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HomeMy WebLinkAboutCDP 2017-0043; FRANCIS RESIDENCE; GEOTECHNICAL SUMMARY OF ROUGH GRADING; 2020-02-24Geotechnical • Geologic • Coastal • Environmental 5741 Palmer Way • Carlsbad, California 92010 • (760) 438-3155 • FAX (760) 931 -0915 • www.geosoilsinc.com February 24, 2020 W.O. 7279-B/F-SC Mr. Mark Francis 3385 Blodgett Drive Colorado Springs, Colorado 80919 Subject: Interim Geotechnical Report of Rough Grading and Retaining Wall Construction, Planned Single-Family Residence, 1585 Triton Street, Carlsbad, San Diego County, California, Assessor's Parcel Number (APN) 215-070-51, City of Carlsbad Project No.: CDP2017-0043, Drawing No.: 507-5A Dear Mr. Francis: In accordance with your request and authorization, GeoSoils, Inc. (GSI), is providing this interim geotechnical report of rough grading and retaining wall construction within the subject property, as shown on the project grading plans (Engineering Design Group [EOG], 2019 [seethe Appendix]). During grading and retaining wall construction, line and grade was the responsibility of others, and not GSI. A comprehensive final compaction report, presenting the tabulated compaction test results and a map showing the approximate locations of the compaction tests, and the as-graded geotechnical conditions will be provided at the conclusion of all earthwork construction activities within the subject property. Unless specifically superseded herein, the conclusions and recommendations provided in the referenced geotechnical reports (see the Appendix), are still considered valid and applicable, and should be appropriately implemented during the balance of project design and construction. SUMMARY OF GRADING AND RETAINING WALL CONSTRUCTION Grading and retaining wall construction within the subject property began around the middle of January 2020 and was generally completed on February 21, 2020. Geotechnical . observation and field density testing during rough grading and retaining wall construction were performed on an as-needed part-time basis as requested by the project general contractor. Initial earthwork operations involved the excavations for the San Diego Regional Standard (SDRSD) C-04 retaining wall foundation along the southerly and westerly property lines, and the SDRSD C-02 retaining wall foundation near a portion of the easterly property margin. The retaining wall foundation excavations were observed to extend into suitable bearing materials and were completed in general accordance with GSI recommendations. Following construction of the retaining wall footings and stem, subdrains were installed behind the retaining walls and the walls were backfilled. Where performed, our observations indicated that the wall subdrain construction generally conformed to GSI recommendations. Observations and field density testing indicated that the retaining wall backfill was compacted to at least 90 percent of the laboratory standard (per ASTM D 1557), where tested. Remedial grading in the existing building pad was performed concurrently with the retaining wall backfill. This included the removal and recompaction of undocumented artificial fill as well as weathered, near-surface structural fill materials placed during the original phase of site grading in early 2004 (GSI, 2004). In general, remedial grading excavations within the existing building pad extended to depths on the order of 18 inches below the existing grades. Following backfill of the SDRSD C-04 retaining walls, 2:1 (horizontal:vertical [h:v]) fill slopes were constructed above these walls and along a portion of the northerly side of the lot. Prior to constructing the 2: 1 (h:v) fill slope along the northerly side of the property, approximately 1 foot of weathered, near surface fill materials were removed to expose the underlying, suitable fill materials placed during the original phase of site grading, conducted in early 2004 (GSI, 2004). Import fill materials consisting of manufactured sand were blended with the onsite earth materials in order to achieve the planned grades. Where conducted, our observations and field density testing indicated that remedial grading was performed in general accordance with GSI recommendations and fills were compacted to at least 90 percent of the laboratory standard (per ASTM D 1557). LABORATORY TEST RESULTS General GSI evaluated the expansion potential of soils exposed near pad grade within the building pad area. The results of the expansion index testing are summarized in the following section. Testing to evaluate the corrosion potential of the soils exposed near pad grade is currently in progress. Corrosion test results will be provided under a separate cover when they become available. Expansion Index Testing A representative sample of compacted fill material, exposed near pad grade was evaluated in the laboratory for expansion potential. Expansion Index (E.1.) testing and expansion potential classification were performed in general accordance with ASTM Standard D 4829. The results of the expansion index testing are presented in the following table: I EXPANSION INDEX I EXPANSION POTENTIAL I I <5 I Very Low E.I. = 0-20 -Very Low Expansion Potential, E.I. = 21 to 50 - Low Expansion Potential, E.I. = 51 to 90 -Medium Expansion Potential, E.I. = 91 to 130 -High Expansion Potential, E.I. > 131 -Very High Expansion Potential Francis 1585 Triton Street, Carlsbad File:e:\wp12\7200\7279bf.igr GeoSoils, In~. I W.O. 7279-8/F-SC February 24, 2020 Page 2 CONCLUSIONS Based on our observations and testing, grading, retaining wall foundation and subdrain construction, and fill compaction within the subject property were performed in general accordance with the recommendations contained in GSI (2017) and the requirements of EOG (2019). Therefore, it is our opinion that the prepared lot is suitable for its intended use from a geotechnical engineering perspective. The expansion potential of the compacted fill, exposed near pad grade is very low. Thus, the foundation design shown on Specialty Steel (2018) is appropriate for the as-graded soil conditions described in this report. RECOMMENDATIONS The follow geotechnical recommendations should be incorporated into the balance of project design and construction: • Remedial grading should be performed in the planned driveway area prior to driveway subgrade preparation. • Pad grade soils should moisture conditioned to a depth of at least 12 inches within 72 hours prior to the placement of the underlayment sand and vapor retarder. • The building foundation excavations should be observed by a representative of this firm prior to placement of the reinforcement and concrete. • All additional earthwork within the subject property should be performed under the observation and testing of GSI. • The onsite earth materials are considered erodible. Thus, surface drainage should be directed away from the building foundations and the tops of slopes. Surface drainage should be properly maintained throughout the life of the project. In the respite between the conclusion of grading and final landscaping, all slopes should received the approved erosion control measures. LIMITATIONS Inasmuch as our study is based upon our review and engineering analyses and laboratory data, the conclusions and recommendations are professional opinions. These opinions have been derived in accordance with current standards of practice, and no warranty, either express or implied, is given. Standards of practice are subject to change with time. GSI assumes no responsibility or liability for work or testing performed by others, or their inaction; or work performed when GSI is not requested to be onsite, to evaluate if our recommendations have been properly implemented. Use of this report constitutes an agreement and consent by the user to all the limitations outlined above, notwithstanding any other agreements that may be in place. In addition, this report may be subject to review by the controlling authorities. Francis 1585 Triton Street, Carlsbad File:e:\wp12\7200\7279bf.igr GeoSoils, Inc. W.O. 7279-8/F-SC February 24, 2020 Page 3 The opportunity to be of service is appreciated. If you should have any questions, please do not hesitate to contact our office. Respectfully submitt Ge0S01ls, Inc. b:1.7::! Engineering Geologi /[~· R/4n-B. Boehmer Project Geologist ee Civil Engineer, RCE RBB/JPF /DWS/mn Attachments: Appendix -References Distribution: Francis (1) Addressee (wet signed via US mail and email) (2) Coble Homes, Attention: Mr. Matt Coble 1585 Triton Street, Carlsbad File:e:\wp12\7200\7279bf.igr GeoSoils, Inc. W.O. 7279-B/F-SC February 24, 2020 Page 4 APPENDIX REFERENCES American Concrete Institute, 2014, Building code requirements for structural concrete (ACI 318-14), and commentary (ACI 318R-14): reported by ACI Committee 318, dated September. American Concrete Institute (ACI) Committee 302, 2004, Guide for concrete floor and slab construction, ACI 302.1 R-04, dated June. American Society for Testing and Materials (ASTM), 1998, Standard practice for installation of water vapor retarder used in contact with earth or granular fill under concrete slabs, Designation: E 1643-98 (Reapproved 2005). __ , 1997, Standard specification for plastic water vapor retarders used in contact with soil or granular fill under concrete slabs, Designation: E 17 45-97 (Reapproved 2004). California Building Standards Commission, 2016, California Building Code, California Code of Regulations, Title 24, Part 2, Volume 2 of 2, based on the 2015 International Building Code, 2016 California Historical Building code, Title 24, Part 8, 2016 California Existing Building Code, Title 24, Part 10, and the 2015 International Existing Building Code. Engineering Design Group, 2019, Grading plans for: Francis Residence, Sheets 1 through 3 of 5, various scales, City of Carlsbad Project No.: CDP2017-0043, City of Carlsbad Drawing No.: 507-5A, dated November 13. GeoSoils, Inc., 2018, Geotechnical review of grading and post-tension foundation plans, planned single-family residence, 1585 Triton Street, Carlsbad, San Diego County, California, Assessor's Parcel Number (APN) 215-070-51, W.O. 7279-A-SC, dated April 13. __ , 2017, Geotechnical update evaluation, proposed single-family residence off of Triton Street, Carlsbad, San Diego County, California, Assessor's Parcel Number (APN) 215-070-51, W.O.7279-A-SC, dated June 9. __ , 2004, Final compaction report of grading, Parcels 1 and 3, 6575 Black Rail Road, Carlsbad, San Diego County, California, W.O. 3460-B-SC, dated March 9. __ , 2002a, Soil corrosivity test results, 6575 Black Rail Road, City of Carlsbad, San Diego County, California, W.O. 3460-A 1-SC, dated December 20. __ , 2002b, Preliminary geotechnical evaluation, 6575 Black Rail Road, proposed subdivision, Carlsbad, San Diego County, California, W.O. 3460-A-SC, dated November 27. Specialty Steel, 2018, Francis residence, 1585 Triton Street, Carlsbad, California, Sheets PTO, PTHD, and PT-1, scale: ¼-inch = 1 foot, dated March 29. GeoSoils, Inc.