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A large-scale computer-controlled injection correction system has been developed to continuously and completely mitigate the adverse effects of membrane compliance for undrained testing of coarse soils and rockfill. The magnitude of volumetric compliance was pre-determined as a function of effective confining stress and soil parameters. Computer-controlled injection or removal of water to continuously offset the volumetric errors was then used to eliminate the deleterious effects of membrane compliance throughout the duration of each test.
The measured volumetric compliance errors were evaluated as relationships between effective confining stress and volumetric compliance. A relationship between material grain size and volumetric compliance was expanded with compliance evaluations for a wide range of gravel sizes which supported the use of a “representative” grain size less than the mean grain size as an indicator to estimate expected volumetric compliance for a given soil. Monotonic and cyclic undrained triaxial load tests were performed on uniformly-graded gravels with and without implementation of the computer-controlled compliance mitigation system. The test results support the hypothesis that such soils are much more susceptible to liquefaction than had previously been considered.
membrane compliance, undrained testing, liquefaction, gravels, effective stress, pore pressures
Assistant Professor, University of Hawaii at Manoa, Honolulu, Hawaii
Professor, University of California at Berkeley, Berkeley, California