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 bracing; MGI should be consulted if multiple bracing is planned. We recommend that yielding walls be designed using an equivalent fluid density of 40 and 60 pcf for horizontal backfill surfaces and backfill or cut slope surfaces inclined at 2:1 (horizontal to vertical) above the horizontal, respectively. For undrained conditions,we recommend that yielding walls be designed using an equivalent fluid density of 80 and 100 pcf for horizontal backfill surfaces and backfill or cut surfaces inclined at 2:1, respectively. 4.2.4 Pipe Bedding and Manhole Support Based on our test pits, we expect soils over the length of the project area to generally consist of pre-existing fill soils or loose, fine to medium sand at the base of the trench excavation. We recommend that all manholes be supported on dense soils or on at least 2 feet of granular fill compacted to 95 percent of the maximum dry density defined below. ' Utility pipes should be bedded in sand or smooth rounded gravel, such as specified in the City of Everett Typical Trench Schematic Details, WSDOT Standard Specifications, Section 9-03.12(3) as modified for sanitary sewers, or as recommended by the manufacturer. We recommend that the be covered with beddingmaterial to at least one foot above thepipe. This pipe o e p pe bedding material should be lightly tamped into place. Backfill placed above the bedding material shall consist of ' structural fill compacted as discussed below. Shallow or perched groundwater may infiltrate through the utility trench pipe bedding. We I recommend manactur watps plugs f cntolled deny fi ( F) r both be pced in the pipe trench t to control seepage alongor the pipe. We expect settlement of the proposed pipeline will be negligible pi sit rovidedll the o soils at the basela of the excavation areuf not unduly ed disturbed durinog installation.r Pipe bedding should be placed according to the manufacturers recomstomendations.o 4.2.5 Backfill All fill material should be free of debris, organic contaminants and rock fragments larger than 6 inches. We recommend that backfill be placed in lifts not exceeding 10 inches in loose thickness and mechanically compacted to at least 90 percent of the maximum dry density determined by Test ' Method ASTM D-1557. The upper 5 feet under roadways or road shoulders should be compacted to 95 percent. The moisture content of the backfill material should be adjusted as necessary to achieve this compaction. Based upon our test pit explorations,and field observations,we anticipate that the majority of soils encountered during trenchwork activities will be comprised of relatively clean(less than 12 percent i fines) sands. This material can be adequately reused as structural fill duringmost weather q Y conditions. It should be expected that duringperiodsof wet we ather extended e that some of the on-site soils will become saturated from shallow groundwater. The contractor should be prepared to spread and windrow these soils to the extent necessary to dry them back to a condition suitable for compaction. Any soils too wet to compact should be exported from the site. Migizi Group, Inc. Page 10 of 16 MIGIZI III�III I