UNDRAINED MONOTONIC AND CYCLIC SHEAR LOW AND HIGH CONFINING BEHAVIOUR OF SAND UNDER STRESSES

MASAYUKI HYODO, ADRIAN F. L. HYDE, NORITAKA ARAMAKI and YuKIo NAKATA

ABSTRACT: Monotonic and cyclic loading tests have been carried out on a silica sand over a wide range of stresses in order to compare non-crushing and crushing behaviour. Samples were sieved at several stages of testing to theoretically deter-mine the increase in particle surface area and hence degree of crushing. Undrained shear behaviour was compared for crushing and non-crushing regions above 3 MPa. Samples consolidated to 0.1 MPa demonstrated strong dilative behaviour, while above the yield stress of 3 MPa dilation was suppressed and considerable particle crushing occurred. Shearing caused a marked increase in particle crushing particularly after the phase transformation point. Crushing at the steady state was similar for isotropic and anisotropically consolidated sands. At high confining pressures the cyclic strength curves were similar to those for loose sands except for confining pressure dependency due to particle crushing. For low confining stresses cyclic strength increased with initial stress ratio, while for high confining stresses it decreased with initial shear stress ratio. In the cyclic tests there was no significant crushing for 0.1 MPa. Crushing was seen to in-crease rapidly after the phase transformation point, where high strains developed and where particle rotation and translation contributed to the crushing process.

Key words: compression, cyclic shear, high confining pressure, liquefaction, monotonic shear, particle breakage, sand, triaxial test, undrained (IGC: D6/D7)