313 76TH ST SE WESTERN WIRELESS CORPORATION Geotech Report 2018-01-02 MF Import

ADaPT Engineering, Inc. Western Wireless Corporation ADaPT Job No, WA98-993 April I, 1998 Page 9 Structural Fill The following comments, recommendations, and conclusions regarding structural (ill are provided for design and construction purposes: Materials: Structural fill includes any fill materials placed under footings, pavements, driveways, and other such structures. Typical materials used for structural fill include: clean, well-graded sand and gravel (pit-run); clean sand; crushed rock; controlled-density fill (CDF); lean-mix concrete; and various soil mixtures of silt, sand, and gravel. Recycled concrete, asphalt, and glass, derived from pulverized parent materials may also be used as structural fill. Placement and Compaction: Generally, CDP, and lean-mix concrete do not require special placement and compaction procedures. In contrast, pit-run, sand, crushed rock, soil mixtures, and recycled materials should be placed in horizontal lifls not exceeding 8 inches in loose thickness, and each lift should be thoroughly compacted with a mechanical compactor. Using the modified Proctor maximum dry density (ASTM: D-1557) as a standard, we recommend that structural fill used for various on-site applications be compacted to the following minimum densities: Fill Application Minimum Compaction Slab/Footing subgrade 90 percent Gravel drive subgrade(upper I foot) 95 percent Gravel drive subgrade(below I foot) 90 percent Suberadcs and Testing: Regardless of location or material, all structural fill should be placed over firm. unyielding subgrade soils. We recommend that a representative from ADaPT be retained to observe the condition of subgrade soils before fill placement begins, and to perform a series of in-place density tests during soil fill placement. In this way, the adequacy of soil compaction efforts may be evaluated as earthwork progresses. Fill Content: Soils used for structural fill should not contain individual particles greater than about 6 inches in diameter and should be free of organics, debris, and other deleterious materials. Given these prerequisites, the suitability of soils used for structural fill depends primarily on the grain-size distribution and moisture content of the soils when they are placed. When the "fines" content (that soil fraction passing the U.S. No. 200 Sieve) increases, soils become more sensitive to small changes in moisture content. Soils containing more than about 5 percent fines (by weight) cannot be consistently compacted to a furan, unyielding condition when the moisture content is more than about 2 percentage points above optimum. The existing surficial soils at this site contain an elevated fines content and should be considered highly moisture sensitive. The use of"clean" soil is necessary for fill placement during wet-