4320 THOMSON AVE GEOTECHNICAL ENGINEERING REPORT Geotech Report 2023-08-10

" GeoTest Services, Inc. 4320 Thomson Avenue, Everett, WA Site Preparation and Earthwork March 17, 2022 Project No. 22-0285 The portions of the site proposed for foundations should be prepared by removing topsoil and loose soils (if present), deleterious material, and significant accumulations of organics. GeoTest anticipates approximately 12 inches of stripping to expose suitable subgrade soils. Prior to placement of any foundation elements or structural fill, the exposed subgrade under all areas to be occupied by soil -supported spread or continuous foundations should be recompacted to a firm and unyielding condition. Verification of firm and unyielding conditions should be performed by qualified geotechnical personnel. The purpose of this effort is to identify loose or soft soil deposits so that, if feasible, the soil disturbed during site work can be recompacted. Proof rolling should be carefully observed by qualified geotechnical personnel. Areas exhibiting significant deflection, pumping, or over -saturation that cannot be readily compacted should be overexcavated to firm soil. Overexcavated areas should be backfilled with compacted granular material placed in accordance with subsequent recommendations for structural fill. During periods of wet weather, proof rolling could damage the exposed subgrade. Under these conditions, qualified geotechnical personnel should observe subgrade conditions to determine if proof rolling is feasible. Fill and Compaction Structural fill must be properly placed and compacted. In most cases, suitable, non -organic, predominantly granular soil may be used for fill material provided the material is properly moisture conditioned prior to placement and compaction, and the specified degree of compaction is obtained. Material containing topsoil, wood, trash, organic material, or construction debris is not suitable for reuse as structural fill and should be properly disposed off - site or placed in nonstructural areas. Soils containing more than approximately five percent fines are considered moisture sensitive and are difficult to compact to a firm and unyielding condition when over the optimum moisture content by more than approximately two percent. The optimum moisture content is that which allows the greatest dry density to be achieved at a given level of compactive effort. Reuse of On -Site Soil The non -organic, native Advance Outwash soil are suitable for reuse as structural fill when placed at or near optimum moisture content, and if allowed for in the plans and specifications. The soils observed on site contain high percentages of fines and should be considered moisture sensitive. Reuse of these soils may be considerably more difficult to use at or near perched groundwater elevations and during the wet weather season. 4