10930 HOLLY DR Geotech Report 2025-08-08

Helix Design Group,Inc.-Greenwood Heating&Air Conditioning,Everett,WA April 22,2022 Geotechnical Engineering Report Z0219 Temporary Cut Slopes: At this time, final designs and construction sequencing have not been completed. To facilitate project planning we provide the following general comments regarding temporary 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 1/H:1V, and • Temporary slopes should conform to Washington Industrial Safety and Health Act (WISHA)regulations. These general guidelines are necessarily somewhat conservative(steeper temporary slopes may be possible). As the project progresses,temporary grading plans are developed,final site features are better defined, and a contractor is engaged, MGI may modify these general guidelines to allow steeper slopes. Subgrade Compaction: Exposed subgrades for the foundation and floor slabs of the proposed structures 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 subgrade should be compacted to a density commensurate with the surrounding soils. In contrast,any organic,soft,or pumping soils observed within a subgrade should be overexcavated and replaced with a suitable structural fill material. Site Filling: Our conclusions regarding the reuse of onsite soils and our comments regarding wet weather filling are presented subsequently. Regardless of soil type, all fill should be placed and 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: • Surficial Organic Soil and Organic-Rich Fill Soils: Where encountered,surficial organic soils, like duff, topsoil, root-rich soil, and organic-rich fill soils are not suitable for use as structural fill under any circumstances, due to high organic content. Consequently, this material can be used only for non-structural purposes,such as in landscaping areas. • Glacial Till: Encountered at near surface elevations,or below a variable thickness of fill soils, glacial till deposits are present beneath the project area. This material contains a relative fines (percent silt and clay) of 20 to 40 percent and should be considered moderately to extremely moisture sensitive. This material type will be difficult to reuse in wet weather conditions,and precautions should be taken to prevent over-saturation. 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 21 H:1V) would further reduce long-term erosion and facilitate revegetation. Migizi Group,Inc. Page 9 of 16 rdIG121 11i11.,