Indentation of a sharp penetrometer in a poroelastic medium

Abstract

Solution is developed for the build-up, steady and post-arrest dissipative pore fluid pressure fields that develop around a conical penetrometer advanced in a poroelastic medium. The analog with cone penetrometer testing is direct, and is used to enable continuous distributions of permeability and diffusivity to be determined, with depth. Solution for a point normal dislocation migrating in a poroelastic medium is extended to incorporate the influence of a tapered tip. Steady pressures develop relative to the migrating tip geometry with distribution conditioned by the non-dimensional penetration rate, U D , incorporating penetration rate, hydraulic diffusivity and penetrometer radius. The near-spherical pressure distribution, recovered for low penetration velocities, becomes radial as penetration rate increases. Along the penetrometer shaft, non-dimensional induced pore fluid pressures, P D , are independent of penetration rate, U D , and asymptote to an inverse radial distribution remote from the tip as P D = 1\\ x D . This importantly identifies the control on penetration induced pore fluid pressure as the magnitude of permeability, embodied in the non-dimensional pressure, P D , rather than a dependence on hydraulic diffusivity, as had previously been considered. Induced pore pressures are singular in the zone of tip taper for the assumed zero radius of the penetrometer, negating the direct evaluation of permeability magnitudes from pressures recorded on the cone face. However, the finite magnitudes of fluid pressures evaluated on the shaft may be correlated with field data to independently evaluate magnitudes of permeability during steady penetration.