Centrifuge modeling and numerical analysis of reservoir bank landslides triggered by a fast two-step drop in water level

To meet flood control requirements, reservoir water levels undergo a two-step drop process before the rainy season. To examine the relationship between the deformation characteristics of the accumulation body and this water level drop, a large-scale centrifuge modeling study was conducted. The dropping scheme involved a second drop stage rate twice that of the first stage. The macroscopic deformation, pore pressure, and earth pressure change laws during the two-step drop were analyzed. Numerical simulations were also performed to assess the impact of water level rate on deformation and stability. The results showed that during reservoir impoundment, accumulation deformation was minimal. In the 1st drop stage, tensile cracks initially formed at the front edge and rapidly extended, creating a fault zone. As the fault zone collapsed, tensile cracks propagated toward the middle and back of the slope. In the 2nd drop stage, the slope continued to slide along the previously formed fault zone, albeit with reduced intensity. Vertical compaction in the middle and rear sections contributed to stabilizing crack expansion. Pore pressure exhibited hysteresis during reservoir impoundment but gradually weakened in each drop stage. Earth pressure on the leading edge underwent significant changes in each stage, with the highest intensity observed during the first drop stage in the middle and rear sections. The water level drop rate triggering slope instability ranged from 0.7 to 1.5 m/d in the 1st drop stage. Deformation and failure demonstrated a progressive weakening pattern from the front to the rear.