Pore Pressure Response to Dynamically Installed Penetrometers

Abstract

Potentially, a seabed may be characterized rapidly and economically by using dynamically installed free-falling penetrometers (FFPs). Because of their relatively rapid deployment and recovery, FFPs may be preferred over conventional full-flow or cone penetrometers for characterizing seabeds. However, despite several successful field trials of FFPs, significant uncertainty still exists about the data interpretation, mainly because of the fast nature of the penetration process, during which regions of the soil body close to the penetrometer experience very high strain rates. The consequence of such high strain rates on pore pressure measurement is not well known. Furthermore, the rigorous numerical analysis of the problem is notoriously difficult because it involves large deformations, dynamics, hydrodynamic coupling, highly nonlinear material behavior, rate dependency, and contact mechanics. A finite-element procedure was developed and used in this study to provide a dynamic coupled solution for the penetrometer impact and burial into saturated clay. Subsequently, some mechanisms involved in the generation of excess pore pressures were investigated with specific attention given to the effects of the penetrometer tip geometry and the location of the pore pressure measuring devices. An important numerical challenge in modeling this problem is highlighted in this paper. It concerns the numerical diffusion that can occur because of the remeshing process required in this large deformation, moving boundary problem.