6101 23RD DR W NORPRO Geotech Report 2025-07-29

I June 3,2011 Project No. T-6578 I Our study indicates that the near-surface weathered and lower unweathered glacial till soils contain a sufficient percentage of fines (silt and clay size particles) that will make them difficult to compact as structural fill if they I are too wet or too dry. Accordingly, the ability to use these native soils from site excavations as structural fill will depend on their moisture content and the prevailing weather conditions when site grading activities take Iplace. At the time of our investigation, the native soils below a depth of approximately three feet were generally at or near optimum moisture content. If native soils become too wet to properly compact they could be dried by I aeration during dry weather conditions or mixed with an additive such as cement, cement kiln dust (CKD), or lime to stabilize the soil and facilitate compaction. If an additive is used, additional Best Management Practices (BMPs) for its use will need to be incorporated into the Temporary Erosion and Sedimentation Control plan (TESL) for the project. The contractor should be prepared to moisture condition soils as needed. If grading activities are planned during the wet winter months or if they are initiated during the summer and Iextend into fall and winter, the owner should be prepared to import wet weather structural fill. For this purpose, we recommend importing a granular soil that meets the following grading requirements: IU.S. Sieve Size Percent Passing 3 inches 100 No.4 75 maximum II No. 200 5 maximum* *Based on the 3/4-inch fraction. IPrior to use, Terra Associates, Inc. should examine and test all materials imported to the site for use as structural fill. IStructural fill should be placed in uniform loose layers not exceeding 12 inches and compacted to a minimum of 95 percent of the soil's maximum dry density, as determined by American Society for Testing and Materials I (ASTM) Test Designation D-698 (Standard Proctor), The moisture content of the soil at the time of compaction should be within two percent of its optimum, as determined by this ASTM standard. In nonstructural areas, the Idegree of compaction can be reduced to 90 percent. II5.3 Excavations and Slopes IExcavations All excavations at the site associated with confined spaces, such as utility trenches, must be completed in I accordance with local, state, or-federal requirements. Based on current Washington Industrial Safety and Health Act (WISHA) regulations, the near-surface, weathered glacial till and deeper outwash sediments would be classified as Type C soils. The dense to very dense unweathered till soils would be classified as Type A soils. 1 I Page No.7