3815 SHORE AVE 2020-05-20 - Laserfiche WebLink

Geologically Hazardous Areas: Geotechnical Letter Kennedy Single Family Residence 3815 Shore Avenue March23 2018 RN File No. 3279-001A Page 9 Slabs-On-Grade Slab-on-grade areas should be prepared as recommended in the Site Preparation and Grading subsection. Slabs should be supported on medium dense or firmer native soils, or on structural fill extending to these soils. Where moisture control is a concern, we recommend that slabs be underlain by 6 inches of pea gravel for use as a capillary break. A suitable vapor barrier, such as heavy plastic sheeting, should be placed over the capillary break. An additional 2-inch-thick damp sand blanket can be used to cover the vapor barrier to protect the membrane and to aid in curing the concrete.This will also help prevent cement paste bleeding down into the capillary break through joints or tears in the vapor barrier.The capillary break material should be connected to the footing drains to provide positive drainage. Drainage We recommend that runoff from impervious surfaces, such as roofs, driveway and access roadways, be collected and routed to an appropriate storm water discharge system that extends down the slope. The finished ground surface should be sloped at a gradient of 5 percent minimum for a distance of at least 10 feet away from the buildings, or to an approved method of diverting water from the foundation, per IBC Section 1804.3, Surface water should be collected by permanent catch basins and drain lines, and be discharged into a storm drain system. We recommend that footing drains be used around all of the structures where moisture control is important. The interruption of the underlying alternating layers of dense sand and stiff silt during excavation of the footings is likely to pond water that could accumulate around footings and in crawlspaces. It is good practice to use footing drains installed at least 1 foot below the planned finished floor slab. Where used, footing drains should consist of 4-inch-diameter, perforated PVC pipe that is surrounded by free-draining material, such as pea gravel. Footing drains should discharge into tightlines leading to an appropriate collection and discharge point. Crawlspaces should be sloped to drain, and a positive connection should be made into the foundation drainage system. For slabs-on-grade, a drainage path should be provided from the capillary break material to the footing drain system. Roof drains should not be connected to wall or footing drains. Where footings are dug down to accommodate a basement, the footing drains will be located at or below the observed groundwater level in our explorations. In this circumstance, we anticipate the footing drains around the structure will function as a cutoff drain for groundwater flow down to the footing drains depth, decreasing flow to the steep slope area and decreasing the landslide and erosion risk relative to existing conditions. CONSTRUCTION OBSERVATION We should be retained to provide observation and consultation services during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, and to provide recommendations for design changes, should the conditions revealed during the work differ from those anticipated. As part of our services, we would also Robinson Noble, Inc.