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s <br /> r, � Mr. Charles Thompson <br /> � Project BL-04-05907 <br /> � October 27, 2004 <br /> Page 7 � <br /> � ' <br /> � <br /> � C.4.c. Bearing Pressure. It is our opinion that footings placed on the natural soils or engineered fill <br /> � may be designed for a net allowable bearing pressure up to 3,000 pounds per square foot(ps fl. <br /> , C.4.d. Settlement. We anticipate total and differenrial settlement of the foundations will be less than <br /> i 1 inch�nd 1/2 inch,respectively under the assumed loads. <br /> � <br /> C.S. Below-Grade Walls <br /> � <br /> � C.S.a. Excavation. It is our opinion that the native and fill soils encountered by the borings can be <br /> � excavated with a backhoe, front-end loader or scraper. The borings indicate that at the anticipated <br /> excavation depths the fill soils and native glacial till or outwash soils in the sidewalls of the excavations <br /> � will be Type C soils and the under Deparhnent of Labor Occupational Safety and Health Administration <br /> � (OSHA) guidelines. <br /> � C.S.b. Exterior Backfill. For below-grade construction,we recommend backfill placed on the exterior <br /> � sides of the foundation walls be compacted to a minimum of 90 percent of its standard Proctor maximum <br /> dry density and within 3 percentage points of its optimum moisture content. An exception is beneath <br /> � steps and slabs where it should be compacted to a minimum of 95 percent. <br /> � Prior to backfill operations, the basement walls should be laterally braced to minimize displacement of <br /> � the basement walls. For the at-grade construction of foundation walls,the backfill should be brought up <br /> � uniformly on both sides of the foundation walls to minimize displacement. <br /> � C.S.c. Lateral Pressures. If granular soils classifying as SP or SP-SM are used as backfill against the <br /> � foundation walls, a lateral equivalent fluid pressure(at-rest condition)of 50 psf per foot of depth should <br /> be used to design the basement walls. For walls that are allowed to rotate at the top, such as retaining <br /> a wall, an active pressure of 35 psf per foot may be used. � <br /> � <br /> If clayey soils are used as backfill against the below-grade foundation walls for the basement, an <br /> � equivalent fluid pressure(at-rest condition) of 75 psf per foot of depth should be used to design the <br /> � basement walls. In addition, a zone of free-draining granular soil at least 2 feet thick should be placed <br /> immediately next to the wall or a drainage mat should be used to allow water trapped in backf`ill soils to <br /> = drain down to a drain tile system located around the perimeter of the building at the top of the foundation <br /> � elevation. <br /> a� <br /> ■ . <br /> ■ <br />