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Home My WebLink AboutMS 2018-0013; REDWOOD BEACH HOMES; RESPONSE TO THIRD PARTY REVIEWER; 2019-05-15SPIN Geotechnical Exploration, * Inc. SOIL AND FOUNDATION ENGINEERING 0 GROUNDWATER 0 ENGINEERING GEOLOGY 15 May 2019 Rincon Real Estate Group Attn. Mr. Kevin Dunn 3005 S. El Camino Real San Clemente, CA 92672 RECORD COPY ------- Date Job No. 18-11893 Subject: Response to Third-Party Reviewer Rincon Residential Redwood Homes 3861-3871 Garfield Street Carlsbad, California Dear Mr. Dunn: RECEIVED MAY 2120;3 LAND DEVELOPMENT ENGINEERING As requested and as required by the City of Carlsbad third-party geotechnical reviewer, Hetherington Engineering, Inc., in a letter dated April 11, 2019, we herein respond to the review comments. The third-party reviewer has reviewed our "Report of Preliminary Geotechnical Investigation," dated June 19, 2018 and grading plans for "Redwood Homes, 3861 Garfield Street" by Pasco Laret, Suiter and Associates, Inc. plot date February 8, 2019 (5 sheets). REVIEW COMMENTS OF GEOTECHNICAL REPORT The consultant should review the project grading, foundation, and improvement plans, 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 report. GE! Response: We have reviewed the project grading and improvement plans (5 sheets) by Pasco Laret Suiter and Associates, print dated February 8, 2019; and found them to be in compliance with the recommendations of our geotechnical report dated June 19, 2018. The foundation plans by HTK Structural Engineers, still need to be revised. Once we review the revised structural plans, we will issue their compliance letter. 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 topography, b) existing improvements, C) proposed 7420 TRADE STREETO SAN DIEGO, CA. 92121 0 (858) 549-72220 FAX: (858) 549-1604 0 EMAIL: geotech@gei-sd.com Rincon Residential Project Job No. 18-11893 Carlsbad, California Page 2 structures/improvements, d) proposed finished grades, e) locations of the subsurface exploration, and f) geologic contacts. GE! Response: We have included an updated geotechnical Plot Plan showing the existing and proposed structures and improvements, proposed finish grades, locations of subsurface exploration and geologic contacts on a topographic base map (attached as Appendix A). The consultant should provide a statement regarding the impact of the proposed grading and construction on adjacent properties and improvements. GE! Response: In our professional opinion, the proposed grading and construction of the subject site will not Impact adjacent properties or right-of- ways if the recommendations presented in our geotechnical Investigation report are implemented during construction of the project and in accordance with City of Carlsbad building codes and grading ordinances. Foundation and slab design criteria for expansive soils should be consistent with Section 1808.6 of the 2016 California Building Code. The consultant should provide expansion index test results and update the foundation recommendations, as necessary. GE! Response: The soils encountered at the site consist of silty sands with less than 20 percent passing the No. 200 sieve with no detectable plasticity. Due to the non-plastic nature of the on-site soils encountered across the site, no expansion index testing was performed. However, considering the reviewer's comment we collected a representative soil sample on April 18, 2019, and performed an expansion index test which yielded an Expansion Index of 1, which classifies the soils as having a very low expansion potential. Based on this test result there is no need to update the foundation recommendations. The recommended maximum allowable bearing capacity, passive soil pressure and coefficient of friction exceed the presumptive values for silty sand (SM) provided in the 2016 California Building Code. The consultant should provide the basis for the recommended values or revise the recommended values accordingly. GE! Response: Based on our experience and a chart provided by NAVFAC Manual, Figure 7, page 7.1-149, we assigned properly compacted on-site silty sands a conservative value of 32 degrees and a cohesion value of 50 psf. We also used a soil total unit weight of 120 pcf to calculate the ultimate and Rincon Residential Project Job No. 18-11893 Carlsbad, California Page 3 allowable soil bearing capacity for footings embedded at least 18 inches in depth and a minimum width of 12 inches. The ultimate soil bearing capacity was calculated based on bearing capacity factors by Meyerhoff, as presented in Foundations Analysis and Design, by Joseph E. Bowles, 5th edition, page 223. The calculated ultimate bearing capacity is 7,761.5 psf. With a factor of safety of 3, we recommend an allowable soil bearing capacity for the shallow foundations of 2,500 psf for an acceptable allowable settlement. To calculate the allowable passive resistance, we used a factor of safety of 1.5 applied to the ultimate passive resistance. The passive resistance was calculated from the equation P.= yh tan (45 + + 2c tan (45 + where y is the soil unit weight in pcf, h is the depth of footing in feet (we used 1 foot rather than 11/2 for calculation purposes), and q, is the soil friction angle in degrees. The calculated ultimate value yielded 570 pcf. With a factor of safety of 1.5, the value is 380 pcf. We recommended 300 pcf in our report. Regarding the allowable friction coefficient, the ultimate value of the soil is tan, (p, which for 32 degrees is 0.62. After applying a factor of safety of 1.5, the allowable friction coefficient is 0.42; we recommended 0.40 in our report. 6. The consultant should specify the sulfate exposure category (ACI 318) based on soluble sulfate testing and provide recommendations for sulfate resistant concrete, if necessary, or default to a severe exposure category if is testing is not available. GEl Response: We collected two soil samples from surficial soils at two locations on April 18, 2019 (see Appendix A). The samples were taken to Clarkson Laboratories to determine the Soluble Sulfates and Soluble Chlorides, (See Appendix B) Sample No. 1 yielded soluble sulfates over 200 ppm, which indicates a classification of Class I (moderate exposure potential) per ACI 318 Classification. Sample No. 2 indicated a classification of Class 0 (negligible exposure potential). Because of the classification of Sample No. 1, we recommend that the concrete for foundations, slabs, and pavement include Cement Type II, with a water/cement ratio equal or lower than 0.50, and compressive strength at 28 days of age of at least 4,000 psi. 7. The consultant should complete and provide Form I-B (Categorization of Infiltration Feasibility Condition) and 1-9 (Factor of Safety and Design• In filtration Rate) from the City of Carlsbad BMP Design Manual. GE! Response: Completed forms 1-8 and 1-9 are included as Appendix C. Rincon Residential Project Job No, 18-11893 Carlsbad, California Page 4 The consultant should provide the basis for the recommended active earth pressures. GE! Response: The recommended soil active equivalent fluid pressure is based on the compacted soil friction angle of 32 degrees and a soil unit weight of 120 pcf. By using the active pressure coefficient Ka =tan (45 - , the value is 0.307 and the assigned soil weight of properly compacted soil (120 pcf), the active pressure equivalent fluid weight is calculated as 36.87 pcf, which we rounded up to 38 pcf. The consultant should provide a list of recommended geotechnical observations and testing to be performed during grading and construction. GE! Response: During grading we should observe the bottom of the excavation of removed soils, perform field density tests of placed and compacted soils at least every 2 feet in thickness, verify the adequacy of soil moisture content and relative compaction, obtain and verify the maximum dry density of the soils being placed as fill material, and verify the adequacy of imported soils by performing sieve tests and expansion index tests as well as maximum dry density and optimum moisture tests. In addition, we should verify soil moisture content and compaction of on-site soils being used for trench and retaining wall backfill, verify adequacy and moisture content of subgrade soils to receive pavement or flatwork improvements, obtin soil samples and perform R-value tests in areas to receive pavement to verify adequacy of pavement cross section, verify adequacy of compaction of asphalt concrete, verify adequacy of grain size of base material as well as determination of maximum dry density in the laboratory as well as relative compaction in the field, and observe the bottom of foundation excavations and evaluate soil compaction adequacy of bearing soils. The consultant should provide a list of references utilized in preparation of this report. GE! Response: The list of references used in this response letter is as follows: NAVFAC Design Manual 7.01, Revalidated September 1986; Foundation Analysis and Design, by Joseph E. Bowles, 5th Edition, 1996, McGraw Hill Companies; Geotechnical Engineering Techniques and Practices, by Roy E. Hunt, McGraw Hill Company,1986; Geotechnical and Geoenvironmental Engineering Handbook, edited by R. Kerry Rowe; Kluwer Academic Publishers, 2001; California Building Code, 2016 Edition. Rincon Residential Project Carlsbad, California Job No. 18-11893 Page 5 If you have any questions regarding this.letter, please contact our office. Reference to our Job No.18-11893 will help expedite a response to your inquiry. Respectfully submitted, LHNIC GE AL OSPE R.C.E. 34422/G.E.2007 Senior Geotechnical Engineer Iona an . Browning C.E. . 26 5/P.G. 9012 Senio Pr ect Geologist ( GE0 UP 02007 k $Y , top. 4511 (OAL 00 JONAThAN• 'Q r'f BROMING \I tL-.1 . CERTIFIED ENGINEERING GEOLOGIST ) \ .o7 S% CA.' C' APPENDIX A L1± NOTE: This Plot Plan is not to be used for legal purposes. REFERENCE: This PLOT PLAN was prepared from an existing Locations and dimensions are approximate. Actual GRADING PLAN provided by PASCO LARET SIJITER & ASSOCIATES I property dimensions-and locations of utilities may be dated 02/08/19 and from on-site field reconnaissance performed by GEl. obtained from the Approved Building Plans or the — As-BuIlt Grading Plans. t . i ?,18 2 1 i i..h.. kthL loll ;19- I WLPMSO104 O*VW87DM4W I 41 ., SIG _ — -— — WOAvE U ¶ Boom 3W £0E154LX TO FCCCM !: !L w Z' VLFW 7 - IA . . I IIIWINT — a5!54 iaot - .' I EXPOM A. POLES70 I ff 1HP-2/INF-2 I IMCFE WVMCCM 12ff wr! III 1t4t2 •.. . It-LQIL.1:'. .• • zi •. MEGrSAV- --' $ £41.0 a EXTEDP I -1/ThF-1 , .; .- at WT3 'j FF14MO 1 1•. ULT OVA 90p 1 jLt TL — — HA-2 k'- AEMI l ;(I5$ - •j:.jiL.. MAUV =A a4w L. .. ........ . •.... - — I 1 us i = = - = = RRYu1s1P' USEWMILAMM . .X f B*%TO Wf .s I I! . .. . . .•. • ••. .• ... . • - - A?M$0 MIF• flN! 1'•' '••5 EMS temaj — -- f4J •® £412 . .;: ... . rsorAcw.aqmsiv l_ 4 I I p ., - . 'I 1 I. l..•' . i 4O-s3•S A 1 / fEA5W II I I REAVA UNIT2 , I I APN 204-253-19-00 3 i ' — - I I RD8a5 LWOFNW -. . Fr HP-3 . •. •1 ... I LOT 16 I •I- .; IE4T2 .%.:..J I. • I a I . iS •.. : ILp — BLOCK tt I. - 1 y:.!l / - MAP 1747 nv;fi.I .. t ..... .. ..•. .... . TOEA5ZV I-)' iai_-._. •.. . •J... :'• 1 . . -aosp ,Ir' r ° .7 i 6W6, cow I v L — — — .. .•. /SUMSOM ------- '8971W J(Q-41 EUMAGWOMOWS FCC AWMMMEMM Dam TORSIM APN:204-253.0200 LEGEND MREUW pcOLARET A UJ LOT 13 I Approximate Location BLOCKG HP-1 of Exploratory Handpit emofl?&SM4flfl Yt P&II t SiAfl 104r IfIff GEOLOGIC LEGEND Approximate Location of Oaf Artificial Fill INFi Infiltration Test Approximate Location of Qop Old Paralic Deposits HA-2 Hand Auger Boring 6-7 Units 6- 7 on 4-18-19 CONSWUCTK)N NOTES 0 0 0 51 51 a 51 0 51 • 51 4ffEPI*flC 51 EXISTING EASEMENTS M"WO (JO Wcf. 020M W49M PROPOMMSEWNTIMWAMN AVM ADDITiONAL SITE NOIES , & 4 & aThO STREET TR.EEISIGHTDISTANCE NOTE ; GRAPIIICSCAI.c io Scale: 1" 20' (approximate) PLOT PLAN Garfield Street Residences 3861-3871 Garfield Street Carlsbad, CA. Figure No. II Job No. 18-11893 ift44 Geotechnical ______ Exploration, Inc. (June 2018) (updated Apo 2019) APPENDIX B LABORATORY REPORT Telephone (619) 425-1993 Fax 425-7917 Established 1928 CLARKSON LABORATORY AND SUPPLY INC. 350 Trousdale Dr. Chula Vista, Ca. 91910 www.clarkson1ab.com ANALYTICAL AND CONSULTING CHEMISTS 11 Date: April 19, 2019 Purchase Order Number: 18-11893 Sales Order Number: 44059 Account Number: GEOE To: *-------------------------------------------------* Geotechnica]. Exploration Inc. 7420 Trade Street San Diego, CA 92121 Attention: Jaime Cerros Laboratory Number: S07295 Customers Phone: 858-560-0428 Fax: 858-549-1604 Sample Designation: * ------------------------------------------------- Two soil samples received on 04/18/19 at 3:00pm, from Redwood Homes marked as follows: ANALYSIS: Water Soluble Sulfate (SO4) California Test 417 (Turbidity Method) Water Soluble Chloride (Cl) California Test 422 (Titration Method) Sample SO4% Cl% #1 S-i 0.146 0.037 #2 S-2 0.018 0.007 Laura Torres LT/dbb APPENDIX C Gsi'fietd Street Project 18-11893 Appendix I: Forms and Checklists Categorization of biffltration Feasibdity I; Form 1-8 Condition l' Part I - Full Infiltration Feasibility Screening Criteria Would infiltration of the full design volume be feasible from a physical perspective without any undesirable consequences that cannot be reasonably mitigated? Criteria Screening Question Yes No Is the estimated reliable Infiltration rate below proposed facility locations greater than 0.5 inches per hour? The response I to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix Ci and Appendix D. Provide basis: The iniltratlon teat results below the proposed facility locations were 2.826 and 3.316 Inches per hour with a minimum facIor of Eatery 012 applied. Simple open pit Ieting wee performed at 2 locations on the silo in accordance watt Appendix Dot U's City of Carlsbad BMP design manual. In oddilk,ri a comprehensive evaluatIon of the site was conducted In accordence wilt Appendix C.2. Please rater to our 'Report oProfmlnray GeotocItnical Invosligatlon' dated June 19, 2018 for detefis of the comprehensive evaluation and Irweatlga1lon conducted. s!mpio open pit tesi rates and simple open pit rats to infiltration rats calculatIons and maps representative of the study. Summarize findings of studies; provide reference to studies, calculations, maps, data sources. etc. Provide narrative discussion of study/data source applicability. Can Infiltration greater than 0.5 inches per hour be allowed without increasing risk of geotechnlcal hazards (slope stability, 2 groundwater mounding, utilities, or other factors) that cannot x be mitigated to an acceptable level? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.2. Provide basis: The infittretian teat results below the prupnaed facility locations ranged from 2.828 to 3.316 Inches pet hour with a minimum factor of safely of 2 applied. In our opinion, any tong tatm to Inliltratlon at the site w.11 not result in geotechnical Iezonla v41t1ch cannot be rescnablo mitigated to an acceptable level. However, we recommend that the sidewalls of the proposed basins be lined. Please refer to our 'Report of Prefnnery Goalechnical tnvestigntion' dated June 19. 2010 for defalic of the comprehensive evaluation and Investigation conducted, simple open pO test rates and simple open pit rete to Infitrallon rate catoulailona and mps representative of tire study. Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability. 1-3 February 2016 Garfield Street Project 18-11893 Appendix I: Forms and Checklists nt a Screening Question Yes No Can infiltration greater than 0.5 inches per hour be allowed without increasing risk of groundwater contamination (shallow water table, storm water pollutants or other factors) that cannot be mitigated to an acceptable level? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C3. Provide basis: The infiltration test results below the praposed facility locations ranged from 2.826 to 3.316 inches per hour with a minimum factor of safety of 2 applIed. In our opinion, any long term full Inflhtmion at the site will not result In a significant risk for groundwater related concerns. Please safer to our 'Report of Prelimlnasy (3eotechinlcal InvostigaIlors dated June 19, 2018 for details of the crnptehanstve evaluation and invesfigaflon conducted, simple open pit test rates and simple open pit rate to Infiltration rate caimletione and snaps representative of the study. Suronianze findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability. Can Infiltration greater than 0.5 inches per hour be allowed without causing potential water balance issues such as change of seasonality of ephemeral Streams or Increased discharge of contaminated groundwater to surface waters? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.3. Provide basis: Question to be answered by the design engineer. Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability. If all answers to cows 1 -4 are 'Yea" a full infiltration design is potentially feasible. Part 1 The feasibility screening category is Pull Infiltration Result If any answer from row 1-4 is "No", infiltration may be possible to some extent but would not generally be feasible or desirable to achieve a "full infiltration" design. Proceed to Part 2 10 tic completed using gathered site information and best professional judgment considering the definition of MEP in the MS4 Permit Additional testing and/or studies may be required by the City to substantiate findings. 14 February 2016 Gaflteld Struet Prect 18-11893 Appendix I: Forms and Checklists L_ Part 2— Partial Infiltration vs. No Infiltration Feasibility Screening Criteria Would Infiltration of water In any appreciable amount be physically feasible without any negative consequences that cannot be reasonably mitigated? Criteria Screening Question Yea No Do soil and geologic conditions allow for infiltration in any appreciable rate or volume? The response to this Screening X Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.2 and Appendix D. Provide basis: The Infiltration test results below the proposed fatildy lOQ3tJQn ranged from 2.826 to 3.318 Inches per hour with a ntinlmum factor of safety of 2 applied. Based on our lnilitratlon test rates and limited geotechnical Investigation of the she, it Is our opinion that the soil and geologic conditions altw, for appredablit infiltration rateS, Please refer to our 'Report of Preliminary Gtsthnlcal Investigation' dated June 19, 2018 fur dIai1s of the compiettensiva evaluation and investigation Conducted. simple open pIt test rates and simple open pit rate ID InNhOon rote calculations and maps representative of the study. Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide,oazrauve discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates. Can Infiltration in any appreciable quantity be allowed without Increasing risk of geotechnical hazards (elope 6 stability, groundwater mounding, utilities, or other factors) x that cannot be mitigated to an acceptable level? The response to this Screening Question shall be based one comprehensive evaluation of the factors presented in Appendix C.2. Provide basis: In our opinion, any tong term partial infiltration at the site will not result in geolediniesi hazards which cannot be reasonable mItigated to an acceptable level. Howevar, we recommend that the aldevalls Of the proposed basins be lined. Please refer to our 'Report of Preliminary Geotedtnlcsl Investigation' dated June 19, 201$ for details of the comprehensive evaluation and Investigation conducted, simple apart pit test rates and simple open pit rats to infiltration rate caitullions and maps representative of the study. Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates. 1-5 February 2016 Garfield Street Project 18.11893 Appendix I: Forms and Checklists r- ---. Criteria Screening Question Yea No Can Infiltration In any appreciable quantity be allowed without posing significant risk for groundwater related concerns (shallow water table, storm water pollutants or other factors)? The response to this Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix Ci. Provide basis: In our opinion, any long term partial lnlilwatlon at the eke will not result in a significant risk (orgmundweler related concerns. Please refer to our 'Report of Preliminary Gectechnical Inves"aW dated June 19, 2018 for delats of the comprehensive evaluation and investigation conducted. simple open pit test rates and simple open pit rate to InflillatlOn rate calculations and maps representative of the study. Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide nsraativc discussion of study/data source applicability and why it was not feasible to mitigate low infiltration races. Can Inftltration be allowed without violating downstream 8 water rights? The response to thit Screening Question shall be based on a comprehensive evaluation of the factors presented in Appendix C.3. Provide basis: Question to be answered by the design engineer. t' 1OS4GtTs,. Summarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative discussion of study/data source applicability and why it was not feasible to mitigate low infiltration rates. If all answers from row 5-8 are yes then partial infiltration design is potentially feasible. Pan 2 The feasibility screening category is Partial Infiltration. Result* If any answer from sow 5.8 is no, then infiltration of any volume Is considered to be infeasible within the drainage area. The feasibility screening catcgosyis No Infiltration. 10 be completed using gathered ste information and best professional judgment considering the definition of MEP in the MS4 Permit. Additional resting and/or studies may be required by the City to substantiate findings. 1-6 February 2016 Gricd St. "W. 13-1183 Appendix I: Forms and Checklists To LAO 1Xñ) Factor Category Factor Description . Product (p)ption , Factor , CI Weight wgiitWj Value (y) pwxv Soil assessment methods 0.25 2 0.5 Predominant soil texture 0.25 2 05 A Suitability Site soil variability 0.25 2 0.5 .Assessment Depth to groundwater / impervious layer 2 05 Suitability Assessment Safety Factor, SA = Ip 2.0 Level of pretreatment/ expected 05 sediment loads B Design Redundancy/resiliency 0.25 Compaction during construction 0.25 Design Safety Factor, So = Ip Combined Safety Factor, Sw= SAX So Observed Infiltration Rate, inch/hr, Kv,,a (corrected for test-specific bias) Design Infiltration Rate, ui/hz, K4,.j11,, = Kw..d / S,,,, Supporting Data Briefly describe infiltration test and provide reference to test forms: Simk cn t 2 Cf C3 01 t3 C 2r Mn u;Thn) of, h Cy of ti S nn Wctor Srr, Dn Monuol. hi ecre&,io Aca . ' faza r4ur to outot of Pr n'ry G lln!tC4 !.t'on &tcd .furta 19, 2010 for ot•: 0fo oopoaciVo ev*utoi 4r1 n1!on co,uetd, G*,I:a o ptcri rcts cid thii as pr rala to MLcon risS fl2iO r toIvo of 2t c1udi. 1-7 February 2016