ENERGY-DISSIPATION IN INELASTIC FLOW OF SATURATED COHESIONLESS GRANULAR MEDIA

The results of a study of energy dissipation in cohesionless granular media are presented. The relation between the excess pore water pressure, accumulated in a water-saturated granular mass, and the corresponding external work in undrained cyclic loading is studied experimentally, under displacement-controlled conditions. A micromechanical model of internal energy dissipation due to slip between contacting granules is introduced, and the results are compared with experimental measurements. The specimens are subjected to two sequences of loading with an intermediate reconsolidation to simulate reliquefaction. External work per unit volume is calculated from the experimental results, and its correlation with the excess pore water pressure is examined. In the first loading, a unique non-linear relation exists between the excess pore water pressure and the external work per unit volume which is independent of the shear strain amplitude. In the second loading this relation is a function of strain amplitude. Based on a micromechanical model, it is shown that the internal dissipation per unit volume in cohesionless granular media can be expressed in terms of the time history of the applied effective pressure and a single scalar parameter which depends on the density and strain amplitude. The model is further validated by torsion tests with random variation in the applied strain amplitude, and excellent agreement with the experimental results is obtained.