4.4 EAW Attachment - Laserfiche WebLink

Home Browse Search

8 Foundations We recommend the perimeter footings bear a minimum of 42 inches below the exterior grade for frost protection. Interior footings may be placed immediately below the slab provided construction does not occur during below freezing weather conditions. Foundation elements in unheated areas (i.e., deck or porch footings) should bear at least 5 feet below exterior grade for frost protection. We anticipate the foundations and floor slabs will bear on compacted sandy engineered fill or sandy native alluvial soils. With the building pads prepared as recommended, it is our opinion the footings can be designed for a net allowable bearing pressure up to 2,000 pounds per square foot (psf). We anticipate total and differential settlement of the foundations will be less than 1 inch and ½ inch, respectively, across a 30-foot span. 4.4 Dewatering Groundwater was encountered in the soil borings while drilling and sampling at depths of about 12 ½ feet, or deeper, below the ground surface. We generally do not anticipate that groundwater will be encountered during construction and do not anticipate that dewatering will be required. In the event dewatering is required, we recommend the groundwater level be temporary 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. 4.5 Interior Slabs The anticipated floor subgrade will consist of compacted sandy engineered fill or sandy native alluvial soils. It is our opinion a modulus of subgrade reaction, k, of 100 pounds per square inch per inch of deflection (psi) 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.