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Pressuremeter tests in sand : effects of dilation Eldridge, Terry Lewis


An analysis of the response of sand to the pressuremeter is presented. An incremental linear elastic finite element program incorporating shear-volume coupling was modified such that it could efficiently handle axisymmetric plane strain stress-deformation problems. The shear-volume model was modified so that it gave a reasonable approximation to triaxial test data. A modified form of Rowe's stress dilatancy theory was used in the shear-volume coupling model. The finite element program was used to analyze the pressuremeter test conditions. The distribution of displacements, strains and stresses around the pressuremeter were determined for soils with various volumetric responses to shear. Upon full mobilization of the soils strength, volume change characteristics have no effect on the stress distribution in the failed zone. The distribution of strain does depend upon the volume change characteristics, but beyond about three cylinder radii, such effects are small. The assumed shape of the soil stress-strain relation significantly affects the computed response to pressuremeter type loading. An elastic-plastic material is much stiffer than a non-linear elastic material with the same initial modulus and strength. Dilation stiffens a material's response, but even a highly dilatant material is less stiff than an elastic-plastic material. The method of determining the friction angle and dilation angle of frictional materials from pressuremeter data proposed by Hughes, Wroth and Windle was checked in the analysis. The method gives results in good agreement with the finite element results. A method of determining the initial shear modulus and the insitu horizontal soil stress is presented. This method gives good agreement with the finite element results. When applied to actual pressuremeter test data, the shear moduli determined by this method were in better agreement with the rebound moduli than with the moduli determined from the initial portion of the pressure-expansion curve.

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