Second-order work, kinetic energy and diffuse failure in granular materials

Failure in soils and the yielding mechanisms involved are essential to many civil engineering issues such as slope stability. Sudden collapse affecting slopes can be observed after rainfalls, sometimes leading to the devastating flow of a soil-water mixture. Although the notion of failure in soils was long described as a perfect plastic limit, the scientific community now recognizes that failure can occur well before the Mohr-Coulomb criterion is met. This paper considers the collapse of granular soils in relation to a sudden burst of kinetic energy. First, a correlation between the bursts of kinetic energy (leading to sudden avalanches) and the vanishing of the second-order work is clearly obtained from discrete element simulations. Then the link between the vanishing of the second-order work and the increase in kinetic energy is established from a theoretical approach. Finally, these results are confirmed based on laboratory experimental tests where the sudden collapse of soil specimens was obtained.