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Mr. Sam Roberto <br />Project BBXX- 01 -119A <br />May 24, 2001 <br />Page 7 <br />D.2.a. Embedment Depth <br />For frost protection, perimeter footings should be embedded at least 42 inches below the lowest <br />exterior grade. Interior footings may be placed directly below floor slabs. Unheated footings <br />associated with canopies, stoops or sidewalks should be embedded at least 60 inches below the <br />lowest exterior grade. <br />D.2.b. Net Allowable Bearing Pressure <br />Spread footings supported on compacted backfill can be sized to exert a net allowable bearing <br />pressure of 2,000 pounds per square foot (psf), including all transient loads. This value includes <br />a safety factor of 3 with regard to bearing capacity failure. <br />D.2.c. Settlement <br />We estimate that total and differential settlements among new footings will be less than 1 inch <br />and % inch, respectively, under the assumed loads. <br />D.3. Basement Walls <br />D.3.a. Drainage Control <br />We recommend installing subdrains behind basement walls, adjacent to the wall footings, below <br />the slab elevation. Preferably the subdrains should consist of perforated pipes embedded in <br />washed gravel, which in turn is wrapped in filter fabric. Perforated pipes encased in a filter <br />"sock" and embedded in washed gravel, however, may also be considered. We recommend <br />routing the subdrains to a sump and pump capable of routing any accumulated groundwater to a <br />storm sewer or other suitable disposal site. <br />General waterproofing of basement walls surrounding occupied or potentially occupied areas is <br />recommended even with the use of free- draining backfill because of the potential cost impacts <br />related to leaks after construction is complete. <br />