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• rock bucket augers, downhole hammers or other methods. The drilled pier contractor <br />should be prepared to penetrate the sandstone erratics. <br />(11) Care should be taken that the drilled piers are not oversized at the top. Mushroomed <br />drilled pier tops can reduce the effective dead load pressure on drilled piers. <br />(12) Concrete should be placed in drilled piers the same day they are drilled. The clays are <br />expected to weather and slake in a matter of hours from exposure to atmospheric <br />conditions. Failure to place concrete the day of drilling will normally result in a <br />requirement for additional penetration. <br />(13) A representative of the geotechnical engineer should observe installation of the drilled <br />piers to check that the appropriate bearing stratum is being penetrated and to monitor <br />other pier construction procedures. <br />General Spread Footing Criteria: The design and construction criteria presented below should <br />be observed for a spread footing foundation system. The construction details should be <br />considered when preparing project documents. <br />(1) Footings supported on native very stiff to hard clays or similar new fill compacted as <br />outlined previously, should be designed for an allowable soil bearing pressure of 4,000 <br />psf, and a minimum dead load pressure of 800 psf, or higher, if possible. These criteria <br />assume that total and differential settlements of about 1-inch are acceptable. <br />(2) Spread footings should have a minimum width of 12 inches for continuous footings and <br />of 16 inches for isolated pads. <br />(3) Exterior footings and footings beneath unheated areas should be placed at least 36 inches <br />below grade for frost protection. <br />1• <br />23 <br />