Failure Mode and Mechanisms of Gneiss Open-Pit Slopes in Cold Regions—A Case Study of the 14 September 2023 Landslide at the Jinbao Mine in Xinjiang, China

Extensive high and steep open-pit slopes in gneiss are distributed in cold regions at high altitudes or high latitudes of China, such as Qinghai, Tibet, and Xinjiang, posing significant hazards to mine safety. Several recent slope failure incidents highlight the urgent need to study the failure modes and mechanisms of gneiss open-pit slopes in these cold regions. This study focuses on the 14 September 2023 landslide at the Jinbao Mine in Xinjiang. Initially, field investigation and displacement monitoring were employed to analyze its failure characteristics and mode. Subsequently, utilizing mechanical parameters of the gneissic foliation and the rock mass obtained under various conditions, discrete element numerical modeling was conducted to study the failure mechanisms. The results indicate that the landslide was a typical bedding failure characterized by an upper bedding-controlled sliding zone, combined with buckling and crushing of the slope toe. Under the long-term combined effects of rainfall, freeze–thaw cycles and blasting, the shear strength of the gneissic foliation decreased. This reduction led to a decrease in the anti-sliding force and an increase in the sliding force within the upper bedding-controlled sliding zone. Consequently, the load transferred to the rock mass at the slope toe progressively increased. Under prolonged compression, the toe rock mass experienced bending, which intensified over time. Coupled with the strength reduction caused by the repeated action of rainfall, freeze–thaw cycles and blasting, the toe rock mass gradually fractured and ultimately failed in a buckling mode. This led to the loss of support for the upper mass, which then subsided along the foliation, precipitating the landslide’s overall instability.