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1 1 ' , , � ' t� ' , LJ ' 1 ' ' , Geotecluiical Engineering Letter Alhussaini Slope Stabilization and Retaining Walls Everett, Washington NGA File No. 867612 December ] 0, 2012 Page 12 Iilter fabric should be placed at the bottom of the drainagc blanket. Tl�e drain should be sloped to drain i�ito a perinailent discharge point placed at the bottoill of the slope. Stratagrid 200 geogcid (or equivaleut) is recommeilded in the wall designs that� ai�e greater than four feet in tot�al height. The geogrid should be cut to the recommended (eugths, attached to the blocks as i-ecoiluue�lded by the mailufacturei-, a�id extended back into Thc reinforced till zoiie. 1'l�e grid should be pulleci tigl�t before tl�e 1�711 is placcd over tlle geogrid. Care should bc taken not to dan�age the geogrici by operatillg construction equipment on the exposed grid, or by allowiilg large rocks to be placed directly on the grid. All fill placed in the retained till zone belund the retaining walls sl�ould be placed as structural fill. Stiuctural fill, by detinition, is placed in accordance with prescribed methods aud standards and is nlonitored by an experienced geotechnical professional or soils techniciau. F ield �Izoiiitoriilg procedures would include the perfoi-mance of a represenCative number of in-place density tests to docunlent the attainment of the desired degree of relative conlpaction. The fill subgrade sllould consist of �lative mediuiii dense or better native soil or fill soils compacted to a non-yielding condition. 1'I�e fill subgrade should consist of level benches. Structural iill sllouid coilsist of� a good quality, granular soil, li-ee of organics and otl�er dclet�crious material and be wcll graded to a maximum size of about threc inches. �I'he material should Ilave no nlore tha�1 10 percent by weight of the portion passing the US #200 Sieve. We sllould be retained to evaluate proposed fill material ��rior to construction. Following subgrade preparation, placen�eut of structural till may proceed. All fill placements should be accomplished in unifonil lifts up to eight inches thick. Each lift should be spread evenly and be thoroughly compacted prioc to pl�cement of subsequent lifts. All sti-uctural fill should be compacted to a minimum of 95 percent of the material's maximum dry density. Maxiinun� d�y densiCy, in this report�, refers to that density as determined by the ASTM D 1557 Conlpaction Test procedui-e. The nzoisture content of the soils to be conzpacted should be within about two percent of optimunl so that a readily compactnble condition exists. It may be necessary to over-excavate and reil�ove wet soils in cases where dryinb to a compactable condition is not NELSON GEOTECHNICAL ASSOCIATES, INC.