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Home My WebLink AboutCDP 15-52; SCHMALTZ RESIDENCE; UPDATED GEOTECHNICAL REPORT; 2016-01-13GEOCON INCORPORATED GEOTECHNICAI a ENVIRONMENTALiMATERIALS Project No. 05851-52-07 January 13, 2016 Mr. Joseph Schmaltz - 6349 Alexandria Circle - Carlsbad, California 92011 Subject: UPDATE GEOTECHNICAL REPORT SCHMALTZ RESIDENCE LA COSTA DOWNS BLOCK 22, UNIT NO. 1 -,LOT 4 6468 FRANCISCAN ROAD CARLSBAD, CALIFORNIA Reference: Final Report of Testing and Observation Services During Site Regrading. La Costa Downs Block 22, Unit No. I - Lot Nos. I through II, prepared by Geocon Incorporated, dated January 24, 1997 (Project No. 05851.12-01). Dear Mr. Schmaltz: .. We prepared this letter to update the status and applicability of the referencedgeotechnical report for the planned residence on the subject lot. In order to prepare this update letter, we have reviewed the referenced report and plans. We understand that proposed improvements will consist of constructing a two-story, wood-framed residence supported on conventional shallow foundation and concrete slab- on-grade system. Based on our review of the referenced report, it is our opinion that the referenced reports remain applicable for the design and construction of the improvements. However, updated seismic design parameters are presented herein. Based on the referenced report and our observations during a recent site visit, it is our opinion that Lot No. 4, graded as a fill lot, remains in essentially the same condition since the completion of grading as stated in the referenced report approximately 19 years ago. Currently, there are several trees at the site and the near surface materials are disturbed by burrowing animals. We recommend removing, reprocessing and compacting at least the upper I to 2feet of the existing fill materials. EXCAVATION AND SOIL CHARACTERISTICS A review olthe As-Graded Geologic Map presented in the referenced reports indicates Lot 4 is a fill lot with a maximum fill thickness of up to approximately 5 feet and a maximum fill differential thickness of up to approximately 2 feet. The near surface soil possesses an expansion index of 14 and is considered to be "non-expansive" (expansion index [El] of 20 or less) as defined by 2013 California Building Code (CBC) Section 1803.5.3. We expect the onsite soil possesses a "very low" to "low" expansion potential (expansion index of 50 or less). 6960 Flanders Drive • Son Diego, California 92121.2974 • Telephone 858.558.6900 . Fox 858558.6159 a±ac We have performed laboratory tests on samples of the near surface materials from neighboring lots to evaluate the percentage of water-soluble sulfate content. Results indicate that the on-site materials generally possess "Not Applicable" and "SO" sulfate exposure to concrete structures as defined by 2013 CBC Section 1904 and ACI 318-I1 Sections 4.2 and 4.3. We should perform sampling and testing of the material during processing and regrading of the lot. SEISMIC DESIGN CRITERIA To update the referenced update geotechnical report to the 2013 CBC, we used the computer program Seismic Hazard Curves and Uniform Hazard Response Spectra, provided by the USGS. Table I summarizes site-specific design criteria obtained from the 2013 California Building Code (CBC; Based on the 2012 International Building Code [IBC]), Chapter 16 Structural Design, Section 1613 Earthquake Loads. The short spectral response uses a period of 0.2 seconds. The building structure and improvements should be designed using a Site Class C. TABLE I 2013 CSC SEISMIC DESIGN PARAMETERS Parameter Value 2013 CBC Reference Site Class C Section 16133.2 Spectral Response — Class B(short),Ss 0.1.169g Figure 1613.3.1(1) Spectral Response — Class B(lsec),Si 0.450g Figure 1613.3.1(2) Site Coefficient, FA 1.000 Table 1613.3.3(1) Site Coefficient, Fv 1.350 Table 16 1333(2) Maximum Considered Earthquake Spectral Response Acceleration (short), SMS 1. 169g Section 16 13.3.3 (Eqn 16-37) Maximum Considered Earthquake Spectral Response Acceleration (I sec), SMI 0.608g Section 1613.3.3 (Eqn 16-38) 5% Damped Design Spectral Response Acceleration (short), ss 0.779g Section 16 13.3.4 (Eqn 16-39) 5% Damped Design Spectral Response Acceleration (I sec), SDI 0.405g Section 1613.3.4 (Eqn 16-40) Conformance to the criteria in Table I for seismic design does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur if a large earthquake occurs. The primary goal of seismic design is to protect life, not to avoid all damage, since such design may be economically prohibitive. FOUNDATION AND CONCRETE SLABS-ON-GRADE RECOMMENDATIONS According to the referenced report Lot 4 is considered Category I foundation system. It should be noted that during the grading operations structural fill placement was limited to an area bounded within 15 and 10 feet as measured from the front and rear property line, respectively. The proposed structure should be sited within the zone of structural fill with foundations located no closer than 5 feet inside from the limits of the structural fill. Project No. 05851-52.07 -2- January 13, 2016 JE+àz-&q '4 ,• -: -'L4 •_•: - - ''-I •;HI •;4' - - •- i-. 4_- -'• -- - 'L - - •-. ,4• •. ..--• •:;- '•- -•,• b - ---:-.- -- c - • - 4- 4' - 4 4 •1 -'1 - --- 4- • -• 4 t44_. - -,'- ,• - - •4 ---'•' -,4- ;-• •4,;44-•'•- _- u -- - - -'_:• - • - I - • ' •- - 4 , - t4- - Foundations for the structure should consist of continuous strip footings and/or isolated spread footings. Continuous footings should be at least 12 inches wide and extend at least 12 inches below lowest adjacent pad grade. Isolated spread footings should have a minimum embedment depth and width of 12 inches. Steel reinforcement for continuous footings should consist of at least two No. 4 steel reinforcing bars placed horizontally in the continuous footings, one near the top and one near the bottom. Steel reinforcement for the spread footings should be designed by the project structural engineer. The conclusions and recommendations presented in the referenced reports remain applicable for the development of the project. .. The foundations may be designed for an allowable soil bearing pressure of 2,000 pounds per square foot (psf) (dead plus live load). This bearing pressure may be increased by one-third for transient loads due to wind or seismic forces. The estimated maximum total and differential settlement for the planned structures due to foundation loads is 1 inch and 4 inch, respectively. Interior concrete slabs-on-grade should be at least 4 inches thick and be reinforced with 6x6-10I10 - welded wire mesh at slab mid-point. The concrete slab-on-grade recommendations are based on soil. support characteristics only. The project structural engineer should evaluate the structural requirements of the concrete slabs for supporting planned loading. Thicker concrete slabs may be required for heavier loads. The structural engineer should consider additional slab thickness and steel reinforcement and reduced crack control spacing if an exposed slab is planned. . Slabs that may receive moisture-sensitive floor coverings or may be used to store moisture-sensitive materials should be underlain by a vapor retarder. The vapor retarder design should be consistent with the guidelines presented in the American Concrete Institute's (ACI) Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials (ACI 302.2R-06). In addition, the membrane should be installed in accordance with manufacturer's recommendations and ASTM requirements and installed in a manner that prevents puncture. The vapor retarder used should be specified by the project architect or developer based on the type of floor covering that will be installed and if the structure will possess a humidity controlled environment. The project foundation engineer, architect, and/or developer should determine the thickness of bedding sand below the slab. In general, 3 to 4 inches of sand bedding is typically used in the southern California area. Geocon should be contacted to provide recommendations if the bedding sand is thicker than 6 inches. The foundation design engineer should provide appropriate concrete mix design criteria and curing measures to assure proper curing of the slab by reducing the potential for rapid moisture loss and subsequent cracking and/or slab curl. We suggest that the foundation design engineer present the concrete mix design and proper curing methods on the foundation plans. It is critical that the foundation contractor understands and follows the recommendations presented on the foundation plans. Special subgrade presaturation is not deemed necessary prior to placing concrete; however, the exposed foundation and slab subgrade soil should be moisture conditioned, as necessary, to maintain a moist condition as would be expected in any such concrete placement. . Geocon Incorporated should review the foundation plans for the project prior to final design submittal to determine if additional analysis and/or recommendations are required. The foundation excavations should also be observed by a representative of Geocon Incorporated. - Project No. 05951-52-07 .3- January 13,2016 a aa r. . .' 'd :; . ...', r.'-•i. :... - .,-/•-1 ' .- 4 2 '-i- • '- 4?,l_. S__u :y.4(!--' ,.-- . :- . :-" •. •, S '_• S -S . S•S S• •;5 --S 41 'S •"33• 3 5.'4 • '.. _'_•'3 .5...- 5..- 5 .4 543 • • • •_•j ':'. - -_-mw ,,. ,•t_ ,_ -. ••- ,. -. .,_ . . ' % 353 . ' _'_•,___•• . '.-ti' X lint it 71 - ••.- , -.,.-,. \'( .: -d ';. - --, .. '; F. .- -; -. . _ .., ,•4 .-T --to ,,- .5__ ._.J ,'4_• .4444 i c:'.' u*. ':'.. - ' . 3 - 7 .- -5,4t •4,._;,. '-S. .3,: •S),,55 . '- . . 510 .•• 5 . 'U. 5,,__• 4,, -. ' --','- , •.-. - ..; '."'' ., 'S •- • !. ". -J .. -' - i,3 . Z-. :• -- - ..• .-: ... ."i ::'- - 'L:_ 't ..34,.--. -''.•-- -- S_• '' ' -., 4. 34 S ' r - • S - 3 ,)3_.'_' %-'','. 'S '4 1.,, If you have any questions regarding this letter, or if we may be of further service, please contact the undersigned at your convenience. Very truly yours, GEOCON INCORPORATED Ii r Shawn Foy Weedon CEG1778 GE 2714 AS:SFWimc (4) Addressee 0 AU SADR co No. IM ENGINEERING cr- --0 I'rojccl No. 05351-52-07 -4- January 13. 2016 a5aa V