A Practical Method for Extrapolating Ambient Pore Pressures from Incomplete Pore Pressure Dissipation Tests Conducted in Fine Grained Soils

Author: Jordan Scheremeta, M.S., E.I.
Conference: Tailings and Mine Waste 2014
Date: October 5-8, 2014

The estimation of ambient pore water pressures in an existing soil stratum for use in developing appropriate pore pressure distributions for input to various geotechnical engineering analyses often presents the engineer with challenges in locations devoid of sufficient piezometer coverage.

One method of obtaining pore pressure data is by utilizing Pore Pressure Dissipation (PPD) testing conducted during cone penetration tests (CPTs). If the CPT advancement is paused for a sufficiently long time, the excess pore pressures generated during probe advancement decay to ambient levels. This stabilization of pore pressures can be exceedingly lengthy in actual practice if the existing stratum consists of a very low permeability soil. Often, PPD tests are terminated prior to the test reaching equilibrium which may result in misleading inputs to subsequent geotechnical analyses if the data is used without appropriate corrections.

Based on equations presented by Mayne (2002) describing the decay of excess pore pressure during a pore pressure dissipation test, a technique for predicting ambient pore pressures from incomplete PPD data has been developed utilizing the solver function in Microsoft ® Excel, and is presented herein.