Rock mass failure at a great depth near underground openings often has a zonal character. The mechanism of this phenomenon consists in the periodic character of the stresses in the surrounding rock mass and the development of tensile macrocracks at the places (zones) of maximum tangential stresses. A mathematical model of a highly stressed rock mass is developed on the basis of the principles of defect medium mechanics and non-equilibrium thermodynamics. A method of determining the model parameters has also been developed and a satisfactory correspondence between the experimental research on faulted zonal structures near to openings at great depths and the mathematical model calculation has been achieved. The main relationships between the width of the cracking zones and the rock mass strength property have also been determined.

1 Introduction

Failure conditions can occur in the boundary parts of the openings at great depths of excavation and wall drilling. In some cases the failure has a zonal character where tensile macrocrack zones alternate with a relatively monolithic rock mass (Shemyakin 1986, Adams& Jager 1980). Many attempts have been made to describe the zonal character of rock mass failure near openings based on classical mechanics (Shemyakin et al. 1987, Reva & Tropp 1995, Odintsev 1996; Alexeev et al. 1996). However, no one has been able to explain all of the properties of zonal failure structures without the introduction of newassumptions in each new case.

Recently, a new gauge theory has been applied to solids to describe the whirl fields of plasticity in high energy conditions (Kadich & Edelen 1983, Panin et al. 1990, Panin 1990).The main principle of gauge theory is the incompatibility of a deformation in a solid, but this does not apply to the zonal failure phenomenon of rock masses near openings. In this paper we demonstrate an example of a description of the phenomenon using the gauge mathematical model.

The description can be done from the position of consideration of the rock mass hierarchical block systems (Xu 2009). A rock sample in this conception is shown as the first level of a hierarchical system and the rock mass at the opening scale corresponds with the second one.

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