2710 14TH ST BLDG A Geotech Report 2023-12-29

' 4.2.4. Footing Drains ' We recommend perimeter footing drains be installed around the proposed buildings. The perimeter drains should be installed at the base of the exterior footings, as shown in Figure 4. The perimeter drains should consist of at least 4-inch-diameter perforated pipe placed on a 4-inch bed of, and surrounded by, 6 inches of drainage material enclosed in a nonwoven geotextile filter fabric such as Mirafi 140N (or approved equivalent). The perimeter drains should be provided with cleanouts. The footing drainpipe should be installed at least 18 inches below the top of the adjacent floor slab. The drainage material should consist of "Gravel Backfill for Drains" per Section 9-03.12(4) of the 2018 Washington State Department of Transportation (WSDOT) Standard Specifications. We recommend the drainpipe consist of either heavy -wall solid pipe (SDR-35 PVC, or equal) or rigid corrugated smooth interior polyethylene pipe (ADS N-12, or equal). ' We recommend against using flexible tubing for footing drainpipes. The perimeter drains should be sloped to drain by gravity, if practicable, to a suitable discharge point, preferably a storm drain. We recommend the cleanouts be covered and placed in flush mounted utility boxes. Water collected in roof downspout lines must not be routed to the footing drain lines. 4.2.5. Construction Considerations ' We recommend that the excavations for the footings be completed with an excavator equipped with a smooth -edge bucket to minimize subgrade disturbance. Immediately prior to placing concrete, all debris and loose soils that accumulated in the footing excavations during forming and steel placement must be ' removed. Debris or loose soils not removed from the footing excavations will result in increased settlement. If wet weather construction is planned, we recommend that all footing subgrades be protected using a lean ' concrete mud mat. The mud mat should be placed the same day that the footing subgrade is excavated and approved for foundation support. 4.3. Slab -on -Grade Floors 4.3.L Subgrade Preparation We recommend that concrete slabs -on -grade be constructed on a gravel layer to provide uniform support and drainage, and to act as a capillary break. We expect that slab -on -grade floors can be supported on: (1) medium dense to very dense native glacial soils encountered in our test pits, or (2) on properly compacted structural fill extending down to these materials, or (3) on suitable on -site soils. Prior to placing the gravel layer, the subgrade should be proofrolled as described in Section 4.5 of this report. The exposed subgrade should be evaluated during construction and compacted to a firm and unyielding condition, although unsuitable soils should be removed and replaced with structural fill where needed. 4.3.2. Design Parameters A 6-inch-thick capillary break layer of 1-inch minus clean crushed gravel with negligible sand and silt (WSDOT 9-03.1(4)C, Grading No. 67) should be placed to provide uniform support and form a capillary break beneath the slabs. For slabs designed as a beam on an elastic foundation, a modulus of subgrade reaction of 75 pci may be used for subgrade soils prepared as recommended above. This value assumes the slabs are bearing directly on structural fill placed over medium dense to dense native glacial soils and will require evaluation during construction. GEOENGINEER� October 30, 2019 Page 8 Poe No. 2'. 288-002 00