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Home My WebLink AboutCT 13-05; 2531-2589 STATE STREET; GEOTECHNICAL RECOMMENDATIONS; 2014-10-15Geotechnical, Inc. October 15, 2014 Project No. 13200-01 Ms. April Tornillo Taylor Morrison 8105 Irvine Center Drive, Suite 1450 Irvine, CA 92618 Subject: Geotechnical Recommendations for Proposed Deepened Caisson Footings Adjacent to the Existing 66-inch Storm Drain Easement, State Streel Townhomes, 2531 through 2589 State Street, City of Carlsbad, California Introduction In accordance with your request, LGC Geotechnical, Inc. has prepared this report to provide recommendations for the proposed deepened caisson footings for building foundations adjacent to the existing storm drain easement for the proposed State Street Townhomes between 2531 and 2589 State Street, in the city of Carlsbad, California. Background An existing 66-inch storm drain transects the proposed residential development site at a depth of approximately 9 feet below ground surface to top-of-pipe. Following development, homes will be located approximately 7.5 feet horizontally from the edge of the buried storm drain. As noted by the City Engineer, building foundations adjacent to the storm drain easement are not to induce horizontal or vertical loading of any kind onto the existing storm drain line. As a result, deepened caisson footings are required to satisfy the said requirements imposed by the City. Deep Foundation Recommendations We recommend the proposed deepened footings be designed utilizing support from Cast-In-Drilled Hole (CIDH) piles. These piles may be designed to resist axial dead and live loads using an allowable skin friction of 500 psf from the top of the existing storm drain elevation to the tip elevation of the proposed caisson. Per the City Engineer, the designed caissons must extend below the bottom elevation of the existing storm drain- line. An allowable end bearing of 3,500 psf may be utilized in the design of these piles. Piles shouldi,e spaced at a minimum on-center spacing of three times the pile diameter For short duration seismic loading pile capacities may be increased by '/3. The pile capacities are based n soil resistance only and may be further limited by the pile-head connection details and structural material strength. Total soil settlemeLdue to structural foundation loads is estimated to be less than '/2 cf an inch or less. Differential settlement may be taken as V2 of the total (i.e., '/4 of an inch over 40 horizontal feet). The attributed loading applied to the proposed deepened caisson footings is to be taken as the structural loads within a one to one projection from the bottom of the existing storm drain through to the adjacent building slab-on-grade. Pile borings should be plumb and free of loose or softened material. Extreme care in drilling, placement of reinforcement steel and the pouring of concrete will be essential to avoid excessive disturbance of pile boring walls. The pile reinforcing cage should be installed and the concrete pumped immediately after drilling is completed. Concrete mix design should include provisions to minimize shrinkage which can reduce frictional resistance of the pile shaft. A representative from LGC Geotechnical should be onsite full time during the drilling of piles to verify the assumptions made during the design stages. Pile holes must not be left open overnight. Geotechnical Observation/Testing During Grading and Construction The recommendations provided in this report are based on limited subsurface evaluation, field observations, and geotechnical analysis. The interpolated subsurface conditions should be checked in the field during grading and construction by a representative of LGC Geotechnical. Geotechnical observation and/or testing should be performed by a field representative from our office at the following stages: During drilling and installation of Cast-In Drilled Hole (CIDH) foundations; and When any unusual soil conditions are encountered during any construction operation subsequent to issuance of this report. Limitations Our services were performed using the degree of care and skill ordinarily exercised, under similar circumstances, by reputable soils engineers and geologists practicing in this or similar localities. No other warranty, expressed or implied, is made as to the conclusions and professional advice included in this report. Project No. 13200-01 Page 2 October 15, 2014 We appreciate this opportunity to be of service. Should you have any questions or concerns regarding this letter, please do not hesitate to contact our office. Sincerely, LGC Geotechnical, Inc. of ES CERTIFIED C') (\::o ENGINEERING T'No. çE217 GEOLOGIST 26M ZD Tim Lawson, CEG 1821, GE 2626 14 /16 Geotechnical Engineer/Geologist CA?L* OF CA TJL/ASR/kmb Attachments: References Geotechnical Map and Cross Sections Distribution: (3) Addressee (3 wet-signed copies, 1 via email) (1) Adams Streeter Civil Engineers, Inc. (via email) Attention: Mr. Mohammad Adabadi (1) Amid Engineering Group, Inc. (via email) Attention: Mr. Mansour Amid (1) Mr. Marshal Mead (via email) Project No. 13200-01 Page 3 October 15, 2014 References Adams Streeter Civil Engineers, Inc., 2014, Precise Grading Plan, State Street Townhomes, Carlsbad, California, date plotted October 14, 2014. Lew, et al, 2010, Seismic Earth Pressures on Deep Basements, Structural Engineers Association of California (SEAOC) Convention Proceedings. LGC Geotechnical, Inc., 2014a, Preliminary Geotechnical Evaluation for the Proposed State Street Townhomes, 2531 through 2589 State Street, City of Carlsbad, California, Project No. 13200-01, dated July 3, 2014. 2014b, Geotechnical Recommendations for Trench Excavation to Expose Existing 66-inch Storm Drain after Construction of the Proposed Development, State Street Townhomes, 2531 through 2589 State Street, City of Carlsbad, California, Project No. 13200-01, dated October 9, 2014. Project No. 13200-01 References October 15, 2014 sson Footings Actual Locations tr! Fnaief 1' LtiLJ State Street SCALE: 1"=20' 20' 0 20' 40' 2 2' Design UNIT Profile 1j UNIT 10 FF42.50 FF=42 40 ClV TTCN .AC:v, DEEPENED CAISSON FOOTING Af ENGINEER EXISTING W- PER STRUCTURAl. Qt - - ELEV.=24,5 2SwT2V. BOTTOM OF CAISSON Horizontal Distance (Feet) 1 1' Design ProfileProfile UNIT 31 UNIT 30 FF=45.00 - ., FF=45 30 DEEPENED COSSOR FOOTING PER STRUCTURAL A f EXISTING 6&- ENGINEER STORM DRAIN / Qt V, -U' ELEV.=24.5 25T01NV. BOTTOM OF CAISSON Horizontal Distance (Feet) SCALE: 1"=20' 20' 0 20' 40' Legend: Approximate Limits of Deepened Caisson Footings. Actual Caisson Locations to be Determined by Structural Engineer 2 Approximate Location of Geotechnical Cross Section I I .' Approximate Report Limits Af Engineered Fill Material (::0 :) Quaternary Terrace Deposits, circled where buried Geo technical Map of Caisson Supported Footings CLIENT: Taylor Morrison 8105 Irvine Center Drive, Suite 1450 Irvine, CA 92618 CIVIL ENGINEER: Adams Streeter 15 Corporate Park Irvine, CA 92606 PROJECT NAME State Street - Carlsbad PROJECT NO. 13200-01 ENG./GEOL. TJL SCALE 1 inch = 20 feet DATE October 2014