406 SE EVERETT MALL WAY BASE FILE 2018-01-02 MF Import

errs J Auto Mall Associates E-2976 May 16, 1986 rage 5 Slab -on -Grade Floors Slab -on -grade floors may be supported on the recompacted native soil subgrade or on structural fill. Any disturbed native soils must either be recompacted or replaced with structural fill. The slab should be provided with a minimum of four inches of free draining sand or gravel. We also recommend that a vapor barrier such as a 6 mil plastic membrane be placed beneath the slab to reduce water vapor transmission through the slab and the resultant moisture accumulation. Two inches of sand may be placed over the membrane for protection during construction and to aid in curing of the concrete. Retaining and Foundation Walls Retaining and foundation walls should be designed to resist lateral earth pressures imposed by the soils retained by these structures. Walls that are designed to yield an amount equal to at least 0.002 times the wall height can be designed to resist the lateral earth pressure imposed by an equivalent fluid with a unit weight of thirty five (35) pcf. If walls are to be restrained at the top from free movement, a uniform force of one hundred (100) psf should be added to the equivalent fluid pressure force. These values assume a horizontal lackfill. For calculating the base resistance to sliding, we recommend using a passive pressure equivalent to that exerted by a fluid having a density of thirteen hundred (1300) pcf and a coefficient of friction of 0.35. It is assumed that hydrostatic pressures do not act behind the wall nor that surcharge slopes or loads will be placed above the walls. If surcharges are to be applied they should be added to the above lateral pressures. Retaining and foundation walls should be backfilled with compacted free -draining soils with no organics. The soil should contain no more than 5 percent silt or clay and no particles greater than four inches in diameter. The percentage cf particles passing the No. 4 sieve should be between 25 and 70 percent. Alternatively, a geotextile product such as Miradrain may be used. We recommend the use of footing drains at the base of all perimeter footings. The footing dra'*.ns should be surrounded by at least six inches of one inch minus washed rock, and provided with a positive gradient towards sulLaule discharge facilities. The pipe invert should be at least as low as the bottom of the footing. For retaining walls, other than basement walls, weep - holes can be used. The weepholes should be as low as possible to maintain drainage behind the walls. When weepholes are provided, all backfill within eighteen (18) inches of the weephole should consist of one inch minus washed rock. Earth Consultants, Inc.