A two dimensional computer model based on the theory of stochastic process is applied to simulate time-dependent failure and deformation of rock mass around underground roadway in deep mine. In this model, the failure process of rock is assumed as a probabilistic rate process in which the rate constant is given by a power function of stress severity, and FEM technique is used to model deformation of rock mass and rock bolt supports. According to which of shear or tensile is the failure mode, different anisotropic mechanical properties are assumed for post-failured elements in the fractured zone. Through the computer modelling, it is found that grouted rock bolt can retard the convergence of roadway, however, at great depth, the effect of rock bolt is not so remarkable as expected from experiences at present mine roadways.
Strata control is one of the most important problems in deep underground mines, where many roadways suffer from severe rock pressure. The severity of rock pressure depends upon the depth of roadway as well as the strength of rock formation around the roadway. In other words, it depends upon the competence factor which is defined as the ratio of uniaxial compressive strength of rock to the overburden pressure. In Japan, most of coal bearing formations belong to Tertiary system, and coal measure rocks are frequently weak and fractured. Most of output are mined from coal faces at the depth of several hundreds meters from ground surface. Furthermore, various non-ferrous metallic ore deposits are frequently buried in weak volcanic rock formations (Nishimatsu, 1981). Frequently, the rock formation is assumed as an elastic body for theoretical analysis in rock mechanics. However, it is indispensable to take time-dependent behaviours of rock into account for analyzing or modelling the convergence of mine road way, because the elastic deformation takes place instantaneously after face advancing or heading, and gradual time-dependent increase of convergence and support load can not be explained by elastic theory. Furthermore, progressive failure or yield is frequently observed around underground openings. The progressive failure would play an important role in the time dependent rock pressure phenomena, and be assumed as a rate process to consider effect of time elapsed. For examples, creep of rock sample has been analyzed under the assumption that crack extension is a probabilistic rate process (stochastic process)(Scholz, 1968). Recently, the authors have assumed that crack growth is a stochastic process and conducted a computer modelling of time-dependent deformation and failure process of rock samples under various test conditions (Okubo and Nishimatsu,1986). In this paper, under the same assumption as the previous paper, the authors conduct a computer modelling of sometime-dependent behaviours of rock formation around underground mine roadway by means of F.E.M.technique.
For the purpose of modelling the time dependent behaviour of rock, it is assumed that time-dependent component of strain appears as a consequence of reduction in the effective elastic stiffness of rock resulting from localized brittle fracture or crack extension.
