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REGG Pore Pressure Dissipation Tests (PPDT) <br />Pore Pressure Dissipation Tests (PPDT's) conducted at various intervals measured <br />hydrostatic water pressures and determined the approximate depth of the ground water <br />table. A PPDT is conducted when the cone is halted at specific intervals determined by <br />the field representative. The variation of the penetration pore pressure (u) with time is <br />measured behind the tip of the cone and recorded by a computer system. <br />Pore pressure dissipation data can be interpreted to provide estimates of. <br />• Equilibrium piezornetric pressure <br />• Phreatic Surface <br />• In situ horizontal coefficient of consolidation (c.) <br />• In situ horizontal coefficient of permeability (4) <br />In order to correctly interpret <br />the equilibrium piezometric <br />pressure and/or the phreatic <br />surface, the pore pressure <br />must be monitored until such <br />bme as there is no variation in <br />pore pressure with time, <br />Figure PPDT. This time is <br />commonly referred to as tioo, <br />the point at which 100% of the <br />excess pore pressure has <br />dissipated. <br />U <br />1 1 0-5181 <br />U <br />U <br />mee-edhere <br />U <br />4 -* <br />A complete reference on pore <br />pressure diss,pation tests is <br />presented by Robertson et al. <br />1992. <br />Doole -O.-0 COn.1 0 -//,*0.-- <br />Dwili, -De# b Wa- Table 0 <br />'6Illr - Mid Of Wil= <br />Water Table C alcu-on <br />Dwater = Dcone - Hwater <br />where Hwater - Ue (depel units) <br />A summary of the pore <br />pressure dissipation tests is <br />summarized in Table 1. <br />Useful Conversion Feclors:lp= = 0 704rn = 231 leet (waler) <br />1W = 0.956 bar = 13.9 pei <br />im = 3.25 feet <br />Figure PPOT