2410 RAILWAY AVE Geotech Report 2023-04-06

Penske Truck Leasing-Proposed Service Facility,2410 Railway Ave, Everett,WA Mar.8,2019/Rev.Feb.25,2020 Geotechnical Engineering Report P1493-T18 4.5 Slab-On-Grade Floors In our opinion,soil-supported slab-on-grade floors can be used in structures after preloading if the subgrades are properly prepared. The floor slabs may also be structurally supported on pile foundations. We offer the following comments and recommendations concerning slab-on-grade floors. Floor Subbase: We recommend placement of at least 2 feet of properly compacted structural fill as a ' floor subbase. If floor construction occurs during wet conditions,it is likely that a geotextile fabric, placed between the structural fill floor subbase and native soils,will be necessary. All subbase fill should be compacted to a density of at least 95 percent(based on ASTM:D-1557). Capillary Break and Vapor Barrier: To retard the upward wicking of moisture beneath the floor slab,we recommend that a capillary break be placed over the subgrade. Ideally,this capillary break would consist of a 4-inch-thick layer of pea gravel or other clean, uniform, well-rounded gravel, such as"Gravel Backfill for Drains"per WSDOT Standard Specification 9-03.12(4),but clean angular gravel can be used if it adequately prevents capillary wicking. In addition, a layer of plastic sheeting (such as Crosstuff, Visqueen, or Moistop) should be placed over the capillary break to serve as a vapor barrier. During subsequent casting of the concrete slab, the contractor should exercise care to avoid puncturing this vapor barrier. 4_6 Drainage Systems In our opinion,structures should be provided with permanent drainage systems to reduce the risk of future moisture problems. We offer the following recommendations and comments for drainage design and construction purposes. Perimeter Drains: We recommend that buildings be encircled with a perimeter drain system to collect seepage water. This drain should consist of a 4-inch-diameter perforated pipe within an envelope of pea gravel or washed rock,extending at least 6 inches on all sides of the pipe, and the gravel envelope should be wrapped with filter fabric to reduce the migration of fines from the surrounding soils. Ideally,the drain invert would be installed no more than 8 inches above the base of the perimeter footings. Discharge Considerations: If possible, all perimeter drains should discharge to a storm drain system or other suitable location by gravity flow. Check valves should be installed along any footing drainpipes that discharge to a storm drain system to prevent sewage backflow. If gravity flow is not feasible,a pump system is recommended to discharge any water that enters the drainage system. Runoff Water: Roof-runoff and surface-runoff water should not discharge into the perimeter drain system. Instead, these sources should discharge into separate tightline pipes and be routed away from the building to a storm drain or other appropriate location. Grading and Capping: Final site grades should slope downward away from the buildings so that runoff water will flow by gravity to suitable collection points, rather than ponding near the Migizi Group, Inc. Page 13 of 17