Automated bidirectional search for key blocks on complex high-steep slopes using spatial loops formed by intersections of discontinuities

Abstract

High-steep rock slopes develop numerous random discontinuities, and the unstable blocks formed by their intersection pose a serious threat to traffic engineering construction. Current methods for identifying these blocks are limited by the complex morphology of the slope surface and often overlook the impact of line-type discontinuities, leading to slow and inaccurate identification processes. To address this, this study presents an innovative method for identifying 3D unstable rock blocks by integrating UAV multi-angle nap-of-the-object photogrammetry with a spatial loop bidirectional search algorithm. The method comprises four steps: 1) Collaborative extraction of line-type and face-type discontinuities from a high-precision 3D model; 2) Rapid determination of discontinuity intersections using an R-tree data structure; 3) Retrieval of closed polygons via a bidirectional search algorithm; 4) Screening of finite blocks using geometric topological constraints. Engineering verification shows that this method successfully identified 120 closed cycles on the slope of the Eastern Himalayan Syntaxis, resulting in 74 finite blocks and 22 unstable blocks. This study introduces a novel point-line-face multi-level progressive search architecture. By coupling the analysis of line-type discontinuities with block spatial combinations, this method addresses a limitation of traditional approaches that inadequately consider the role of line-type discontinuities in block formation. Applicable to any complex structure of high-steep slopes, this method enhances both the accuracy and efficiency of identifying unstable blocks in complex geological settings. Furthermore, by integrating subsequent modules for geometric characterization and mechanical analysis, this method provides a theoretically sound and broadly applicable technical solution for preventing and controlling rockfall disasters on high-steep slopes.