1010 N BROADWAY EVCC 2018-01-01 MF Import

PROPOSED LIBERTY HALL,EVERETT COMMUNITY COLLEGE Everett,Washington be needed below the subbase layer and localized additional overexcavation of soft areas may be needed during construction. Design Parameters The capillary break gravel layer below slabs-on-grade should consist of 6 inches of clean crushed gravel with a maximum particle size of 11/2 inches and negligible sand or silt overlying the subbase layer. For slabs designed as a beam on an elastic foundation, a modulus of subgrade reaction of 50 pci may be used for subgrade soils prepared as recommended above. If water vapor migration through the slabs is objectionable, the gravel should be covered with a heavy plastic sheet, such as 10-mil plastic sheeting, to act as a vapor retarder. This will be desirable where the slabs 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. Undersiab Drainage Perched groundwater in the majority of the borings was observed up to 3 feet below the ground surface. Groundwater could accumulate below the slab-on-grade floor depending on the finished floor elevation. To help mitigate potential build-up of groundwater below the slabs,we recommend that the concrete slabs-on-grade be provided with under drainage to collect and discharge potential groundwater from below the slab. This can be accomplished by installing a 4-inch diameter, heavy wall perforated collector pipe in a shallow trench placed below the capillary break gravel layer. The trench should measure about 1 foot wide by 1.5 feet deep and should be backfilled with clean 3/8-inch pea gravel. We recommend installing a single underdrain collector pipe in an east-west direction below the slab along approximately gridline C and C' and connect each end of the drain pipe into the perimeter footing drain pipe or into the existing subsurface drain pipe. The condition of the existing subsurface drain pipe should be evaluated to make sure it is not damage and is free of debris and functioning properly. If connected to the footing drain system, the invert of the underdrain pipeshould be higher than the invert of the footing drain pipe where they connect. The collector pipe should be sloped to drain and discharge into the storm water collection system to convey the water off site. The pipe should also incorporate cleanouts,if possible. The cleanouts could be extended through the foundation walls to be accessible from the outside,or could be placed in flush-mounted access boxes cast into the floor slabs. Below-Grade Walls and Retaining Walls The following recommendations should be used for the 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. GEOENGINEERSI; June 10,2010 Page 17 File No.5836-010-00