Rapid and Slow Unlocking-Induced Startup Mechanisms of Locked Segment-Dominated Landslides

Locked segment-dominated landslides initiate when locked segments are sufficiently damaged to be unlocked. The evolution of such slopes toward instability displays either an exponentially or stepwise accelerated displacement pattern, but the underlying mechanisms of these patterns are elusive. We show that the displacement pattern is governed by mechanical synergy (resistance homogenization) between the ruptured locked segment and the transfixion segment. Using a mechanical model, we demonstrate that rapid and slow resistance homogenizations, which depend mainly on the brittleness of locked segments, cause two unlocking-induced startup mechanisms that lead to loss of slope stability: one occurring at the peak-stress points and the other at the residual-strength points of the locked segments. Accordingly, the evolution toward instability exhibits one of the two abovementioned patterns. External factors, such as rainwater, can deteriorate the strength of geomaterials but hardly alter the inherent mechanical rules that a locked segment adheres to. These findings provide insights into the mechanism of locked segment-dominated landslides and pave the way for reliably predicting their occurrence.