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Home My WebLink AboutCT 75-04; La Costa Lot 105; Soils Report; 1983-01-10GRADING AND COMPACTION REPORT LOT 105, CARLSBAD TRACT 75-4 LA COSTA AREA, CITY OF CARLSBAD SAN DIEGO COUNTY, CALIFORNIA Project No. 12S4W36-01 January 10, 1983 Prepared for: Mr. Wesley Hamilton 2715 Abejarro Road Carlsbad, California 92008 (619) 438-4627 ENGINEERING DEPT. LIBRARY City of Carl&ad 2075 Las Palmas Drive CarlsbaQ CA 92009-4959 ALIFORNlAGEOTEK,INC. 43094 Via DOS Picas, Suite B . Rancho California, CA 92390 l (714) 676-2782 January 10, 1983 Project No. 12S4W36-01 INTRODUCTION The subject lot has been tested for compliance with applicable City and County specifications. The work was authorized by IQ-. Wesley Hamilton and included: (1) inspecting the clearing and stripping, (2) performing earthwork quality control testing on the compacted fill, and (3) preparing this report presenting the findings, conclusions, and recommendations. Plate 1 - Test Location Plan (20-scale) in pocket Appendix A - Reference 12S4W36-01 FINDINGS Proposed Development A three bedroom, single level home is proposed. The construction in- cludes a lanai and patio area and a sub-level swimming pool. The swimming pool is to be constructed on the west half of the pad. Access to the pad will be provided by a concrete driveway extending easterly from Altiva Place along the southerly property line. Site Description The project is located on the east side of Altiva Place within Lot 105 of the La Costa Estates North development, Carlsbad Tract 75-4, in the La Costa area of Carlsbad, San Diego County, California. The lot slopes toward the west at a near uniform grade ranging from 16 to 20 percent. The site is covered with a growth of annual grass, weeds and shrubbery. A concrete lined drainage ditch exists at the base of the lot immedi- ately adjacent to Altiva Place. The ditch receives nuisance run- off from the upper areas and discharges the runoff directly into Altiva Place. The grading was performed by Beaver Construction (San Marcos) during the period between December 13 and December 21, 1982. A report titled "Report of Soil Investigation" dated August 27, 1982 and prepared by Geotechnical Exploration, Inc., was utilized during grading operations. The earth materials consist of a silty clay in the upper three to four feet which grades into a mottled sandy clay with occasional boulders. The upper three to four feet of the upper clayey material is in a natural state of near saturation and appears to be expansive. The presence of this moisture condition in the upper clayey material necessitated care- ful blending and mixing with the sandier soils. Any potentially detri- mental clays that would not readily mix with the sandier materials were discarded in a rock stockpile. Excavated boulders having a maximum average diameter less than, or equal to 12-inches were allowed to remain in the lower fill material. Boulders larger in size were stockpiled, to be removed from the site at a later time. The natural ground in the area to be graded was stripped and cleared and the vegetation was stockpiled for removal from the site. Pad grading was a function of balancing cut and fill site soils. Approx- imately 800 cubic yards were surplus after placing and compacting the fill. This surplus yardage was mostly comprised of rock and other un- suitable materials. The maximum cut is approximately 17 feet and the maximum fill depth is approximately 13 feet. -2- 1254#36-01 Grading (continued) A keyway was constructed along the toe of the entire fill slope for purposes of slope stability. The keyway ranges in width from 13 to 20 feet and slopes at approximately two percent into the natural ground slope. The maximum cut at the natural downslope end is two feet, while the maximum cut at the upslope end is approximately six feet. The material at the base of the keyway was scarified and precompacted to a minimum of 90 percent relative compaction. A portion of the clay material within the keyway was determined to contain excessive moisture, and was removed and mixed with drier, sandier soils. The fill soils were placed in lifts of approximately 6-inches uncompacted thickness, and track rolled using a Caterpillar D6D and a dual sheepsfoot roller. Pad area excavation was accomplished using a Caterpillar D8K. Initial site scarification, clearing and keyway excavation and pre- compaction was achieved using a Case 1450 tractor, with a dual sheeps- foot roller. Natural moisture in the soil was adequate for compaction during the complete grading operation.. The fill slopes were rolled with a dual sheepsfoot and sloped at inclinations approximately 2.0 horizontal to 1.0 vertical except along the southerly fill slope, adjacent to the driveway. At this location the lower five to six feet of fill were cut to a near vertical position. A retaining wall will be constructed along this face. The cut slopes were graded to an approximate inclination of 1.5 hori- zontal to 1.0 vertical except along the far northeast corner where the bank is cut to a near vertical position and a retaining wall will be constructed. Sloping was achieved with a slope board mounted on the D8K tractor. A brow ditch was constructed along the top of the cut slope. A portion of the fill area anticipated for placement of a swimming pool was left at a finished grade difference of approximately 2.5 feet. This area is along the west end of the fill. Several non-rippable rocks re- main on the pad grade. They extend approximately a maximum height of three feet above existing pad grade. Compaction All tests were performed in accordance with ASTM D1556-64. The maximum density applied was determined in accordance with ASTM D1557-78. The test locations are shown on Plate 1 and the results are summarized below: -3- 1254W36-01 ;yl/ A 1 2 3. 4 4A 5 6 7 8 9 10 11 Location Depthl-’ Keyway 9.0 Keyway 8.0 Keyway 6.0 Keyway 9.5 Keyway 9.5 Pad 7.0 Pad 4.0 Pad 5.0 Pad 3.0 Pad 1.5 Pad 1.0 Pad 1.0 11 4A represents a retest. The retest was required due to the excess Dry Density, pcf Moisture, % Relative Field Max Field DJ& Compaction, % -- 101.8 102.0 107.3 88.8 105.6 105.4 112.9 111.1 112.7 106.8 105.5 104.8 113.0 113.0 117.0 113.0 117.0 117.0 117.0 117.0 117.0 117.0 117.0 117.0 17.1 16.0 90 22.7 16.0 90 11.4 11.5 92 31.0 16.0 79 12.6 11.5 90 13.8 11.5 90 13.2 11.5 97 16.6 11.5 95 16.0 11.5 96 13.3 11.5 91 14.7 11.5 90 13.0 11.5 90 natural moisture in the soil. The material was removed, blended with more suitable material and then recompacted. 11 To center of test below finish grade, feet -4- 12S4W36-01 CONCLUSIONS AND RECOMMENDATIONS Conclusions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. The fill has been compacted to a minimum of 90 percent relative compaction based on ASTM D1557-78 (unweighted -average - 92 percent). A single level, three bedroom house is proposed for construction. The lot slopes in a westerly direction at a near uniform grade ranging from 16 to 20 percent. The vegetation was removed from the grading area prior to place- ment of the compacted fill. Boulders to a maximum size of 7 feet were encountered during the excavation. Boulders having a maximum average diameter greater than 12-inches were not utilized within the fill. The 12-inch and smaller rock was placed in the fill below the upper three feet. The unusable rock was stockpiled for subsequent removal. The residential pad is a transition pad (i.e., cut and fill). The upper three to four feet of in-situ soil is a blocky, silty clay, with desiccation cracking in the upper 12-inches and approaching near saturation in the lower three feet. The soils below the blocky clay layer consist of a mottled, sandy clay with intermingled boulders. Several boulder exposures remain on the pad achieving a maximum height of three feet. A report titled, "Report of Soil Investigation", dated August 27, 1982 was utilized for grading control purposes. The findings indicated in that report are consistent with the field conditions encountered during this grading activity, with the exception of the magnitude of the encountered boulders. -5- 12S4W36-01 Recommendation 1. The recommendations as called out in the report titled "Report of Soil Investigation" prepared by Geotechnical Exploration, Inc., are adequate for design purposes. Respectfully submitted, &iJ@&i+ David F. D'Auria Civil Engineering Associate Bruce R. Lee VE 23396 DFD/BRL/al Distribution: Addressee (3) 12S4W36-01 APPENDIX A Reference Geotechnical Exploration, Inc., "Report of Soil Investigation, Proposed Residential Lot Split, 346+ Feet South of the Northern Terminus of Altiva Place, La Costa area, Carlsbad, California", August 22, 1982 Ai