Volume 27, Issue 2 (March 2004)
Measurement of Energy and Strength of Sand at Critical State
The energy input during shear deformation of sand is expended by three components: resistance against particle-to-particle frictional deformation, volumetric or nonrecoverable plastic deformation, and elastic deformation of the soil grains. These three components are identified for the shearing deformation of sand in triaxial compression using the energy balance principle. A new experimental technique to measure the elastic energy of sands is proposed. Shear resistance against particle-to-particle frictional deformation is then determined after applying corrections to the measured shear strength for plastic volumetric and elastic deformations. The shear resistance against particle-to-particle frictional deformation is shown to be the critical state strength of sand.
The technique is illustrated with drained triaxial compression tests on Ottawa Sand. It has been found that the shear resistance against particle-to-particle friction deformation or the critical state strength attains a constant value at small strains. The conventional techniques to determine the critical state strength require it to be strained to large strains. At such large strains, it is not possible to achieve the critical state condition uniformly throughout the sample in a laboratory setup. This has led to many problems with the reliable measurement of the shear strength of sands at the critical state and the establishment of the critical state condition. The ability to measure the critical state strength at small strain levels overcomes such difficulties.