YIELDING OF LOOSE SAND IN THREE-DIMENSIONAL STRESS CONDITIONS

ABSTRACT Two series of drained and undrained cyclic tests were performed statically on cubic specimens of loose saturated sand, using a true triaxial test apparatus. Changes in three principal stresses were programmed so that they could twice produce two load cycles, each having different directions on the octahedral plane in three principal stress space. The first load cycle was always executed in the direction corresponding to the conventional triaxial compression. The second load cycle was executed in the direction different plane, from that of the first loading. The third and fourth load cycles were carried out in the same directions as the first and the second load cycles, respectively, but with an increased amplitude. Analysis of the drained test results showed that both volumetric and octahedral shear strains produced in the second loading tend to increase as the direction of the second loading deviates from that of the first load cycle. Similar results were also obtained for the pore water pressure and octahedral shear strain behavior in the undrained tests. It was then concluded that the effect of previous load history tends to taper off as the direction of the current loading swerves from that of the previous loading, and when the current loading takes a direction exactly opposite to that of the previous loading, its memory almost completely disappears and the sand behaves as if it were in a virgin state.