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HomeMy WebLinkAboutCT 04-26; ROBERTSON RANCH EAST VILLAGE PA 16, 17, & 18; COMPACTION REPORT OF BUILDING PAD RE-CERTIFICATION PHASE 16; 2011-05-17CTO12S L_) Gèotechnical . GèoloOic..,Coastàl Environmental 57.41 Palmer Way • Carlsàd, California 92010. (760) 438-3155 • FAX (760)931-0915. www.geosoilsinc.com Myi7, 2011 . W.O. 5949-B-SC Brookfield Homes ' 12865 Pointe Del Mar, Suite 200 Del Mar, California 92014'. Attention: Ms. Teri McHugh Subject: Compaction Report of-Building Pad Re-Certification, Planning Area 16, ProdüctionPhase5, Lots 160 through 165, and 184 through 189,'Robertson Ranch Development, CarIsbd, San Diego County, California Dear -Ms. McHugh: As requested, GeoSoUs, Inc. (GSI) is providing this'summary of our observtiôn and testing services of re-grading on Lots 160 through 165, and 184' through 189,. Vvithin Planning Area 16, at the Robertson Ranch Subdivision in the City of Carlsbad, California Planning 'Area 16 was initially graded with observation and testing services provided by GSI (2009b). The pupose of remedial grading was to re-condition the building pads, and consisted of re-processing surlicial soils, moisture conditioning, and compacting the soil to a minimum relative compaction of 90 percent per ASTM.D 1557 (GSI; 2009a, 2010). This operation was generally complete by mid-April-2011. Based on our observations and testing, the building pads appear to have been prepared, in general àccordanëë with the recommendations provided by'this office (GSI; 2009a, 2010), and are considered suitable for their intended use. FIELD OBSERVATION AND TESTING Fie ld densittests were performed using nucler (densometer) ASIM test methods D,2922 and 'D 3017. The test 'results taken during grading operations are presented in the attach ed..copiesôf our "Field Testing Re'pots.'.- . •, The laboratory maximum dry density and optimum moisture content for the major soil'ty'pe within this construction phase were determined according to test method ASTM D 1557. The following table presents the results: , S 4SOILTYPE DENSITY (PCF) (PERCENT)k A - Brown, Silty SAND , 127.0 10.0 E - Dark Brown toBrown; Silty SAND 1260 . 11.0 Field compaction testing indicates that the soils appear to meet the minimum compaction reuirements previously established and adopted by the City of Carlsbad ([2010 California Building Code {2010 CBC}] i.e., at least 90 percent relative compaction per ASTM D 1557), and:testing also indicates adequate soil moiture. However, based on ' the expansive character of site soils, and the anticipated additional time that will pass prior to slab construction, additional moisture conditioning and verificationwill likely be necessary priorto placement of the urderslab vapor retarder (see Table A, Note 11, and Page 12 of. GSI, 2009b). - SOIL EXPANSION, AND CORROSION POTENTIAL A review of GSI (2009b) indicates that very kw expansive r soil underlie Lots 160 through 164 (expansion index [E.l.] <20), low expansive soils underlie Lots 184 through 189 (expansion' index [E.l.] >20, and <50),andmedium expansive soils underlie Lot 165 (E.l. >50, and <90), as classified by 2001 California Building Code ([2001 CBC], lnterntional Confernce of Building Officials [ICBO], 2001), Table 18-lB. Please note that GSI is -utilizing -this previous CBC code only to classifI the soils, as the 2010 CBC (California Building Standards Commissioh [CBSC], 20'l 0) does not provide this index. Subsequent corrosion testing of soils within 3 feet of finish grade indicate that these soils present a negligible (sulfate class SO) sulfate exposure to concrete,' per Table 4.2.1 and 4.3.1 of the American Concrete Institute (ACI) document 318708 (2010 CBC [CBSC,2010]). Soils are relatively neutral with respect to soil acidity/alkalinity (pH of 7.9),- and are considered corrosive to exposed ferrous metals in asaturated'statO. The chloride ion contert in soil was also noted to generally be in.the range of 84 to 194 ppm, and ,is co'nsidered below action levels (300 ppm [see GSI, 2009b]). Itis our understanding that standard concrete cover over reinforcing steel is usually appropriate' for these conditions; however, a corrosion engineer should be consijlted to provide specific recommendations regarding foundations and piping, etc. FOUNDATION DESIGN/CONSTRUCTION Post-tension slabs are proposed for all lots. Based. on a review of GSI (2009b) and observations/testing performed during this phase of site grading, post-tension foundations should be designed and constructed in accordance with at least the minimal recommendations presented in GSI (2009b) for Category I (Lots 160 through 164, and Lots 184 through 189), and Category II (Lot 165) posttension foundations. Please note Brookfield Homes W.O. 5949-B-SC Phase 5, PA 16, Robertson Ranch May 17, 2011 File:e:\wpl2\5900\5949b.cro.ph5 Page 2 GeoSoils, Inc. that GSl (2009b) referenced the 2007 Code; however, while some sections numbers have• changed from the 2007 Code to the 2010 CBC, the geotechnical design parameters are the same. Unless specifically superceded herein, the findings, conclusions, and recommendations presented in GSI (2009b) are generally considered valid and applicable with respect to the construction and development of the subject building pads. Based on the duration of time following pad completion, pre-wetting/saturation is recommended, as indicated in the referenced GSI reports. SUBSURFACE WATER As directed by the client during mass grading of the project, the slope descending from the south side of Lots 160 through 164 was constructed as a fill over cut slope. As has been observed at the face of slope, subsequent to rainstorm events, perched water accumulates along the fill/formation contact, and results in seepage where the contact daylights at the slope face. It should also be noted that perched groundwater was observed toward the front (north) of these same lots, during trenching operations for water utilities-. The relatively permeable "shade sand" placed within the water !ine trench is anticipated to drain off some of the perched water, primarily toward the front of the lots. However, in order to mitigate perched conditions within the remaining portion of the building pads, and the observed seepage at the slope face, a french drain is recommended to be constructed near the top of slope, and convey the collected water eastward towards Cascade Street, where a tie in to an existing storm drain inlet can be made. The drain may generally consist of 3 to 4 inch perforated PVC pipe (SDR 35, or equivalent) embedded in % to 3/4 inch drain rock encapsulated in filter fabric. The drain should be deep enough (at least 4 feet) to penetrate the fill/formation contact and sloped a minimum 1 percent to drain. The subdrain should be perforated (perforations down) through Lots 160 to 164, and maybe tight-lined down-gradient from the lots. Specific subdrain construction guidelines (see "Toedrain") are presented in GSI (2009b). A schematic drain location is presented as Plate 1. The flowline drainage and storm drain tie-lin should be reviewed by the design civil engineer for functionality and conflicts with other utilities. Brookfield Homes W.O. 5949-B-SC Phase 5, PA 16, Robertson Ranch May 17, 2011 FiIe:e:\wpl2\5900\5949b.croph5 Page 3 GeoSoils, Inc. CLOSURE The materials encountered on. the project site and utilized for our analysis are believed representative of the area; however, soil and bedrock materials vary in character between excavations and natural outcrops or conditions exposed during mass grading. Site conditions may vary due to seasonal changes or other factors. 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 maybe subject to review by the controlling authorities. Thus, this report brings to completion our scope of services for this portion of the project. Brookfield Homes - W.O. 5949-8-SC Phase 5, PA 16, Robertson Ranch May 17, 2011 FiIe:e:\wpl2\5900\5949b.cro.ph5 Page 4 GeoSoils,' Inc The opportunity to be of service is sincerely appreciated. If you should have any questions, please do not hesitate to contact our office. Respectfully subn)ittéSNPAL QN GeoSoils, Inc 4ci ( ) RCE 47857 .,1 )* A \ CL eriiiied FflgineeringJ / \Geologist / Robert G Crism 0 David W. Skelly ''p1 CP-7 Engineering GeoIot-G6i934 Civil Engineer, RCE 857 RCG/DWS/JPF/jh Attachments: Distribution Plate 1 - Schematic Drain Location Map, PA-16, Lots 160-164 Appendix - References "Field Testing Reports" (4) Addressee Brookfield Homes W.O. 5949-B-SC Phase 5, PA 16, Robertson Ranch May 17, 2011 File:e:\wpl2\5900\5949b.cro.ph5 GeoSoils, Inc. Page 5 109.7 945 Sr 6211 SF \ !'EIM \ -J2 HO, 517 TC k-1X-X-`7 55OO8 \ ; \ 5.0 \ 55 106.9 72 SF 5210 SF Q. 5000 SF 5000 SF X-705 jQ0.J 16 \X-547 Af 108? -707 ) - 48 - -.- \ 50 0 -- 3 2 125 - HOA. - 1899 5f - 0 -140 - 118 ,1J9 929 116 E LS..E 934 6805 SF 26 SF 6595 5F 927 5814 57 ' \\ 6608 SF - BASE ADAPTED FROM GSI (2009b) 1" = 40' scale SCHEMATIC SUBDRAIN LOCATION MAP PA-16, LOTS 160-164 DATE 5/11 Iwo N0.5949-B-SC Geotechnical. Geologic. Environmental FORM 89/22 PLATE 1 APPENDIX REFERENCES California Building Standards Commission, 2010, California Building Code, California Code of Regulations, Title 24, Part 2, Volume 2 of 2, Based on the 2009 International Building Code, 2010 California Historical Building Code, Title 24, Part 8; 2010 California Existing Building Code, Title 24, Part 10. GeoSoils, Inc., 2010, Supplemental discussion of slab subgrade pre-wetting, planning area 16 of Robertson Ranch, City of Carlsbad, California, W.O 5949-C-SC, dated August 17. 2009a, Discussion of building slab subgrade pre-wetting, planning area 16 of Robertson Ranch, City of Carlsbad, California, W.O. 5949-C-SC, dated October 8. 2009b, Report of rough grading, planning area 16 of Robertson Ranch, East Village (Lots 44 through 63, 89 through 99, 117-through 140, and 160 through 189), Carlsbad Tract 04-26, Drawing 453-8A, Carlsbad, San Diego County, California, W.O. 5353-131-SC, dated February 16. International conference of Building Officials, 2001, California Building Code. O'Day Consultants, Inc., 2008, Grading plans for Robertson Ranch PA 16,17; 18, Sheets 10 and 13, Job no. 01-1014, Carlsbad Tract C.T. 004-26, Drawing no.453-8A, dated August. Ii GeoSoils, Inc. w.o.-- DATE NAME Cco HOURS CLIENT ______TRACT LOCATION •'? 4r.) SUPT.- CONTRACTOR • ,• EQUIPMENT 1— D4 H- bT' l -j)ii'J Ave\ )H TEST NJ. LOCATION -- ELEV. OR DEPTH MOISTURE CONTENT % ' DRY DENSIT'C P.C.F. % RELATIVE COMPACTION TEST TYPE SOIL TYPE /17.1 L) E .3 JoT-) FT. - COMMENTS': .-••LQ. Y .. . ,_ GeoSoils, Inc. BY: PAGE OF This field report presents a summary of observations and testing by Geosoils, Inc. personnel. Our work does not include supervision or direction of the actual work of the contractor, his employees, or agents. The Contractor should be informed that neither the presence of our field representative, nor the observation and testing by our firm, shall excuse him in any way fou defects discovered in his work. It is understood that our firm will not be responsible for job or site safety on this project. FIELD TESTING REPORT W.O. s4'g-,q-cc DATE '-/-1.2-1/ NAME C/41-i5 0. HOURS - CLIENT TRACT PA/,f4 f LOCATION__________________ SUPT. _G/. /4 CONTRACTOR 2 . EQUIPMENT TEST NO. LOCATION ELEV. OR DEPTH MOISTURE CONTENT % DRY . DENSITY P.C.F. % RELATIVE COMPACTION TEST TYPE SOIL TYPE Al A /0 L ,'i jir/ 'vp, q A 11,0 /143 V. I iJ A /1 Lr j/j ,J A COMMENTS: O75/7 1 ..&% 7. r I / _r.(_ is (-LLt1V(J __,1I Sm,14IL ,L :i. f4'> £-.' a(14'. >'3o) GeoSoils, Inc. BY: PAGE' OF / This field report presents a summary of observations and testing by Geosoils, Inc. personnel only where the tests were performed. Our work does not include supervision or direction of the actual work of the contractor, his employees, or agents. The Contractor should be informed that neither the presence of our field representative, nor the observation and testing by our firm, shall excuse him in any way for defects discovered in his work. It is understood that our firm will not be responsible for job or site safety on this project.