1001 N BROADWAY 2020 EVCC 2025-10-03

4.4.2.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 slab. For slabs designed as a beam on an elastic foundation, a modulus of subgrade reaction of 100 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 till and will require evaluation during construction. If water vapor migration through the slabs is objectionable, the capillary break gravel layer should be covered with heavy plastic sheeting at least 10-mil thick to act as a vapor retarder. This will be desirable where the slabs are in occupied spaces or will be surfaced with tile or will be carpeted. It may also be prudent to apply a sealer to the slab to further retard the migration of moisture through the floor. The contractor should be made responsible for maintaining the integrity of the vapor barrier during construction.Additional water proofing measures that may be needed should be evaluated during design. 4.8. Below-Grade Walls and Retaining Walls We understand that below-grade retaining walls may not be needed for the project; however, if needed, the following recommendations should be used in design of below-grade walls that are intended to act as retaining walls and for other retaining structures that are used to achieve grade changes. 4.5.1.Design Parameters Lateral earth pressures for design of below-grade walls and retaining structures should be evaluated using an equivalent fluid density of 35 pcf provided that the walls will not be restrained against rotation when backfill is placed. If the walls will,be restrained froth rotation,we "recommend using an equivalent fluid density of 55 pcf. Walls are assumed to be restrained if top movement during backfilling is less than H/1000, where H is the wail height. These lateral soil pressures assume that the ground surface behind the wall is horizontal. For unrestrained`walls with backfill sloping up at 2H:1V, the design lateral earth pressure should be increased to 55 pcf, while restrained`walls with a 2H:1V sloping backfill should be designed using an equivalent fluid density of 75 pcf.These lateral soil pressures do not include the effects of surcharges such as floor loads, traffic loads or other surface loading. Surcharge effects should be included as appropriate. Below-grade walls for buildings should also include seismic earth pressures. Seismic earth pressures should be determined using a rectangular distribution of 8H in psf, where H is the wall height. If vehicles can approach the tops of exterior walls to within half the height of the wall, a traffic surcharge should be added to the wall pressure. For car parking areas,the traffic surcharge can be approximated by the equivalent weight of an additional 1 foot of soil backfill (125 psf) behind the wall. For delivery truck parking areas and access driveway areas, the traffic surcharge can be approximated by the equivalent weight of an additional 2 feet (250 psf) of soil backfill behind the wall. Other surcharge loads, such as from foundations, construction equipment, or construction staging areas, should be considered on a case-by-case basis. Positive drainage should be provided behind below-grade walls and retaining structures as discussed below. GEOENGINEER� Ju1,22,2 Pa efi FileeNo.Sao.5E?,B-i:l 1-00