5010 DOVER ST Geotech Report 2025-07-31

August 22nd 2022 G-5756 Ben Erickson Page 7 Subgrade Preparation Shallow subsurface soils at the project area on the site are anticipated to typically consist of dense silty sand.If specific areas of especially soft soils, organics, or other deleterious materials are encountered during this work,they should be over-excavated to an appropriate depth as recommended by the geotechnical engineer and replaced with gravel or crushed rock. Structural Fill Structural fill is defined as fill soil supporting building foundations,floor slabs,pavements, sidewalks or other fat work. Structural fill should be free of organic and other deleterious substances and have a maximum fragment size of 3 inches. The site soils contain silt. It can be difficult to achieve compaction with soils containing silt, especially during wet weather, subject to the material's moisture content. During wet weather we recommend a free-draining granular material containing no more than 5 percent fines content(silt and clay-size particles passing the No. 200 mesh sieve). Other materials, such as recycled crushed concrete or crushed rock may be used.The site soils should not be used as structural fills for the proposed development. Structural fill should be placed and compacted at or near the material's optimum moisture content and in lifts that are 10 inches thick or less. Below slab-on-grade floors,foundations, and other structural elements, structural fill should be compacted to a minimum of 92 percent of the material's maximum dry density, as determined by ASTM Test Designation D-1557 (Modified Proctor). For driveways, structural fill should be compacted to 90 percent,with the exception of the top 12 inches which should be compacted to 95 percent. Fill behind retaining walls and next to building foundation walls should be compacted to a minimum of 90 percent(92 percent if supporting structural elements;if supporting pavements,the top 12 inches should be compacted to 95 percent). Utility trench backfill within the City right-of-way should be compacted to the specifications required by the City, sewer or water district. Observation and compaction testing will be required at the time of fill placement to document and verify that the compaction specifications are achieved. GEO Group Northwest,Inc.