Study on instability evolution mechanism of intermediate bridge retaining slope

Abstract Excavation is one of the key factors inducing slope instability in open-pit mines, particularly for intermediate bridge-supported slopes subjected to dual excavation disturbances. Improper handling of such conditions may lead to large-scale landslides. Therefore, it is essential to investigate the instability evolution mechanism of intermediate bridge-supported slopes under dual excavation conditions. In this study, the southern slope of the Zhahanaoer Open-Pit Coal Mine was selected as the research area, and a physical model of the intermediate bridge-supported slope capable of simulating eight excavation stages was constructed. Field monitoring was conducted using non-reflective cameras, earth pressure sensors, and a distributed optical fiber system to analyze the evolution characteristics of cracks, surface deformation, internal strain, and stress in the slope model during excavation. The reliability of the physical model tests was validated by comparing the results with field landslide cases using numerical simulation techniques. The results indicate that internal strain precedes surface displacement in predicting or inferring slope instability and can serve as an early warning indicator for landslides. The failure process of the intermediate bridge-supported slope model can be divided into five stages: crack initiation, crack propagation, deformation onset, crack penetration, and local and global instability on both sides of the intermediate bridge. Furthermore, excavation significantly increases the height of the arched failure surface on both sides compared to its span, and the increase in the height-to-span ratio is a critical characteristic of failure surface evolution. These findings provide a prerequisite for related slope stability analyses, intermediate bridge demolition engineering design, and slope remediation projects.