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HomeMy WebLinkAboutPD 2021-0019; SPEER RESIDENCE; GEOTECHNICAL GRADING PLAN REVIEW UPDATE AND RESPONSE TO THIRD PARTY REVIEW COMMENTS; 2021-08-13LMT GEOTECHNICAL SOLUTIONS, INC. Consulting Geotechnical Engineers 5931 Sea Lion Place, Suite 109 Carlsbad, California 92010 Office: 760-602-7815 smsgeosol.inc®gmail.com Project No. GI-20-09-136 August 13, 2021 Mr. Jeff Speer 16325 Alamo Canyon Road Santa Clarita, California 91387 GEOTECHNICAL GRADING PLAN REVIEW UPDATE AND RESPONSE TO THIRD- PARTY REVIEW COMMENTS, PROPOSED RESIDENTIAL REDEVELOPMENT, 3342 DONNA DRIVE, CARLSBAD, CALIFORNIA (PROJECT ID: GR2021-0014/PD2021-0019) Project most current Grading Plans prepared by Christensen Engineering & Surveying, dated July 29, 2021 for the proposed single-family residential redevelopment at the above-referenced property, were provided to us for review and comments. An excerpt copy of the project plan (Sheet 3 of 7) is reproduced herein and included with this report as a Geotechnical Map, Figure 1. We are also in receipt of a "Third-Party Geotechnical Review (First)" of our original report (referenced below), prepared by Hetherington Engineering, Inc. dated April 19, 2021. A copy of the Hetherington Engineering, Inc. review letter is attached herein as an Appendix. Reference is made to the following reports prepared by this office in support of this project: Geotechnical Investigation Proposed Residential Redevelopment 3342 Donna Drive Carlsbad, California (A.P.N. 205-160-62) Project No. GI-20-09-136, dated October 13, 2020 The referenced reports are on file with our office and copies can be obtained upon request. The purpose of this effort was to review the project most current Grading Plans (Figure 1) from a geotechnical engineering viewpoint, and confirm its compatibility with the indicated site geotechnical conditions and recommendations given in the referenced report. Updated/added recommendations and clarifications to the third-party review comments are also presented in the following sections. RiB d011 D3740 E329 AAS HID ACC R EDITED I I I I I I I I I I I I I I I I I I I Geotechnical Grading Plan Review Update and August 13, 2021 Response to Review Comments, 3342 Donna Drive, Carlsbad, California Page 2 I. SITE DESCRIPTION / GEOTECIINICAL CONDITIONS The project property remains substantially unchanged from those described in the referenced report. Topographic conditions and proposed development at the project property are shown on the enclosed I Geotechnical Map, Figure 1. As shown, the property is mostly characterized by an existing cut-fill transition building pad that is situated roughly 12 feet above the Donna Drive street grades. A graded slope modified with terraced short keystone type segmental retaining walls ascends from the I street grade to the level building pad grades above. A long concrete driveway with maximum longitudinal profiles approaching 20% provides access from Donna Drive to the building pad. A nearly 7-foot high maximum transition retaining wall marks the eastern level building pad margins, I where graded slopes with modified faces ascend to neighboring property(ies) above, situated roughly 10 feet higher in pad elevation(s). The eastern pad margin transition retaining wall appears leaning I and failing. Detailed descriptions of the underlying geologic units at the project property are provided in the referenced reports. In general, the property is chiefly underlain by relatively shallow to modest I sections of fill/wall backfill and undifferentiated topsoils over dense and competent Very Old Paralic Deposits, which are widely spread in coastal areas of the city of Carlsbad. Approximate location of exploratory borings, as well as distribution of the underlying geologic units, are transferred and depicted on the Figure 1. Pertinent geotechnical data and engineering properties of the underlying soils are provided in the referenced report(s). New Geologic Cross-Sections A-A' and B-B' depicting existing/proposed grades and site subsurface profile are included as Figures 2 and 3. I II. PROPOSED REDEVELOPMENT Based on our review, project most current plans substantially propose a similar redevelopment I concept, as it was anticipated, and considered and used as a basis of our original study. The existing building and associated structures and improvements will be demolished and removed to allow for I construction of a new larger multi-level residence consisting of a street-grade partial basement type garage level, an upper split-level pad first floor level, and a partial second floor level. An elevator will provide lift from basement level to upper floor levels. New plans however, proposed a new swimming pool and spa near the center of the eastern side yard. Proposed new building pad and I finish floor elevations have remained substantially unchanged. I Basement-type masonry retaining walls will be utilized to achieve ground elevation transitions between the lower basement and upper first floor split-level pad grades. Earthwork quantities are estimated to be on the order of 634 CY of cutting and 99 CY of filling with roughly 535 CY of I export. Temporary wall backcuts on the order of 10 feet high are anticipated in connection with the planned basement wall construction. I [] I I Geotechnical Grading Plan Review Update and August 13, 2021 I Response to Review Comments, 3342 Donna Drive, Carlsbad, California Page 3 Detail construction plans are not yet available. However, planned new construction is anticipated I to consist of a combination of lower concrete/masonry block basement type retaining walls and upper floor levels conventional wood-frame and exterior stucco structure, supported on shallow stiff concrete footings with slab-on-grade floor foundations. I 111. GEOTECHNICAL GRADING PLAN REVIEW Based on our review, project most current plans substantially propose a similar design concept and remain acceptable to us from a geotechnical viewpoint. However, the following additional/amended comments and recommendations are appropriate and shall be incorporated into the project designs and construction: The project Geotechnical Investigation Report dated October 13, 2020, and this Plan Review Update transmittal shall be referenced on, and considered a part of the project grading and foundation plans. A note shall be provided on the plans stating "in the event of a conflict between the plans and soils report, the most stringent recommendations or detail shall govern." A Typical Detail is included in this transmittal, as Figure 4 supplementing the Typical Grading Detail included as Figure 13 in the referenced report. The included details depict the proposed minimum requirements for site excavations, remedial grading and undercutting, benching and keyway development, composite/crushed rocks blanket drain, wall back drain and waterproofing. Recommendations of these details shall be incorporated into the cross- sections provided in the project plans. The need for dewatering, underdrainfbackdrain installation and shoring shall be clearly shown on the project plans. Top of temporary basement backcut excavations shall be shown on the project plans (see attached Figure 1). Temporary excavation backcuts are expected to encounter daylight seepage requiring proper mitigation and stabilization. Typical mitigation consists of installing a subdrain (4-inch perforated pipe surrounded with crushed rocks wrapped in filter fabric) in the backcut bench(es) at the seepage location(s), and/or developing backcut in the limited sections. Excavation shoring may also become necessary and should be expected. I We recommend preparing a separate sheet included with the project grading plans titled "Excavation Plan" depicting bottom of over-excavations/undercutting elevations, temporary construction slopes, dewatering specification, keyway and benching detail, I underdrainlbackdrain elevations and locations, and new retaining wall and offsite properties and public right-of-way excavation protection to be prepared in coordination with the project architect, structural engineer, and shoring and swimming pool design/build contractors. I I I El F, Geotechnical Grading Plan Review Update and August 13, 2021 I Response to Review Comments, 3342 Donna Drive, Carlsbad, California Page 4 D. The proposed eastern retaining wall will be supported by a new retaining wall (under I separate permit). The new retaining wall design and construction shall consider stability of the existing wall and the proposed new pool and spa construction undermining of existing wall shall not be allowed. The pool design/build contractor shall be provided with the I project pertinent reports and plans for properly incorporating pertinent design parameter and recommendations to his/her designs. I Final pool/spa designs should be provided by the project pool design consultant. However, the following minimum requirements are also appropriate and shall be considered in the I project pool designs and construction: 1. Bottom of pool excavation shall uniformly expose very dense and competent formational rock, as approved in the field, or supported entirely on well-compacted fill. Cut/fill I transition shall not be allowed under the pool/spa subgrade. In the event of cut-fill transition pool/spa subgrade, the exposed bottom shall be over-excavated and reconstructed to the design finish subgrade levels with well-compacted fills so that there I will be a minimum of 2 feet of well-compacted fills below the bottom of the pool/spa. In case of wet bottom of pool excavation/over-excavation exposures, and in order to facilitate bottom of pool subgrade recompaction and reconstruction, the over-excavated I pool areas may be backfihled to design subgrade levels with Caltrans Class 2 crushed base materials (recycled base should not be used), mechanically compacted to minimum 95% compaction levels, based on ASTM Dl 557, unless otherwise noted. A sub-drainage I system consisting of a 2-foot by 2-foot trench excavated near the center of pool excavation/over-excavation provided with a minimum 4-inch diameter perforated (Sch. I 40) pipe surrounded with 3%-inch crushed rocks all wrapped in the filter fabric (Mirafi 140N) may also be required based on actual field excavation exposures and should be anticipated. I 2. Site bearing soils are anticipated to consist of clayey, silty sand (SMJSC) ranging to medium expansion potential (expansion index less than 90 based on ASTM D4829 I index classification). However, an apparent "very high" expansion soil condition (expansion than 130) shall be used for the project swimming pool/spa design. greater I 3. The pool/spa should be designed empty (counter pressure from water in the pool should be neglected) and incorporate pertinent design parameters provided in the referenced report, with pool wall/bottom thickness and steel reinforcement per structural designs. I 4. Adjacent building foundation surcharging on the pool wall shall be considered in the designs. Pool (or any trench) excavation shall not be extended below a 2:1 projected line I from 9 inches above the bottom of the building foundations. For this purpose deepened building footings adjacent to the pool may be required to satisfy this condition. We recommend a cross-section depicted bottom of the foundation with respect to the pool excavation included on the project plans. I I Geotechnical Grading Plan Review Update and August 13, 2021 I Response to Review Comments, 3342 Donna Drive, Carlsbad, California Page 5 The planned pool/spa should also be provided with minimum 15 inches wide by 18 I inches deep grade (bond) beam reinforced with a minimum of two #5 bars top and bottom around the top of the perimeter walls, unless determined otherwise by the project design consultant. Use concrete consisting of Portland cement Type II (ASTM C150) with minimum 28 days compressive strength (fc) of 5000 psi and maximum 0.40 water-cement ratio (also I see Site Corrosion Assessment in the referenced report). I IV. RESPONSE TO THIRD PARTY REVIEW The following provide added information, clarifications and our response to the review comments outlined in the "Third-Party Geotechnical Review (First)" by Hetherington Engineering, Inc. dated I April 19, 2021. Our responses are provided in the same order as the Third-Party Geotechnical Review (see Appendix): I Item #1: We concur. Project grading plans were provided to us and reviewed as a part of this effort. Added and updated/amended recommendations consistent with the current plans are provided herein and should be considered in the project designs and I incorporated into the final plans for conformance to our report(s) and recommendations. Project shoring and foundation plans shall also be provided to I us for review and comments. Item 42: An updated Geotechnical Map utilizing the most current Grading Plan shows the existing topography, proposed structures and final design grades, geologic conditions I and approximate contacts, top of temporary excavations and shoring locations as well as the approximate locations of the exploratory test pit/borings is included with this I transmittal as Figure 1. Item #3: Updated Cross-Sections A-A' and B-B' utilizing the current grading plan showing I the existing topography, proposed structures and final design grades, approximate geologic contacts, boring locations and pertinent geologic conditions is attached to this transmittal as Figures 2 and 3. Item #4: We concur. All earthwork operations including excavations and shoring, removals and over-excavations, suitability of earth deposits used as compacted fills and I backfills, blanket/wall backdrainlsubdrain installations, and fill/backfill placement and compaction procedures should be continuously observed and tested by the project geotechnical consultant and presented in daily field reports and a final report. I The nature of finished bearing and subgrade soils should be confirmed in the final report at the completion of project earthworks construction. I I I I Geotechnical Grading Plan Review Update and August 13, 2021 I Response to Review Comments, 3342 Donna Drive, Carlsbad, California Page 6 Geotechnical engineering observations and testing shall include but are not limited I to the following: * Initial observation - After the demolition and clearing limits have been staked but I before excavation /brushing starts. * Shoring caisson/pile shaft drilling, and bottom of over-excavation observation - I During caisson/pile shaft drilling to insure adequate embedment and when bottom of over-excavations and removals are exposed, but before fill or backfill I is placed. * Shoring observations - During shoring installation. Local and Cal-OSHA safety I requirements for open excavations apply. * Blanket drainlsubdrain observations - During actual installations to verify materials and construction procedures. All drains/subdrains and final outlet I locations shall be shown on the project final plans. * Fill/backfill observation . After the fill/backfill placement is started but before I the vertical height of fill/backfill exceeds 2 feet. A minimum of one test shall be required for every 2 feet vertical gain. Wall backfihls should consist of good quality sandy granular soils and also be mechanically compacted to a minimum I of 90% (or 95% where necessary) compaction levels unless otherwise specified. All fills/backfills placed within a potentional saturation and inundation shall be I compacted to minimum 95% compaction levels, unless otherwise approved. Finish rough and final pad grade tests shall be required regardless of fill thickness. Foundation trench/slab subgrade observation - After foundation trench excavations but prior to the placement of steel reinforcement or concrete for depths to proper bearing strata., proper moisture and specified compaction levels. Trenching efforts typically result in disturbed bottom of foundations, thereby requiring in-place recompaction using hand-held equipments (wacker) prior to steel placement and concrete pour, unless otherwise approved. * Geotechnical foundation/slab steel observation - After the steel placement is completed but before the scheduled concrete pour. I I I I [1 I I Geotechnical Grading Plan Review Update and August 13, 2021 Response to Review Comments, 3342 Donna Drive, Carlsbad, California Page 7 * Underground utility/plumbing trench observation - After the trench excavations but before placement of pipe bedding or installation of the underground facilities. Local and Cal-OSHA safety requirements for open excavations apply. Observation of pipe bedding may also be required by the project geotechnical engineer. Underground utility/plumbing trench backfill observation - After the backfill placement is started above the pipe zone but before the vertical height of backfill exceeds 2 feet. Testing of the backfill within the pipe zone may also be required by the governing agencies. Pipe bedding and backfill materials shall conform to the governing agencies' requirements and project soils report if applicable. All trench backfills shall consist of sandy granular soils and mechanically compacted to a minimum of 90% (or 95% where necessary) compaction levels unless otherwise specified. Plumbing trenches more than 12 inches deep maximum under the floor slabs should also be mechanically compacted and tested for a minimum of 90% compaction levels, unless otherwise specified. Flooding or jetting techniques as a means of compaction method should not be allowed. V. 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 its recommendations into the project design, plans and construction works, where appropriate, and as applicable. Our review and comments are for general geotechnical conformance of the project plans with the intent of the project soil reports and design recommendations. Review of structural and civil engineering calculations, architectural intent and structural and civil engineering design modeling and basis, verification of set back 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 provided copies of all pertinent soil report(s), updates, addendums and plan review letters to respective design consultant(s), and general contractor and his (her) subcontractor(s) for full compliance. Should any questions arise concerning this report, please do not hesitate to contact this office. Reference to our Project: GI-20-09-136 will help to expedite our response to your inquiries. I I LI I I I I U I I I LI 1 I I I 11 I Geotechnical Grading Plan Review Update and August 13, 2021 I Response to Review Comments, 3342 Donna Drive, Carlsbad, California Page 8 This opportunity to be of service again is sincerely appreciat I 9M9 Geotechnical Solutions, Inc. I I , JAY 4OAL No 2362 c,.1cl:J CERTIFIED :i\ ... ENGINEERING 4,I GEOLOGIsT I 'Op cx.V ~Z~7 - Steven J. Melz/ CEO #2362 I Enclosures: Figures 1 through 4 Appendix I Distribution: Addressee (3, email) Christensen Engineering (email) I [1 I 1 I I I I I I AM GEOTECHNICAL SOLUTIONS, INC. I 1 T'1TL1 GEOTECHNICAL SOLUTIONS, INC. Consulting Geotechnical Engineers 5931 Sea Lion Place, Suite 109 Carlsbad, California 92010 Office: 760-602-7815 smsgeosol.incgmail.com Project No. GI-20-09-136 October 13, 2020 Mr. Jeff Speer 16325 Alamo Canyon Road Santa Clarita, California 91387 jeff@imspeer.com Geotechnical Investigation, Proposed Residential Redevelopment 3342 Donna Drive, Carlsbad, California (A.P.N. 205-160-62) Pursuant to your request, SMS Geotechnical Solutions, Inc. has completed the attached Geotechnical Investigation report for the proposed residential redevelopment at the above-referenced property. The following report summarizes the results of our research and review of the pertinent geotechnical reports and plans, subsurface explorations, sampling and laboratory testing, engineering analysis and provides conclusions and recommendations for the proposed redevelopment, as understood. From a geotechnical engineering standpoint, it is our opinion that the project property is suitable for the planned residential redevelopment, provided our recommendations presented in this report are incorporated into the project designs and implemented during the construction phase. If you have any questions or need clarification, please do not hesitate to contact this office. Reference to our Project No. GI-20-09-136 will help to expedite our response to your inquiries. We appreciate this opportunity to be of service to you. SAN Geotechnical Solutions, Inc. No. 2885 idi S. Shariat #2885 I I I I I U I I I I I I LI I cZZ J R18 C1077 D3740 E329 AAS HID ACe RED IED I 11 Lars APN 187064480 AOOR 34$$ 8EA!GT O. - GEOTECHNICAL MAP 3342 DONNA DRIVE, CARLBAD, CA SCALE: 1" = 20'01 I 20 Legend Proposed Building Location Geologic Cross Section Approximate Location of Boring Approximate Geologic Contact IL Undocumented Fill Very Old Paralic Deposits New Retaining Wall (By Others, Under a Separate Report) .7 ire " - B-i 1. [ Approx. lop of 1:1 ;emp. backcut Slope & -- SWUM r .. 1.i --S-8 s:s GEOTCfl'iC.k... SOLUTIONS INC 5931 Sea Lion Place, Suite 109 Carlsbad, CA 92010 Project Number: GI-20-09-136 Figure Number: 1 SCALE: Y'= 10' 0' 10' L)t-l)AlLij ..jIiLU UIL -SLi1iN A-A 3342 DONNA DRIVE, CARLSBAD, CA Legend I Proposed Building S Existing Topography Location Groundwater Uaf Artifical Fill Very Moist/Wet Zone Time of Drilling Very Old Paralic Deposits Boring Location Geologic Contact Approximated - Approximated .L. 280 - 271 270 Proposed Second Floor Existing Retaining Wall P1 Proposed First Floor 265 Existing Retaining Walls (To Be Removed) PL B-3 2511 • Proposed Driveway I . . . . --- 245 240_I SOLI. lIONS INC 5931 Sea Lion Place. Suite ur1JA1tLi GtOtO(i IC CROSS-SkiCIiON i3 - Legend Proposed Building -. . Existing Topograph\ Location I Boring Location Geologic Contact U Approximated Approximated Groundwater F Uaf Artifical Fill Very Moist/Wet Zone Qvop Very Old Paralic Deposits T.D. Time of Drilling 3342 DONNA DRIVE, CARLSBAD, CA SCALE:1"10' I I 0' 10' 280 Proposed Second Floor 275 - Existing CMU Freestanding Wall Existing 270— / Retaining Wall : I (To Be Removed) Pl, I 265 -Proposed Existing Residence Proposed First Floor Wall I Pi /IosedGrade . . B-2fB-3(Projected) Existing Grade 260 — ---- - 255- ---_ - - -- - - Proposed Basement - - - 250— - -- -- - - . . - - .. ._ ...:..: ....- TD, tlO'inB2 .:. - - - - - Very Old Paralic Deposits (Qvop) - - - - 245 :77 — . . ............ .... 77i Th- - -. .. -- .:_. . -:-..-.---;T.D.atl9inB-3 . °. . -- - - .......-. . - ----- - - 240— SOLL' liONS IN- 5931 Sea Lion Place, S Existing Grade Proposed Grade B-1 ," !4' min, Btm.ofOX. Level Benches Back Drain (Typ.) Very Old Paralic Deposits (Qvop) G.W. at 8' .. ," Proposed Walls Temporary Excavation Slope TYPICAL DETAIL SCHEMATIC AND CONCEPTUAL ONLY SCALE: F'= 10' 0' 10' 265 260 255 245 240 Proposed Second Floor Existing Retaining Walls (To Be Removed) PL / \ --- 'N - - Proposed Basement Artiflcal Fill (Uaf) Proposed Driveway - - -' - - - - - - / T.D. at 10' / Btm. of OX. Composite/Crushed Rock Blanket Underdrain (Tyl,) 'Min 15' Keyway may be Necessary as Directed in Field (See Report) Temporary Excavation Slope A' 280 275 —j Protect Off Site Improvement During Excay. and Grading. Temp. Shoring May be Required Based on Field/GW Condition and Should be Expected. New Ret. Wall (By Others, Under Separate Permit) Proposed Draingac Waterproofing (Tsp.) Per Waterproofing Consultant Waterproofing Per Project -, Proposed First Floor Waterproofing Consultant / Note: Dewater as Necessary Fills/Backfihls Placed in Potential Groundwater Saturation/Inundation Zones Shall Be Compacted to Mm. 95% Compaction Levels Per ASTM D1557. SMS GEOTECHNICAL SOLUTIONS INC 5931 Sea Lion Place, Suite 109 Carlsbad, CA 92010 Project Number: GI-20-09-136 Figure Number: 4 ENGUNEERUNG, OCD SOIL & FOUNDATION ENGINEERING • ENGINEERING GEOLOGY • HYDROGEOLOGY April 19, 2021 I Project No. 9336.1 Log No. 21386 City of Carlsbad I Land Development Engineering 1635 Faraday Avenue Carlsbad, California 92008-7314 I Attention: Ms. Kyrenne Chua I Subject: THIRD-PARTY GEOTECHNICAL REVIEW (FIRST) U Proposed Residential Development 3342 Donna Drive I Carlsbad, California Project ID: 0R2021-00141PD2021-0019 I References: 1. "Geotecb.nical Investigation, Proposed Residential Development, 3342 Donna Drive, Carlsbad, California (A.P.N. 205-160-62)", by SMS Geotechnical Solutions Inc., dated October 13, 2020. 1 2. "Grading Plans For: Donna Drive Residence) GR2021-0014", by Christensen Engineering & Surveying, undated (Sheets 1 through 5). I Dear Ms. Chua: In accordance with your request Hetherington Engineering, Inc. has provided third-party I geotechnical review of Reference 1. The following comments are provided lbr analyses and/or response by the (3eotechnical Consultant. 3EOTECINICAL REVIEW CO 1. The Consultant should review the project grading, shoring, and foundation plans, I provide any additional geotechnical recommendations considered necessary, and confirm that the plans have been prepared in accordance with the geotechnical recommendations provided in the referenced reports. The Consultant should provide an updated geotechnical map(plot plan utilizing the latest grading plan for the project to clearly show (at a minimum), a) existing site I topography, b) proposed structures/improvements, c) proposed finished grades, d) locations of the subsurface exploration, e) geologic contacts, and ) remedial grading limits. etc. The Consultant should provide geologic cross-sections utilizing the cuiTent .grading. plan to clearly show (at a minimum), a) existing site topography, b) proposed finished I structures/improvements, c) proposed finished grades, d) geologic contacts, e) 5365 Avenida Enctnas, Suite A e Carlsbad, CA 92008.4369 • (760) 9311917 ° Fax (780) 931-0545 333 Third Street, Suite 2 a Laguna Beach, CA 92851-2306° (949)715-5440° Fax (760) 931-0545 www.hetheringtonengineering.com I I I I I I I I I I I I I I I I 1 I I ii flIli l'i\I l.' ff\,ff\.\l (lR:r) Project Nu. 9336.1 Lug No. 21386 April 19, 2021 1 Page 2 geologic St flielliFe, fl locations ol [lie subsurface cpIoration, g) temporary construCtiOn slopes, and h) remcclhil grading, etc. 11. 1 he ( 'onsullani should provide a list or recollillicildud obsctvalwi) and testing (f(lrin site gml(lillg and construction. The Oppurlilnhly to he of service is sincerely appreciated. 11 you have any questions regar Ii n I his reviews please contact this oil ice at your convenience. Sincerely, 11 F?.] '1 IERTNGTON fNG1NEfl.R IN U, I NC. nF /'t1/ Civil Engineer 30 J Geotecimical Engineer 397 / (expires 3/31/22) Distribution: ]-via c-mail (Kyrenne.Chuacar1sba(lca.gov) 1-via e-mail (E1issa.TovarcarJsba(lca.gov) Ej7MGpjjjlEEFgURqr, II.