Laserfiche WebLink
M, <br /> [r atmospheric). The pore pressure acting at the filter location is measured by the <br /> transducer and transmitted to a computerized data acquisition system. <br /> P <br /> Pore pressure measurements can also be rsiade as a function of time,while the piezocore is <br /> kept statiolary at a selected depth. This is referred to as a dissipation test. The <br /> purooso of a dissipation test is to measure the rate of dissipaVon of the ,excess" pare <br /> Pressure and to determine the hydrostatic (in situ) pore pressure within a formation. <br /> Excess pore pressure is generated due to the disturbance caused by the movement of the <br /> piezocone through :he}soil. Once the penetration is stopped, the excess pore pressure <br /> that has built up around the probe will dissipate, eventually stabilizing at the in situ <br /> or hydrostatic pore pressure. In layered sails, the r re pressure sometimes increases <br /> before descending to the equilibrium in situ level due to differences in {excess pore <br /> pressure dissipation rates in tha .different layers. The data obtained from pore pressure <br /> dissipation tests enables determination of the positions of piezometric sur ices in the <br /> soil profile. <br /> 2.1.3 Probe Geometry <br /> Electric friction cones are typically available in two sizes, as follows; <br /> w, <br /> Original Version Modified Version <br /> Cross-Sectional Area 10 cm2 (1.6 in� 15 cm <br /> (2.3 int) <br /> .* Disrrsater 3.6 cm (1.4 in) 4.4 cm (1.7 in) <br /> Friction Siseve Area 150 cm2(23 int) 200 cm2(31 int) <br /> Cone Apex Angle 60 degrees 60 degrees <br /> i <br /> The measured cone tip and friction sleeve loads are automatically divided by tha <br /> cross-sectional probe area and sleeve surface area, respectively, to obtain CPT <br /> measurements in pressure units (i.e. tonslft�. Once converted to these units, oo <br /> apparent difference exists in the cone tip and sleeve friction measurements between the <br /> two probes. This lack of size effects has been verified by researchers <br /> using <br /> a , <br /> large-diameter calibration chamber. <br /> For this investigation, the modified (larger) version of the electric friction cone was <br /> used. This version has the advantage of being able to accomodate higher capacity load <br /> C <br /> ells. Use of the smaller probe,which has the same diameter as the push pipes, requires <br /> 4 <br /> t <br />