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Home My WebLink About30091 (Lot 99)coi y 5 - So dSl GEOTECHNICAL CONSULTANTS, INC. e* O."t, GEOTECHNICAL CONSULTANTS, INC. 0 1 November 29, 1977 S77192 Geotechnical Investigation, Lot 99, Tract 30091, Diamond Bar, County of Los Angeles, California For Mr. James Vaughn OC 7 P'o 7 2001 East 4th Street, Suite 102, Santa Ana, California 92705• Phone (714) 547-5413 INTRODUCTION This report presents the results of our geotechnical review and field observation of Lot 99, Tract 30091, Diamond Bar, County of Los Angeles, California. The purpose of our review and inspection was to obtain sufficient geotechnical data such that the stability of the lot could be evaluated and recommendations for lot development could be provided. Data obtained during our field observation, in addition to work by others, are presented on Plate 1 - Geotechnical Map which was adapted from a grading plan prepared by Caldwell -Klein, Architects, dated November 11, 1977. Subsurface geologic structure is depicted on Plate 2 - Geotechnical Section A -A'. The scope of our work was developed through discussions with Mr. James Vaughn and included: 1. Subsurface exploration with hand shovels and backhoe equipment, 2. Geologic logging of test pits and mapping surface exposures on the property, 3. Review of our files, 4. Analyses of all available data, and 5. Preparation of this report presenting our findings, a geologic map with a cross section and recommen- dations for foundation design. S77192 PROPOSED DEVELOPMENT 2 We understand that a one or two-story, sewered, single- family residence will be constructed on Lot 99. Proposed grading will created a nearly level pad at approximate elevation 1130 feet for partial support of the residence by excavating and exporting earth materials. No fill will be placed on the lot. The structure will be located along the eastern side of the lot adjacent to Flint Rock Road and will be sup- ported by conventional continuous wall footings on the front with floor slab on grade and by caisson grade -beam foundation system on the rear and sides. Two retaining walls, one above the other, ranging in height up to four feet will be constructed to support the proposed cut slope on the north corner of the lot. PREVIOUS REPORTS The fol I owing reports were reviewed by us during our inves- tigation: 1. "Final As -Graded Geologic Report, Rough Grading Completed, Tract 30091, Diamond Bar, California,' dated November 30, 1970 for E. L. Pearson and Associates (Job Num- ber 1-68-303-30). This report states that from a geologic standpoint, the rough grading is approved and there is a safe building area on each lot. Sheet 5A of the grading plans indicates that grading on Lot 99 consisted of creating an east -facing 12 horizontal to 1 vertical cut slope ranging in height to ten feet during construction of Flint Rock Road. Sheet 5A also indicates that bedding planes in the Puente Formation strike generally f' S77192 3 northeast and dip easterly at angles ranging from eight to 40 degrees. Some undulations and variations from the general trend are also noted. A restricted use area is noted on the western edge of the lot. 2. "Soil Engineering Report on Compaction Testing, Tract 30091, Lots 1 through 79, Diamond Bar, County of Los Angeles, California, 11 dated Nov- ember 30, 1970 for E. L. Pearson and Associates Job Number 1-68-303-31). This report indicates areas where compacted fill was placed under the control of Robert Stone and Associates. No fill was placed on Lot 99. This report also indicates that a small restricted use area exists on the western edge of Lot 99. Table II, "Analysis of Building Areas," lists Lot 99 under foundation category IIC, meaning the slope of the building area is steeper than 2 horizontal to 1 vertical and 11 horizontal to 1 vertical. The soil covering the natural slope is des- cribed as a sandy clay with a swell factor of 9.5 percent under a sur- charge of 60 pounds per square foot. The bedrock unit is designated as sandstone with a swell factor of 2. 5 percent under a similar load. EXPLORATION Exploration of the site was performed on September 29, 1977 and consisted of excavating one test pit to a depth of ten feet with back- hoe equipment. The steepness of the slope precluded access to lower parts of the property with the backhoe equipment and several pits were manually excavated on the steeper parts of the slope in the area of the proposed residence. All test pits were Logged in detail by an engineering geologist and a summary of the data obtained from the backhoe test pit are presented on Plate 3 - Log of Test Pits. A legend to the logs is presented on Plate 4. F S77192 FINDINGS 4 SITE CONDITIONS The site is on the west side of Flint Rock Road in Diamond Bar. As shown on Plate 1, previous grading on Lot 99 consisted of creating an east -facing 11- horizontal to 1 vertical cut slope up to ten feet in height during construction of Flint Rock Road. From the top of the cut slope, the property slopes westerly at an inclination of approxi- mately 12 horizontal to 1 vertical to a south -trending drainage channel. Maximum topographic relief on the property is approximately 95 feet. The majority of the site is covered with a moderate to dense growth of shrubs and weeds. Several large trees exist on the lower elevations of the lot. EARTH MATERIALS AND GEOLOGIC CONDITIONS Artificial Fill (af). Artificial fill was encountered to a depth of six feet in Test Pit 1 and consists of dry, loose, light brown, sandy silt with shale and sandstone fragments. As shown on Plate 1, fill exists only adjacent to Flint Rock Road and near the storm drain alignment on the southerly property line. As observed in the test pit, the fill is uncompacted and was probably placed as a result of excess material generated from excavation for the storm drain. Puente Formation (Tp) . As observed in the test pits, the Puente Formation consists of tan, dense, hard, massive, fine to medi- um -grained sandstone interbedded with brown and gray shale and silt - stone. iIt- stone. Bedding in the shale and siltstone units is spaced from one-half inch to one inch apart and is curvel inear and undulating in character. S77192 5 Bedding exposed in the east -facing roadcut strikes northwest to northeast and dips to the east from six to 15 degrees. On the natural west -facing slope, bedding strikes northeast to northwest and dips westerly from 18 to 34 degrees. Sandstone exposures in the stream channel display a gen- eral east -west strike and a northerly dip on the order of 12 to 15 degrees. The upper part of the slope is essentially a dip slope and the lower part of the slope exposes massive sandstone (see Plate 2). Topsoil and weathered Puente Formation materials were ob- served in the hand -dug test pits to be as thick as four feet. Local areas could have as much as eight feet of loose material that is subject to down- slope creep. GROUND WATER Ground water was neither observed in the test pits, nor found at the ground surface during our field observation. CONCLUSIONS AND RECOMMENDATIONS 1.0 FEASIBILITY Based upon the results of our review of available data and our field investigation, it is our opinion that it is geotechnically feasible to develop Lot 99 generally as proposed, provided the recommendations presented in this report are incorporated in the final plans. 2.0 SLOPE STABILITY The 12 horizontal to 1 vertical cut slope on Lot 99, approxi- mately ten feet high was created during construction of Flint Rock Road under the control of Robert Stone and Associates. This I S77192 6 slope will be removed during the proposed grading. No evidence of any instabi I ity was noted on the west -facing natural slope during our site observation. 3.0 DRAINAGE Drainage should be directed away from all structure founda- tions toward the street or other approved drainage device. Water should not be allowed to pond on the property or flow uncontrolled over the slope surfaces. 1 4.0 FOUNDATION DESIGN 4.1 General. The proposed one or two-story residential struc- ture can be satisfactorily supported on a combination of conventional continuous wall footings with floor slab on grade and a caisson - grade beam foundation system. The foundation materials will be essentially non -expansive under the anticipated footing and caisson loads. 4.2 Wall Footings. Support Penetrate all loose surface soils and weathered Puente Formation materials subject to downslope creep, into firm undisturbed bedrock of the Puente Formation. Bearing Value 2000 pounds per squarefoot for live and dead loads. Depth Minimum 12 inches below the lowest adjacent grade. Width Minimum 12 inches. Concrete As recommended by the local building code for residential foundation, but with a slump not exceeding four and one-half inches at the time of pouring. S77192 7 Reinforcement Two No. 4 bars - one at the top and one at the bottom. 4.3 Caissons. Support Penetrate all loose surface soils and weathered Puente Formation materials subject to downslope creep, into firm, undisturbed bedrock of the Puente Formation. Bearing Value 4000 pounds per square foot for live and dead loads. Lateral Bearing 400 pounds per square foot per foot of embedment into Puente Formation to a maximum value of 2000 pounds per square foot. Creep Loads 1000 pounds per foot of penetration through topsoil and weathered Puente Formation. Depth Minimum three feet into undisturbed bedrock of the Puente Formation. Diameter Minimum 18 inches. Concrete As recommended by the local building code for residential foundations, but with a slump not exceeding four and one- half inches at the time of pouring. 4.4 Floor Slab on Grade. Support Firm, undisturbed Puente Formation. Thickness At least three and five-eighths inches. Concrete As required by the local building code for residential foundations, but with a slump not exceeding four and one- half inches at the time of pouring. I577192 8 6.0 GEOTECHNICAL INSPECTION All foundation excavations should be inspected and approved by an engineering geologist to assure that all topsoil and weathered Steel Reinforcement 6 X 6 No. IO/No. 10 welded wire mesh properly centered in the slab. Moisture Barrier Plastic membrane, such as Visqueen, covered with at least one and one-half 1 inches of sand. 5.0 RETAINING WALL DESIGN Excavation for the proposed retaining walls in the north corner of the property may expose dayl ighted bedding planes. Analyses of the retaining walls were made to determine the earth loads on them and the overall stability of the slope. The analyses are attached as Plates 5. 1 and 5.2 - Stability Analyses. The re- sults of the analyses indicate the walls should be designed for active earth pressures equivalent to the pressures exerted by fluids weighing 30 pounds per cubic foot and 55 pounds per cubic foot for level and IZ horizontal to 1 vertical sloping surcharges, respective- ly. In addition to the active pressures, retaining walls should be designed for 30 percent of any other surcharge. Retaining walls should be backfilled with free -draining mater- ial. Footings can be designed using a bearing value of 2000 pounds per square foot; a friction coefficient of 0. 40 and a lateral bearing value of 400 pounds per square foot. 6.0 GEOTECHNICAL INSPECTION All foundation excavations should be inspected and approved by an engineering geologist to assure that all topsoil and weathered S77192 0 Puente Formation materials subject to downslope creep have been penetrated, and that the foundation system will be supported on undisturbed bedrock of the Puente Formation. The following attachments complete this report: Plate 1 - Geotechnical Map Plate 2 - Geotechnical Section A -A' Plate 3 - Log of Test Pit Plate 4 - Legend to the Logs Plates 5. 1 and 5. 2 - Stability Analyses Respectfully submitted, GEOTECHNICAL CONSULTANTS, INC. Ray Griffin Engineering Geologist 992 I I Joseph F. Montagna Civil Engineer 13408 JFM:RG:cb Q 0 O O N O O O O 1 -7 3 N/ /V 0/1 b'/1 -77-7 N U Q W I Q Q O a N Z O Z o N U z W a ti cr) J a) DJ kn Z Q O O U Z u J a V Z W rn ti W C) C!i O m W w V O Q 0 O O N O O O O 1 -7 3 N/ /V 0/1 b'/1 -77-7 S77192 Plate 3 LOG OF TEST PIT EXCAVATED September 29, 1977 WITH Backhoe T P -I PIT DIMENSIONS IN FEET W 2 L 8 D 10 SURFACE ELEVATION IN FEET 1115 DATUM Mean Sea Level GEOLOGICAL z 0w w o W ENGINEERING TEST DATA CLASSIFICATION Wuw m a- CLASSIFICATION AND D DESCRIPTION iZ oz U) W DESCRIPTION M ( RC) O FILL (af) SANDY SILT (ML_) I ight brown, 7. dry, loose with shale and sandstone fragments. Abun- dant roots throughout. 1110 5- SANDSTONE (R) tan, dry, dense, hard, massive, some - PUENTE 44 FORMATION (Tp) what friable, fine to medium - J N80W 56NE grained. J N 12E 80SE1 1 05 10 SHALE (R) gray and brown, B N38W 32SW moist, dense, bedding i inch B N27W 24SW apart. Bottom of test pit at 10 feet. No water, no caving. Test pit backf i I I ed. 15 PIT DIMENSIONS IN FEET W SURFACE ELEVATION IN FEET L D TP LEGEND ON PLATE A-2 5 10 15 LEGEND ON PLATE A-2 S77192 Plate 4 L EG E N D TO LOG S GEOLOGICAL ENGINEERING CLASSIFICATION CLASSIFICATION AND TEST DATA M DESCRIPTION DESCRIPTION RC) SOILSOIL -UNIFIED SOIL CLASSIFICA- MOISTURE CONTENT CONVENTIONAL TION SYSTEM WITH LETTER PERCENT OF DRY WEIGHT,'S- SYMBOL IN PARENTHESIS TERMINOLOGY INDICATES COMPLETE SATURATION ROCK -CONVENTIONAL TERMI- NOLOGY WITH (Rl FOR ROCK DRY DENSITY SYMBOLS POUNDS PER CUBIC FOOT y WATER LEVEL WATER SEEPAGE rOTHER TESTS PERFORMED M_ D _0 DS=DIRECT SHEAR TEST HEAVY CAVING-- SAMPLES AND CORES RC) UC =UNCONFINED COMPRESSION TEST TC=TRIAXIAL COMPRESSION TEST UNDISTURBED CN=CONSOLIDATION TEST EX=EXPANSION TEST LIGHT CAVING -- DISTURBED CP=COMPACTION TEST GS=GRAIN SIZE DETERMINATION UNSUCCESSFUL SAMPLING PM=PERMEABILITY TEST G E O L O G I C ATTEMPT SE=SAND EQUIVALENT DETERMIN- ST R U CT U R E CORING RUN ATION AL(45/10 = ATTERBERG LIM ITS B N 75W 50S BLOW COUNT FOR 12 INCH LIQUID LIMIT/PLAS- B=BEDDING) SAMPLER PENETRATION TICITY INDEX) CN15E 75W O.D.=321NCHES,12INCH DROP) RELATIVE COMPACTION C=CONTACT) 7 LBS.(DRIVING WEIGHTS) PERCENT OF MAXIMUM DRY STRIKE JN45W 85E 13) DENSITY OBTAINED BY LABORATORY AND DIP (J = JOINT) COMPACTION TEST ON REPRESENTATIVE l61 SAMPLE S N30E 45W S=SHEAR) FN15E20W F=FOLIATION) SYMBOLS FOR EARTH MATERIALS 000 COBBLES 000 0 0 O p o GRAVE L °o°o s ° O O SAN D SILT -- CLAY t SANDSTONE SILTST0N E SHALE CLAYSTONE GRANITE 1 Job No. S7?)2)7- R-ATa 5.-2- Title 2TitleST^L31 +f rr Apa AL- 5aS Project LOT9-) ' TQ-AC,7 005) By O Y M Chkd. 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