7800 EVERGREEN WAY HYUNDAI Wetland Report 2025-08-05

4.2.3.Construction Considerations 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. We recommend that all completed footing excavations be observed by a representative of our firm prior to placing mud mat, reinforcing steel, and structural concrete. Our representative will confirm thatthe bearing surface has been prepared in a manner consistent with our recommendations and that the subsurface conditions are as expected. 4.3. Floor Slab Conventional slabs may be supported on -grade on undisturbed native glacial soils or on at least 12 inches of recompacted existing fill soils provided the subgrade is prepared as recommended in Section 4.7. The prepared subgrade should be evaluated by probing and performing a proof -rolled as described in Section 4.7.2. We recommend that concrete slabs -on -grade be constructed on a 4-inch-thick layer of clean crushed rock to provide uniform support and to act as a capillary break. The 4-inch crushed rock layer should be placed on recompacted suitable fill or approved native glacial soils. The capillary break layershould consist of at least 4 inches of clean crushed rock with a maximum particle size of 1 inch and negligible sand and silt, in accordance with Section 9-03.1(4)C, grading No. 67 of the 2020 Washington State Department of Transportation (WSDOT) Standard Specifications. For slabs designed as a beam on an elastic foundation, a modulus of subgrade reaction of 75 pounds per cubic inch (pci) may be used for subgrade soils prepared as recommended above. If water vapor migration through the slabs is objectionable, the capillary break material should be covered with a heavy plastic sheet, such as a minimum of 10-mil plastic sheeting, to act as a vapor retarder. We recommend that the vapor barrier be constructed in accordance with the American Concrete Institute (ACI 302.11R) and that the plastic sheet be placed over the capillary break layer. The contractor should be made responsible for maintaining the integrity of the vapor barrier during construction. 4.4. Foundation Drainage We recommend that perimeter footing drains be installed around the planned building addition and the perimeterdrains should be installed atthe base of the exterior footings (see Figure 3). The perimeter footing drains should be provided with cleanouts and should consist of at least 4-inch-diameter perforated pipe placed on a 2-inch bed of, and surrounded by, 6 inches of drainage material enclosed in a nonwoven geotextile such as TenCate Mirafi 140N (or approved equivalent) to prevent fine soil from migrating into the drain material. We recommend thatthe drain pipe consist of either heavy -wall solid pipe (SDR-35 PVC, orequal) or rigid corrugated smooth interior polyethylene pipe (ADS N-12, orequal). We recommend against usingflexible tubing for footing drain pipes. GEOENGINEER� December6,2021 Pages File No. 24 59-003-00