Squeezing is a phenomenon that may occur in deep tunneling and could bring about a large plastic deformation, tunnel closure and collapse of tunnel supports. Therefore, quantitative estimations of deformation and stress from squeezing and its possibility are necessary for establishment of a rational tunneling method. This study carried out three dimensional numerical analyses using a strain softening model in order to simulate the behaviour of squeezing and to estimate deformation and yield area around tunnels quantitatively. Numerical analyses were performed for 42 cases of various stress and strength conditions. As a result, the maximum tangential stress and strength of rock mass ratio could estimate plastic deformation and yield depth around tunnels and equations of relations between them were proposed.
The failure of rock mass around deep tunnel, different from shallow tunnel largely affected by discontinuities, is dominated by magnitudes and directions of stresses, and the failures dominated by stresses can be divided into ductile and brittle features according to the conditions of stresses and the characteristics of rock mass. It is important to know the range and the depth of the V-shaped notch type failure resulted from the brittle failure, such as spalling, slabbing and rock burst, because they are the main factors for the design of excavation and support of deep tunnels. The main features of brittle failure are that it consists of cohesion loss and friction mobilization according to the stress condition, and is progressive. In this paper, a three-dimensional numerical model has been developed in order to simulate the brittle behavior of rock mass around deep tunnel by introducing the bi-linear failure envelope cut off, elastic-elastoplastic coupling and gradual spread of elastoplastic regions. By performing a series of numerical analyses, it is shown that the depths of failure estimated by this model coincide with an empirical relation from a case study.
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