Abstract: The identification of blocks cut by finite discontinues could be realised by which polyhedrons are cut by discontinues and then merged. Although the object of cutting arithmetic is a convex polyhedron, rock mass model in practical engineering is not limited to the convex polyhedron. To solve this issue, the method of convex decomposition was proposed to decompose concave polyhedron model into convex sub-regions. Firstly, rock mass model was established by the surface element method and then a cuboid was set to wrap the rock mass model. Secondly, the cuboid was cut into some sub-regions by all surface element planes based on the algorithm of a plane cutting convex polyhedron. Finally, the convex decomposition of rock mass model was obtained by judging space position relations between sub-regions and the model. The explanation of key algorithms was given as well. In the cutting algorithms, the rough and accurate judgment method was successively presented to determine space position relations between discontinues and blocks. The efficiency of the computation complexity was greatly improved. Two typical examples were conducted to achieve the process and result of this identification method. The results show that the form and number of identified blocks are not limited by this method, which proves its applicability and efficiency of the concave polyhedron model.

Key words: block identification, rock mass model, convex decomposition of concave polyhedron, finite discontinues