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HomeMy WebLinkAboutCT 05-03; Lincoln and Oak Mixed Use; Soils Report for CT 05-03; 2010-10-27RECORD COPY Initial Date Geotechnical • Geologic • Coastal • Environmental 5741 Palmer Way • Carlsbad, California 92010 • (760)438-3155 • FAX (760) 931-0915 • www.geosoilsinc.com September 27, 2010 OCT 25TO.4147-A1-SC Mr. Russell Bennett P.O. Box 356 Solana Beach, California 92075 Subject: Geotechnical Update for Structural Design, 3112 Lincoln Street, San Diego County, California Dear Mr. Bennett: In accordance with your request and authorization, GeoSoils, Inc. (GSI) has performed an update of our preliminary geotechnical investigation (GSI, 2004b, seethe Appendix) for the proposed development at the subject site. The purpose of this study was to update the geotechnical recommendations related to project structural design for confbrmance with the 2007 California Building Code ([2007 CBC], California Building Standards Commission [CBSC], 2007). The scope of services GSI provided for this geotechnical update included: 1) a brief site reconnaissance; 2) a review of previous geotechnical reports prepared for the site GSI (2007,2004a, and 2004b); and 3) the preparation of this geotechnical update letter. Unless specifically superceded herein, the conclusions and recommendations contained in the GSI (2007,2004a, and 2004b) remain valid and applicable and should be appropriately implemented during project design and construction. PROPOSED DEVELOPMENT It is our understanding that proposed development consists of preparing the site for the „ construction of three, 3-story mixed-used structures. GSI anticipates thatthe buildings will f~-\ incorporate wood, steel, and/or concrete masonry construction with concrete slab-on » ^ grade-floors. Building loads are assumed typical for this type of commercial/residential **" development. ^ b SITE RECONNAISSANCE ^ GSI performed a site reconnaissance on September 23, 2010. Site conditions were CJI generally similar to those observed during field work in preparation of GSI (2004b) with the « exception of a recently constructed residential development immediately east of the ^j* subject site. "^ UPDATE SEISMIC SHAKING PARAMETERS Based on the site conditions, the table below summarizes the site-specific seismic design criteria obtained from the 2007 CBC (CBSC, 2007), and the 2006 International Building Code (IBC), Chapter 16 Structural Design, Section 1613. We used the computer program Seismic Hazard Curves and Uniform Hazard Response Spectra, provided by the United States Geological Survey ([USGS], 2009). The short spectral response uses a period of 0.2 seconds. Site Class D Table 1613.5.2 Spectral Response - (0.2 sec), Ss 1.33g Figure 1613.5(3) Spectral Response - (1 sec), S1 O.SOg Figure 1613.5(4) Site Coefficient, F 1.0 Table 1613.5.3(1) Site Coefficient, Fv 1.5 Table 1613.5.3(2) Maximum Considered Earthquake Spectral Response Acceleration (0.2 sec), SMS 1.33g Section 1613.5.3 (Eqn 16-37) Maximum Considered Earthquake Spectral Response Acceleration (1 sec), SM1 0.75g Section 1613.5.3 (Eqn 16-38) 5% Damped Design Spectral Response Acceleration (0.2 sec), SDS 0.89g Section 1613.5.4 (Eqn 16-39) 5% Damped Design Spectral Response Acceleration (1 sec), SD1 O.SOg Section 1613.5.4 (Eqn 16-40) Distance to Seismic Source (Newport - Inglewood [offshore]) from Blake (2000a)5.0 mi. (8.1 km) Upper Bound Earthquake (Newport - Inglewood [offshore])Mw 6.9* Probabilistic Horizontal Site Acceleration ([PHSA] 10% probability of exceedance in 50 years) from Blake (2000c)0.34g * International Conference of Building Officials (ICBO, 1998) Conformance to the above criteria 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. In order to reduce the effects of cumulative seismic damage, GSI recommends a visual inspection by qualified geotechnical and structural engineers following significant local seismic events (Mwj>4.5), should any indications of distress or cracking be apparent. Mr. Russell Bennett 3112 Lincoln Street, Carlsbad Rle:e:\wp9\4900\4972a1 .uop W.O. 4147-A1-SC September 27, 2010 Page 2 UPDATE PRELIMINARY RECOMMENDATIONS - FOUNDATIONS Preliminary Foundation Design In the event our understanding of the proposed development is not correct or any changes in the design, location, or loading conditions of the proposed structures are made, the conclusions and recommendations contained in this report shall not be considered valid unless the changes are reviewed and conclusions of this report are modified or approved in writing by this office. The information and recommendations presented in this section are considered minimums and are not meant to supercede design(s) by the project structural engineer or civil engineer specializing in structural design. Upon request, GSI could provide additional consultation regarding soil parameters, as related to foundation design. They are considered preliminary recommendations for proposed construction, in consideration of our field investigation, and laboratory testing and engineering analysis. Our review, field work, and previous laboratory testing (GSI, 2004a and 2004b) indicates that onsite soils have a very low expansion potential (E.I. 0 to 20) with a plasticity index (PI) less than 15. Preliminary recommendations for foundation design and construction are presented below. Final foundation recommendations should be provided at the conclusion of grading based on laboratory testing of fill materials exposed near finish grade. All foundations should be designed in accordance with the 2007 CBC. Design 1. An allowable soil bearing pressure of 1,500 psf may be used for the design of continuous footings with a minimum width of 12 inches and minimum depth of 12 inches, and for the design of isolated pad footings 24 inches square and 24 inches deep founded entirely into engineered fill or competent formational material (terrace deposits). The bearing value may be increased by 20 percent for each additional 12 inches in depth to a maximum value of 2,500 psf. Foundations for a given structure should not be simultaneously supported by engineered fill and formational materials. Otherwise differential settlement and distress may occur. Isolated pad and column footing should be connected to the main foundation by grade beam or tie beam in at least one direction to prevent lateral drift. 2. An allowable coefficient of friction between concrete and engineered fill or bedrock of 0.35 may be used with the dead load forces. 3. When combining passive pressure and frictional resistance, the passive pressure component should be reduced by one-third.. Mr. Russell Bennett W.O. 4147-A1 -SC 3112 Lincoln Street, Carlsbad September 27, 2010 File:e:\wp9\4900\4972a1.uop Page 3 GeoSoils, Inc. 4. Passive earth pressure may be computed as an equivalent fluid having a density of 250 pounds per cubic foot (pcf) with a maximum earth pressure of 2,500 psf. 5. All footings should maintain a minimum 7-foot horizontal distance between the base of the footing and any adjacent descending slope, and minimally comply with the guidelines depicted on Figure 1805.3.1 of the 2007 CBC (CBSC, 2007). Foundation Settlement Provided the recommendations in GSI (2004aand 2007) and herein are properly followed, foundations systems may be designed to accommodate a worst-case differential settlement of 1 inch in a 40-foot horizontal span (angular distortion = 1/480). Footing Setbacks All footings should maintain a minimum 7-foot horizontal setback from the base of the footing to any descending slope. This distance is measured from the footing face at the bearing elevation. Footings should maintain a minimum horizontal setback of H/3 (H=slope height) from the base of the footing to the descending slope face and no less than 7 feet nor need to be greater than 40 feet. Footings adjacent to unlined drainage swales should be deepened to a minimum of 6 inches below the invert of the adjacent unlined swale. Footings for structures superjacent to retaining walls should be deepened so as to extend below a 1:1 projection from the heel of the wall. Alternatively, walls may be designed to accommodate surcharge loads from buildings or appurtenances as evaluated by the project structural engineer. Planned retaining walls and building foundations near the eastern property line may need to be deepened below a 1:1 projection up from wall footings on the easterly, adjacent property. This will require further evaluation during the grading plan review stage. Construction The following foundation construction recommendations are presented as a minimum criteria from a soils engineering standpoint. The onsite soils expansion potentials are generally very low (E.I. 0 to 20) with a PI less than 15. Recommendations for very low expansive soil conditions are presented herein. Recommendations by the project structural engineer or architect, which may exceed the soils engineer's recommendations, should take precedence over the following minimum requirements. Final foundation design will be provided based on the expansion potential of the near-finish grade soils at the conclusion of grading. Mr. Russell Bennett W.O. 4147-A1 -SC 3112 Lincoln Street, Carlsbad September 27, 2010 File:e:\wp9\4900\4972a1.uop Page 4 GeoSofls, Inc. Very Low Expansion Potential (E.I. 0 to 20) with a PI Less Than 15 1. Exterior and interior footings should be founded into engineered fill or formational materials at a minimum depth of 12 inches for one-story floor loads, 18 inches for two-story floor loads, and 24 inches for three-story floor loads, below the lowest adjacent ground surface. Isolated column and panel pads, or wall footings should be 24 inches square and founded at a minimum depth of 24 inches. All footings should be reinforced with two No. 4 reinforcing bars, one placed near the top and one placed near the bottom of the footing. Continuous footing widths should be a minimum of 12 inches for one-story loads, 15 inches for two-story loads, and 18 inches for three-story loads. 2. A grade beam, reinforced as above, and at least 12 inches wide should be provided across large (e.g., doorways) entrances. The base of the grade beam should be at the same elevation as the bottom of adjoining footings. Isolated, exterior square footings should be tied within the main foundation in at least one direction with a grade beam. 3. Slab-on-grade floors (including garages)should be a minimum of 5 inches thick, and should be reinforced with No. 3 reinforcing bars 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" of reinforcement is not considered an acceptable method of positioning the reinforcement. The structural engineer should evaluate slab thickness and reinforcement based on anticipated loading and use. 4. Garage slabs should be poured separately from the structural 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. 5. Presaturation is not required for these soil conditions. The moisture content of the subgrade soils, however, should be equal to or greater than optimum moisture content in the slab areas prior to the placement of the vapor retarder. SOIL MOISTURE CONSIDERATIONS GSI has evaluated the potential for vapor or water transmission through interior concrete slabs-on-grade, in light of typical residential floor coverings and improvements. Please note that slab moisture emission rates, range from about 2 to 27 lbs/24 hours/1,000 square feet from a typical slab (Kanare, 2005), while floor covering manufacturers generally recommend about 3 lbs/24 hours as an upper limit. Thus, the client will need to evaluate the following on a cost v. benefit basis, along with disclosure to all interested/affected parties. Mr. Russell Bennett W.O. 4147-A1-SC 3112 Lincoln Street, Carlsbad September 27, 2010 Rle:e:\wp9\4900\4972a1.uop Page 5 Inc. Considering the anticipated typical water vapor transmission rates, floor coverings and improvements (to be chosen by the client) that can tolerate those rates without distress, the following alternatives are provided: 1. Concrete slabs should be a minimum of 5 inches thick. 2. Concrete slab underlayment should consist of a 10-mil to 15-mil vapor retarder, or equivalent, with all laps and penetrations (i.e., pipe, ducting, rebar, etc.) sealed per the 2007 CBC (CBSC, 2007) and the manufacturer's recommendation. The vapor retarder should comply with the ASTM E 1745 - Class A or B criteria, and be installed in accordance with ACI 302.1 R-04 and ASTM E 1643. 3. Slab underlayment should consist of 2 inches of washed sand (SE >30) placed above the vapor retarder. The vapor retarder shall be underlain by 2 inches of washed sand (SE>30) placed directly on properly prepared subgrade soils, and should be sealed to provide a continuous water-resistant barrier under the entire slab, as discussed above. All slabs should be additionally sealed with suitable slab sealant. 4. Concrete should have a maximum water/cement ratio of 0.50. This does not supercede the 2007 CBC (CBSC, 2007) for corrosion or other corrosive requirements. Additional concrete mix design recommendations should be provided by the structural consultant and/or waterproofing specialist. Concrete finishing and workablity should be addressed by the structural consultant and a waterproofing specialist. 5. Where slab water/cement ratios are as indicated above, and/or admixtures used, the structural consultant should also make changes to the concrete in the grade beams and footings in kind, so that the concrete used in the foundation and slabs are designed and/or treated for more uniform moisture protection. 6. Owners(s) and all interested/affected parties should be specifically advised which areas are suitable for tile flooring, wood flooring, or other types of water/vapor-sensitive flooring and which are not suitable. In all planned floor areas, flooring shall be installed per the manufactures recommendations. 7. Additional recommendations regarding water or vapor transmission should be provided by the architect/structural engineer/slab or foundation designer and should be consistent with the specified floor coverings indicated by the architect. Regardless of the mitigation, some limited moisture/moisture vapor transmission through the slab should be anticipated. Construction crews may require special training for installation of certain product(s), as well as concrete finishing techniques. The use of specialized produces) should be approved by the slab designer and water-proofing Mr. Russell Bennett W.O. 4147-A1-SC 3112 Lincoln Street, Carlsbad September 27, 2010 File:e:\wp9\4900\4972a1.uop . Page 6 ©eoSotls, Inc. consultant. Atechnical representative of the flooring contractor should review the slab and moisture retarder plans and provide comment prior to the construction of the residential foundations or improvements. The vapor retarder contractor should have representatives onsite during the initial installation. WALL DESIGN PARAMETERS Conventional Retaining Walls The design parameters provided below assume that either non expansive soils (typically Class 2 permeable filter material or Class 3 aggregate base) or native onsite materials (up to and including an E.I. of 50) are used to backfill any retaining walls. The type of backfill (i.e., select or native), should be specified by the wall designer, and clearly shown on the plans. Below grade walls should be waterproofed. The foundation system for the proposed retaining walls should be designed in accordance with the recommendations presented in this and preceding sections of this report, as appropriate. Footings should be embedded a minimum of 18 inches below adjacent grade into engineered fill or formational materials (excluding landscape layer, 6 inches) and should be 24 inches in width. There should be no increase in bearing for footing width. Recommendations for specialty walls (i.e., crib, earthstone, geogrid, etc.) can be provided upon request, and would be based on site-specific conditions. Restrained Walls Any retaining walls that will be restrained prior to placing and compacting backfill material or that have re-entrant or male corners, should be designed for an at-rest equivalent fluid pressure (EFP) of 65 pcf, plus any applicable surcharge loading. For areas of male or re-entrant corners, the restrained wall design should extend a minimum distance of twice the height of the wall (2H) laterally from the corner. Canti levered Walls The recommendations presented below are for cantilevered retaining walls up to 10 feet high. Design parameters for walls less than 3 feet in height may be superceded by City and/or County standard design. Active earth pressure may be used for retaining wall design, provided the top of the wall is not restrained from minor deflections. An equivalent fluid pressure approach may be used to compute the horizontal pressure against the wall. Appropriate fluid unit weights are given below for specific slope gradients of the retained material. These do not include other superimposed loading conditions due to traffic, structures, seismic events, or adverse geologic conditions. When wall configurations are finalized, the appropriate loading conditions for superimposed loads can be provided upon request. Mr. Russell Bennett W.O. 4147-A1 -SC 3112 Lincoln Street, Carlsbad September 27, 2010 File:e:\wp9\4900\4972a1.uop Page 7 GeoSoils, Inc. Seismic Surcharge for Retaining Walls For retaining walls that are over 6 feet in height, or within 6 feet or less of a building, that may impede ingress/egress, GSI recommends that the walls be evaluated for a seismic surcharge (Section 1630A.1.1.5 of the 2007 CBC [CBSC, 2007]). The site walls in this category should maintain an overturing Factor-of Safety (FOS) of about 1.2, 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 10H, 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. In addition to the above comments, GSI recommends that our field representative observe the temporary backcuts and footing excavations for the walls. Temporary cuts for all wall installations should not exceed 11/2:1 (h:v) inclinations, and should not be open for more than 90 days per cut, from start to finish. When wall configurations are finalized, the appropriate loading conditions for superimposed loads can be provided upon request. Level* 2to1 35 50 45 60 * Level backfill behind a retaining wall is defined as compacted earth materials, properly drained, without a slope for a distance of 2H behind the wall. ** As evaluated by testing, P.I. <15, E.I. <21, S.E. X30, and <10% passing No. 200 sieve. *** As evaluated by testing, E.I. .<50, S.E. >25 and ,<15% passing No. 200 sieve. Retaining Wall Backfill and Drainage Positive drainage must be provided behind all retaining walls in the form of gravel wrapped in geofabric and outlets. A backdrain system is considered necessary for retaining walls that are 2 feet or greater in height. Details 1, 2, and 3, present the back drainage options discussed below. Backdrains should consist of a 4-inch diameter perforated PVC or ABS pipe encased in either Class 2 permeable filter material or %-inch to 11/2-inch gravel wrapped in approved filter fabric (Mirafi 140 or equivalent). For low expansive backfill, the filter material should extend a minimum of 1 horizontal foot behind the base of the walls and upward at least 1 foot. For native backfill that has an E.I. up to 50, continuous Class 2 permeable drain materials should be used behind the wall. This material should be continuous (i.e., full height) behind the wall, and it should be constructed in accordance Mr. Russell Bennett 3112 Lincoln Street, Carlsbad Rle:e:\wp9\4900\4972a1 .uop W.O. 4147-A1-SC September 27, 2010 PageS (1) Waterproofing membrane CMUor reinforced-concrete wall Structural footing or settlement-sensitive improvement Provide surface drainage via an engineered V-ditch (see civil plans for details) "•-. ->-^ (2) :Gravel/. V (3} Filter :fabri Proposed grade sloped to drain per precise civil drawings (5) Weep hole Footing and wall design by other Native backfill 11 (h=v) or flatter backcut to be properly benched (6) Footing (1) Waterproofing membrane. (2) Graveh Clean, crushed, % to 1)£ inch. (3) Filter fabric: Mirafi 140N or approved equivalent. (4) Pipe: 4-inch-diameter perforated PVC, Schedule 40, or approved alternative with minimum of 1 percent gradient sloped to suitable, approved outlet point (perforations down). (5) Weep hole; Minimum 2-inch diameter placed at 20-foot centers along the wall and placed 3 inches above finished surface. Design civil engineer to provide drainage at toe of wall. No weep holes for below-grade walls. (6) Footing: If bench is created behind the footing greater than the footing width, use level fill or cut natural earth materials. An additional "heel" drain will likely be required by geotechnical consultant. RETAINING WALL DETAIL - ALTERNATIVE A Detail 1 (1) Waterproofing membrane (optional) CMUor reinforced-concrete wall Structural footing or settlement-sensitive improvement Provide surface drainage via engineered V-ditch (see civil plan details) 2=1 GYV) slope Footing and wall design by others (5) Weep hole — > I — Proposed grade ' / sloped to drain / per precise civil I drawings Native backfill >r flatter backcut to be properly benched (6) 1 cubic foot of %-inch crushed rock (7) Footing (1) Waterproofing membrane (optional)1 Liquid boot or approved mastic equivalent. (2) Drain: Miradrain 6000 or J-drain 200 or equivalent for non-waterproofed walls; Miradrain 6200 or J-drain 200 or equivalent for waterproofed walls (all perforations down). (3) Filter fabric: Mirafi 140N or approved equivalent; place fabric flap behind core. (4) Pipe: 4-inch-diameter perforated PVC, Schedule 40, or approved alternative with minimum of 1 percent gradient to proper outlet point (perforations down). (5) Weep hole; Minimum 2-inch diameter placed at 20-foot centers along the wall and placed 3 inches above finished surface. Design civil engineer'to provide drainage at toe of wall. No weep holes for below-grade walls. (6) Gravel; Clean, crushed, % to 1% inch. (7) Footing; |f bench is created behind the footing greater than the footing width, use level fill or cut natural earth materials. An additional "heel" drain will likely be required by geotechnical consultant. RETAINING WALL DETAIL - ALTERNATIVE B Detail 2 (1) Waterproofing membrane CMUor reinforced-concrete wall ±12 inches (5) Weep hole- Proposed grade sloped to drain per precise civil drawings (h=v) Structural footing or settlement-sensitive improvement Provide surface drainage slope -Slbpdi'or feyef- -..-'. ..-.'. minimum- Footing and wall design by others (8) Native backfill (6) Clean sand backfill 1=1 (h=v) or flatter backcut to be Filter fabric proper|y benched Gravel (4) Pipe (7) Footing (1) Waterproofing membrane: Liquid boot or approved masticequivalent. (2) Graveh Clean, crushed, % to 1>2 inch. (3) Filter fabric; Miraf i 140N or approved equivalent. (4) Pipe: 4-inch-diameter perforated PVC, Schedule 40, or approved alternative with minimum of 1 percent gradient to proper outlet point (perforations down). (5) Weep hole; Minimum 2-inch diameter placed at 20-foot centers along the wall and placed 3 inches above finished surface. Design civil engineer to provide drainage at toe of wall. No weep holes for below-grade walls. (6) Clean sand backfill: Must have sand equivalent value (S.E.) of 35 or greater; can be densified by water jetting upon approval by geotechnical engineer. (7) Footing; If bench is created behind the footing greater than the footing width, use level fill or cut natural earth materials. An additional "heel" drain will likely be required by geotechnical consultant. (8) Native backfill; If El <21 and S.E. >35 then all sand requirements also may not be required and will be reviewed by the geotechnical consultant. RETAINING WALL DETAIL - ALTERNATIVE C Detail 3 with the enclosed Detail 1 (Typical Retaining Wall Backfill and Drainage Detail). For limited access and confined areas, (panel) drainage behind the wall may be constructed in accordance with Detail 2 (Retaining Wall Backfill and Subdrain Detail Geotextile Drain). Materials with an E.I. greater than 50 should not be used as backfill for retaining walls. For more onerous expansive situations, backfill and drainage behind the retaining wall should conform with Detail 3 (Retaining Wall And Subdrain Detail Clean Sand Backfill). Outlets should consist of a 4-inch diameter solid PVC or ABS pipe spaced no greater than ±100 feet apart, with a minimum of two outlets, one on each end. The use of weep holes, only, in walls higher than 2 feet, is not recommended. The surface of the backfill should be sealed by pavement or the top 18 inches compacted with native soil (E.I. <50). Proper surface drainage should also be provided. For additional mitigation, consideration should be given to applying a water-proof membrane to the back of all retaining structures. The use of a waterstop should be considered for all concrete and masonry joints. Wall/Retaining Wail Footing Transitions Site walls are anticipated to be founded on footings designed in accordance with the recommendations in this report. Should wall footings transition from formation to fill, the civil designer may specify either: a) A minimum of a 2-foot overexcavation and re-compaction of cut materials for a distance of 2H, from the point of transition. b) Increase of the amount of reinforcing steel and wall detailing (i.e., expansion joints or crack control joints) such that a angular distortion of 1/360 for a distance of 2H on either side of the transition may be accommodated. Expansion joints should be placed no greater than 20 feet on-center, in accordance with the structural engineer's/wall designer's recommendations, regardless of whether or not transition conditions exist. Expansion joints should be sealed with aflexible, non-shrink grout. c) Embed the footings entirely into formational materials (i.e., deepened footings). If transitions from cut to fill transect the wall footing alignment at an angle of less than 45 degrees (plan view), then the designer should follow recommendation "a" (above) and until such transition is between 45 and 90 degrees to the wall alignment. DRIVEWAY. FLATWORK. AND OTHER IMPROVEMENTS Some of the soil materials on site may be expansive. The effects of expansive soils are cumulative, and typically occur over the lifetime of any improvements. On relatively level areas, when the soils are allowed to dry, the dessication and swelling process tends to cause heaving and distress to flatwork and other improvements. The resulting potential Mr. Russell Bennett W.O. 4147-A1-SC 3112 Lincoln Street, Carlsbad September 27, 2010 Rle:e:\wp9\4900\4972a1 .uop Page 12 GeoSofls, Inc. for distress to improvements may be reduced, but not totally eliminated. To that end, it is recommended that disclosure be provided to all interested/affected parties of this long- term potential for distress. To reduce the likelihood of distress, the following recommendations are presented for all exterior flatwork: 1. The subgrade area for concrete slabs should be compacted to achieve a minimum 90 percent relative compaction, and then be presoaked to 2 to 3 percentage points above (or 125 percent of) the soils' optimum moisture content, to a depth of 18 inches below subgrade elevation. If very low expansive soils are present, only optimum moisture content, or greater, is required and specific presoaking is not warranted. The moisture content of the subgrade should be proof tested within 72 hours prior to pouring concrete. 2. Concrete slabs should be cast over a non-yielding surface, consisting of a 4-inch layer of crushed rock, gravel, or clean sand, that should be compacted and level prior to pouring concrete. If very low expansive soils are present, the rock or gravel or sand may be deleted. The layer or subgrade should be wet-down completely prior to pouring concrete, to minimize loss of concrete moisture to the surrounding earth materials. 3. Exterior slabs should be a minimum of 4 inches thick. Driveway slabs and approaches should additionally have a thickened edge (12 inches) adjacent to all landscape areas, to help impede infiltration of landscape water under the slab. 4. The use of transverse and longitudinal control joints are recommended to help control slab cracking due to concrete shrinkage or expansion. Two ways to mitigate such cracking are: a) add a sufficient amount of reinforcing steel, increasing tensile strength of the slab; and, b) provide an adequate amount of control and/or expansion joints to accommodate anticipated concrete shrinkage and expansion. In order to reduce the potential for unsightly cracks, slabs should be reinforced at mid-height with a minimum of No. 3 bars placed at 18 inches on center, in each direction. If subgrade soils within the top 7 feet from finish grade are very low expansive soils (i.e., E.I. <20), then 6x6-W1.4xW1.4 welded-wire mesh may be substituted for the rebar, provided the reinforcement is placed on chairs, at slab mid-height. The exterior slabs should be scored or saw cut, 1/2 to % inches deep, often enough so that no section is greater than 10 feet by 10 feet. For sidewalks or narrow slabs, control joints should be provided at intervals of every 6 feet. The slabs should be separated from the foundations and sidewalks with expansion joint filler material. Mr. Russell Bennett W.O. 4147-A1 -SC 3112 Lincoln Street, Carlsbad September 27, 2010 File:e:\wp9\4900\4972a1.uop Page 13 GeoSoils, Inc. 5. No traffic should be allowed upon the newly poured concrete slabs until they have been properly cured to within 75 percent of design strength. Concrete compression strength should be a minimum of 2,500 psi. 6. Driveways, sidewalks, and patio slabs adjacent to the house should be separated from the house with thick expansion joint filler material. In areas directly adjacent to a continuous source of moisture (i.e., irrigation, planters, etc.), all joints should be additionally sealed with flexible mastic. 7. Planters and walls should not be tied to the house. 8. Overhang structures should be supported on the slabs, or structurally designed with continuous footings tied in at least two directions. If very low expansion soils are present, footings need only be tied in one direction. 9. Any masonry landscape walls that are to be constructed throughout the property should be grouted and articulated in segments no more than 20 feet long. These segments should be keyed or doweled together. 10. Utilities should be enclosed within a closed utilidor (vault) or designed with flexible connections to accommodate differential settlement and expansive soil conditions. 11. Positive site drainage should be maintained at all times. Finish grade on the lots should provide a minimum of 1 to 2 percent fall to the street, as indicated herein. It should be kept in mind that drainage reversals could occur, including post-construction settlement, if relatively flat yard drainage gradients are not periodically maintained by the homeowner. 12. Air conditioning (A/C) units should be supported by slabs that are incorporated into the building foundation or constructed on a rigid slab with flexible couplings for plumbing and electrical lines. A/C waste water lines should be drained to a suitable non-erosive outlet. 13. Shrinkage cracks could become excessive if proper finishing and curing practices are not followed. Finishing and curing practices should be performed per the Portland Cement Association Guidelines. Mix design should incorporate rate of curing for climate and time of year, sulfate content of soils, corrosion potential of soils, and fertilizers used on site. UTILITIES Utilities should be enclosed within a closed utilidor (vault) or designed with flexible connections to accommodate differential settlement and expansive soil conditions. Due Mr. Russell Bennett W.O. 4147-A1-SC 3112 Lincoln Street, Carlsbad September 27, 2010 File:e:\wp9\4900\4972a1.uop Page 14 Inc. to the potential for differential settlement, air conditioning (A/C) units should be supported by slabs that are incorporated into the building foundation or constructed on a rigid slab with flexible couplings for plumbing and electrical lines. A/C waste waterlines should be drained to a suitable outlet. OTHER DESIGN PROFESSIONALS/CONSULTANTS The design civil engineer, structural engineer, post-tension designer, architect, landscape architect, wall designer, etc., should review the recommendations provided herein, incorporate those recommendations into all their respective plans, and by explicit reference, make this report part of their project plans. This report presents minimum design criteria for the design of slabs, foundations and other elements possibly applicable to the project. These criteria should not be considered as substitutes for actual designs by the structural engineer/designer. Please note that the recommendations contained herein are not intended to preclude the transmission of water or vapor through the slab or foundation. The structural engineer/foundation and/or slab designer should provide recommendations to not allow water or vapor to enter into the structure so as to cause damage to another building component, or so as to limit the installation of the type of flooring materials typically used for the particular application. The structural engineer/designer should analyze actual soil-structure interaction and consider, as needed, bearing, expansive soil influence, and strength, stiffness and deflections in the various slab, foundation, and other elements in order to develop appropriate, design-specific details. As conditions dictate, it is possible that other influences will also have to be considered. The structural engineer/designer should consider all applicable codes and authoritative sources where needed. If analyses by the structural engineer/designer result in less critical details than are provided herein as minimums, the minimums presented herein should be adopted. It is considered likely that some, more restrictive details will be required. If the structural engineer/designer has any questions or requires further assistance, they should not hesitate to call or otherwise transmit their requests to GSI. In order to mitigate potential distress, the foundation and/or improvement's designer should confirm to GSI and the governing agency, in writing, that the proposed foundations and/or improvements can tolerate the amount of differential settlement and/or expansion characteristics and other design criteria specified herein. PLAN REVIEW Final project plans (grading, precise grading, foundation, retaining wall, landscaping, etc.), should be reviewed by this office prior to construction, so that construction is in accordance with the conclusions and recommendations of this report. Based on our Mr. Russell Bennett 3112 Lincoln Street, Carlsbad Rle:e:\wp9\4900\4972a1.uop W.O. 4147-A1-SC September 27, 201 0 Page 15 Inc. review, supplemental recommendations and/or further geotechnical studies may be warranted. 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 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 may be subject to review by the controlling authorities. Thus, this report brings to completion our scope of services for this portion of the project. Mr. Russell Bennett W.O. 4147-A1 -SC 3112 Lincoln Street, Carlsbad September 27, 2010 Rle:e:\wp9\4900\4972a1.uop Page 16 GeoSoils, Inc. The opportunity to be of service is sincerely appreciated, questions, please do not hesitate to contact our office. Respectfully submitt GeoSoils, inc. If you should have any 1340 Certified Ineering eologlst John P. Franklin \%> \fV / David W. Skelly Engineering GeologjsiS&^pa^O Civil Engineer, RCE 4785/ Ryanfeoehmer Project Geologist RB/DWS/JPF/jh Attachment: Appendix - Referenes Distribution: (1) Addressee (via email) (4) Karnak Planning & Design, Attn: Mr. Robert Richardson (2 wet signed) (1) Concorde Consulting Group, Inc., Attn: Mr. Koladi M. Kripanarayanan (via email) (1) Conway and Associates, Attention: Mr. Mike Pasko (via email) Mr. Russell Bennett 3112 Lincoln Street, Carlsbad Fi!e:e:\wp9\4900\4972a1 .uop GeoSoils, Inc. W.O.4147-A1-SC September 27, 2010 Page 17 APPENDIX REFERENCES ACI Committee 318,2008, Building code requirements for structural concrete (ACI318-08) and commentary, dated January ACI Committee 302,2004, Guide for concrete floor and slab construction, AC1302.1 R-04, dated June. American Society for Testing and Materials, 1998, Standard practice for installation of water vapor retarder used in contact with earth or granular fill under concrete slabs, Designation: E 1643-98 (Reapproved 2005). , 1997, Standard specification for plastic water vapor retarders used in contact with soil or granular fill under concrete slabs, Designation: E 1745-97 (Reapproved 2004). California Building Standards Commission, 2007, California Building Code. GeoSoils, Inc., 2007, Geotechnical review of rough grading plans (first submittal), Lincoln and Oak Project, 3112 Lincoln Street, Carlsbad, San Diego County, California, W.O. 4147-A-SC, dated May 4. , 2004a, Soil corrosivity results, 3112 Lincoln Street, Carlsbad, San Diego County, California, W.O. 4147-A-SC, dated January 22. , 2004b, Preliminary geotechnical evaluation, 3112 Lincoln Street, Carlsbad, San Diego County, California, W.O. 4147-A-SC, dated January 14. International Code Council, Inc., 2006, International building code and international residential code, Country Club Hills, Illinois, IRC and IBC. International Conference of Building Officials, 1998, Maps of known active fault near- source zones in California and adjacent portions of Nevada. Kanare, Howard, M., 2005, Concrete floors and moisture, Engineering Bulletin 119, Portland Cement Association. Romanoff, M., 1989, Underground corrosion, National Bureau of Standards Circular 579, Published by National Association of Corrosion Engineers, Houston, Texas, originally issued April 1,1957. State of California, 2009, Civil Code, Sections 895 et seq. United States Geological Survey, 2009, Seismic hazard curves and uniform hazard response spectra - V5.0.9, dated October 21. GeoSoils, Inc.