Deformation Failure Mechanism and Motion Laws of Near-horizontal Thick-layer with Thin-layer Columnar Dangerous Rock Mass in the Chishui Red Bed Area

Abstract

The collapse of dangerous rock masses, either due to natural causes (such as weathering by rain) or anthropogenic factors (such as engineering construction in the rock area), poses a threat to both life and property. Therefore, investigating deformation failure mechanisms and determining the movement characteristics of the rock masses after collapse can provide practical guidance for conducting linear projects while taking adequate measures to prevent the collapse. In this study, a dangerous rock mass on the right side of the Yuanhou Toll Station of the Rongzun Expressway was used to study the deformation and failure mechanism of near-horizontal and thick layer with thin-layer columnar dangerous rock masses in the Chishui red bed area. A high-definition 3D-surface model was generated by using unmanned aerial vehicle (UAV) tilt photography technology to obtain an aerial image of dangerous rock masses with spatial coordinates in the research area. The three-point method was used to interpret the structural surface of the dangerous rock mass based on the 3D model. A model for the deformation and failure of dangerous rock masses was developed via an engineering geological analysis. We simulated and analyzed the cause of deformation and failure of dangerous rock masses using FLAC3D software. In addition, the motions of rock fall were studied by performing simulations using Rockfall software. From the interpretation of the 3D model of the UAV, the dangerous rock mass developed two sets of dominant structural planes that were nearly vertical and perpendicular to the stratum level, cutting the rock mass into cuboids. Based on the analysis of a stereographic projection, the dangerous rock mass was in an unstable state. The results showed that the dangerous rock mass had a high stress concentration in the middle and lower soft rock, which is likely due to dumping collapse under self-weight and differential weathering. Moreover, rock fall has a 60% probability of causing damage to the road below the rock mass if it collapses, threatening the safety of passing vehicles and people’s lives and property.