2514 RAINIER AVE Geotech Report 2022-10-25

amec foster wheeler Subqrade Compaction: Exposed subgrades for footings, floors, pavements, and other structures should be compacted to a dense, unyielding state. Any localized zones of loose granular soils observed within a subgrade should be compacted to a density commensurate with the surrounding I soils. Any organic, soft, or pumping soils observed within a subgrade should be overexcavated and replaced with a suitable structural fill. On-site Soils: We offer the following evaluation of the on-site soils relative to potential use as structural fill. ► Surficial and Subsurface Organic-Rich Soils: The sod, duff, topsoil, and organic-rich soils mantling the unpaved area of the site and isolated relic topsoil layers encountered below the surface are not suitable for use as structural fill under any circumstances, due to their long-term compressibility. Consequently, these materials can be used only for non- structural purposes, such as in landscaped areas. ► Existing Fill Soils: The loose to medium dense fill soils varied but were generally composed of a fine-grained sandy silt, appeared at or above optimum moisture, and would be difficult to reuse as structural fill. The fill soils encountered within the athletic field had variable amounts of organics (topsoil) and are not suitable for reuse as structural fill. Because the fill soils encountered had a relatively high silt content, these soils would be difficult or impossible to compact during wet weather conditions. ► Lacustrine Silts: The silts underlying the site were at or over optimum moisture content and very moisture sensitive. The silts will be difficult to reuse as structural fill except under ideal moisture and weather conditions. If the ESD wishes to attempt to use the silts as structural fill, the silts should be laid out over a sizable area, aerated during a period of warm weather, and turned a number of times to reduce the moisture content to acceptable levels for use a structural fill. These soils will be difficult or impossible to reuse during wet weather due to the high silt content. ► Advance Outwash: The sands and gravelly sands underlying the site at depths of 10 to 18.5 feet below the ground surface would provide a favorable source of structural fill and can be used in a broad range of weather conditions. However, laboratory testing indicates the Advance Outwash soils to be below optimum moisture content; these soils would need ' to be moisture conditioned for use as structural fill. Athletic Field Fill Soils: A relic topsoil layer approximately 1 foot thick was encountered 3.5 feet bgs in the southeast area of the field. The relic topsoil layer should be overexcavated and replaced with structural fill if encountered during installation of the field underdrain or within 2 feet of the athletic field ' final elevation. 1 Utility Trench Backfill: None of the explorations encountered utility trench backfill. As such, the depths, lengths, alignment,or density of any utility trench backfill intersecting the proposed building footprint was not determined as part of this study. In general, granular backfill would not adversely affect site ' Amec Foster Wheeler Project No.6-917-18116-0 9 \\Sea-fs1\WordProc\ Projects\18000s\18116 Everett School District\Geotech Report\Revised\2017_10-19_Everett Middle School Geotech_Sx.docx