The existence of discontinuities significantly affects the mechanical properties and behavior of rock mass, making it exhibit anisotropy and size-effect. Discontinuities usually become one of the controlling factors determining the stability and safety of rock mass engineering. Using discontinuities information is the research basis for the stability analysis and calculation of rock mass engineering. In this paper, the MC method is used to construct the program of generating 3D joint network by using the statistical information of joints, and the joint sketch of the tunnel excavation surface is simulated. The rock classification method RMR was used to evaluate the validity and applicability of the threedimensional joint network under the same statistical sample. From the rock surface characteristics, the reason why the numerical model of the three-dimensional rock mass is often not accurate is explained. The methods and ideas for improvement in the future are proposed.

1. Introduction

Drilling and blasting construction is widely used excavation tunnel method. One of the risk factors in drilling and blasting method is that there is no protection against the excavation surface in front of the construction technician in the high stress environment. The destruction of the surface is mostly characterized by block instability. (Kulatilake PHSW et al,1997) With the excavation of the tunnel, the block formed by the joint cutting and the tunnel excavation face loses the equilibrium state before excavation, and then leads to the destruction of the surrounding rock of the tunnel. (Da'an Liu et al 2000) Therefore, the discontinuities research is very important in the analysis of tunnel construction stability.

The structural plane of the rock mass is often hidden in the actual rock mass. Except for the traces exposed on the rock surface, it is difficult to investigate all the rock mass discontinuities and explore their properties. at the same time, discontinuities are generally developed in rock masses randomly and in sets. Statistical methods are often used to quantitatively study the nature and characteristics of discontinuities.

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