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ameO length of 10 to 13 inches. Our analysis indicates that Stratagrid SG 200 geogrid will be appropriate for the RSS, but other geogrids having equivalent properties could be used instead, if desired. Subgrade Preparation: The entire area beneath the reinforced backfill zone should be stripped of all vegetation, organic soils, and slide debris. All subgrade soils should be undisturbed native soil. Wall Embedment: For erosion protection and stability, we recommend that the Geoweb cells at the face of the slope be embedded at least 18 inches below final grades in front of the slope toe. Temporary Cut Slopes: In order to construct the geogrid reinforced zone, it will be necessary to excavate some of the existing slope. Based on the previous exploration by others and site observations, the soils are classified as Type B per OSHA construction excavation standards. This means that the temporary slopes should be sloped no steeper than 1 H:1 V (horizontal:vertical) when there will be workers below. The temporary cut slopes should be re-assessed when the actual soil conditions can be observed during construction. Benching: We recommend benching the native slope during cutting and filling in an effort to increase the stability of the fill mass. We recommend creating a maximum 2 foot tall vertical cut in the native slope and a minimum 2 feet horizontal bench at the location of each geogrid reinforcement layer. Geocell Placement: Each course of Geoweb cells should be placed per the manufacturer's recommendations. Each course should be set back from the course below, to achieve an overall slope face slope of approximately 1.5H:1 V. The outer 12 inches of the geocells (at the face of the slope) may be filled with a mix of sand and topsoil in order to facilitate the growth of vegetation. The interior the geocells should be filled and compacted with granular soil as each course is completed. Geogrid Layout: Geogrid should be placed every 2 feet vertically (four stacked Geoweb cells). Our analysis indicates that geogrid reinforcement layers will need to be at least 12 feet long. Fill Soils: Fill soils placed within the Geoweb cells, the reinforced backfill and retained backfill zones should consist of compacted granular soils. A mix of sand and topsoil may be used in the outer 1 foot of the Geoweb facing in order to facilitate vegetation growth. The rest of the backfill should not contain any organic matter, sod, or topsoil, only compacted granular soils should be used as fill. Drainage Blanket: Because minor seasonal perched groundwater seepage could occur, we recommend that a blanket drain be placed directly on the native cut slope behind the reinforced zone. This drain should consist of a 12-inch-thick layer of imported granular soils, such as "Gravel Backfill for Walls" per WSDOT Standard Specification 9-03.12 (2), with a 4-inch diameter perforated drainpipe AMEC Project No.3-917-17245-A 4 W:\_Projects\17000s\17245 Alverson-Maulsby Bluff Property LLC\17245-A\Geotech Report\Finley Geotech Report 130722.docx