Agenda - Council - 09/14/2021 - Laserfiche WebLink

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4.4 Dewatering Groundwater was encountered in the soil borings at depths of about 71/2 to 19 1/2 feet below the ground surface. We generally do not anticipate that groundwater will be encountered during grading operations but could be encountered during utility installations and dewatering could be required. Where dewatering is required, we recommend the groundwater level be temporarily lowered to a minimum of 2 feet below the lowest anticipated excavation elevation to allow for construction. In sand soils we do not recommend attempting to dewater from within the excavation. Upward seepage will loosen and disturb the excavation, resulting in a "quick condition". Rather, we recommend groundwater be drawn down below the anticipated excavation bottom. It may be appropriate to consult a dewatering contractor to review the soil boring logs and develop a dewatering plan and evaluate the impact of dewatering on adjacent structures. 4.5 Interior Slabs The anticipated floor subgrade will consist of compacted engineered fill (sand fill) or sandy alluvial soils. It is our opinion a modulus of subgrade reaction, k, of 150 pounds per square inch per inch (psi/inch) of deflection may be used to design the floor. If floor coverings or coatings less permeable than the concrete slab will be used, we recommend that a vapor retarder or vapor barrier be placed immediately beneath the slab. Some contractors prefer to bury the vapor barrier or vapor retarder beneath a layer of sand to reduce curling and shrinkage, but this practice often traps water between the slab and vapor retarder or barrier. Regardless of where the vapor retarder or vapor barrier is placed, we recommend consulting the floor covering manufacturer regarding the appropriate type, use and installation of the vapor retarder or vapor barrier to preserve the warranty. We recommend following all state and local building codes with regards to a radon mitigation plan beneath interior slabs. 4.6 Below Grade Walls We recommend general waterproofing of the below grade walls. We recommend either placing drainage composite against the backs of the exterior walls or backfilling adjacent to the walls with sand having less than 50 percent of the particles by weight passing the #40 sieve and less than 5 percent of the particles by weight passing the #200 sieve. The sand backfill should be placed within 2 feet horizontally of the wall. We recommend the balance of the backfill for the walls consist of sand however the sand may contain up to 20 percent of the particles by weight passing the #200 sieve. We recommend installing drain tile behind the below grade walls, adjacent to the wall footing and below the slab elevation. Preferably the drain tile should consist of perforated pipe embedded in gravel. A geotextile filter fabric should encase the pipe and gravel. The drain tile should be routed to a storm sewer, sump pump or other suitable disposal site. 9