Pseudo anisotropy induced by membrane compliance in cemented granular soils

The pore pressure response of elastic stiff materials during undrained loading is a function of the volumetric stiffness of the skeleton and stiffness anisotropy. This paper presents experimental results examining the influence of these factors on the pore pressure response in conventional triaxial tests. In order to explore fully the undrained behaviour, the total stress path (TSP) was rotated to cover 180 degrees in the triaxial plane. It was found that a unique linear relationship exists between the pore pressure coefficient (Delta u/Delta q) and the direction of the TSP (Delta p/Delta q) with a slope equivalent to the Skempton pore pressure parameter (B), which may be below unity for stiff materials. The intercept of this linear relationship reflects the effect of the material's anisotropy. It has been demonstrated that a pseudo anisotropy of repeatable and consistent nature was induced by membrane compliance in granular cemented soils. The results have shown that, unless eliminated or taken into account, the membrane compliance may lead to erroneous interpretation of pore pressure response. The paper discusses the implications of this finding.