Study on Toppling Failure Back Analysis using Spatial-Temporal Approach in Open Pit Coal Mine Lowwall Area

Abstract Toppling failure is a structurally complex and operationally disruptive mode of slope instability, particularly critical in open-pit mining settings where steep, jointed rock masses are exposed. In this study, a prominent toppling failure event along the lowwall of an active pit slope caused significant excavation delays and raised concerns over geotechnical safety. Conventional site investigations in the affected area were hindered by ongoing slope deformations, prompting the adoption of a remote-sensing-based alternative. To address these constraints, a spatial–temporal back-analysis framework was developed using terrestrial laser scanning (TLS) data acquired before and after the failure. High-resolution post-failure terrain models were aligned with pre-failure topography obtained from conventional surveys and photogrammetry referenced by ground control points (GCPs). The comparison of these datasets revealed distinct lateral and rotational displacements, consistent with progressive block movement and detachment along steeply dipping discontinuities. These topographic changes served as empirical indicators for delineating the potential detachment surface, which then formed the basis for numerical back analysis. A probabilistic approach was employed to iteratively calibrate the shear strength parameters until a failure-consistent condition was achieved. The analysis demonstrated that toppling failures in weak, layered rock masses are predominantly governed by frictional resistance along discontinuities rather than by cohesive bonding. Importantly, this study highlights the critical role of accurately identifying the potential detachment zone as a precursor to reliable back analysis. The integration of TLS-based deformation monitoring with probabilistic parameter evaluation enhances the spatial realism, safety, and reliability of slope failure assessment in complex geotechnical environments.