design criteria shall be withheld until development plans are formulated. It is considered advisable, but not mandatory, to perform a percolation test at the time the seepage pit is ex- cavated in order to verify adequate permeabaity of sub- surface bedrock commensurate with code requirements.. Verifying an adequate percolation rate at the time the site is drilled could obviate periodic maintenance pump out expenditures or the necessity of drilling an addi- tional seepage pit at 'a later -date. Foundation Support All spread footings shall be placed 18 inches into bedrock. The foundation engineer or engineering geo- logist shall inspect the footing excavations during construction and approve the material on which the founda- tions are to be placed. ( An allocable bearing value of 2000 psf may be assumed for foundations placed in bedrock. The bearing value may be increased by 400 psf for each foot of additional depth of footing below adjacent ground to a maximum of 3000 psf. • ;CLASSIFICATION DESCRIPTION 0.0-2.0': Silty Clay (topsoil horizon; loose, —moist, brown;20-30% residua] bedrock fragments & chunks to 0.6' scattered throughout. Occasional resi- dual boulders to 2.0'. 2.0-5.0': Interbedded Very Fine Grained Sandstone & Bentonitic Siltstone. (Tma) Altamira member Monterey formation, Miocene geologic age. Bedding strikes and dips N60°W, 17°SW $ N70°E, 15°SE; bedding moderately well developed, planar to undulatory, tight, spaced (0.1-0.2'), discontinuous; moderately well indurated; intensely to moderately fractured (50% bedding, 50% joints); moderately weathered; separates preferentially along bedding surfaces; slick, moist to wet clay coating on some bedding planes; buff to light brown. MOISTURE U Z Z pI Z 0 caw tp»0O W _ Z Z_U) -11- or- CO- O L;t0... OVA p CO CZN WJ m= .tn NO co La °ZN~ . U _ W �U01L0 'GEOLOGIC SKETCH N 78° E ; �, 1 �� �� Y 1 1 YRock fragments Y 1 y Y 1 1 1 Y Y Y 1 0 1 1+ Y S.__r___ - residual boulder. ilty Clay ding :.� . Tma • Y d . Test pit bottom OM 'flail 1 1 1 1 1 1 1 1 1 1 ill 1 1 EQUIPMENT Case 1000 LOG. OF TEST PIT No.i, SURFACE ELEVATION513± PROJECT...Fieg.ex. C.x.e.St ., PROJECT No390- 52 LOCKWOOD-SINGH 6 ASSOC. _PLATE B-1 • • MN '5 .CLASSIFICATION DESCRIPTION 0.0-1.5': Silty Clay (topsoil horizon) looseymoist, medium brown; 30-40% caliche coated residual shale & sand- stone fragments & chunks to 0.6' scattered throughout. Occasional 2.0' residual boulders at surface. 1.5-5.0': Interbedded Clayey Very Fine -Grained Sandstone & Diatomaceous Siltstone W U Z Z �} p CC Z 0 taw o0 D W Y — Z Z I— Ln i J I— U F— q, p 5' ix ct• mz O Nz Z W mw wN m�tn ti o 0U Wr UO0 Bedding strikes and dips N15°-16°W, 15`- 23°SW; bedding poorly' to moderately we]1 developed, planar, tight, spaced (0.05'- 0.1'), discontinuous; poorly to moderately well indurated; intensely to moderately fractured (70% bedding) 30% joints); moderately weathered; limonite stains cn joints and bedding; does not saparate preferentially along bedding surfaces; buff to light red brown. GEOLOGIC SKETCH 1 1 1 1 1 h 1 I Y Rock fragments h J a N 80° E 0 i I 1 a a i residual boulde urface .-Silty Clay" f o 0 on test pit bottom 0 Y I 1 1 till 1 1 1 I EQUIPMENT Case 1000 LOG OF TEST PIT No. 2 SURFACE ELEVATIOa00t PROJECT..Eie.g.e.r.; J.r.e. t PROJECT No 3 9 0 _5 2 LOCKWOOD-SINGH S ASSOC, PLAT $- 2 • • ,CLASSIFICATION DESCRIPTION 0.0-1.5': Silty Clay (topsoil horizon) loose, moist, medium brown; 30-40% caliche coated.residual shale E sand- stone fragments & chunks to 0.6' scattered throughout. Occasional 2.0' residual boulders at surface. 1.5-4.0',: Interbedded Silicious'Shale, Sandy Shale & Diatomaceous Siltstone (Tma) Bedding strikes and dips N 83° W, 16° SW; bedding moderately well developed, planar, open,spaced (0.1-0.2'), contin- uous; moderately well developed; inten- sely fractured (50o bedding, 50% joint:) moderately weathered; limonite stains on joints and .bedding; separates pref- erentially along bedding i=,.}oint sur- faces; buff to light brown and gray. I 1Y .0 residua bouldero ' _ 5 . MOISTURE >- I- WZ Z Z YO Z W JN UOa 00- 0 0 Z p m W U Z W GEOLOGIC SKETCH N 68° B u Y X 1 1 1 d us Y Y Y r y I 1 tlY surface crock fragments silty clay 0 Tma ` Test pit bottomc....11 1 1 , 1 • 1 I 1 1 1 I 1 1 1 , 1 1 1 1 1 I ^- EQUIPMENT Case 1000 LOG OF TEST PIT NO.3 SURFACE ELEVATION 508 PROJECT Fieger-Crest PROJECT No 390-52 LOCKWOOD-SINGH_ S ASQC. PLATE B-3 i 9 BERLIALtiAli SCALE : I = 16` LOT 55 / 0 0 ot- 0 0 rn v- 518 - 502-- F-- w u 486-, Z 0 Q 470— w 0 0 451 R+ Natural Ground Stratification Tma stratification .undulatory GEOLOGIC CROSS SECTION A=A T N 60°E rC. Flying Mane Road T/C HORIZ. & VERT. SCALE: 1"=161 TO CREST. ROAD EXPLANATION. Tma - . Altamira member Monterey formation Miocene geologic age SYMBOLS 16 Strike & dip of strata Exploratory test pit GEOLOGIC MAP & CROSS SECTION FIEGER PARCEL LOT 55 55 E CREST ROAD ROLLING HILLS, CALIFORNIA LOCKWOOD-SINGH & ASSOCIATES ENGINEERS -GEOLOGISTS PROJECT 'N2 390 52 MAY,I975 PLATEV:A �.r • •