A new method for eliminating membrane compliance in cyclic triaxial tests on gravelly soils

A new computer controlled flow pump is developed to continuously mitigate the adverse effects of membrane compliance in conjunction with implementation of image processing for volume change measurement. The flow pump eliminates the membrane compliance by injecting or pumping out the required volume of water into or from the gravelly specimens to compensate for the erroneous volume change associated with the membrane compliance during undrained cyclic triaxial tests. This error is compounded in gravelly soils due to the large size of the grains and voids. In order to measure the volume of the specimen during the isotropic consolidation stage and calibrate the flow pump for cyclic loading, an image processing technique was used for measuring the volume change during the isotropic consolidation stage of loading while calculating membrane compliance associated with the amount of input water from the flow pump into the specimen. The results of image processing show that the increase in density of the specimens leads to an increase in the ratio of volumetric skeletal strains to axial strains and a decrease in the normalized membrane penetration. The study yields promising results for minimizing the errors associated with membrane compliance during undrained cyclic loading on gravels.