2514 RAINIER AVE Geotech Report 2022-10-25

, ,,, , x40 I ame ,ia, foster I wheeler development, unless excavations or foundations are required adjacent to pea gravel or similar I materials that would tend to ravel. Utility trench backfill under any new building footings or structures may require overexcavation and replacement with structural fill that is compacted to project 1 specifications. Wet-Weather Considerations: As discussed above, most of the on-site soils will be difficult to use as structural fill during wet weather. Consequently, the project specifications should include provisions for importing clean, granular fill in case site filling must proceed during wet weather. For general structural fill purposes, we recommend using a well-graded sand or gravel, such as "Ballast" or "Gravel Borrow" per WSDOT Standard Specification 9-03.9(1) and 9-03.14, respectively, except that the percent passing the U.S. No. 200 Sieve should be less than 5 percent. I Permanent Slopes: All permanent cut slopes and fill slopes should be adequately inclined to minimize long-term raveling, sloughing, and erosion. We generally recommend that no slopes be steeper than 111 2H:1 V. For all soil types, the use of flatter slopes (such as 3H:1 V) would further reduce long-term erosion potential and facilitate vegetation growth. I Slope Protection: We recommend that a permanent berm, swale, or curb be constructed along the top edge of all permanent slopes to intercept surface flow. Also, a hardy vegetative groundcover should be established as soon as feasible to further protect the slopes from erosion due to runoff water. 1 4.2 FOUNDATIONS In our opinion, conventional spread footings will provide adequate support for the proposed construction if the subgrades are properly prepared. We offer the following comments and recommendations for the purposes of footing design and construction. Figure 3 also displays our foundation recommendations. I Footing Depths and Widths: For frost and erosion protection, the bottoms of all exterior footings should bear at least 18 inches below adjacent outside grades, whereas the bottoms of interior footings need bear only 12 inches below the surrounding slab surface level. To minimize post-construction settlements, continuous (wall) and isolated (column) footings should be at least 18 inches and III 24 inches wide, respectively. trine newly Bearing Pad and Subqrades: Footing subgrade soils will generally consist of I acus silts or e wl y placed and compacted structural fill, depending on location and elevation. In order to utilize reasonable-sized spread footings with an adequate bearing pressure, we recommend a gravel I Amec Foster Wheeler I 10 Project No.6-917-18116-0 \\Sea-fs1\WordProc\_Projects\18000s\18116 Everett School District\Geotech Report\Revised\2017_10-19_Everett Middle School Geotech_Sx.docx