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r , Bob Collett JN 10292 November 9, 2010 Page 2 event of future shallow slope movement. These piles can be installed with small equipment or hand-carried jackhammers. We recommend that concrete grade beams be extended in a north-to- south direction between the isolated pile caps and the house's foundation to, in essence, tie back the pile caps. This will lend additional lateral support in the event of soil movement. Grade beams should not extend east-to-west between the pile caps, as this would create more lateral load on the system if soil movement occurs on the slope. On the easternmost portion of the house, the ground surface is relatively flat and is far from the steep slope. If dense glacial till is encountered in the foundation excavations in this area, then conventional footings without pipe piles could be used. These footings could support an allowable bearing capacity of 2,000 pounds per square foot(psf). PIPE PILES Three-diameter pipe piles driven with a 650- or 800- or 1,100-pound hydraulic jackhammer to the following final penetration rates may be assigned an allowable compressive capacity of 6 tons. INSIDE FINAL DRIVING FINAL DRIVING FINAL DRIVING ALLOWABLE PILE RATE RATE RATE COMPRESSIVE DIAMETER (650-pound (800-pound (1,100-pound CAPACITY hammer) hammer) hammer) 3 inches 12 sec/inch 10 sec/inch 6 sec/inch 6 tons Note: The refusal criteria indicated in the above table are valid only for pipe piles that are installed using a hydraulic impact hammer carried on leads that allow the hammer to sit on the top of the pile during driving. If the piles are installed by alternative methods,such as a vibratory hammer or a hammer that is hard-mounted to the installation machine, numerous load tests to 200 percent of the design capacity would be necessary to substantiate the allowable pile load. The appropriate number of load tests would need to be determined at the time the contractor and installation method are chosen. A 2-inch-diameter pipe pile driven with a minimum 90-pound jackhammer or a 140-pound Rhino hammer to a final penetration rate of 1 inch or less for one minute of continuous driving may be assigned an allowable compressive load of 3 tons. Schedule 40 pipe should be used for 3-inch piles, and 2-inch piles should utilize extra-strong steel pipe. The site soils should not be highly corrosive. Considering this, it is our opinion that standard "black" pipe can be used, and corrosion protection, such as galvanizing, is not necessary for the pipe piles. Subsequent pipe sections should be connected together using threaded or slip couplers, or by welding. If slip couplers are used, they must fit snugly into the ends of the pipes. This can require that shims or beads of welding flux be applied to the couplers. Pile caps should be used to transmit loads to the piles, and as recommended in the General section above, the pile caps should be tied back to the house foundation with grade beams. For 3- inch piles, we recommend that each pile cap include a minimum of two piles, with one pile driven vertically and the other installed with a 1:5 (Horizontal:Vertical) batter down toward the north. If 2- inch piles are used, each cap should contain three piles, with one pile driven vertically and the other two battered down toward the north at a 1:5 (Horizontal:Vertical) inclination. GEOTECH CONSULTANTS,INC.