3322 KROMER AVE Geotech Report 2023-05-25

GeoTest Services, Inc.—Revision 1 April 10,2020 Kikuchi Retaining Wall, Everett,Washington Project No.20-0344 Allowable Bearing Capacity Assuming the above foundation support criteria are satisfied, continuous or isolated spread footings founded directly on stiff native soils or on compacted structural fill placed directly over undisturbed native soils may be proportioned using a net allowable soil bearing pressure of 2,000 pounds per square foot (psf)for transitional beds and 3,000 psf if on at least 1.5 feet of granular structural fill. The "net allowable bearing pressure" refers to the pressure that can be imposed on the soil at foundation level. This pressure includes all dead loads, live loads, the weight of the footing, and any backfill placed above the footing. The net allowable bearing pressure may be increased by one-third for transient wind or seismic loads. Lateral Earth Pressures The lateral earth pressures that develop against retaining walls will depend on the method of backfill placement, degree of compaction, slope of backfill, type of backfill material, provisions for drainage, magnitude and location of any adjacent surcharge loads, and the degree to which the wall can yield laterally during or after placement of backfill. If the wall is allowed to rotate or yield so the top of the wall moves an amount equal to or greater than about 0.001 to 0.002 times its height(a yielding wall),the soil pressures exerted will be the active soil pressure.Wall restraint may develop if a rigid structural network is constructed prior to backfilling or if the wall is inherently stiff. The active pressures listed in Table 2 do not account for surcharges that may be present. If surcharges are present, the designer must include these surcharges in the design. It is assumed that most design software will calculate and include slope surcharges, if present, using the inclination of the wall, the slope behind the wall, the dry density of the retained soil, and the internal angle of friction. For the purposes of design, GeoTest did not include cohesion in general accordance with most retaining wall design standards. Drainage Considerations Drainage is essential for proper performance of retaining wall. It is generally assumed that hydrostatic pressure will not build up behind the wall. Thus, the densities presented in Table 2 are representative of drained conditions. Typical wall construction includes a minimum 12-inch wide drainage layer constructed immediately behind the wall.The drainage layer typically has a geotextile fabric (local practice includes Mirafi 140N or performance equivalent) separating native soil to reduce siltation and clogging of the drainage layer. Most conventional wall systems include a perforated PVC pipe installed at the base of the retaining wall, with perforations oriented downward to allow for the collection of water that 17