9620 19TH AVE SE Geotech Report 2024-03-28

Pacific Ridge — DRH, LLC ES-7829.01 August 26, 2021 Page 12 We anticipate new pavement sections will be subjected primarily to passenger vehicle traffic. For lightly loaded pavement areas subjected primarily to passenger vehicles, the following preliminary pavement sections may be considered: • A minimum of two inches of hot-mix asphalt (HMA) placed over four inches of crushed rock base (CRB), or; • A minimum of two inches of HMA placed over three inches of asphalt-treated base (ATB). Heavier traffic areas generally require thicker pavement sections depending on site usage, pavement life expectancy, and site traffic. For preliminary design purposes, the following pavement sections for occasional truck traffic and access roadways may be considered: • Three inches of HMA placed over six inches of CRIB, or; • Three inches of HMA placed over four and one-half inches of ATB. A representative of ESNW should be requested to observe subgrade conditions prior to placement of CRIB or ATB. As necessary, supplemental recommendations for achieving subgrade stability and drainage can be provided. If on-site roads will be constructed with an inverted crown, additional drainage measures may be recommended to assist in maintaining road subgrade and pavement stability. Final pavement design recommendations, including recommendations for heavy traffic areas, access roads, and frontage improvement areas, can be provided once final traffic loading has been determined. Road standards utilized by the governing jurisdiction may supersede the recommendations provided in this report. The HMA, ATB, and CRIB materials should conform to WSDOT specifications. All soil base material should be compacted to a relative compaction of 95 percent, based on the laboratory maximum dry density as determined by ASTM D1557. Drainage Groundwater seepage may be encountered within site excavations depending on the time of year grading operations take place. Temporary measures to control surface water runoff and groundwater during construction would likely involve interceptor trenches, interceptor swales, and sumps. ESNW should be consulted during preliminary grading to identify areas of seepage and provide recommendations to reduce the potential for seepage-related instability. Surface grades must be designed to direct water away from slopes and buildings. The grade adjacent to slopes and buildings should be sloped away from the buildings at a gradient of at least 2 percent for a horizontal distance of at least four feet or more as setbacks allow. In our opinion, perimeter footing drains should be installed at or below the invert of the building footings. A typical footing drain detail is provided on Plate 4 of this report. If footing drains are not installed, we recommend backfilling footings with a relatively impermeable soil. Earth Solutions NW, LLC