2320 RAILWAY AVE Geotech Report 2023-02-01

Interwest Construction Co.-Everett Contractor Yard Site Improvements, Everett,WA March 12,2021 Geotechnical Engineering Report P2184-T20 1 such as well points, could be necessary in order to temporarily dewater excavations. We recommend that the appropriate dewatering system be selected during construction, when the specific subgrade conditions encountered are directly observable. The contractor should be prepared for more extensive dewatering at that time should it be needed. Temporary Cut Slopes: All temporary soil slopes associated with site cutting or excavations should be adequately inclined to prevent sloughing and collapse. Temporary cut slopes in site soils should be no steeper than 11 H:1V, and should conform to Washington Industrial Safety and Health Act (WISHA) regulations. subgrade Compaction: Exposed subgrades should be compacted to a firm,unyielding state before new concrete or fill soils are placed. Any localized zones of looser granular soils observed within a I I I I subgrade should be compacted to a density commensurate with the surrounding soils. In contrast, I anyorganic, soft, or pumping soils observed within a subgrade should be overexcavated and g P P g g replaced with a suitable structural fill material. Site Filling: conclusionsregarding n onsite soilsandwet- weather g the reuse ofo s our comments regarding wet weather filling are presented subsequently. Regardless of soil type, all fill should be placed and 1 compacted according to our recommendations presented in the Structural Fill section of this report. Specifically,building pad fill soil should be compacted to a uniform density of at least 95 percent (based on ASTM:D-1557). Onsite Soils: We offer the following evaluation of these onsite soils in relation to potential use as structural fill: • Existing Fill Soils: A 5 to 6-foot-thick fill horizon caps the site,being comprised of recycled concrete/asphalt and "pit-run" like soils. This material was encountered near optimum I moisture content conditions and would make an excellent source of structural fill. We anticipate that this material could be reused nearly year-round under wet-weather conditions. • Alluvial Sands: Encountered immediately beneath the fill cap,this material is comprised of fine to medium sand with some gravel, was encountered near optimum moisture content conditions and would make an excellent source of structural fill. We anticipate that this material could be reused nearly year-round under wet-weather conditions. • Organic-Rich Silt/Peat: Encountered beneath the alluvial sands across the southern portion of the site, this material is comprised of mostly fines and a varying organics content, I 1 I I I including large woody debris. Due to the fact that these soils are highly moisture sensitive, I contain organic material, and are generallyin an over-saturated condition, we do not g recommend the re-use of this soil group as structural fill. Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined to reduce long-term raveling,sloughing,and erosion. We generally recommend that no permanent slopes be steeper than 2H:1V. For all soil types, the use of flatter slopes (such as 21H:1 V) would further reduce long-term erosion and facilitate revegetation. Migizi Group, Inc. Page 8 of 16 �)