6801 SEAWAY BLVD Geotech Report 2025-08-19

Seaway Commercial Center Subsurface Exploration,Geologic Hazard, 7007 Seaway Boulevard and Geotechnical Engineering Evaluation Everett, Washington Design Recommendations attempted. In lieu of recompaction, the area to receive fill should be blanketed with washed rock or quarry spalls to act as a capillary break between the new fill and the wet subgrade. Where the exposed ground remains soft and further overexcavation is impractical, placement of an engineering stabilization fabric may be necessary to prevent contamination of the free-draining layer by silt migration from below. After recompaction of the exposed ground is tested and approved, or a free-draining rock course is laid, structural fill may be placed to attain desired grades. 10.2 Structural Fill Compaction Structural fill is defined as non-organic soil, acceptable to the geotechnical engineer, placed in maximum 8-inch loose lifts, with each lift being compacted to at least 95 percent of the modified Proctor maximum dry density using ASTM D-1557 as the standard. Utility trench backfill should be placed and compacted in accordance with applicable municipal codes and standards. The top of the compacted fill should extend horizontally a minimum distance of 3 feet beyond footings or pavement edges before sloping down at an angle no steeper than 2H:1V. Fill slopes should either be overbuilt and trimmed back to final grade or surface-compacted to the specified density. 10.3 Use of On-Site Soils as Structural Fill The on-site lodgement till sediments are suitable for use as structural fill provided they are free of roots or other deleterious materials and have a moisture content suitable for achieving the specified compaction. At the time of our exploration, the moisture content of the majority of the sediments encountered in our explorations appeared to be near optimum for achieving suitable compaction. Soils in which the amount of fine-grained material (smaller than No. 200 sieve) is greater than approximately 5 percent (measured on the minus No. 4 sieve size) should be considered moisture-sensitive. The on-site lodgement till contains a substantial amount of silt and are considered highly moisture-sensitive.Therefore,we recommend that mass grading activities for this project be planned to occur in the drier summer months between July and September; otherwise, proper moisture-conditioning in the wet season will be very difficult or impossible to obtain. Additionally, construction equipment traversing the site when the silty native sediments are very moist or wet can cause considerable disturbance. During the wetter portion of the year, typically from October to June, we recommend assuming that the on-site soils will not be suitable for reuse in structural fill applications. Possible alternatives would include cement treating on-site soils or using only a select import material consisting of a clean, free-draining gravel and/or sand. Free-draining fill consists of non-organic soil with the amount of fine-grained material limited to 5 percent by weight when measured on the minus No. 4 sieve fraction. December 17,2021 ASSOCIATED EARTH SCIENCES,INC. PEL/Id-20200319E001-002 Page 12