2109 MCDOUGALL AVE 2018-01-02 MF Import

Geotechnical Engineering Evm ation 2109 McDougall Ave, Everett -Cobb February 14, 2007 RMI File No. 34206 Page 4 Slabs -On -Grade Afler removal of loose soil, the subgrade should be compacted to a dense, non -yielding condition. We recommend that all floor slabs be underlain by at least G inches of free -draining sand or gravel for use as a capillary break. A suitable vapor ban ier, such as heavy plastic sheeting (10-mil minimum should be considered), should be placed over the sand or gravel. A 4-inch-thick crushed rock blanket may be used to cover the vapor barrier to protect it. The capillary break should be designed to drain into the foundation drain system. Lateral Pressures on Subsurface and Retaining Walls The lateral pressure acting on subsurface and ret wining walls is dependent on the nature and density of the soil behind the will, the amount of lateral wall movement which can occur as backfill is placed, wall drainage conditions, and the inclination of the backfill. For walls that are free to yield at the top at least one thousandth of the height of the wall (active condition), soil pressures will be less than if movement is limited by such factors as wall stiffness or bracing (at -rest condition). We recommend that walls supporting horizontal backfill and not subjected to hydrostatic forces be designed using a triangular earth pressure distribution equivalent to that exerted by a fluid with a density of 35 pcf for yielding (active condition) walls, and 60 pcf for non -yielding (at -rest condition) walls. These recommended lateral earth pressures are based on the assumption of a horizontal ground surface adjacent to the wall for a distance of at least the subsurface height of the wall, and do not account for surcharges. Additional lateral earth pressures should be considered for surcharge loads acting adjacent to the subsurface walls and within a distance equal to the subsurface height ol'the wall. This woulu include the effects of surcharges such as traffic loads, floor slab loads, slopes, or other surface loads. Surcharge effects should be considered if appropriate. The lateral pressures on walls may be resisted by friction between the foundation and subgrade soil, and by passive resistance acting on the below -grade portion of the foundation. Recommendations for frictional and passive resistance to lateral loads are presented in the Foundations subsection of this report. All wall backfill should be well compacted. Care should be taken to prevent the buildup of excess lateral soil pressures, due to overcompaction of the wall backfill. This can be accomplished by placing wall backfill in 8-inch thick loose lifts and compacting it with small hand -operated compactors within a distance behind the wall equal to at least one-half the height of the wall. RMI ASSOCIATES LLC 0�4