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HomeMy WebLinkAboutCDP 2020-0018; FORESTER RESIDENCE; GEOTECHNICAL ADDENDUM AND RESPONSES TO GEOTECHNICAL REVIEW NO. 3; 2022-11-30 ADVANCED GEOTECHNICAL SOLUTIONS, INC. 485 Corporate Drive, Suite B Escondido, California 92029 Telephone: (619) 867-0487 Fax: (714) 786-5661 ORANGE AND L.A. COUNTIES INLAND EMPIRE SAN DIEGO AND IMPERIAL COUNTIES (714) 786-5661 (619) 867-0487 (619) 867-0487 John Forester November 30, 2022 300 Carlsbad Village Drive, Suite 108a-335 P/W 1901-03 Carlsbad, California 92008 Report No. 1901-03-B-6 Attention: Mr. John Forester Subject: Geotechnical Addendum and Response to Geotechnical Review No. 3, Proposed Single-Family Residence, 4464 Adams Street, Carlsbad, California Gentlepersons: In accordance with your request, Advanced Geotechnical Solutions, Inc. (AGS) has prepared this response to geotechnical review comments issued by the City of Carlsbad regarding the geotechnical investigation report and addendums prepared by AGS (2020, 2021, & 2022) for the proposed single-family residence project to be located at 4464 Adams Street. The review comments are summarized below followed by our response. A copy of the review comment sheet is attached in Appendix B. Comment 1: Provide permission to grade letter or temporary shoring plans and calculations. AGS Response: It is our understanding that permission for offsite grading has not been procured at this time. As alternative to temporary shoring along property boundaries for remedial grading purposes, removal of unsuitable soils may be accomplished utilizing the slot-cutting method. The slot-cutting method employs the use of the earth as a buttress and allows the excavation to proceed in phases. The initial excavation is made at a 1:1 ratio inward from the property line extending to competent materials, which are anticipated to be encountered at depths on the order of 2 to 5 feet below existing grade. Subsequently, vertical slots are cut using the ABC method, in which all slots are of the same width (up to 8 feet). The initial slot "A" is cut, leaving the "B" and "C" slots to buttress the excavation. The slot is backfilled with compacted soil and the excavation proceeds to the following slot “A”. After all slots “A” are completed, excavation and backfill proceeds with slots “B” and finally slots “C”. Improvements in the vicinity of the excavation should be continuously monitored for any sign of distress. Conditions of the referenced reports remain applicable unless specifically superseded herein. Advanced Geotechnical Solutions, Inc., appreciates the opportunity to provide you with geotechnical consulting services and professional opinions. If you have any questions, please contact the undersigned at (619) 867-0487. Respectfully Submitted, Advanced Geotechnical Solutions, Inc. ___________________________________ ________________________________ ANDRES BERNAL, Sr. Geotechnical Engineer PAUL J. DERISI, President RCE 62366/GE 2715, Reg. Exp. 9-30-23 CEG 2536, Reg. Exp. 5-31-23 Distribution: (1) Addressee Attachments: Appendix A - References Appendix B - Geotechnical Review Comments November 30, 2022 Page 2 P/W 1901-03 Report No. 1901-03-B-6 ADVANCED GEOTECHNICAL SOLUTIONS, INC. APPENDIX A REFERENCES Advanced Geotechnical Solutions, 2020, Geotechnical Investigation and Preliminary Design Recommendations for Proposed Single-Family Residence, 4464 Adams Street, Carlsbad, California, dated December 31, 2019, Report No. 1901-03-B-2. ---, 2021, Geotechnical Addendum and Response to Third-Party Geotechnical Review, Proposed Single- Family Residence, 4464 Adams Street, Carlsbad, California, dated December 17, 2021, Report No. 1901-03-B-3. ---, 2022, Geotechnical Addendum and Response to Third-Party Geotechnical Review, Proposed Single- Family Residence, 4464 Adams Street, Carlsbad, California, dated September 6, 2022, Report No. 1901-03-B-5. City of Carlsbad, 2022a, Geotechnical Report Review, Forester Residence, 4464 Adams Street, Carlsbad, California (2nd review), Project ID: CDP2020-0018, GR2022-0031 dated August 2, 2022. ---, 2022b, LDE Review No. 3, Forester Residence, 4464 Adams Street, Carlsbad, California, dated November 7, 2022. Fusion Eng Tech, 2022, Grading and Improvement Plans for Forester Residence, 4464 Adams Street, Sheet 4 of 10, plot dated April 22, 2022. Hetherington Engineering, 2021, Third-Party Geotechnical Review Comments (First) 4464 Adams Street, Carlsbad, California, GR2021-0037/CDP2021-0037, their Project No. 9541.1, Log No. 21675, dated November 11, 2021. ADVANCED GEOTECHNICAL SOLUTIONS, INC. APPENDIX B GEOTECHNICAL REVIEW COMMENTS John For , tcr ADVANCED GEOTECHNICAL SOLUTIONS, INC. 485 orporatc Drive, Suite B Escondido, ali fornia 92029 Telephone: (6 19) 867-0487 Fax: (714) 786-5661 300 arl bad Village Drive, uite 108a-335 arlsbad, alifornia 92008 September 6, 2022 P/W 1901-03 Report No. 1901-03-B-5 ttention: ubj t: Gent! p r ons: Mr. John or t r ot hni al ddendum and R spouse to bird-Party Geotechnical Review, Propo d ingl -Family Residence, 4464 Adams Street, Carlsbad, alifornia In a rdan e with your request, Advanced Geotechnical olutions, Inc. (AGS) has prepared this response t third party geotechnical review comments iss ued by the City of Carlsbad regarding the geotechnical inv tigation report and addendum prepared by AGS (2020, 2021) for the proposed single-family residence project to be located on 4464 Adams treet. The review comments are presented below followed by our r ponse . A copy of the review comment sheet is attached in Appendix B. Comment 1: Due to the age of the geotechnical investigation, the Consultant should update the project seismic, grading and foundation recommendations to comply with requirements of the 2019 California Building Code and ASCE 7-16. (repeat comment-as only seismic design parameters were address in the "Geotechnical Addendum and Response to Third-Party Geotechnical. Review ... ", please discuss if any updates to the grading and foundation recommendations are necessary based on the geotechnical update.). AG Response: As noted, AGS provided updated seismic design parameters for the project based on 2019 California Building Code and ASCE 7-16. Based on our review of the geotechnical investigation report and addendum by AGS (2020, 2022), no additional seismic, grading and foundation recommendations are necessary to comply with requirements of the 2019 California Building Code and ASCE 7-16. Comment 2: The Consultant should address the gross and surficial stability of proposed slopes (repeat comment -please provide the plots of the direct shear tests foir the onsite soils that is discussed in the consultant's response to this comment, and please also provide the complete data print-outs of the slope stability analysis (static and pseudo-static) that is presented in the Geotechnical Addendum and Response to Third-Party geotechnical Review. AGS Response: The plots of the direct shear tests performed on samples recovered at the project site were presented in Appendix C -Laboratory Test Results of referenced project geotechnical report by AGS (2020). A copy of the direct shear plots from the referenced report is presented in Appendix C and summary of the direct shear test results is presented in Table 1, below: TABLE 1 -DIRECT SHEAR TEST RESULTS Boring and Description DS Test Moist Unit Friction Angle -Peak Cohesion -Peak Sample Depth (USCS) Weight (pd) (degrees) (pst) B-1 @8.5-9 ft. Qop (SM) Undisturbed 125.2 39 198 B-2@0-3 ft. Afu (SM) Remolded to 90% 129.5 31 288 B-2@ 10-10.5 ft. Qop (SM) Undisturbed 118 .l 32 252 Based on the direct shear test results and our engineering judgement, the following shear strength ORANGE AND L.A. COUNTIES INLAND EMPlRE SAN OTEGO AND IMPERIAL COUNTIES (714) 786-5661 (619) 867-0487 (619) 867-0487 op page2 Report No. 1901-03-B-S ious r sponsc tor view comments (AGS, 2021) were selected for 30 200 32 200 Moist Density (pcf) 130 125 -'-----=~='""=,,======,==--'===-~~~==' · n I t :iata printout of the slope stability analyses (static and pseudo-static) are presented D. hould address the impacts to adjacent property and improvements as a result and con tru tion (repeat comment -as the Consultant's response to this comment in the dd ndum and Response to Third-Party Geotechnical Review ... "indicates off-site grading t ROW and the adjacent vacant lot may be necessary for construction of the fill key at the so1.1the111 rti n of the site, please provide alternative recommendations for the grading if permission is not ) th city and/or adjacent neighbor.). R pon e: Based on AGS' review, site grading and construction will not impact the adjacent roperties or improvements. If permission for offsite grading into Adams Street right-of-wayoi.. and the adjacent vacant lot to the east is not granted, temporary shoring along Adan;,.s Street right-of-way-and the adjacent vacant lot to the east may be used to complete theJirading and ce;,reJ--- keyway construction on the southern limits of the ro·ect. • pfUAl I 06 f{!:jt,IW' £.½ ({.f\./tl) C,.~,v'/'(0£ og.~{}. 5H&tt-1f'l4 Pl.Ar.b t 0/}US Comment 4: The Consultant should provide recommendations for fill keys; benching and subdrainage fl)b,/l,A{)J~ (widths, depths, etc.). (repeat comment -please provide tlhe composition of the backdrain (size, and type of Pl.ANS_. pipe, amount and size of gravel, filter fabric, etc.) for the fill key.) ~ ~, _orJ~~'t\f:> ~ ,:JlPttJ~ AG Response: Fill slopes on the project are designed at 2: 1 ratio (horizWt~JJfclitltt{J/-Lo CC,t#L-, Fill_ slopes, ~hen prope~ly constr~cted with o~site m~terials, are expected to be grossly stable as -~~ designed. Fill slopes will be subJect to surfic1al erosion and should be landscaped as quickly as flSHS,N~ possible. ~ Keyways should be constructed at the toe of all fill slopes "toeing" on existing or cut grade. Fill keys should have a minimum width equal to one-half the height of ascending slope, and not less than 15 feet. Unsuitable soil removals below the toe of proposed fill slopes should extend from the;! catch point of the design toe outward at a minimum 1: 1 projection into approved material to establish the location of the key. Backcuts to establish that removal geometry should be cut no steeper than 1: 1 or as recommended by the Geotechnical Consultant. Additional fill key and backdrain construction recommendations are provided in the details below: ADVANCED GEOTECHNICAL SOLUTIO , I C. September 6, 2022 P/W 1901-03 CODE COMPLIANT Page 3 ReportNo. 1901-03-B-5 BLANKET FILL -AS REQUIRED BY GEOTECHNICAL CONSULTANT AND/OR CODE COMPLIANCE (3 FOOT MIN.) \ :SETBACK, 15FOOTMIN."" \ ~>i I CONSTRUCT DRAIN OUTLET A MINIMUM 1-FOOT ABOVE GRADE CODE COMPLIANT KEYWAY WITH MINIMUM DIMENSIONS: TOE 2 FOOT MIN. HEEL 3 FOOT MIN. WIDTH 15 FOOT MIN. SEE DETAIL 2 FOR DRAIN SPECIFICATIONS NOTES: 1. DRAIIN OUTLETS TO BE PROVIDED EVERY 100 FEET CONNECT TO PERFORATED DRAIN PIPE BY "L" OR "T" AT A MINIMUM 2% GRADIENT. 2. THE NECESSITY AND LOCATION OF ADDITIONAL DRAIINS SHALL BE DETERMINED IN THE FIELD BY THE GEOTECHNICAL CONSULTANT. UPPER STAGE OUTLETS SHOULD BE EMPTIED ONTO CONCRETE TERF~CE DRAINS. 3. DRAIN PIPE TO EXTEND FULL LENGTH OF STABILIZATION/BUTTRESS WITH A MINIMUM GRADIENT OF 2% TO SOLID OUTLET PIPES. 4. LOCATION OF DRAINS AND OUTLETS SHOULD BE DOCUMENTED BY PROJECT CIVIL. ENGINEER. OUTLETS MUST BE KEPT UNOBSTRUCTED AT ALL TIMES. Detail 1 -Fill Key Recommendations DRAIN 2-FT. MIN ~;iRIAL ~-····:_·._-,:····I FILTER FABRIC .·_':.'·. ·.·.·>/· 2-FT. :;=tb/ MIN 4-INCH SOLID 2-INCH MIN OUTLET PIPE BELOW PIPE DRAIN 2-FT. MIN. ~~;iRIAL ~IE.·.'· .-:tr FILTER FABRIC _:_/· ):_-.' :;,= = ht£ ~iN' 4-INCH SOLID 2-INCH MIN. OUTLET PIPE BELOW PIPE OPTION 1 OPTION 2 DRAIN MATERIAi · GRAVEL TRENCH TO BE FILLED WITH 3/4-INCH MAX ROCK OR APPROVED EQUIVALENT SUBSTITUTE FILTER FABRIC· MIRAFI 140 FILTER FABRIC OR: EQUIVALENT SUBSTITUTE Will-I A MINIMUM 6-INCH OVERLAP .flEE; 4-INCH ABS OR PVC PIPE OR APPROVED EQUIVALENT SUBSTITUTE WITHA MINIMUM OF 6 PERFORATIONS (1/4-INCH DIAMETER) PER LINEAL FOOT IN BOTTOM HALF OF PIPE (ASTM 02751, SDR-35 OR ASTM 03034, SDR-35 ASTM 01527, SCHD. 40 OR ASTM 01765, SCHD. 40) Detail 2 -Backdrain Recommendations ADVANCED GEOTECHNICAL SOLUTIONS, INC.