Lim . iting stress states in granular avalanches

The SavageHutter theory fo r granula r avalanches assumes that the g ranula r materia l is in either of two limiting stress sta tes, depending on whether the motion is convergent o r di ve rgent. At transitions be tween conve rgent and dive rgent regions, aj ump in stress occurs, which necessarily implies that there is a jump in the avalanche velocity and /or its thickness. In this paper, a regularization scheme is used, which smoothly switches from one stress sta te to the other, a nd avoids the genera tion of such singula r surfaces. The resulting algorithm is more stable than previous numerical methods but shocks can still occur during rapid convergence in the run-out zone. Results a re presented from two-dimensional calcula tions on complex geometry which illustrate that some necking features obse rved in laboratory experiments can be explained by the regularized SavageHutter model.