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1 <br /> OqjMMEAG pore PressureDissip ation Tests <br /> (PPDT) <br /> Pore Pressure Dissipation Tests (PPDT's) conducted at various intervals <br />' measured hydrostatic water pressures and determined the approximate depth of <br /> the ground water table A PPDT is conducted when the cone is halted at specific <br /> intervals determined by the field representative The variation of the penetration <br />' pore pressure (u) with time is measured behind the tip of the cone and recorded <br /> by a computer system <br /> Pore pressure dissipation data can be interpreted to provide estimates of <br />' . Equilibrium piezometne pressure <br /> • Phreatic Surface <br />' • In situ horizontal coefficient of consolidation (ch) <br /> e In situ hanzontal coefficient of permability (kh) <br />' In order to correctly interpret the equilibrium piezometric pressure and/or the <br /> phreatic surface, the pore pressure must be monitored until such time as there is <br /> no variation in pore pressure with time (refer to Figure PPD) This time is <br />' commonly referred to as t1oo, the point at which 100% of the excess pore <br /> pressure has dissipated <br />' Interpretation of either c;, and kh from dissipation results can be most easily <br /> achieved using either of two analytical approaches cavity-expansion theory or <br />' the strain-pa}.h approach Comparisons of the available solutions anr4 results <br /> from field studies suggest that the cavity-expansion method of Torstensson <br /> (1977) and the strain math approaches of Levadouts (1980) and Teh (1987) all <br />' provide similar predications of consolidation parameters from GPTU dissipation <br /> o ��.,: _-. -1.9..-.1, Fn arvscn et <br /> alaata (Ni asespiG { Vr .f. t, Lut� � r (1991) <br /> Robertson et at (1991) have shown that these methods, although developed for <br />' normally consolidated soils, can t e equally applied to a oar r o-sohdatedSolis <br /> Furthermore, comparisons' of field and laboratory data i EUECate that the u e�ids ,n <br /> the -n-mas.sr teal t �� <br /> #ar ava 1) and p:e-lica ed (CP i U) cata are cio sins u-,ii pr coir idec <br /> the micro fabric and nature of the soils being tested are taken into consideration <br /> (Danziger 1990, Robertson et a, 1919,41) <br />' A complete reference on pore pressure dissipation tests is presented by <br /> Robertson et al 1991 <br /> • A summary of the pore pressure dissipation tests is sr_rrnrF anzed in Table � <br /> Pore pressure dissipation data is presented in grapnicai form in Appendix PPDT <br /> 1 <br />