Permeability Determination from On-the-Fly Piezocone Sounding

Solutions are developed for the steady, partially drained, fluid pressure field that develops around a moving penetrometer. These include rigorous solution for a point volumetric dislocation moving in a saturated elastic soil and an approximate solution for a pseudostatic, finite-volume, penetrometer moving in a nondilatant soil. These solutions provide a consistent framework for viewing the penetration process, and enable the nondimensional sounding indices of normalized tip resistance $Q_t$ , friction factor $F_r$ , and pore pressure ratio $B_q$ , to be straightforwardly linked to important material properties of the soil, most notably that of permeability, via a nondimensional permeability $K_D$ . This factor $K_D$ is inversely proportional to penetration rate, and is directly proportional to both permeability and vertical in situ effective stress. Simple relationships are developed to link these nondimensional sounding metrics, via $K_D$ . Most notably, the resulting simple relationship $K_D=1∕B_q{Q}_t$ enables soil permeability to be determined from peak fluid pressures recorded on-the-fly. Importantly, these parameterizations enable plots of $B_q-Q_t$ , $F_r-Q_t$ , and $B_q-F_r$ to be contoured for $K_D$ , and hence for permeability. These plots define the relative superiority of using $B_q-Q_t$ data pairs over those for $F_r-Q_t$ and $B_q-F_r$ , in defining permeability. Similarly, the feasible range of permeabilities that may be recovered from peak pressure data are defined; permeabilities must be sufficiently high that penetration is not undrained, and sufficiently low that the resulting pressure response is not null (fully drained). These limits are a natural product of the analysis and represent permeabilities in the range ${10}^{-4}–{10}^{-7}\mathrm{m}∕\mathrm{s}$ . The utility of these characterizations is confirmed with data from two locations where cone soundings are correlated with independently estimated permeabilities.