2320 RAILWAY AVE Geotech Report 2023-02-01

Interwest Construction Co.-Everett Contractor Yard Site Improvements,Everett,WA March 12,2021 Geotechnical Engineering Report P2184-T20 Compaction and Observation: All subbase 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 I concrete should be compacted to at least 92percent of the Rice value (ASTM D-2041 . We P ) recommend that an MGI representative be retained to observe the compaction of each course before I any overlying layer is placed. For the subbase and pavement course,compaction is best observed 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: No asphalt pavement is maintenance-free. The above described I pavement sections present our minimum recommendations for an average level of performance I 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 and/or thicker base and subbase courses would offer better long-term Iperformance but would cost more initially; thinner courses would be more susceptible to P "alligator" cracking and other failure modes. As such, 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. 4.7 Structural Fill The term"structural fill"refers to any material placed under foundations,retaining walls,slab-on- grade floors, sidewalks, pavements, and other structures. Our comments, conclusions, and I recommendations concerning structural fill are presented in the following paragraphs. I I Materials: Typical structural fill materials include clean sand, gravel, pea gravel, washed rock, crushed rock,well graded mixtures of sand and gravel(commonly called"gravel borrow"or"pit run"),and miscellaneous mixtures of silt,sand,and gravel. Recycled asphalt,concrete,and glass, I which are derived from pulverizing the parent materials,are also potentially useful as structural fill in certain applications. Soils used for structural fill should not contain any organic matter or debris or any individual particles greater than about 6 inches in diameter. Fill Placement: If used, clean sand, gravel, crushed rock, soil mixtures, and recycled materials should be placed in horizontal lifts not exceeding 8 inches in loose thickness,and each lift should be I thoroughly compacted with a mechanical compactor. I I Compaction Criteria: Using the Modified Proctor test (ASTM:D-1557) as a standard, we recommend that structural fill used for various onsite applications be compacted to the following minimum densities: Fill Application Minimum Compaction Asphalt pavement base 95 percent Asphalt pavement subgrade(upper 2 feet) 95 percent Footing subgrade and bearing pad 95 percent Foundation backfill 90 percent I I Slab-on-grade floor subgrade and subbase 95 percent I Migizi Group, Inc. Page 14 of 16 miG111 Milli, i..