7500 HARDESON RD Geotech Report 2022-10-25

1 Geotechnical Engineering Report SSGC Flardeson Road Retail Everett,Washington SSGC Project No. 18072 September 18,2018 GEOTECHNICAL DESIGN CONSIDERATIONS The planned development is considered feasible based on observed soil conditions in the test pits. However, substantial thicknesses of unsuitable fill materials are present on the site. Although we are unaware of planned finish grades for the proposed development,removal of substantial amounts of fill is anticipated to lower grades for access. The amount of planned fill removal will influence final design and ' construction. As the fill is variable in type and consistency,it is not considered suitable for direct support of foundations or slabs. Native soils or new engineered structural fill over native soils should be used for support of conventional spread footing foundations and slab-on-grade floors. Some of the existing fill could potentially be left in parking areas depending on final grades. Native soils generally consist of dense glacial till which will limit infiltration for stormwater control. One ' infiltration test completed in the southeastern portion of the site suggests very limited infiltration may be feasible in the upper native soils. However, groundwater movement in these soils is considered lateral and will limit the type of feasible infiltration system. Recommendations presented in the following sections should be considered general and may require modifications when final grades have been established and earthwork and grading occur. As final grades ' are unknown at this time, final recommendations may differ from those in this report. Subsurface conditions across the site may vary from those depicted on the exploration logs and can change with time. Therefore, proper site preparation will depend upon the weather and soil conditions encountered at the ' time of construction. We recommend SSGC review final plans and assess subgrade conditions at the time of construction. General Site Preparation Site grading and earthwork should include procedures to control surface water runoff. Grading the site without adequate drainage control measures may negatively impact site soils,resulting in increased export of impacted soil and import of fill materials, thereby potentially increasing the cost of the earthwork and subgrade preparation phases of the project. Site grading should include removal (stripping) of all fill in the building area. Building subgrades should consist of firm native soils following stripping. Fill in pavement areas should be stripped to a depth of at least one foot below planned finish grades. Final stripping depths can only be determined at the time of construction. ' General Subgrade Preparation We recommend exposed subgrades in building and conventional pavement areas are proofrolled using a large roller, loaded dump truck, or other mechanical equipment to assess subgrade conditions following stripping. Proofrolling efforts should result in the upper 1 foot of subgrade soils achieving a compaction level of at least 95 percent of the maximum dry density (MDD)per the ASTM D1557 test method. Wet, ' loose, or soft subgrades that cannot achieve this compaction level should be removed (over-excavated) 3