Experimental analysis and theoretical interpretation of triaxial loadcontrolled loose sand specimen collapses

A series of triaxial load-controlled tests is performed. Finite load increments are imposed. The single load-steps are followed by a time period during which the axial load is kept constant. At low stress levels the mechanical response is stable and characterized by a continuous decrease in strain rate with time. At higher stress levels, the mechanical response changes and, subsequently, the collapse takes place. The collapse is unexpected and occurs at a stress level less than that associated with the steady state, experimentally observed by performing strain triaxial controlled tests. In order to interpret such a behaviour, a theoretical discussion is introduced. This is based on a dynamical reinterpretation of the micromechanical fabric rearrangement of granular assembly. In particular, the role played by the kinetic energy of the system, as well as that played by the anisotropy of the microstructure, have been analysed