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January 3, 2025 <br />HWA Project No. 2021-159-21 <br />Geotechnical Engineering Report 48 HWA GEOSCIENCES INC. <br />Port Gardner Storage Facility <br />The design and implementation of any dewatering system should be the responsibility of the <br />contractor and their delegated design professionals. Dewatering specifications should include <br />language requiring the contractor to design and install wells to minimize fines removal during <br />pumping, including requirements for fines/sand content measurement and reporting. HWA <br />understands that the project specifications include a detailed settlement monitoring program to <br />track any potential settlement of structures during dewatering. <br />4.13 GENERAL EARTHWORK CONSIDERATIONS <br />4.13.1 Structural Fill <br />Materials used as backfill for the project are considered "Structural Fill." The onsite soils are <br />highly variable in composition and moisture sensitive. HWA does not recommend reusing the <br />onsite soils as structural fill for this project. Structural fill should consist of clean, free-draining, <br />granular soils free from organic matter or other deleterious materials. Structural fill should have <br />a maximum particle dimension less than 4 inches and should contain less than 7 percent fines <br />(portion passing the U. S. Standard No. 200 sieve). The fine-grained portion of structural fill <br />soils should be non-plastic. The native soils and exiting fill are generally not suitable for reuse as <br />structural fill due to their high fines content and the presence of organic material. <br />Structural fill for new pavements and shallow foundation pads should consist of Crushed <br />Surfacing Base Course (CSBC) as specified in Section 9-03.9(3) of the 2024 WSDOT Standard <br />Specifications. <br />4.13.2 Compaction <br />Structural fill soils should be moisture conditioned and compacted to the project requirements. <br />To minimize subsequent settlement of excavation backfill and new pavements, HWA <br />recommends that backfill soils be placed in loose lifts no thicker than 8 inches; each lift should <br />be compacted to at least 95 percent of its Modified Proctor maximum density (ASTM D 1557). <br />Achievement of proper density of a compacted fill depends on the size and type of compaction <br />equipment, the number of passes, thickness of the layer being compacted, and soil moisture- <br />density properties. In areas where limited space restricts the use of heavy equipment, smaller <br />equipment can be used, but the soil must be placed in thin enough layers to achieve the required <br />relative compaction. <br />Note that fill consisting of ballast should be compacted to a dense and unyielding condition – but <br />not to a specified degree of compaction.