Laserfiche WebLink
EGG <br /> A;W <br /> Pore Pressure Dissipation 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 piezometnc pressure <br /> • Phreatic Surface <br /> • In situ horizontal coefficient of consolidation (ch) <br /> • In situ horizontal coefficient of permability (kh) <br /> In order to correctly interpret the equilibrium piezometric pressure and/or fie <br /> phreatic surface, the pore pressure must be monitored until such time as there is <br /> no variation in pore pressure with time, Figure PPDT This time is commonly <br /> referred to as t1oo, the point at which 100% of the excess pore pressure has <br /> dissipated <br /> A complete reference <br /> on pore pressure w <br /> dissipation tests is in ® t w.• .�...... <br /> presented by CIMLOd r Uhl <br /> Robertson et al 1991 • »NW <br /> U <br /> A summary of the pore a <br /> pressure dissipation = �++Stef ° %, A"M,,�p. <br /> tests is summarized In 4=. <br /> Table 1 Pore pressure "°( ob*—W.� ... <br /> dissipation data is Pore Pressure <br /> °� <br /> presented in graphical measumd here <br /> form in Appendix a� OVw+1oCorm <br /> tW��° ° w... �,....,,.. <br /> PPDT its-r+Mamwamr <br /> Water Table CWcWatfon <br /> Dwate r = D CO <br /> where Hmw=Uq(depth units) <br /> • useful GOrwermon Facbm 1pS)-U 7C4m -2 31 feet (water] <br /> itsf=0 958 Dar=13.9 psi <br /> im =3 26 feet <br /> Figure PPDT <br />