Loading...
HomeMy WebLinkAboutCT 07-03; ROBERTSON RANCH PA 14; SUPPLEMENT TO COMPACTION REPORT OF ROUGH GRADING; 2011-06-06c1-o10 . Geotechnical ' Geologic. Coastal . Environmental 5741 Palmer Way • Carlsbad, California 92010 • (760) 438-3155 • FAX (760) 931-0915 . www.geosoilsinc.com June 6, 2011 W.O. 5949-B-SC Brookfield Homes 12865 Pointe Del Mar, Suite 200 Del Mar, California 92014 Attention: Ms. Teri McHugh Subject: Supplement to the Compaction Report of Rough Grading, and Geotechnical Update for Planning Area 14, Robertson Ranch, East Village, Carlsbad Tract 04-26, Drawing 453-8C, City of Carlsbad, San Diego County, California Dear Ms. McHugh: As requested, GeoSoils, Inc. (GSI) is providing this supplement to our compaction report of rough grading (GSI, 2010c) with respect to the observation and testing services provided during grading within Lot 16 and that portion of Glenn Avenue within Planning Area 14, at the Robertson Ranch Subdivision in the City of Carlsbad, California. This report was also prepared in order to update our report for PA-1 4 (GSI, 201 Oc) with respect to the current building code (2010 California Building Code [{2010 CBC}, California Building Standards Commission {CBSC}, 2010]). EXISTING WORK AND ADDITIONAL GRADING General Planning Area 14 was initially graded with observation and testing services provided by GSI (2010c). Upon completion of site grading under the geotechnical observation and testing of GSI (GSI, 2010c), grading and foundation construction was generally completed within Lots 1 through 7. Lots 8 through 15 were also graded (GSI, 2010c),but remained vacant. Lot 16, and the adjacent portion of Glen Avenue, were left low to function as a desilting basin. The purpose of additional grading, under the purview of this report, was to perform the recommended remedial grading within an existing desilting basin located within Lot 16 and the adjacent portion of Glen Avenue, then bring these areas to plan grades. As observed, the work generally consisted of remediating near surface soils through removal, re-processing, moisture conditioning, and compacting the soil to a minimum relative compaction of 90 percent per ASTM D 1557. Grading operations generally occurred between April 13 and April 18, 2011. Based on our observations and testing, the building pad (Lot 16) and the adjacent roadway appears to have been prepared in general accordance with the recommendations provided by this office (GSI; 2008, 2010c), and is considered suitable for the intended use. Field Observation and Testing Field density tests were performed using nuclear (densimeter) ASTM test methods D2922 and D 3017. The test results taken during grading operations are presented in the attached Table 1 The laboratory maximum dry density and optimum moisture content for the major soil type within this construction phase were determined according to test method ASTM D 1557. The following table presents the results: Field compaction testing indicates that the soils appear to meet the minimum compaction requirements previously established and adopted by the City of Carlsbad ([2010 CBC] i.e., at least 90 percent relative compaction per ASTM D 1557), and testing also indicates adequate soil moisture. 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 verification will likely be necessary prior to placement of the underslab vapor retarder (see Table A, Note 11, and Page 12 of GSI [2010c]). Soil Expansion and Corrosion A review of GSI (201 Oc), and subsequent testing indicates that very highly expansive soils underlie Lot 16 (expansion index [E.I.] <130), as classified by 2001 California Building Code ([2001 CBC], International Conference of Building Officials [ICBO], 2001), Table 18-1-B. Please note that GSI is utilizing this previous CBC code only to classify the soils, as the 2010 CBC (CBSC, 2010) does not provide this index. Corrosion testing of soils indicate that these soils present a negligible (sulfate class S0) sulfate exposure to concrete, per Table 4.2.1 and 4.3.1 of the American Concrete Institute (ACl) document 318-08 (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 a saturated state. The chloride ion content in soil was also noted to generally be in the range Brookfield Homes W.O. 5949-B-SC Planning Area 14, Robertson Ranch June 6, 2011 File: e:\wpl 2\5900\5949b.stt. pal 4 Page 2 GeoSoils, Inc. of 84 to 194 ppm, and is considered below action levels (300 ppm [see GSI, 2010c]). It is our understanding that standard concrete cover over reinforcing steel is usually appropriate for these conditions; however, a corrosion engineer should be consulted to provide specific recommendations regarding foundations and piping, etc. GEOTECHNICAL UPDATE General Unless specifically superceded herein, the findings, conclusions, and recommendations presented in GSI (2010c) are generally considered valid and applicable with respect to the construction and development of the subject building pads. Please note that GSI (2010c) references the 2007 Code; however, while some section numbers have changed from the 2007 Code to the 2010 CBC (see following table, and CBSC, 2010), the geotechnical design parameters indicated in GSI (2010c) are the same. Additional recommendations regarding future earth work, foundation design/construction, peak horizontal ground acceleration, and seismic surcharge are provided later in this document. Remedial Grading Based on the duration of time following the construction of Building Pads 8 through 15, under the purview of GSI (2010c), pre-wetting, and/or surficial processing is recommended, as indicated in GSI (2009 and 2010a). Should subgrade soils within Lot 16 be exposed for any significant duration of time, pre-wetting, and/or surficial processing would also be recommended, as indicated in GSI (2009 and 2010a). Foundation Design/Construction Post-tension slabs are proposed for all remaining lots within PA-1 4. Based on a review of GSI (2010d) and observations/testing performed during this phase of site grading, post- tension foundations should be designed and constructed in accordance with recommendations presented in GSI (2010c) for Category Ill (Lots 4, 5, 6, 7, ii, 12, 13, 14, and 15), and Category IV (Lot 1, 2, 3, 8, 9, 10, and 16) post-tension foundations. In addition to the recommendations presented in GSI (201 Oc), all foundation systems should be designed and constructed in accordance with guidelines presented in the 2010 CBC (CBSC, 2010). Seismic Shaking Parameters Based on the site conditions, the following table summarizes the site-specific design criteria obtained from the 2010 CBC (CBSC, 2010), Chapter 16 Structural Design, Brookfield Homes W.O. 5949-B-SC Planning Area 14, Robertson Ranch • June 6,2011 FiPe:e:\wpl2\5900\5949b.sn.pal4 Page 3 GeoSoils, Inc. Section 1613, Earthquake Loads, which is based on the 2009 edition of the IBC (International Building Code), and ASCE Standard 7-05 (American Society of Civil Engineers, 2005). The computer program Seismic Hazard Curves and Uniform Hazard Response Spectra, provided by the United States Geologic Survey (U.S.G.S.) was utilized for design The short spectral response utilizes a period of 0.2 seconds. CBC SEISMIC DESIGN PARAMETERS PARAMETER VALUE 2010 CBC REFERENCE Site class D Table 1613.5.2 Spectral Response -(0.2 sec), S 1.15g Figure 1613.5(1) Spectral Response - (1 sec), S1 0.44g Figure 1613.5(2) Site coefficient, Fa 1.04 Table 1613.5.3(1) Site coefficient, F 1.56 Table 1613.5.3(2) Maximum considered Earthquake Spectral Response Acceleration (0.2 sec), SMS 1 g Section 1613.5.3 (Eqn 16-36) Maximum considered Earthquake Spectral Response Acceleration (1 sec), SM1 068 g Section 1613.5.3 (Eqn 16-37) 5% Damped Design Spectral Response Acceleration (0.2 sec), S 079 . g Section 1613.5.4 (Eqn 16-38) 5% Damped Design Spectral Response Acceleration (1 sec), SD1 0.46g . Section 1613.5.4 (Eqn 16-39) GENERAL SEISMIC DESIGN PARAMETERS Distance to Seismic Source (Rose Canyon fault zone) . 7.5 mi. (12.0 km) Upper Bound Earthquake (Rose Canyon fault zone) MW 6.9** Probabilistic Horizontal Ground Acceleration ([PHGA] 10% and 2% probability of exceedance in 50 years) 0.28g/0.39g ** International Conference of Building Officials (lCBO, 1998) Conformance to the criteria above for seismic design does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur in the event of a large earthquake. The primary goal of seismic design is to protect life, not to eliminate all damage, since such design may be economically prohibitive. Cumulative effects of seismic events are not addressed in the 2010 CBC (CBSC, 2010) and regular maintenance and repair following locally significant seismic events (i.e., M5.0) will likely be necessary. Brookfield Homes W.O. 5949-B-SC Planning Area 14, Robertson Ranch June 6, 2011 File: e:\wpl2\5900\5949b.stt.pal4 Page 4 GeoSoils, Inc. Peak Horizontal Ground Acceleration A probabilistic peak horizontal ground acceleration (PH GA) of 0.28 g was evaluated for this site (GeoSoils, Inc, 2010c). This value was chosen as'it corresponds to a 10 percent probability of exceedence in 50 years (or a 475-year return period). Per the 2010 CBC (CBSC, 2010), a PHGA of 0.39 was also evaluated. This value was chosen as it corresponds to a 2 percent probability of exceedence in 50 years (or a 2,475-year return period). Seismic Surcharge for Retaining Walls For retaining walls that are over 6 feet in height, or within 6 feet or less of residences, that may impede ingress/egress, GSI recommends that the walls be evaluated for a seismic surcharge (Section 1603.1.5 of the 2010 CBC). If those conditions do not exist, evaluation of a seismic surcharge is not required. The site walls in this category should maintain an overturing Factor-of Safety (FOS) of about 1.3, when the seismic surcharge is applied. The seismic surcharge should be applied as a uniform load from the bottom of the footing (excluding shear keys), to the top of the backfill at the heel of the wall footing for restrained walls and an inverted triangular distribution for cantilever walls. This seismic surcharge pressure may be taken as 14H, where "H" is the dimension taken as the height of the retained material for the top of backfill. The resultant force should be applied at a distance 0.6H up from the bottom of the footing. For the evaluation of the seismic surcharge, the bearing pressure may exceed the static value by one-third, considering the transient nature of this surcharge. LIMITATIONS 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, engineering analyses, and laboratory data, these conclusions and recommendations are professional opinions. These opinions have been derived in accordance with current standards of practice, and no warranty is express or implied. 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. Site drainage is under the purview of the civil engineer. 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 may be subject to review by the controlling authorities. Brookfield Homes W.O. 5949-B-SC Planning Area 14, Robertson Ranch June 6, 2011 Fi1e:e:\wp12\5900\5949b.sttpal4 Page 5 GeoSolls, Inc. The opportunity to be of service is greatly appreciated. If you have any questions, please do not hesitate to call our office. ,2çOESSi0, Respectfully submitted, ((' GeoSoils, Inc. IVO Na. GE232fl CP XExp. 1934 Ij)* 4( ( Certified / ) Ennerin OF CAIXS~ Robert G. Crisman Engineering Geologil /" Andrew T. Guatelli Geotechnical Engineer, GE 2320 RGC/ATG/PLM/jh Attachments: Table 1 - Field Density Test Results Appendix - References Distribution: (4) Addressee Brookfield Homes W.O. 5949-B-SC Planning Area 14, Robertson Ranch June 6, 2011 FiIe:e:\wp12\5900\5949b.stt.pal4 Page 6 GeoSoils, Inc. Table 1 FIELD DENSITY TEST RESULTS TEST NO. DATE TEST LOCATION PLANNING AREA ELEV OR DEPTH (ft) MOISTURE CONTENT (%) DRY DENSITY (pcf) REL COMP (%) TEST METHOD SOIL TYPE 90 4/13/11 Glen Ave Bottom PA-14 72.5 19.4 102.3 92.2 ND L 91 4/13/11 Glen Ave Bottom PA-1 4 73.0 13.5 110.4 91.2 ND j 92 4/13/11 Glen Ave Bottom PA-14 74.0 12.8 111.6 92.2 SC j 93 4/14/11 Glen Ave Desilting Basin PA-14 74.5 13.5 109.2 90.2 ND J 94 4/14/11 Glen Ave Desilting Basin PA-14 76.0 14.1 110.1 91.0 ND J 95 4/14/11 Glen Ave Desilting Basin PA-14 78.0 13.8 110.7 91.5 SC J 96 4/14/11 Glen Ave Desilting Basin N. Side Parkway PA-14 79.0 12.7 111.4 92.1 ND J 97 4/15/11 Glen Ave Parkway Lot 16 PA-14 78.0 13.9 112.3 92.8 ND J 98 4/15/11 Glen Ave Parkway Lot 16 PA-14 79.0 14.4 113.4 93.7 ND J 99 4/15/11 Glen Ave Parkway Lot 16 PA-14 80.0. 12.7 111.5 92.1 Sc J 100 4/15/11 Glen Ave Parkway Lot 16 PA-14 81.0 13.0 112.0 92.6 ND J 101 4/18/11 Glen Ave West End PA-1 4 78.0 19.3 102.3 92.2 ND L 102 4/18/11 Glen Ave West End PA-14 79.0 13.9 109.4 90.4 ND J 103 4/18/11 Glen Ave West End PA-1 4 80.0 20.4 100.2 90.3 ND L 104 4/18/11 Glen Ave West End PA-14 81.0 1 14.2 110.6 91.4 SC J LEGEND: ND = Nuclear Densometer SC = Sand Cone Brookfield Homes W.O. 5949-B-SC Phase 5, PA 14, Robertson Ranch June 2010 File: C:\excel\{ables\5900\5949b.att.pal4 Page 1 GeoSoils, Inc. APPENDIX REFERENCES American Concrete Institute, 2008, Building code requirement for structural concrete (ACI 318-08) and commentary, an ACI standard reported by ACI Committee 318, dated January. 2004, Guide for concrete floor and slab construction: reported by ACI Committee 302; Designation ACI 302.1 R-04, dated March 23. American Society of Civil Engineers, 2005, ASCE Standard 7-05. 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," dated 2010, by the California Building Standards Commission. 2007, California Building Code, California Code of Regulations, Title 24, Part 2, Volume 2 of 2, Based on the 2006 International Building Code, 2007 California Historical Building Code, Title 24, Part 8; 2007 California Existing Building Code, Title 24, Part 10. Caltrans, 1999, Interim corrosion guideline for foundation investigations, Corrosion and Technology Section, Office of Materials and Foundations, dated May. GeoSoils, Inc., 2010a, 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. 2010b, Geotechnical update for Lots 1 through 7 of Planning Area 14, Robertson Ranch, East Village, Carlsbad Tract 07-03, Drawing 453-8A, City of Carlsbad, San Diego County, California, W.O. 5949-B-SC, dated April 22. 2010c, Report of rough grading, Planning. Area 14 (Lots 1 through 16), including H.O.A. Lot 18 of Robertson Ranch, East Village Carlsbad Tract 04-26, Drawing 453- 8A, Carlsbad, San Diego County, California, W.O. 5949-B-SC, dated April 12. 2009, Memorandum: 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. GeoSolls, Inc. 2008, Interim report of rough (mass) grading, Planning Area 14 (Lots 1 through 16 and Lot 18/1-10A) of Robertson Ranch East Village, Carlsbad Tract 04-26, DWG 453-8A, City of Carlsbad, San Diego County, California, W.O. 5353-B-SC, dated October 20. International Conference of Building Officials, 2001, California building code O'Day Consultants, 2009, Grading plans for Robertson Ranch PA 14, Sheet 3, Job no. 01- 1014, Carlsbad Tract C.T. 07-03, Drawing no.453-8A, print dated November 23. I Brookfield Homes File: e:\wpl2\5900\5949b.attpal4 Appendix Page 2 GeoSoils, Inc.