From creep to rapid sliding: Back analysis of the vajont landslide with the numerical dda method

The catastrophic Vajont landslide was preceded by a long creeping phase concentrated in a clay basal layer. Recent experimental investigations performed at high velocities under both dry and wet conditions contributed to the understanding of the friction degradation experienced by those clays. Here we analyze the Vajont failure with the numerical DDA method by implem enting two alternative friction degradation models: (1) scale dependent roughness degradation, appropriate to clean and initially rough rock discontinuities, and (2) transition from creep to runout, appropriate to clay-filled discontinuities. Our back-analyzed results expand the range that can be obtained from laboratory rotary shear tests by an order of magnitude with respect to both velocity and shear distance. We found that the upper limit for degradation is μss = 0.16 assuming clean and initially rough basal plane; the lower limit is μss = 0.035 to 0.052 assuming sliding commenced by creeping on wet clays.