The URL can be used to link to this page

Home My WebLink AboutCDP 2020-0044; GIBSON FAMILY RESIDENCE; GEOTECHNICAL GRADING PLAN REVIEW; 2021-03-15~ VINIE & MIDDLETON ENGINEERING, INC. Ref Job #20-178-P March 15, 2021 Mr. Curt Gibson 7089 Leeward Street Carlsbad, CA 92011 2450 Auto P.1rk War Escondido, California 92029-1229 Phone (760) 743-1214 Fax (760) 739-0343 GEOTECHNICAL GRADING PLAN REVIEW, PROPOSED RESIDENTIAL DEVELOPMENT, SOUTHWEST CORNER OF PARK DRIVE AND HILLSIDE DRIVE, CARLSBAD, CALIFORNIA (APN 156-160-15) The referenced property consists of a vacant lot previously studied by this office in regards to geotechnical and geologic conditions in support of a single-family residential development. Our findings, conclusions and development recommendations were provided in the following technical report: "Geotechnical Investigation, Proposed Residential Development, Southwest Comer of Hillside Drive and Park Drive, Carlsbad, California," V & M Job #20-178-P, report dated August 18, 2020 The preceding report was reviewed in connection with this grading plan review and is on file with our office. We have received the most recent project Precise Grading Plans, prepared by bHA Engineering, lnc.(6 sheets -received by email February 2021. A copy of the grading plan has been reproduced as a Geotechnical Map attached as Plate 1. A Geologic Cross Section based on the grading plan and our test pits is included as Plate 2. Based on our review of the Grading Plans, which are substantially similar to the plans utilized in our Geotechnical Investigation report, they largely represent a feasible design from a geotechnical engineering viewpoint and are in substantial compliance with the referenced report. The following comments should be considered, where appropriate and applicable: • The referenced report and this review letter should be considered a part of the project Grading Plans. • All excavations, grading, earthwork, construction and bearing soil preparation should be completed in accordance with Chapter 18 (Soils and Foundations) and Appendix "J" (Grading) of the 2019 California Building Code (CBC), the Standard Specifications for Public Works Construction, City of Carlsbad Grading Ordinances, the requirements of the governing agencies, the referenced report and this review letter. Mr. Curt Gibson March 15, 2021 Page2 All grading and bearing soil conditioning should be conducted under the observation and testing by the project geotechnical engineer. The final building pad and foundation construction should be inspected, tested as necessary and approved by the project geotechnical engineer. Geotechnical engineering construction inspections and test results should be presented in written field and final as- constructed geotechnical reports. All recommendations should be further field- verified, confirmed or revised if necessary at that time, based on actual as-graded soil properties. A Final As-Graded Report should then be issued outlining the remedial grading and bearing soil preparation activities, test results and confirm (or revise) foundation and pavement recommendations. • Compaction procedures remain as outlined in the referenced reports, except where superceded herein. All recommendations should be further field-verified, confirmed or revised if necessary at that time. Based on the project arborists recommendations for protecting the existing Torrey Pine, there is a 25-foot offset from the trunk of the tree in which no excavations or undercutting can be done. Outer edges of this offset are adjacent to the retaining wall associated with the BMP basin, within 1-foot of planned pool/jacuzzi improvements, and approximately 2 feet from a portion of the planned dwelling. Removals for surficial compressible soil is anticipated to be on the order of 5 feet minimum below existing surfaces. With the recommended removals and planned finish grades, this will equate to approximately 11 to 12 feet of fill (supported on approved Old Paralic deposits) beneath the planned structure and improvements adjacent to 6 feet of fill supported on 5 feet of potentially compressible soil. The Allen Block Wall planned to circumvent the Torrey Pine, and support the toe of a fill slope ascending to the building pad, will also be supported on potentially compressible soil. In order to mitigate and minimize the amount of potential surficial soil consolidation the following recommendations are provided for fill placement and grading within the 25-foot Torrey Pine offset: A layer of Tensar BX-1200 geogrid should be placed over the areas of natural existing ground within the recommended 25-foot offset and overlap a minimum of 5 feet outside of the offset along the building/improvement pad side. An additional layer of geogrid should be placed after 2 feet of fill in the building pad and pad fill slope area of the offset (schematically shown on Plate 2). All fill placed within the 25-foot offset circle within the fill slope/building pad side should be compacted to a minimum of 95% of its corresponding maximum dry density. Elsewhere, 90% minimum compaction will be required. V1NJI: & MmDLldON ENGINl.b!UNG, I Ne • 2450 Auto Park War• Escondido, Gilifornia 92029-1229 • Phone (760) 743-1214 Mr. Curt Gibson March 15, 2021 Page3 All preliminary foundation and slab-on-grade recommendations, as well as soil design parameters and seismic ground motion values, will remain the same as specified in the referenced Geotechnical Investigation report dated August 18, 2020. Final foundation and slab-on-grade recommendations will be provided in the As-Graded Compaction Report (issued after completion of grading) and will be based upon the characteristics of the imported soil required to complete grading and achieve design grades. Additional foundation/construction recommendations for structures and improvements within the influence of the Torrey Pine 25-foot offset may also be warranted and provided in the As-Graded Report. A minimum of 2% gradient should be maintained away from all foundations. Roof gutters and downspouts should be installed with all discharge water from the downspouts directed away from the foundations and slab to a suitable location. Area drains should be installed in the yards to collect surface water. Planter areas adjacent to foundations should be provided with water proofing, using an impermeable liner against the footings, if determined appropriate. It should be noted that shallow groundwater conditions may still develop in areas where no such conditions existed prior to site development. This can be contributed to by substantial increases of surface water infiltration resulting from landscape irrigation, which was not present before the development of the site. It is almost impossible to absolutely prevent the possibility of shallow groundwater on the entire site. Therefore, we recommend that shallow groundwater conditions be remedied if and when they develop. The property owner should be made aware that altering drainage patterns, landscaping, the addition of patios, planters, and other improvements, as well as over irrigation and variations in seasonal rainfall, all affect subsurface moisture conditions, which in tum affect structural performance. VtN/1: & MmDttl ON ENulNU.IUNu, IN<.:. • 2450 Auto Park Way• Escondido, California 92029-1229 • Phone (760) 743-1214 Mr. Curt Gibson March 15, 2021 Page4 LIMITATIONS This geotechnical plan review is not a "Plan Check Review'' and does not relieve the responsibility of the project design consultant(s) and contractor(s) to get completely familiarized with the requirements of the project soil report(s) and fully incorporate their recommendations into the project design, plans and construction work, where appropriate and as applicable. Our review, corrections, and comments are for general geotechnical conformance of the project plans with the intent of the project soil report and design recommendations. Review of structural and civil engineering calculations, architectural intent, structural and civil engineering design modeling and basis, verification of setback requirements, easements, and right-of-ways, as well as code, city, and county compliance are beyond geotechnical engineering services. It is the owner's or his (her) representative's responsibility to provide copies of all pertinent soil report(s), updates, addendum letters and plan review letters to respective design consultant(s), general contractor and his (her) subcontractor(s) for full compliance. This opportunity to be of service again is sincerely appreciated. If you have any questions or need clarification, please do not hesitate to contact the undersigned. Reference to our Job #20-178-P will help to expedite our response to your inquiries. VINJE & MIDDLETON ENGINEER! G, INC. Ste CEG #2362 V1NJE & MmDI 1:·10N ENGINFrRING, ]Ne.• 2450 Auto Park Way• Escondido, Califorma 92029-1229 • Phone (760) 743-1214