Effects of Membrane Penetration on Modulus and Poisson’s Ratio for Undrained Cyclic Triaxial Conditions

Abstract

The effects of membrane penetration on the cyclic deformation properties for undrained cyclic triaxial tests of granular soils are discussed in this paper. The soils used are six types of sands with different grain size distributions. Test results indicated that the relationship between the shear modulus at small strain obtained from a cyclic torsional test and an undrained cyclic triaxial test, and between the Young’s modulus obtained from the drained and undrained cyclic triaxial tests are dependent on the grain size distribution of the sands. It is assumed that the main reason for this is caused by a decrease of the Poisson’s ratio under undrained cyclic triaxial condition due to the membrane penetration effect. The Poisson’s ratio in undrained cyclic triaxial tests has been estimated from the membrane penetration value and the pore pressure fluctuation under undrained cyclic loading. Consequently, it was determined that the Poisson’s ratio of the soil skeleton in undrained cyclic triaxial tests decreases from 0.5 at small strain, as the grain size increases. In addition, the shear modulus calculated from the estimated Poisson’s ratio and the measured Young’s modulus in undrained cyclic triaxial tests is almost equal to those in cyclic torsional tests irrespective of grain size.