Rate Effects in Pressuremeter Tests in Clays

The response of soil loaded in a pressuremeter test is inherently time-dependent; even for an "undrained" test in a clay, some consolidation will occur. The pressuremeter expansion will also be affected by creep of the soil skeleton, and thus both the results and the derived parameters will be influenced by the testing technique adopted. To examine the influence of time, the problem has been examined both experimentally and numerically. Pressuremeter tests have been simulated in the laboratory by expanding cylindrical cavities using different incremental prssure techniques in three types of clay prepared with known stress history, and the results compared with finite-element predictions. The finite-element program is based on critical-state soil mechanics and includes both consolidation and deviatoric creep. This has given a new insight into the behavior of clays during pressurementer tests. The results indicate that any simple standardization of pressureteter test technique should be approached with caution.