10200 19TH AVE SE COSTCO FUEL STATION Geotech Report 2022-10-25

GEOTECHNICAL ENGINEERING STUDY Costco Wholesale c/o Barghausen Consulting Engineers E-8556 January 13, 1999 Page 10 If temporary slopes cannot be successfully constructed, the use of shoring may be necessary. ECI can provide shoring recommendations, if requested. Permanent cut and fill slopes should be inclined no steeper than 2H:1 V. All cut slopes should be observed by ECI during excavation to verify that conditions are as anticipated. Supplementary recommendations can then be developed, if needed, to improve stability, including flattening of slopes or installation of surface or subsurface drains. In any case, water should not be allowed to flow uncontrolled over the top of slopes. Permanently exposed slopes should be seeded with an appropriate species of vegetation to reduce erosion and improve stability of the surficial layer of soil. Utility Trench Backfill Based on the soil conditions encountered at the time of our exploration, the native and existing fill soils should provide adequate support for utilities. The competent native soils encountered at the proposed twenty (20) to twenty-five (25) foot depth of the proposed underground storage tanks should provide adequate support for the tanks. The excavation of the native soils will be difficult because of the very dense condition of the soil. Utility trench backfill, and backfill around the underground storage tanks will be a primary concern in reducing the potential for settlement of the overlying pavement areas. It is important that the utilities and tanks be adequately supported in the bedding material. The material should be hand tamped to ensure support is provided around the haunches of these structures. Fill should be carefully placed and tamped to about twelve (12) inches above the crown of the pipe or tanks before heavy compaction equipment is brought into use. The remainder of the backfill should be placed in lifts having a loose thickness of less than twelve (12) inches. A typical trench backfill section and compaction requirements for load supporting and non-load supporting areas is presented on Plate 4. Earth Consultants, Inc.