Analysis of the pressuremeter test by FEM formulation of the elasto-plastic consolidation

Abstract

A decade has passed since the development of the self-boring pressuremeter (SBPM). Even though the device has been recognized by the geotechnical engineering profession as having high promise for evaluating in-situ stress-strain behavior of soils, its use is limited. In large part, this is due to the fact that there are important unanswered questions about the SBPM test. One of the major issues concerns the influence of drainage in the soil as it is sheared. In clays, the test is assumed to be undrained, but there is no way to control this other than by the rate of loading and no method has been put forth heretofore to define the required rate.

This dissertation addresses the drainage issue by applying a numerical model capable of simulating the pressuremeter test under variety of conditions. To develop parameters for the soil model, a comprehensive laboratory testing effort was needed. The validity of the numerical model and the soil parameters is established by comparing it to SBPM tests performed in the field.

The numerical model uses the finite element method in a special code capable of handling large strains, consolidation effects, and nonlinear soil behavior. Particular attention is addressed to the issue of pore pressure development and its dissipation. Relative influences of important soil parameters such as the permeability are checked against various rates of loading in the SBPM test. The results demonstrate that drainage likely occurs in most cases using conventional test procedures, and that this, in turn, leads to an error in interpretation of SBPM data. Based on the findings in the analyses, a procedure is proposed which should lead to a more rational method of performing the SBPM test where nearly undrained conditions are desired.