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File: 218267 November 30, 2018 Slabs which will be subject to light vehicular loads and through which moisture transmission is not a concern(e.g. driveway)should be underlain by at least 6 inches of compacted baserock,in lieu of any sand and gravel. The 6 inches of granular subgrade may be included as part of the 24 inches of non- expansive materials. Exterior landscaping flatwork(e.g.patios and sidewalks)may be placed directly on proof-rolled soil subgrade materials (e.g. no granular subgrade),however,they will be potentially subject to greater amounts of shifting and moisture transmission. As stated previously, in pavement(concrete or asphalt) areas to receive vehicular traffic,all baserock materials should be compacted to at least 95 percent of their MDD. Also,the upper 6 inches of native soil subgrade beneath any pavements should be compacted to at least 90 percent of its MDD. The garage slabs should "float" independently from the perimeter grade beam. The slab should be separated from the grade beam with an expansion joint completely around the perimeter and at any interior isolated columns. Ideally, the grade beam at the front of the garage should continue to final floor elevation, with the slab inside the grade beam. This will help to assure that the garage doors always shut upon the grade beam, which should experience little or no movement(while the slab has the potential for greater movements). To reduce post-construction expansive soil movements(i.e. heave) of any slabs,care should be taken to keep the subgrade moist for an extended period of time prior to pouring the slabs. Shrinkage cracks should not be allowed to develop in the soil beneath any proposed slabs. Ideally, all slab areas and crawlspace subgrade areas should be sprayed, and covered with 10 mil visqueen and any granular materials as soon as exposed by grading. Pool Shells - The pool (and spa) shell(s) should be designed to resist an active soil pressure of 45 pcf Equivalent Fluid Weight (EFW) in supporting soils with retained slopes less than 4:1 (H:V). An active pressure of 65 pcf EFW should be utilized for retained slopes with an inclination of 2:1 (H:V). Where retained slopes are greater than 4:1, though less than 2:1, the designer should linearly interpolate between 45 and 65 pcf EFW. Where the pool or spa shell extends above grade and retains water (free-standing), it should be designed to resist an active water pressure of 63 pcf EFW on the inside face of the shell, in addition to the active soil forces on the outside of the shell below the free-standing portions. Where the pool or spa shell extends above the water line and retains soil, the aforementioned active soil pressures should be utilized for the design of this "wall". Behind any section of wall above the water line, a back-of-wall drain will need to be installed to prevent build-up of hydrostatic pressures. This drainage system may consist of a prefabricated drainage panel (i.e. Miradrain)or a gravel and filter fabric type system. Such drains can discharge into a perforated pipe which carries any collected water to an appropriate discharge location, or they may connect to the gravel layer at the base of the pool (see below). 1I