11229 19TH AVE SE SILVER LAKE TOWNHOMES WHOLE SITE Geotech Report 2022-10-25

• Geotechnical Report Proposed Development: 11229 - 19th Avenue SE, Everett, WA September 16, 2016 5.4.4 Wall Drainage Provisions for wall drainage should consist of a 4-inch diameter perforated drainpipe placed behind and at the base of the wall footings, embedded in 12 to 18 inches of clean crushed rock or pea gravel wrapped with a layer of filter fabric. A minimum 18-inch wide zone of free draining granular soils (i.e., pea gravel or washed rock) is recommended to be placed adjacent to the wall for the full height of the wall. Alternatively, a composite drainage material, such as Miradrain 6000, may be used in lieu of the clean crushed rock or pea gravel. The drainpipe at the base of the wall should be graded to direct water to a suitable outlet. 5.4.5 Wall Backfill Wall backfill should consist of imported, free draining granular material, such as Seattle Type 17 or a soil meeting the requirements of Gravel Borrow as defined in Section 9-03.14(1) of the WSDOT Standard Specifications for Road, Bridge, and Municipal Construction(WSDOT,2014). In areas where space is limited between the wall and the face of excavation, pea gravel may be used as backfill without compaction. In our opinion, the predominately silty sand and gravel soils underlying the site are not suitable for use as wall backfill. Wall backfill should be moisture conditioned to within about 3 percent of optimum moisture content, placed in loose, horizontal lifts less than 8 inches in thickness, and systematically compacted to a dense and relatively unyielding condition and to at least 95 percent of the maximum dry density,as determined using test method ASTM D-1557. Within 5 feet of the wall,the backfill should be compacted with hand-operated equipment to at least 90 percent of the maximum dry density. 5.5 PERMANENT CUT AND FILL SLOPES Permanent cut and fill slopes should be graded no steeper than 2H:1 V. Erosion control measures such as erosion-control mats and/or vegetation should be applied to the permanent slopes as soon as feasible. Prior to placing fill,the existing topsoil and loose fill should be removed. The grade to receive fill should be properly compacted to a dense condition. Fills placed on existing slopes having slope ratios steeper than 5H:1V should be keyed and benched into firm and stable existing soils. The filling operations should start at the lowest point and continue up in level horizontal compacted layers in accordance with the fill placement recommendations above. Fill slopes, if any, should 16-210 11229 19th Ave SE Rpt Page 12 PanGEO, Inc.