2410 RAILWAY AVE Geotech Report 2023-04-06

I Penske Truck Leasing-Proposed Service Facility,2410 Railway Ave,Everett,WA Mar. 8,2019/Rev.Feb. 25,2020 IGeotechnical Engineering Report P1493-T18 building. Ideally, the area surrounding the building would be capped with concrete, asphalt, or low-permeability (silty) soils to minimize or preclude surface-water infiltration. 4.7 Subgrade and Retaining Walls We offer the following recommendations for subgrade and retaining walls. Wall Foundations: Subgrade and retaining walls can be supported on shallow footings bearing on Isuitable soils as described in the Spread Footings section of this report. Footings should be designed using the recommended allowable bearing pressures and lateral resistance values presented for building foundations. I Wall Drainage: Drainage should be provided behind subgrade and retaining walls by placing a I zone of drain rock containing less than 3 percent fines(material passing No.200 sieve)against the wall. This drainage zone should be at least 24 inches wide(measured horizontally)and extend from the base of the wall to within 1 foot of the finished grade behind the wall. Smooth-walled I perforated PVC drainpipe having a minimum diameter of 4 inches should be embedded within the sand and gravel at the base of the wall along its entire length. This drainpipe should discharge into a tightline leading to an appropriate collection and disposal system. I Backfill Soil: Ideally,all wall backfill would consist of clean,free-draining,granular material,such as"Gravel Backfill for Walls"per WSDOT Standard Specification 9-03.12(2). A geotextile should be Iplaced between the drainage zone and the backfill soil to prevent drain clogging. I Backfill Compaction: Because soil compactors place significant lateral pressures on subgrade and retaining walls, we recommend that only small, hand-operated compaction equipment be used within 2 feet of a backfilled wall. Also, all backfill should be compacted to a density as close as I possible to 90 percent of the maximum dry density (based on ASTM:D-1557); a greater degree of compaction closely behind the wall would increase the lateral earth pressure, whereas a lesser degree of compaction might lead to excessive post-construction settlements. I Grading and Capping: To retard the infiltration of surface water into the backfill soils, we recommend that the backfill surface of exterior walls be adequately sloped to drain away from the Iwall. Ideally, the backfill surface directly behind the wall would be capped with asphalt,concrete, or 12 inches of low-permeability (silty) soils to minimize or preclude surface water infiltration. IApplied Soil Pressure: Walls that are designed to move 0.1 percent of the wall height during and after construction are usually referred to as unrestrained walls. We recommend that unrestrained I cantilever walls supporting slopes inclined at 2H:1V or flatter be designed to resist an active pressure (triangular distribution) of 55 pounds per cubic foot (pcf). The recommended pressure does not include the effects of surcharges from surface loads hydrostatic pressures, or structural Iloads. If such surcharges are to apply,they should be added to the above design lateral pressures. I I Migizi Group, Inc. Page 14 of 17 ,hill,