2320 106TH ST SW Geotech Report 2022-10-25

October 14,2015 Project No.T-6116-2 ibsurface In our opinion, with impervious pavement extending to the building perimeter, dock high floor elevations and surface drainage controlled and directed away from the structures, installation of perimeter foundation drains would not be necessary. Infiltration The glacial till soils composed of silty sand characteristically exhibits low permeability and would not be a suitable receptor soil for discharge of development stormwater using infiltration/retention facilities. Conventional stormwater detention with controlled release to the drainage basin should be used to manage development stormwater. 5.9 Utilities Utility pipes should be bedded and backfilled in accordance with American Public Works Association(APWA)or the City of Everett specifications. As a minimum, trench backfill should be placed and compacted as structural fill, as described in Section 5.2 of this report. As noted, most native soils excavated on the site should be suitable for use as backfill material during dry weather conditions. However, if utility construction takes place during the wet winter months, it will likely be necessary to import suitable wet weather fill for utility trench backfilling. 0 Pavements Ivements should be constructed on subgrades prepared as described in Section 5.2 of this report. Regardless of the relative compaction achieved, the subgrade must be firm and relatively unyielding before paving. The subgrade should be proofrolled with heavy construction equipment to verify this condition. The thickness of the various components of the pavement depends not only on the subgrade soils, but also the traffic loading conditions to which the pavement will be subjected. For design, we have assumed the traffic loading can be represented by design 18-kip equivalent single axle loads (ESALs) of 85,000 for light traffic and 430,000 for heavy traffic areas. These ESALs represent traffic loading equivalent to 5 and 25, loaded (80,000 pound gross vehicle weight) tractor-trailer rigs, respectively, traversing the pavement per day over a 20-year design life. If heavier traffic loading or volumes are expected,we should reevaluate the following recommended pavement sections: Light Traffic: • Two inches of hot mix asphalt (HMA) over four inches of crushed rock base (CRB) or four inches full depth HMA Heavy Traffic: • Three inches of HMA over six inches of CRB or six inches full depth HMA =e paving materials used should conform to the current Washington State Department of Transportation 4✓SDOT)specifications for V2-inch hot mix asphalt(HMA)surfacing and CRB. Page No. 11