10-26-1994 Council Agenda - Laserfiche WebLink

Home Browse Search

pale Six ILr•;cment WaIIs. Estimated Lateral Earth Pressures and water Control hue to the presence of slow- draining clay soils at and above preferred slab grade at the site. we recommend basement walls be waterproofed and an exterior drain tile system he installed around basement areas. The backfill above the drain tile should he constructed so infiltrating water can freely pass through the drain tile. This could be accomplished using free - draining sand backfill. The drain tile should also be provided with a means of discharge to remove the collected water. The top of the backfill trench should be capped with a layer of less permeable (i.e.. clay) toil sloping away from the building to minimize surface water intrusion into the backfill. The attached sketch indicates the features of one such exterior drain tile system. The basement walls should be structurally designed to withstand lateral pressures exerted by the backfill soils. We caution that cohesive (clay) soils will exert a much higher lateral loading than granular (sand) soils. This pressure is greatly magnified when water is allowed to build up within the backfill. In a drained condition. we estimate sands having 100 or less material passing the 4200 sieve would exert an at -rest equivalent fluid pressure of about 45 pounds per cubic foot on the walls. Clays. especially when saturated. can exert up to 120 pounds per cubic foot in the drained condition. CONSTRUCTION CONSIDERA'T'IONS We wish to point. out that the naturally deposited brown sandy lean clays are susceptible to disturbance when subjected to construction traffic. especially when wet. In the event that disturbance of the naturally deposited soils does occur during excavation. it will be necessary to extend the excavation deeper to expose competent undisturbed soils. The earthwork equipment used for placing and compacting engineered fill should he carefully matched to the site conditions at the time the work is heing performed. The engineered fill should he placed in lifts thin enough so that the entire thickness of each lift can he compacted with the type of equipment heing used. For proper compaction. clay soils being used as fill should be compacted within about 3% of the optimum moisture content value at the time the material is placed. Winter time construction. particularly the earthwork, should he dome with particular care. We are attaching an information sheet which discusses cold weather earthwork. Page 53