3800 RIVERFRONT BLVD Geotech Report 2023-05-04

July 3, 2019 HWA Project No. 2015-061-21 material near optimum moisture content. HWA recommends that imported Gravel Borrow meeting the requirements of the WSDOT standard specifications be used as trench backfill in wetter times of year. During placement of the initial lifts, the trench backfill material should not be bulldozed into the trench or dropped directly on the pipe. Furthermore, heavy vibratory equipment should not be permitted to operate directly over the pipe until a minimum of 2 feet of backfill has been placed over the pipe bedding to an in-place density of at least 90 percent of the maximum dry density as determined using ASTM D-1557. Properly prepared backfill, greater than 2 feet above the pipe bedding, should be placed in uniform loose lifts not to exceed 12 inches and densely compacted in a systematic manner using appropriately sized compaction equipment to achieve at least 95 percent of the maximum dry density as determined using ASTM D-1557. Smaller loose lifts may be necessary to achieve compaction where hand held compaction equipment such as jumping jacks, or plate compactors are used. Please note that based on our previous laboratory testing, if LPSB is used at a ga.s barrier, at least 3 feet of this material compacted to at least 95% of the maximum dry density, obtained by ASTM D1557, is required. 0•0 If you have any questions or require additional information, please contact the undersigned at your earliest convenience at (425) 774-0106. HWA GEOSCIENCES INC. �G F\,VASti/jy * ,`k's" cr'-• C,o cn r . a '53 ..-:;#11:7 ..."" ".54wr„,....4.;,,,, y-d______...,,, T---- Exr 9-11-2o Michael Place, P.E. 7.3-11 Senior Geotechnical Engineer Riverfront Boulevard Addendum 2 3 HWA GeoSciences Inc.