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3-D stability analysis of tunnel structures based on geometric stochastic blocks theory


Authors: Wang, S.H., Zhang, Y.B., Zhang, N., Wang, S.
Source: Boundaries of Rock Mechanics: Recent Advances and Challenges for the 21st Century
Pages: 6
Date: 2008-04-28
Location: Beijing, China

Abstract
A numerical approach for modeling progressive failure of rock mass is introduced. 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. In the present paper, according to the geometric stochastic block theory and reliability analysis, a new program GeoSMA (Geotechnical Structure and Model Analysis) 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 and each block is formed by particles arranged in a specific way, thus formulating a combination of block model and particle 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. There are some features distinguishing the approach from conventional numerical methods as FEM. It can be concluded that the new program is an effective tool for modeling blocky rock masses. The results show that parts of the blocks? crown zone are under compressive stress, which gradually increases as the underground opening in Dahuofang waterhouse, China.

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