YANG Yu-hao, YE Tang-jin, HE Jia-lin, ZHOU Xiao-peng, LIU Li
This study investigates the seismic instability mechanisms of colluvial slopes along National Highway G318 in southeastern Tibet using the particle flow code (PFC). A generalized geological model was constructed based on the geological conditions of the study area, incorporating seismic wave data from the MW6.9 Nyingchi earthquake. The dynamic response characteristics, including unbalanced forces, velocity, displacement, and microstructural evolution, were systematically analyzed. Results demonstrate that during the initial seismic phase, unbalanced forces of surface particles transmitted through deep layers induced acceleration amplification, with peak surface particle velocities reaching 5 m/s. In the peak seismic phase, resonance between ground motion and particle natural frequencies led to the formation of accumulation mounds at the mid-slope and crest, where maximum displacement increments occurred. During the post-seismic phase, gravitational stress redistribution maintained mid-slope particle velocities at 0.5 m/s, while increased porosity weakened interparticle interlocking, resulting in continuous displacement growth at the crest and mid-slope. Accumulation mound particles migrated toward the slope toe, forming gentle colluvial deposits. The instability mechanism of colluvial slopes under seismic action manifests as downslope sliding triggered by contact force imbalance, accumulation mound formation dominated by resonance effects, and displacement progression driven by gravitational potential energy. These findings reveal the dynamic response mechanisms of colluvial slope instability under earthquakes, providing theoretical support for hazard prevention of similar slopes.
