Deformation and fracturing behaviour of discontinuous rock mass and damage mechanics theory

Abstract

The mechanical behaviour of a rock mass is strongly affected by discontinuities such as faults and joints. In this paper, a damage mechanics theory is proposed which deals with some sets of discontinuities distributed in a rock mass, for example, joint systems. In this theory, the distributed discontinuities are characterized by a second-order symmetric tensor, called the damage tensor. By introducing the damage concept, the deformation and fracturing behaviour of the rock mass can be treated in a framework of continuum mechanics. A numerical procedure is developed in order to implement the damage mechanics model by using the finite element method. The theory and numerical analysis are applied to several laboratory tests and a practical underground opening problem. Numerical results are compared with measured data.

A Damage Constitutive Model for Rock Mass with Nonpersistently Closed Joints Under Uniaxial Compression

“…But its deficiency is obvious, in which only the joint geometrical property such as its length and dip angle is considered, while its mechanical one such as its shear strength is not included in Eq. (10). That is to say, it thinks that damage cannot transfer the stress, which is nearly true to the rock mass under tension, but not to the rock mass under compression.…”

“…Scholars have proposed many kinds of definitions of the second-order damage tensor to describe anisotropic damage of the jointed rock mass. For instance, Kawamoto et al [10] proposed a damage model for the rock mass with a single set of joints (a series of joints parallel to each other):…”

“…It is often used to define the damage in rock mass geometrical damage theory [10,11,21]. But its deficiency is obvious, in which only the joint geometrical property such as its length and dip angle is considered, while its mechanical one such as its shear strength is not included in Eq.…”

“…But up to now, nearly none of the existing studies on rock mass damage mechanics considers the co-effect of the two kinds of damage on rock mass. For example, Kawamoto et al [10] and Swoboda et al [11] only considered the effect of the macroscopic flaw on the rock mass mechanical behavior and adopted the secondorder damage tensor to reflect the anisotropy in rock mass caused by it, which does not consider the effect of the mesoscopic flaw in the rock blocks cut by joints. Likewise, Grady et al [12] and Taylor et al [13] only considered the effect of the mesoscopic flaw on the rock mass mechanical behavior and defined the damage variable as the function of the microcrack density.…”

“…Now the existing study on rock mesoscopic damage mechanics is often based on the statistical damage constitutive model [16,17], which is well developed. However, the study on rock mass damage constitutive model is comparatively not enough, because the most existing studies mainly adopt the damage tensor to describe the anisotropic damage in the rock mass caused by the joints [10,11], in which only the joint geometrical property such as its length and dip angle is considered, while its mechanical property such as the shear strength is not. So, it is obvious that this definition method for the damage tensor has some deficiency.…”