Frictional properties of the rupture surface of a carbonate rock avalanche

To investigate frictional properties of the rupture surface of the carbonate Jiweishan rock avalanche, we con-ducted high-velocity-friction tests on the limestone and shale samples at different shear rates. The samples showed shear-and rate-strengthening of friction at low shear rates, but transformed to shear-and rate-weakening of friction at large shear rates. The critical shear rate was deduced to be between 0.05 and 0.2 m/s in our tests. The friction coefficient reduced to an extremely low value of less than 0.1 at a shear rate of 2.1 m/s. The sliding rock mass therefore could slide out of the rupture surface at a high velocity and consequently traveled a long distance as granular debris. Two mechanisms may have reduced the frictional resistance. Recrystallized calcite nanograins and CaO nanograins produced through calcite decomposition covered and lubricated the shear surface. Furthermore, the CO2 emitted through calcite decomposition reduced the effective normal stress and therefore the friction on the surface. Our conclusions for Jiweishan rock avalanche are also useful for under-standing the high mobility of other widely distributed carbonate rock avalanches.