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Pacific Ridge — DRH, LLC ES-7852.01 <br /> March 15, 2022 Page 10 <br /> Slab-On-Grade Floors <br /> Slab-on-grade floors should be supported on a firm and unyielding subgrade consisting of <br /> competent native soil or at least 12 inches of new structural fill. Unstable or yielding areas of the <br /> subgrade should be recompacted or overexcavated and replaced with suitable structural fill prior <br /> to slab construction. <br /> A capillary break consisting of a minimum of four inches of free-draining crushed rock or gravel <br /> should be placed below the slab. The free-draining material should have a fines content of 5 <br /> percent or less defined as the percent passing the number 200 sieve, based on the minus three- <br /> quarters-inch fraction. In areas where slab moisture is undesirable, installation of a vapor barrier <br /> below the slab should be considered. If used, the vapor barrier should consist of a material <br /> specifically designed to function as a vapor barrier and should be installed in accordance with the <br /> manufacturer's specifications. <br /> Retaining Walls <br /> Retaining walls must be designed to resist earth pressures and applicable surcharge loads. The <br /> following parameters can be used for retaining wall design: <br /> • Active earth pressure (unrestrained condition) 35 pcf <br /> • At-rest earth pressure (restrained condition) 55 pcf <br /> • Traffic surcharge (passenger vehicles) 70 psf (rectangular distribution) <br /> • Passive earth pressure 300 pcf <br /> • Coefficient of friction 0.40 <br /> • Seismic surcharge 8H psf* <br /> Where H equals the retained height(in feet). <br /> The passive earth pressure and coefficient of friction values include a safety factor of 1 .5. <br /> Additional surcharge loading from adjacent foundations, sloped backfill, or other loads should be <br /> included in the retaining wall design. <br /> Retaining walls should be backfilled with free-draining material that extends along the height of <br /> the wall and a distance of at least 18 inches behind the wall. The upper 12 inches of the wall <br /> backfill may consist of a less permeable soil, if desired. A perforated drainpipe should be placed <br /> along the base of the wall and connected to an approved discharge location. A typical retaining <br /> wall drainage detail is provided on Plate 3. If drainage is not provided, hydrostatic pressures <br /> should be included in the wall design. <br /> Earth Solutions NW, LLC <br />