10312 EVERGREEN WAY SONIC Geotech Report 2023-05-25

Geotechnical Engineering Report 6 January 8,2021 Glint Car Wash and Sonic Everett,Everett,Washington RGI Project No.2020-643-1 5.2.2 EXCAVATIONS All temporary cut slopes associated with the site and utility excavations should be adequately inclined to prevent sloughing and collapse. The site soils consisted of medium dense to very dense silty sand with trace gravel. Accordingly, for excavations more than 4 feet but less than 20 feet in depth, the temporary side slopes should be laid back with a minimum slope inclination of 1.5:1 (Horizontal:Vertical) in upper loose soil and 3H:4H in native glacial till. If there is insufficient room to complete the excavations in this manner, or excavations greater than 20 feet in depth are planned, using temporary shoring to support the excavations should be considered. For open cuts at the site, RGI recommends: ➢ No traffic, construction equipment, stockpiles or building supplies are allowed at the top of cut slopes within a distance of at least 5 feet from the top of the cut. ➢ Exposed soil along the slope is protected from surface erosion using waterproof tarps and/or plastic sheeting. ➢ Construction activities are scheduled so that the length of time the temporary cut is left open is minimized. ➢ Surface water is diverted away from the excavation. ➢ The general condition of slopes should be observed periodically by a geotechnical engineer to confirm adequate stability and erosion control measures. In all cases, however, appropriate inclinations will depend on the actual soil and groundwater conditions encountered during earthwork. Ultimately, the site contractor must be responsible for maintaining safe excavation slopes that comply with applicable OSHA or WISHA guidelines. 5.2.3 STRIPPING AND SITE PREPARATION Stripping efforts should include removal of pavements, vegetation, organic materials, and deleterious debris from areas slated for building, pavement, and utility construction. RGI anticipates that some areas of loose soil may be present on the site after stripping operations are complete. Prior to placement of structural fill, RGI recommends proofrolling building and pavement subgrades and areas to receive structural fill. These areas should be proofrolled under the observation of RGI and compacted to a firm and unyielding condition in order to achieve a minimum compaction level of 95 percent of the modified proctor maximum dry density as determined by the American Society of Testing and Materials D1557-09 Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (ASTM D1557). Proofrolling and adequate subgrade compaction can only be achieved when the soils are within approximately ± 2 percent moisture content of the optimum moisture content. Corporate Office 17522 Bothell Way Northeast Bothell,Washington 98011 Phone 425.415.0551• Fax 425.415.0311 141114'.rilev-group.com