Development of a Laboratory Technique for Correcting Results of Undrained Triaxial Shear Tests on Soils Containing Coarse Particles for Effects of Membrane Compliance

摘要

Undrained loading tests are widely used to assess the susceptibility of soils to liquefaction. Variation, with changes in effective confining stress, of the penetration of the membrane confining stress, of the penetration of the membrane confining a soil sample into the voids between the particles (membrane compliance) invalidates the assumed testing conditions of constant volume without drainage. This can have a serious detrimental impact on the accuracy and validity of such tests, particularly for medium to coarse sands as well as gravels, and no completely reliable procedures currently exist either for mitigation of membrane compliance effects during testing or for post-test correction of the results of conventional undrained tests. The objective of this research program has therefore been to develop and implement improved laboratory testing procedures for elimination of membrane compliance effects during undrained triaxial testing. Mitigation of compliance effects during testing was accomplished by first predetermining the magnitude of volumetric compliance as a function of effective confining stress and soil parameters, and then using computer-controlled injection or removal of water to continuously eliminate (offset) membrane compliance effects during all stages of undrained cyclic or monotonic loading tests.