1304 80TH ST SW EVERETT SCHOOL DISTRICT 2018-01-02 MF Import

Subsurface Exploration and Everett Bas Facility Geotechnical F-ngineering Report Everett, Washington Design Recommendations 11. DESIGN RECOMMENDATIONS 5.0 INTRODUCTION It is our opinion that from a geotechnical standpoint, the site is suitable for the proposed improvements provided that the recommendations contained herein are properly followed. Medium dense to very dense lodgement till was encountered at relatively shallow depths in our explorations on the site. Due to the relative density and elevated silt contents of the encountered soils, infiltration of stormwater is not feasible. The lodgement till and structural fill, placed as recommended below, is suitable for support of the new pavement section. if the upper 2 feet of existing fills can be moisture-conditioned and recompacted, they can be used to support new pavements. The till soils contain large quantities of silt, and during the wet winter and spring months, the contractor and school district should be prepared to manage over-optimum moisture content (wet) soil and subgrade conditions. Construction should be timed to take advantage of dry weather, if possible. 6.0 SITE PREPARATION Site preparation of areas to be graded should include removal of all grass, landscaping, concrete, existing pavements, aggregate base courses and surfacing materials, and any other deleterious material. We expect that the building in the northeast portion of the property will be demolished prior to the start of construction and associated pavements for the properties will be removed. Topsoil, if encountered, and areas containing soft or organic fill, should be removed and the remaining roots grubbed. Stripped topsoils should he assumed to "swell" some 20 to 25 percent upon excavation. Stripping quantity estimaics should include this swell factor. Areas where loose soils exist due to previous grading, filling, or grubbing operations should be considered as uncontrolled rill to the depth of disturbance and treated as subsequently recommended for structural fill placement. Where existing, loose, granular fill or natural sediments are relatively free of organics and near their optimum moisture content for compaction, they can be segregated for reuse as structural fill. We expect that most of the aggregate base course and surfacing material can be reused provided that care is taken to segregate the aggregate material from the underlying silty soils. It should be noted that most on-site native soils were at or above optimum moisture content for compaction during our field study, and therefore may require time to dry prior to use as structural fill. Since the density of the soil is variable, random soft pockets may exist, and the depth and extent of stripping can best be determined in the field by the geotechnical engineer or engineering geologist. Once excavation to subgrade elevation is complete, the resulting surface should be proof-rolled with a loaded dump truck or outer suitable equipment. Any soft, loose, or yielding areas should be excavated to expose suitable bearing soils. The subgrade should then be compacted November 18, 1005 ASSOCIATED EARTII SCIFNG:.S, INC. FGnd KE0360282•Pwira,11001E011KE1WP Page 5