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Y: <br /> i <br /> y� a friction reducer (an oversized collar) to be welded onto the push pipe above the probe <br /> *: <br /> in order to limit the build-up of pipe-soil friction. With the larger prone, no friction <br /> reducer is needed because the probe diameter is larger than the Push pips diameter, and <br /> thus the probe itself acts as a friction reducer. <br /> 2.1.4 i3dtn Acquisition - l <br /> 3 <br /> The millivolt output signals from the electric friction cors are amplified, converted to <br /> digital data, and translated to appropriate measuremont units by means of an on-board <br /> co;nputerized data acquisition system(DAS). A 12-frit OAS analog-to-digital converter was <br /> cased with a programmable gain amplification capability to enhanco the lower range <br /> measurement sensitivity. A depth encoder,which is mechanically triggered by the downward <br /> movement of the electric friction cone p,obe, sends pulses to the DAS, ins•-acting it to <br /> record the data as a function of the penetrated depth. An automatic depth adjustment is <br /> made to the sleeve friction data to compensate for the vertical offset of approximately 12 i <br /> cm (5 in) between ti,.e cone tip and friction sleeve center. <br /> Cone tip resistances can range from less than 2 tons/ftz in very sett clays to over <br /> 700 tonslftZ in dense granular soils or heavily overconsolidated or cemented <br /> _ materials. Sleeve friction values are usually less than. 10 percent of the cone tip <br /> resistance value. 7o maintain enough measurement accuracy in soft soils, digital <br /> increments of 0.1 tonftt2 in the cone tip resistance measurements were maintained at <br /> the lower end of the measurement range, where sensitivity is most critical. Negative cons <br /> tip and sleeve friction readings, while generally notexpected, are recordable in order to <br /> accurately <br /> monitor ;he zero-load outputs of the electric friction cone probe for quality <br /> control purposes. Piezocone pore pressures can range from about -i tonle to over <br /> 38 tons/e. Pare pressures over 36 tonslft2 (500 psi) can seldom be reliably <br /> measured because of the limited capacity of'he built-in pore pressure transducer. <br /> r i <br />