1707 SCENIC DR SNO CO PUD Geotech Report 2022-10-25

� proposed future south transformer pad will not be as deep. Removal of existing fill below foundations should extend beyond the edges of the foundations by the depth of the cut to remove the fill. Suhstation Surfacing Loose to medium dense fill and medium dense to very dense weathered and unweathered glacial soils were observed near the proposed grade of the planned 115kV and 230kV yards. We understand the proposed yards will be surfaced with 4-inches of crushed substation rock. We recommend a gravel subbase layer be constructed below the crushed rock surfacing to provide a firm subgrade to reduce the risk of rutting and deterioration of the substation surfacing. The gravel subbase should consist of at least 12 inches of crushed surFacing base course per Section 9-03.9(3) of the Washington State Department of Transportation (WSDOT) Standard Specifications compacted to at least 95 percent of the maximum dry density (MDD). Where infiltration trenches are located, the crushed surFacing base course should be ��` � replaced with 12 inches of ciean crushed gravel meeting the gradation requirements of WSDOT Standard . �a �Specifications 9-03.1(4)C Grading No. 67 over the full width of the infiltration trench. Additional Subgrade Areas Prior to placing new fills, crushed rock, or foundations, subgrade areas should be evaluated and/or proofrolled to locate any soft or pumping soils. All unsuitable soils should be removed from below structures or structural fill placed on slopes. Proofrolling can be completed using a piece of heavy tire-mounted equipment such as a loaded dump truck. During wet weather, the exposed subgrade areas should be probed to determine the extent of soft soils. If soft or pumping soils are observed they should be removed and replaced with structural fill. After completing the proofrolling, the subgrade areas should be recompacted to a firm and unyielding condition, if possible. The degree of compaction that can be achieved will depend on when the construction is perFormed. If the work is perFormed during dry weather conditions, we recommend that all subgrade areas be recompacted to at least 95 percent of the MDD in accordance with the American Society for Testing and Materials (ASTM) D 1557 test procedure (modified Proctor). If the work is perFormed during wet weather conditions, it may not be possible to re-compact the subgrade to 95 percent of the MDD. In this case, we recommend that the subgrade be compacted to the extent possible without causing undue weaving or pumping of the subgrade soils. Subgrade disturbance or deterioration may occur if the subgrade is wet and cannot be dried. If the subgrade deteriorates during proofrolling or compaction, it may become necessary to modify the proofrolling or compaction criteria or methods. We recommend that subgrades for foundation excavations and the crushed rock surfacing and subbase be evaluated by GeoEngineers. Structural Fill All fill placed for this project should be placed and compacted as structural fill. We recommend that structural fill be placed and compacted to at least 95 percent MDD per ASTM D 1557 under all structures and behind retaining walls used for site access. Fill placed to raise site grades, not under structures, should be placed and compacted to at least 90 percent MDD per ASTM D 1557, except that the upper 2 feet should be compacted to at least 95 percent MDD. GEOENGINEER� October24,2014 Page 7 FIe Na.0482-027-02