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Geotechnical Engineering Evaluation NGA File No. 1033518 Larsen Property Garage May 8,2018 Everett,Washington Page 11 pressure distribution equivalent to that exerted by a fluid with a density of 40 pcf for yielding (active condition) walls, and 60 pcf for non-yielding (at-rest condition) walls. The uphill eastern side of the garage structure is intended to perform as a debris wall,and we recommend that this portion of the garage wall be designed for an active pressure of 80 pcf. These recommended lateral earth pressures are for a drained granular backfill and are based on the assumption of a maximum 2H:1V backfill inclinations and do not account for surcharge loads. Additional lateral earthpressures should be considered for surcharge loads acting adjacent tosubsurface walls and within a distance equal to the subsurface height of the wall. This would include the effects of surcharges such as traffic loads,floor slab and foundation loads,or other surface loads. We are available to provide consultation regarding additional loads on retaining walls during final design,if needed. The lateral pressures on walls may be resisted by friction between the foundation and subgrade soil, and by passive resistance acting on the below-grade portion of the foundation. Recommendations for frictional and passive resistance to lateral loads are presented in the Foundations subsection of this report. All wall backfill should be well compacted as outlined in the Structural Fill subsection of this report. Care should be taken to prevent the buildup of excess lateral.soil pressures,due to over-compaction of the wall backfill. This can be accomplished by placing wall backfill in thin loose lifts and compacting it with small,hand-operated compactors within a distance behind the wall equal to at least one-half the height of the wall. The thickness of the loose lifts should be reduced to accommodate the lower compactive energy of the hand-operated equipment. The recommended level of compaction should still be maintained. Permanent drainage systemsshould be installed for retaining walls. Recommendations for these systems are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to evaluate the proposed wall drain backfill material and drainage systems. Structural Fill General: Fill placed beneath foundations, slabs, pavements, or other settlement-sensitive structures should be placed as structural fill:' Structural fill, by definition, is placed in accordance with prescribed methods and standards,and is monitored by an experienced geotechnical professional or soils technician. Field monitoring procedures would include the performance of a representative number of in-place density tests to document the attainment of the desired degree of relative compaction. The area to receive the fill should be suitably prepared as described in the Site Preparation and Grading subsection prior to beginning fill placement. NELSON GEOTECHNICAL ASSOCIATES,INC.