End Restraint Effects on Undrained Static Triaxial Strength of Sand

Although many studies have been made on the effect of end restraint in triaxial testing of soils, no data were available pertaining to static undrained tests on saturated sands. Therefore, a series of tests were conducted using triaxial specimens with regular and frictionless ends. The results showed that for a medium dense sand there was a significant (up to 20%) increase in static undrained strength with frictionless ends as compared with tests using regular ends. The effect is significantly greater than observed for other studies pertaining to drained tests on sands and undrained tests on clays. The strong effect in this case was shown to be related to the difference in volume change/pore pressure change tendencies between tests with regular and frictionless ends as measured by the critical confining pressure. The study was undertaken as a prelude to a similar companion study on the influence of end restraint in undrained cyclic tests on saturated sand.