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F { El Dorado Apartments April 19, 2002 File No. 1754-006 Page 5 LIQUEFACTION The depth of the free groundwater table and composition of the near surface soils preclude the prospect of liquefaction on this site. SLAB-ON-GRADE Floor slabs may be supported upon the building pads prepared as recommended above. Slabs should contain minimum reinforcement No. 4 bars on 20-inch centers. The floor slabs should be underlain by a minimum of four inches of gravel graded such that 100 percent passes a one-inch sieve and none passes a No.4 sieve. The gravel should be covered with a plastic membrane at least 10-mils thick to form a moisture vapor barrier. One to two inches of clean sand should be spread over the membrane for protection and to aid in concrete curing. The slab subgrade should be in a saturated state to a depth of 12 inches immediately prior to slab concrete placement. The subslab moisture condition should be field checked by our representative no more than 24 hours prior to slab concrete placement. Recent changes in floor covering adhesives have made them more susceptible to problemassociated with slab moisture penetration resulting in increases in flooring performance problems. Care mus st be taken to ensure that the sub-slab gravel is placed to the minimum depth and that the vapor membrane is continuous beneath the slab. The membrane should overlap at least 12 inches and should be cut tight and taped with 10-mil polyethylene tape at all joints,plumbing stands,penetrations, and any other punctures or tears. If moisture vapor remains a significant concern, consideration should be given to use of a commercial concrete slab sealant. PAVEMENTS Pavement sections have been developed based on resistance(R)value testing performed on samples of near surface soils from the site. Resistance values typically range from five for the poorest quality clays to 70 or higher for high quality sands and gravels. The test performed for this study resulted in an R-value of 8. The test results are presented m Plates 12,Resistance Value Data. We have provided sections for traffic indices of 4.0, 4.5, and 5.0 for use in pavement design. Traffic index 4.0 is considered appropriate for parking stalls and 4.5 for channelized portions of the parking lot. Traffic index 5.0 is considered appropriate for entry drives and occasional waste removal truck traffic. Recommended alternate pavement sections are tabulated in Table 1 belay. We can provide additional pavement sections for other traffic indices upon request. Decisions regarding pavement sections should be made based on economics and the desired level of future maintenance. Materials and construction within structural pavement sections should conform to the applicable provisions of the Caltrans Standard Specificatims.