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_, Page 11 - #4220 91-1043 <br /> `" 3.5 Exterior Backfill/Water Control <br /> � , . <br /> We understand a portion of the structure may have a full basement. We recommend <br />`- the construction include the installation of a perimeter drain tile system at footing grade <br /> around this basement area. In addition, we recommend the backfill above the drain tile <br /> , be installed to allow water to freely pass to the drain tile. This could be accomplished <br /> •-� using free-draining sand backfill or drainage mats against the perimeter foundation walls. <br /> The draintile should also be provided with some means of discharge to remove the water <br /> which may collect. The below grade basement walls should be dampproofed. <br /> The basement wall should be structurally designed to withstand the lateral pressures <br /> exerted by the backfill soils. We caution that clayey soils will exert a much higher <br />�. lateral loading than granular soils. This pressure is greatly magnified when water is <br /> allowed to build up within the backfill. In a drained condition, we estimate sands having <br /> 10% or less material passing the #200 sieve and less than 70% passing the #40 sieve <br />_ would exert an at-rest equivalent fluid lateral pressure of about 45 pounds per cubic foot <br /> � on the walls. Clayey fill would exert up to 120 pounds per cubic foot in the at-rest <br />` . <br /> condition. The free-draining sand should occupy a wedge-shaped area extending up from <br />; <br /> the draintile at a 60° with the horizontal. <br />� If a truck dock is to be built as part of the addition, the dock walls should be backfilled <br />? in the same manner as the basement walls, including the sand backfill. This clean sand <br />� • <br />