CONTINUUM SIMULATION OF FLOW FAILURES

Dynamic aspects of several catastrophic slope failures have been evaluated by unsteady flow modelling, assuming two-dimensional (or quasi-three-dimensional) transient flow of an incompressible biviscous fluid with a free surface. Model parameters comprise two viscosity coefficients and a yield stress term, and qualitatively approximate the Bingham rheology. Equivalent Newtonian fluid modelling was also performed. Parameters were adjusted by trial and error to match observed runout, but additional constraints include estimates of velocity, emplacement time and distribution of debris facies. Where abundantly constrained, as at Ontake, Japan, hindcast analysis indicates that substantial changes in rheology occur as a function of displacement. Thus, constant-property models tend to overestimate the peak velocities and to underestimate the emplacement times. Calibrated model strengths and viscosities were obtained from the hindcast analyses of several slides, and the resulting database enables the modelling approach to be used in the mitigation of problems involving hazardous slopes or landslide dams. At sites where significant lateral spreading is expected to occur, three-dimensional modifications to modelling and to parameter selection may be required.