Rock mass deterioration model of bank slope based on high-precision 3D multiperiod point clouds in the Three Gorges Reservoir, China

Karst bank slopes are widely developed in the Three Gorges Reservoir area. Potential bank slope instability caused by the deterioration of rock masses has aroused considerable attention. This paper describes an attempt to use high-precision 3D laser scanning point cloud technology to reveal the deterioration law of a rock mass from a meso-/macroscale perspective and to preliminarily establish the relationship between the characteristics of the rock mass deterioration and 3D point cloud response. The main conclusions are as follows. The point cloud response characteristics of rock mass deterioration can be divided into three types: crack manifestation–extension, collapse-block falling, and translation-rotation. The crack manifestation–extension type can be further subdivided into three subcategories: crack extension, crack widening and crack deepening. These three subclasses of point cloud response characteristics of crack manifestation–extension all exhibit strip-like erosion-induced extensions, but the deformation forms and locations are slightly different. The point cloud response of collapse-block falling shows irregular sheet erosion. The point cloud response characteristics of translational rotation are similar, but associated erosion deformation often presents regular isosurface deformation characteristics. The C2C and M3C2 algorithms are used to calculate the deterioration and deformation, and the difference between recording points at the same location is small, except where the local normal vector N→ changes greatly or the point cloud is sparse, where there are large differences. Based on 3D point clouds, the deterioration rate formula De = n/N for a rock mass is proposed for the first time, where n is the number of degraded and deformed point clouds, and N is the total number of point clouds in the test area. According to the deterioration rates De corresponding to different deformation thresholds, the deterioration degree and state of a rock mass can be described and judged.