The Earthquake Engineering Online Archive

Measurement and elimination of membrane compliance effects in undrained triaxial testing

Nicholson, Peter G.; Seed, Raymond B.; Anwar, Husayn

UCB/EERC-89/10, Earthquake Engineering Research Center, University of California, Berkeley, 1989-12, 274 pages (495/N52/1989)

Undrained loading tests are widely used to investigate the susceptibility of soils to liquefaction. Historically, gravelly soils have typically been assumed to be safe from liquefaction failures. However, recent improvements in understanding of the effects of membrane compliance on triaxial test results, along with documentation of a number of field cases in which gravels have liquefied, have led to the realization that such soils can liquefy. As a result, the importance of developing a method to correctly assess the dynamic strength of these coarser soils has become apparent. Previous attempts at mitigating membrane compliance effects during testing, or making post-test corrections to conventional undrained test results, have not been fully successful in providing verifiably correct test results. An improved testing procedure for the elimination of compliance effects during testing, recently developed for conventional scale (2.8-in. diameter) samples of sand, was verified by comparison to results of large-scale (12-in. diameter) tests of similar materials, for which compliance effects were negligible. The technique was then further developed and implemented for large-scale testing of gravelly soils. The compliance mitigation procedure used in these studies involves 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 membrane compliance effects. Monotonic and cyclic load tests were performed on uniformly graded gravel with and without implementation of the computer-controlled compliance mitigation system. These tests are the first performed on gravels for which membrane compliance effects have been completely mitigated. These tests are used to determine the validity and accuracy of theoretical post-test corrections suggested for gravelly soils.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-89-10.pdf (19 MB)