2514 RAINIER AVE Geotech Report 2022-10-25

1 a.{1eC .. ' foster wheeler Geotextile Separator: Because the subgrade may consist of lacustrine silts, which tend to soften with added moisture and dynamic loading, we recommend a geotextile separator be placed between the subgrade and the base course. This separator is highly recommended for the drive and bus lanes, and may also be beneficial for the lower traffic areas, such as parking areas. The geotextile should meet the requirements of WSDOT Standard Specification 9-33.1 (Table 3) for non-woven stabilization fabric. Pavement Materials: We recommend 3/8-inch HMA for the top asphalt layer. For the base course, we recommend using imported clean, crushed rock, such as "Crushed Surfacing Top and Base Course" per WSDOT Standard Specification 9-03.9(3). Compaction and Verification: Structural fill used to achieve subgrade, subbase material, and base course material should be compacted to at least 95 percent of the Modified Proctor maximum dry density (ASTM D-1557), and all asphalt concrete should be compacted to at least 92 percent of the Rice value (ASTM D-2041). We recommend an Amec Foster Wheeler representative be retained to verify compaction of the subgrade fill and base course before any overlying layer is placed. For the subgrade, compaction is best verified by means of frequent density testing; for the base course, methodology observations and hand-probing are more appropriate than density testing. Pavement Life and Maintenance: It should be noted that no asphalt pavement is maintenance-free. IThe above-described pavement sections represent our minimum recommendations for an average level of performance during a 20-year design life; therefore, an average level of maintenance will likely be required. Furthermore, a 20-year pavement life typically assumes that an overlay will be placed after about 10 years. Thicker asphalt, base, and subbase courses would offer better long-term performance, but would cost more initially; thinner courses would be more susceptible to "alligator" cracking and other failure modes. However, pavement design can be considered a compromise between a high initial cost and low maintenance costs, versus a low initial cost and higher maintenance costs. 4.9 STRUCTURAL FILL The term "structural fill" refers to any materials used for building pads, as well as materials placed under or against foundations and retaining walls; under slab-on-grade floors, sidewalks, and ' pavements; and for permanent fill slopes. Our comments, conclusions, and recommendations concerning structural fill are presented in the following paragraphs. Materials: Typical structural fill materials include sand, gravel, crushed rock, quarry spalls, CDF, lean-mix concrete, well-graded mixtures of sand and gravel (commonly called "gravel borrow" or Amec Foster Wheeler Project No.6-917-18116-0 19 111 \\Sea-fs1\WordProc\ Projects\18000s\18116 Everett School District\Geotech Report\Revised\2017_10-19_Everett Middle School Geotech_Sx.docx