Drained Strength Characteristics of Sands

Drained triaxial compression tests with volume change measurements were performed on samples of two sands at confining pressures up to 140 kg per sq cm to clarify the components contributing to the shearing strength and to determine the strength characteristics under essentially constant volume conditions. Three components of shearing strength were identified as follows: sliding friction, which was almost independent of confining pressure; dilation, which was significant for dense sand at low pressures but decreased and made a negative contribution at high pressures; and particle crushing and rearranging, which increased from an insignificant value at low pressures to make a substantial contribution to the overall shearing resistence at high pressures. Because undrained tests in which cavitation does not occur are similar in many ways to constant volume drained tests, the study was extended to determine the envelope of failure when shear deformation occurs at essentially constant volume by testing at the appropriate critical confining pressure corresponding to that density. The constant volume envelope of failure determined by such tests was shown to be in reasonably good agreement with that obtained for drained tests if dilatancy effects are deducted using the Taylor-Bishop or Rowe dilatancy formulas.