Strain Rate Effects in Model Pressuremeter Testing

Abstract

A series of one-eighth-scale strain controlled model pressuremeter tests were performed using an automated flexible wall calibration chamber testing system. Undrained model pressuremeter tests were performed with and without the internal pore-water pressure measuring piezometer needles at radial strain rates ranging from 1 to 8%/min in a controlled laboratory setup in beds of kaolin clay prepared with known stress histories. Reference strength and deformations properties were determined using one-dimensional consolidation, isotropically consolidated undrained compression (CIUC) and K_o consolidated undrained compression (CK_oUC) laboratory tests, and comparisons are made with the interpreted values from the pressuremeter test data. Interpretations of the undrained shear strength, initial shear modulus, shear stress–radial strain variation, limit pressure, and horizontal stress for each net pressuremeter curve were evaluated using various interpretation procedures, using the Marquardt-Levenberg algorithm. Based on the laboratory test data and the analytical interpretations, several conclusions were made regarding the effects of the rate of probe expansion on the deduced shear modulus, undrained shear strength, and limit pressure in the pressuremeter testing of clays.