Discussion on Key Issues in the Application of Block Theory in Rock Engineering

Block theory, which successfully applies the geometric topology method to the field of rock mass stability analysis, is very suitable for analyzing the problem of local block stability caused by the cutting of structural planes (discontinuities) in engineering rock mass. It is a rare original theory in rock mechanics and engineering. However, compared with the completeness, progressiveness, and originality of the theory, the application of block theory in engineering is not widespread enough. Combining the authors’ long-term experience in fundamental research and engineering applications of block theory, this work first clarifies the differences in the connotation of block analysis before and after the excavation of rock masses. This difference reflects the main ideas of using block theory for engineering applications and also reflects the different focuses of block theory application at different construction stages. Furthermore, it is pointed out that before and after excavation, the core tasks are “block prediction-support drafting” and “block determination-support verification”, respectively. Before the excavation of the rock mass, the main tasks are to group and combine discontinuities, distinguish removable blocks and key blocks based on the whole-space stereographic projection (WSSP) for different discontinuity combinations, estimate the size and shape of unlocated blocks, analyze block stability, and draft support design parameters. After the excavation of the rock mass, the main tasks include analyzing the shape of the located block, analyzing the stability of the block, and verifying the support design parameters for rock blocks. Finally, combined with engineering cases, the key technical issues and work ideas in engineering applications were analyzed, such as how to estimate the size of the unlocated blocks, how to sort out the support-required blocks from key blocks, and how to draft or verify support parameters. The work is of great significance for the application and promotion of block theory in engineering. Highlights Different connotations of block analysis before and after rock excavation are clarified. Before rock excavation, the core tasks are “block prediction-support drafting”. After excavation, the core tasks are “block determination-support verification”. Some key issues are discussed, such as distinguishing the support-required block.