Abstract
The size effect of the height of granular (sand) test specimens in a triaxial compression test is explained by the bifurcation theory. With reference to the analogy between the imperfection-sensitive bifurcation behavior of shell structures and the experimentally-observed size effect of sand specimens, we present a hypothesis that the influence of initial imperfections for sand specimens decreases inversely proportional to their height. We derive several pertinent power laws for imperfection sensitivity that offer information on bifurcation, and have assessed their validity based on experimental data. Further we propose a method for obtaining the idealistic stress ratio versus strain curve for an infinitely-high specimen by asymptotically extrapolating the experimental curves. This method has successfully simulated and categorized the bifurcation-behavioral characteristics of dense and of loose sand. A caution is exercised that the true material properties would be much stronger than those observed in experiments due to the size effect. It has been demonstrated that the softening of the experimental stress versus strain curves arises from the bifurcation, instead of the softening of the material properties.
