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HomeMy WebLinkAboutCT 00-22; REDEEMER BY THE SEA LUTHERAN; SUPPLEMENT TO PROJECT GRADING RPT; 2005-01-10GEOPAC IFK A GEOTECHNICAL CONSULTANTS January 10, 20051 updated February 21, 2005 Mr. Greg Shull Craftsman Development Company 1195 Linda Vista Road, Suite G San Marcos, Califomia 92069 FAX 760-510-6712 RECEIVED ENGJNEERfF*3 DEPARTMENrr Subject: Supplement to Project Geotechnical Grading Report, Clarification/Guidelines Regarding Results of Soil Expansion Potential, Lots 1 - 12, La Suvera Project, Redeemer by the Sea, Carlsbad, Califomia References: 1. Preliminary Geotechnical Investigation, Proposed Church and Residential Development, Redeemer by the Sea, Poinsettia Lane and Black Rail Road, Carlsbad, CA; by Geopacifica Geotechnical Consultants, dated November 20, 2000. 2. Addendum Geotechnical Report, Proposed Church and Residential Development, Redeemer by the Sea, Poinsettia Lane and Black Rail Road, Carlsbad, CA CT 00-22; by Geopacifica Geotechnical Consultants, dated September 12, 2002. 3. Grading Plans for Redeemer-By-The-Sea, Lutheran Church of Carlsbad; by Sowers and Brown Engineering, Inc., 11 sheets, project no. CT 00-22, stamp date September 26, 2002. 4. Project Grading Report, Redeemer by the Sea Project, Carlsbad, Califomia; by Geopacifica Inc., dated November 14, 2004. Dear Mr. Shull: In conformance with request from your company, we are providing the following clarification for the subject project and reports. Expansion index testing was completed but the results were left out of the project grading report (document 4). The results of field observation and compaction testing are contained in document 4. 3 0 6 0 IN DUSTRV ST SUITE 105 OCEANSIDE C A 9 2 0 5 4 TEL: 760.721.5488 FAX: 760.721.5539 CT oo-Z'Z. GEOrALIFKA GEOIfcCHNICAL CONSULTANIS Page 2 La Suvera Updated Febmary 21, 2005 EXPANSION INDEX SAMPLING, TESTING, AND RESULTS Soil test samples for expansion potential were collected in March, 2004. Samples were collected from the approximate middle area of each of the 12 building lots. The results of testing indicated no soil sample with index potential greater than 20 with a range from 12 to 17. This potential is classed as Very Low, however, we recommend that all foundation and slabs be planned and constructed in conformance with the "Low Expansion Potential (Expansion Index 21 to 50)" section on pages 13 and 14 of document 1. Recommendations by the project's design-stmctural engineer or architect, which may exceed the soils engineer's recommendations, should take precedence over the following minimum requirements. FOUNDATION RECOMMENDATIONS The foundation soils for Lots 1 through 12 consist of dense silty sand Terrace Deposits or corapacted stmctural fill primarily derived from the silty sand Terrace Deposits. Conventional continuous footings should be founded at a minimum depth of 18 inches below the lowest adiacent ground surface for one-story stmctures and 24 inches below the lowest adjacent ground surface for 2-story stmctures. Interior footings should be founded at a depth of 18 inches below the lowest adjacent ground surface. Footings for one-story stmctures should have a minimum width of 12 inches, and footings for 2-story stmctures should have a minimum width of 15 inches. All footings should have at a minimum one No. 4 reinforcing bar placed at the top and one No. 4 reinforcing bar placed at the bottom. Isolated interior or exterior footings should be founded at a minimum depth of 24 inches below the lowest adjacent ground surface and be connected in two directions by grade beam to the continuous perimeter foundation. A grade beam, reinforced as above, and at least 12 inches square should be provided across the garage entrance. The base of the reinforced grade beam should be at the same elevation as the adjoining footings. GEOPALIFICA G E O t E C h Page 3 La Suvera Updated Febmary 21, 2005 Residential concrete slabs, where moisture condensation is not desirable, should be underlain with a vapor barrier consisting of a minimum of 10 mil polyvinyl chloride or equivalent membrane with all laps sealed. The membrane should be covered above and below with a minimum of 2 inches of sand (total 4 inches) to aid in uniform curing of the concrete and to protect the membrane from puncture. The residential concrete slabs should be a minimum of 5 inches thick, and should be reinforced with No. 3 reinforcing bar at 18 inches on center in both directions. All slab reinforcement should be supported to ensure placement near the vertical midpoint of the concrete. Hooking the reinforcement is not an acceptable method for vertical emplacement. Residential garage slabs should be reinforced as above for residential slabs and poured separately from the stmctures footings and quartered with expansion joints or saw cuts. A positive separation from the footings should be maintained with expansion joint material to permit relative movement. Pre-saturation is not required for the site soil conditions. Moisture conditioning is required. The moisture content of the foundation/slab sub-grade soils should be equal to or greater than optimum moisture. Prior to placing visqueen or reinforcement, soil moisture content should be verified by this office within 72 hours of pouring concrete. The potential for slab cracking may be reduced by careful control of water/cement ratios. The contractor should take appropriate curing precautions during pouring of concrete in hot weather to minimize cracking of slabs. Cracking can be further controlled by providing saw cuts at column lines. We recommend that a slip sheet (or equivalent) be utilized if grouted tile, marble tile, or other crack sensitive floor coverings planned directly on concrete slabs. DESIGN PARAMETERS Footings constmcted in the manner described above may be designed for a maximum allowable bearing pressure of 2,500 psf. The allowable pressure may be increased by one-third for loads of short duration such as wind or seismic forces. GEDIMIFKA G E O I E C I CONSULTANTS Page 4 La Suvera Updated Febmary 21, 2005 Foundations may be designed using a coefficient of friction of 0.35 (total frictional resistance equals coefficient of friction times the dead load). In lateral resistance applications, a passive resistance of 350 pounds per square foot per foot of depth with maximum value of 3, 500 psf can be used for design. The allowable lateral resistance can be taken as the sum of the frictional resistance and the passive resistance provided the passive resistance does not exceed two-thirds of the total allowable lateral resistance. The coefficient of friction and passive resistance values can be increased by one-third when considering loads of short duration such as wind or seismic loading. • Should you have any questions, please do not hesitate to contact me. Respectfully fames F. Knowiton President, RCE 55754/CEG 1045