ABSTRACT

Numerical analysis provides a useful tool to enhance the understanding of block rock masses. The stability of rock blocks of tunnel or underground opening are commonly analyzed based on rigid body limit equilibrium theory only by considering gravity, while the secondary stress field after excavation of the block is usually not taken into account. Existence of structural planes affects dynamical properties greatly in rock tunnel structures. Especially in hard rock tunnel engineering, the stability of rock is controlled in a sense by the number of blocks, i.e. the size, orientation and locations of the discontinuities. Key-block failures occur where blocks of rock which are separated form the rest of the rock mass by discontinuities slide of fall into an excavation. According to the geometric stochastic block theory and reliability analysis, a new program GeoSMA-3D (Geotechnical Structure and Model Analysis-3D) for simulating tunnel structural planes in rock mass is put forward to develop based on geometric stochastic block theory and modern computer technique. The new model assumed that rock mass consists of blocks, thus formulating a combination of block model. This program adopts vector analysis, which can simulate all excavation planes especially in the tunnel and other underground structure. It can also create three-dimensional structural model and analyze mobility of key-block in the simulation plane by means of geometry and kinematics theory. The distribution of all key blocks and the quantitative data are analyzed by means of the newly developed program. The results show that parts of the blocks' crown zone are under compressive stress, which gradually increases as the underground opening in Shimian Tunnel, Liaoning, China. It can be concluded that the new program is an effective tool for modeling blocky rock masses.

1 INTRODUCTION

In all civil or mining engineering projects, there is an in situ state of blocks in the ground before any excavation or construction is started. It is very important in the development of a numerical model for rock engineering analysis to reproduce this in situ state as closely as possible.

The design is so far mostly empirical. It assumes that the block is rigid and is located in an otherwise fixed body of rock and bounded by a combination of flat discontinuities and excavation surfaces. In practice these conditions are most likely to be approximated when extensive discontinuities occur in hard rock. In common with most other solutions for three-dimensional blocks, possible block movements are assumed to be limited to translation only, and rotation is excluded. Existence of structural planes affects dynamical properties greatly in rock tunnel structures.

It assumes that the block is rigid and is located in an otherwise fixed body of rock and bounded by a combination of flat discontinuities and excavation surfaces. In practice these conditions are most likely to be approximated when extensive discontinuities occur in hard rock. In common with most other solutions for three-dimensional blocks, possible block movements are assumed to be limited to translation only, and rotation is excluded.

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