Dynamic simulation of the motion of fragmenting rock avalanches

A mass-referenced continuum model for dynamic analysis of rapid mass movement (DAN) is verified by laboratory and field data. Increased earth pressure coefficients are used in this model to represent the dispersive pressures caused by fragmentation within a translating rock avalanche. The numerical model demonstrates that increased runout in large rock avalanches can occur with normal friction coefficients if higher than normal internal pressures, such as those believed to be generated by fragmentation, are present. The extent of the Falling Mountain rock-avalanche deposit in New Zealand is reproduced in the model with normal friction and high earth pressure coefficients to represent by analogy the additional internal pressures due to fragmentation. It appears that if internal friction is changed by fragmentation, it is only by a small amount and may increase rather than decrease. To test this, and to move beyond the present analogue model, requires a better understanding of the rheology of fragmenting rock.