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none, Remodel & addition to existing, CorrespondenceLockwood -Singh & Associates A CORPORATION Consulting Foundation Engineers and Geologists 9977 Jefferson Boulevard • Culver City, California 90230 Telephone: (213) 870-7335 R. RRUGE LOCKWOOD, R.E.G A WTAR SINGft. C E November 19, 1975 Dr. Donald Thompkins No. 11 Saddleback Road Rolling Hills, California SUBJECT: Proj. Ref. 466-52 E[vED AUG 03 U5 90274 City of Rolling Hills By GEOTECHNICAL INVESTIGATION LOT 48, ROLLING HILLS 201/32 NO.'11 SADDLEBACK ROAD ROLLING HILLS, CALIFORNIA 90274 Dear Dr. Thompkins: In accordance with your request, we are pleased to submit a report of a geotechnical investigation for proposed residential construction at the address referenced above. The accompanying report has been substantiated by sur- face and subsurface exploration and geologic investi- gation made in accordance with generally accepted engineering practice, including those field and laboratory tests considered necessary in the circumstances. It is the professional opinion of the undersigned that this report presents fairly the information requested by you. Respectfully submitted, LOCKWOOD-SINGH,& ASSOCIATES R. Bruce Lockwood REG 204 RBL/AS/HAT:ml 4 Awtar Singh CE 17727 INTRODUCTION This investigation was undertaken in order to obtain information on surface and subsurface geologic and :soil conditions on Tentative Tract 31906. The tentative tract is a subdivision of Lot 48 of Rol- ling Hills. Since there is an existing residence and no additional development is contemplated on Lot 1, this investigation is concerned primarily with Lot 2. This study provides recommendations concerned with grad- ing and foundation design for a future residence on Lot 2. A 40-scale grading plan of the site prepared by South Bay Engineering Company was utilized herein (Plate A) for delineation of geologic data. A geologic cross-section was prepared and is included on Plate A. Proj. Ref. 466-52 Thompkins -2- November 19, 1975 FIELD INVESTIGATION - Field investigation included geologic reconnaissance of the subject property and adjacent areas together with the examination and logging of 3 exploratory test pits excavated with a backhoe tractor to depths ranging from 5 to 8 feet. Bag samples of site soils were obtained for subsequent laboratory testing. All test pits were backfilled following examination, logging, and geologic mapping. Logs of the test pits are in- cluded as Plates B-i through B-.3, inclusive. SITE CONDITIONS Location $ Topography The 'subject property is located on a north trending ridge on the north flank of the central portion of the Palos Verdes Hills. Elevations above sea level within the proposed area of construction range from about 180 to 196 feet. The ridge slopes northwesterly at ratios of approximately 8 horizontal to 1 vertical in the a ea of proposed grading. Ground Water & DrainaE No conditions of excessive erosion or instability were observed during the course of this investigation. No Proj. Ref. 466-52 Thompkins -3- November 19,,1975 evidence of near -surface ground water was encountered in the test pits and none is anticipated within depths pertinent to proposed construction owing to the elevated position of the site with respect to adjacent drainage courses. Surface drainage comprises sheet flow runoff of incident rainfall derived primarily within the parcel boundaries. GEOLOGIC CONDITIONS Earth Materials Fill No fill was present on the parcel at the time of the investigation. Topsoil The lot is mantled .by'firm,to stiff, moist, dark brown fat clays. Topsoil thickness ranges from 2.0 feet as noted in Test Pit No."3 to 4.0 feet in Test Pits No. 1 and 2. Dessication cracks present in the surface soils indicates them to be expansive. Expansiveness is that soil property whereby a volume change results from a change in moisture content. Bedrocks The site is underlain by marine sediments of the Alta- mira member of the Monterey formation of Miocene geologic Proj. Ref. 466-52 Thompkins -4- November 19, 1975 age. At this location the Altamira consists of poorly indurated, buff colored diatomaceous clayey and sandy shales. No difficulty of excavation is antici- pated. GEOLOGIC STRUCTURE AND STABILITY Bedding plane attitudes exhibited in the Altamira strata are northwesterly dips ranging from 15° to 39°. Minor undulations contribute to isolated anomalous attitudes that deviate from the overall pattern. These structural. variations are common in the relatively soft shales of the Altamira throughout the Palos Verdes area. No evidence of recent or past geologic instability was observed on the subject property, and bedding inclina- tions are considered favorable for continued stability since they are inclined at angles considerably steeper than the natural slope or dip neutrally with respect to the slope direction. Factors contributary to the continued gross site stability, include relatively gently sloping topography and the favorable bedding plane attitudes. •, 0 • 0 Proj. Ref. 466-52 Thompkins -5- November 19, 1975 LABORATORY INVESTIGATION . Laboratory testing was programmed following a review of the field data and consideration of the probable foundation design to be evaluated. Laboratory testing included determination of the compaction characteris- tics of proposed fill soils and swelling indices of site bedrocks and topsoil horizon. Compaction characteristics of probable fill soils derived from site bedrocks and soil horizon are shown on Table I, "Summary of Laboratory Density Determina- tions." The fat clay topsoil (Soil C) horizon ex1bited a swell- ing index of 110 which places it in the highly expan- sive category. Similarly, the clayey diatomaceous shale (Soil A) with an index of 80 may be classified as moderately expansive and sandy diatomaceous shale (Soil B) bedrocks have swelling index of 35.may be classified as slightly expansive. All expansion tests were subject to a surcharge of 144 psf. Proj. Ref. 466-52 Thompkins -6- November 19, 1975 TABLE I. SUMMARY OF LABORATORY DENSITY DETERMINATIONS • Optimum Soil Maximum Dry* Moisture Content Type Description Density (Pcf) (% dry wt) A comminuted, buff diatomaceous shale bedrock 84.0 27.0 B comminuted, buff sandy diatomaceous bedrock 109 .0 16.5 C Black fat clay (topsoil horizon) 100.0 21.5 *Compaction standard ASTM D-1557-70 (5 layers) Proj. Ref. 466-52 Thompkins -7- November 19, 1975 CONCLUSIONS AND RECOMMENDATIONS Based on field and laboratory investigation it is the professional opinion of the undersigned that the pro- posed subdividion is feasible from the standpoint of geotechnical conditions. Since no specific construction plans have been prepared at this time, the following recommendations are to be considered general and subject to review prior to commencement of actual development. Fill Compacted fill slopes with a maximum vertical height of 10 feet are considered satisfactory if constructed at slope ratios not exceeding 2 horizontal to 1 vertical (2:1). If topsoil material is used in the fill the slopes may be subject to downhill creep, however, no structural distress is anticipated if the footings are placed in bedrock (See section on foundation support). Cut Slopes Cut slopes no steeper than 2 horizontal to 1 vertical (2L1) to a maximum height of 8 feet are considered satisfactory. The geologic conditions shall be reviewed by the engineering geologic during construction to verify the absence of potentially unstable conditions. Surface Stability of Fill Slopes Since the probable fill materials are cohesive rather than granular in nature, excessive erosion of fill slopes is not anticipated. Proj. Ref. 466-52 Thompkins -8- November 19, 1975 Drainage An adequate surface drainage system shall be provided to direct runoff to adjacent natural drainage courses in a manner to minimize surface erosion. Foundation Support All spread footings shall be placed a minimum of 12 inches into site bedrocks. No footings are to be placed in the expansive surface soils. Since site bedrocks display low to medium expansion a No. 4 reinforcing steel bar shall be placed at the top and bottom of the footings. An allowable bearing value of 1500`psf may be assumed for foundations placed in site bedrocks. The bearing value may be increased by 400 psf for each foot of addi- tional depth of footing below adjacent ground surface to a maximum of 3000 psf. Floors Since the' soils are expansive, conventional wood floors are recommended., However, if slabs on grade are used they shall be supported by a minimum thickness of 2 feet of granular non -expansive soil in order to mini- mize the effects of the underlying expansive soils. Proj. Ref. 466-52 Thompkins -9- November 19, 1975 Such slabs shall have a minimum thickness of 4 inches and be reinforced with at least No. 3 bars spaced at 24 inches on center both ways, or 6x6-6/6 WWF. At a minimum No. 3 bars;at 24 inches shall be provided in the footings and be bent 3 feet into the slabs. A moisture barrier consisting of at least 4 inches of crushed rock, or plastic waterproof vapor barrier, such as vinyl with a thickness of at least 6 mils, is recommended for placement beneath the slab to prevent upward capillary movement of soil moisture. The compacted subgrade soils up to 30 inches below low- est adjacent gradeof floor slabsand paving shall be premoistened to at least 5% above the optimum moisture content. The placement and compaction of fill soils shall be under the observation of the foundation engineer. Sewage Disposal Since sewers are unavailable, a private sewage dis- posal system will be required. A seepage pit for the site shall be designed to minimize the likelihood of saturation ofproposed fills'or seepage from the natural slope. Proj. Ref. 466-52 Thompkins -10- November 19, 1975 It is considered advisable, but not mandatory, to per- form percolation tests at the time the seepage pits are excavated in order to verify adequate permeability of subsurface bedrock commensurate with code require- ments. Verifying an adequate percolation rate at the time the pits are drilled could obivate costly main- tenance or the necessity of drilling additional pits at a later date. Grading Specifications 1. Prior to placement of compacted fill, the site shall be cleared of all vegetation, loose topsoil, de- bris, and any other deleterious materials. 2. Natural slopes steeper than 5 horizontal to 1 vertical shall be benched prior to placement of fill. The toe of fill slopes shall be provided with a key with a.minimum depth of 3 feet into the firm bedrocks. 3. Exposed surfaces receiving fill soils shall be scarified, aerated or moistened to near optimum moisture content, and compacted to at least 90% of the maximum density as determined by ASTM D-1557-70. Proj. Ref. 466-52 Thompkins -11- November 19, 1975 4. All fill soils shall be placed at or within 3% of optimum moisture content in lifts not exceeding six (6) inches in thickness and compacted until field density tests indicate that a compaction of not less than 900 of the maximum density has been obtained as determined by ASTM D-1557. If the excavated natural soils to be used in the fills are above optimum moisture content, they shall be dried by windrowing or other means. Additional water shall be added in case such fill soils are below optimum moisture content. 5. Field density tests shall be made in accordance with ASTM D-1556. Field density tests shall be made every 2 feet and not less than one test per 500 cubic yards of fill placed. 6. Rocks larger than 6" in greatest dimension shall be excluded from the fill except with the express approval and in accordancewith the recommendations of the foundation engineer. 7.• All slopes shall be compacted in a single continu- ous operation, or all loose soils remaining on the slopes shall be trimmed back until a surface with a compaction no less than 90% is. exposed. 8. Planting and irrigation of cut and fill slopes and installation of erosion control and drainage shall comply with the requirement of the County Building Law. Proj. Ref. 466-52 Thompkins -12- November:.19, 1975 Inspection As'a necessary requisite to the use of this report, the following shall be observed by the foundation engineer. or the engineering geologist. 1. Inspection of clearance of vegetation, loose topsoil, debris, and any other deleterious materials prior to placement of compacted fill. 2. Inspection. and testing of all compaction infill which includes key sections, exposed slopes, and back - fills behind retaining walls. 3. Inspection of all surfaceand subsurface drainage systems and drainage trenches for the compacted fill. 4. Inspection of drainage blankets behind any retain- ing walls. 5. Geologic inspection of all cut slopes in bedrock and natural soil and key sections for compacted fills. 6. ' Inspection of all foundation trenches for the structure of retaining walls. 7. Inspection of subgrade soils, premoistening of sub - grade soil, and placement of sand cushions shall be required prior, to the construction of. slabs. Proj. Ref. 466-52 Thompkins -13- November 19, 1975 REMARKS The conclusions and recommendations contained herein are based on the surface exam nation and the findings and observations of the test pit locations with an interpolation of soil conditions between test pit locations. Although no significant variations in soil conditions are anticipated, if conditions are encountered during construction which appear to be different from those disclosed by the exploratory work, this office shall be notified so as to consider the need for modification. Your atteition is directed to the fact that while cav- ing was not encountered in the test pits, all shoring and bracing shall be in accordance with current require- ments of the Industrial Accident Commission of the State of California and other public agencies having jurisdiction. The report is subject to review by controlling public agencies having jurisdiction. _0 5 CLASSIFICATION DESCRIPTION 0.0-4.0': Topsoil dry to moist, stiff fat clay, 4.0-6.5': Clayey Diatomaceous Shale (Tma) Bedding strikes and dips N50°W, 11°SW, bedding poorly developed; tight, discontinuous; punky to poorly indurated; moderately fractured; intensely to moderately weathered; limonite stains on joints : a,id bedding; Mn02 stains on discontinuitie;; does not separate preferentially along beding surfaces, buff -pastel yellow with rust colored interbeds. GEOLOGIC SKETCH 2uia-faicel Topsoil Tina I w o z z )-OO M w x- z{ t7zr-,n i I- JF- U00.6j tiiN OD 00IL.j o z az w°.. coU Nin o wo UON S 5° W bedd' g Test Pit Bottom 11. EQUIPMENT Backhoe LOG OF TEST PIT No. 1 SURFACE ELEVATIONiS2{ PROJECT Thompkins-Saddleback PROJECT No'466-52 . LOCKWOOD-SINGH € ASSOC. PLATE B-1 . -0 5 CLASSIFICATION DESCRIPTION 0.0-4.0': Topsoil dry to moist, stiff fat clay } I- O r} O z L u O DW Y- 2 - G F- l7 1• -II- UH Q,_, ' In O S�z �0: 0� InZN� m 2 U z CO id c �No 0 0� 4.0-8.0': Sandy Diatomaceous Shale (Tna) Bedding strikes and dips N 10° E, 8-15°NW, bedding poorly developed, tight, discontinuous; punky to poorly indurated; moderately fractured; intensely to moderately weathered; limonite stains on join:s and bedding, MnO stains on discontinuities. does not separatt preferentially along bedding surfaces; buff and pastel yellow' with rust colored interbeds bedd n I i a GEOLOGIC. SKETCH N 75° W ile-surface fTopsoil Tma Test Pit Bottom EQUIPMENT Backhoe LOG OF TEST PIT No.2 SURFACE ELEVATION 196. - PROJECT T.i pkin.S.:5addleback PROJECT No:466-52 LOCKWOOD-SINGH € ASSOC. PLATE:B-;2 _0 • _5 CLASSIFICATION DESCRIPTION 0.0-2.0': Topsoil dry to moist, stiff fat.clay >- H 0 D Z Y0 — Zg z~inO - .I H cad ES a- o a ,;) in 0 ON Occ 00 wzn?t- • hZ aQ ow m-mil or- O z c ONp U 0 2.0-5.0': Clayey Diatomaceous Shale ("ma) Bedding strikes and dips N65-85°E, 25-39°NW; bedding moderately well developed, tight, discontinuous; poorly indurated; intensely to moderately fractured (50o bedding, 50% joints); moderately -intensely weathered; limoni:e stains on joints; separates preferentially along bedding surfaces; mottled buff., and reddish brown. GEOLOGIC SKETCH surface N 45° W • �-Topsoil J ma Test Pit Bottom EQUIPMENT • Backhoe LOG OF TEST PIT No. 3 SURFACE ELLVATIONTB2. PROJECT.,..T.b.QTpkin.s.: Saddleback PROJECT No:...,466. 52 LOCKWOOD-SINGH e ASSOC. PLATE B-3 • dB dtpiton.stN011,sAs5.4rAtt : • ; • ..• ..,„ ' • . . 4' Tentative Map 'No. 319 0G COUNTY 0 F' LOS ANGELES THE REGIONAL PLANNING COMMISSION OWNER'S STATEMENT Date a f 12/15 tft The following information is required by the various County Departments. Failure to furnish required information will delay action. LEGAL DESCRIPTION (All ownerships comprising the proposed division of land.) (U e e tra §hget if ne ess ry.) Bock o 1; Po,tps 2.9 icy 3 5 c, Nkgyp AREA: What is the acreage of this division of land? 32.5 Number of Lots 2 ZONING: Present: 241. -1 Proposed:_, -I DOMESTIC WATER: Source (Water Co.) Ca.Ui�':. Wes.Jtee Seryyse.. Co. SEWAGE: Method of Sewage Disposal Qriva*... GRADING: Is any grading of lots contemplated? Yes No i'e If yes, show the preliminary grading design on tentative map. STREET IMPROVEMENTS:• Are standard street improvements contemplated?. Yes No ye, Are private streets. planned? Yes No }� USE: Indicate lot numbers under proposed use. Single Family li a Multiple Res. Other Record Owner(s) (Attach separate sheet if necessary) • Name D.2. T betntee- G. Tpw.cle.: s Address Al' 11 Seal Raout City Rolli% \kwt zip code cb=14 CONSENT (to be I consent to Signe' f .. j/ At leas one record owner) CERTIFICATION: I hereby certify that the above best of my knowledge. Signed Commercial Industrial Agricultural Subdivider Name G ^"61-L;$ 408g:;0614: Address ;U a, ..(,L_ Phone 377.o1(. , City ip code Subdivider's Agent (Engineer, Licensed Surveyor, other) Name '54 SZ!_ey 'rC.tiReeriv Corr. Address 30¢ -1140,n 9 o,,ct City 4o,Venkos Ez�d�� Phone 172 -1655 , gierk zip code • gned if owner of record is not subdivider) submissi 7of entative map accompanying this .statement. Phone 377-0/ ?. c'.. (Subdivider or Subdivider's Date ,'/'T :'%►��� information is correct to the Date _11'l'241c #8