222 W CASINO RD Geotech Report 2022-10-25

GeoTest Services, Inc. May 3,2019 Mukilteo School District 19-0194 CONCLUSIONS AND RECOMMENDATIONS Based on the evaluation of the data collected during this investigation,it is our opinion that the subsurface conditions at the site are suitable for the proposed development, provided the recommendations contained herein are incorporated into the project design. The existing near surface, loose to dense, previously placed fill soils are not suitable for conventional foundation systems and will require at least 2 feet of removal and replacement with compacted structural fill directly beneath the foundation elements. Due to the high fines content and relative variability of near surface previously placed fill soils, GTS does not recommend reusing on-site materials for structural fill. Site Preparation and Earthwork The portions of the site proposed for foundations and/or sidewalks development should be prepared by removing existing topsoil, deleterious material and significant accumulations of organics to a minimum depth of 2 feet beneath bottom of footing elevation. Prior to placement of any foundation elements or structural fill,the exposed subgrade under all areas to be occupied by spread,or continuous foundations should be recompacted to a firm and unyielding condition. Verification of compaction can be accomplished through proof rolling with a loaded dump truck, large self-propelled vibrating roller, or similar piece of equipment applicable to the size of the excavation. The purpose of this effort is to identify loose or soft soil deposits so that, if feasible,the soil distributed 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 used to obtain final elevations for footings 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 offsite or placed in nonstructural areas. Soils containing more than approximately 5 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 2 percent. The optimum moisture content is that which allows the greatest dry density to be achieved at a given level of compactive effort. 4