This paper briefly describes a three dimensional finite element code called COSFLOW which incorporates unique features that make it ideal for the simulation of interaction between rock fracture, aquifer interference, and water flow in coalmine environment. Both the deformation and the hydraulic conductivity of rock mass are described using an equivalent continuum approach. The rock deformation of bedded coal measures is described using a Cosserat continuum formulation and the hydraulic conductivity of a fractured porous rock is described using an equivalent fracture network formulation where fluid flow through single fracture is expressed using parallel plate analogue. This formulation is amenable to easy evaluation of modifications to the hydraulic conductivities as a function of stress induced changes in fracture aperture.
Rock mass in coalmining environment essentially occurs in stratified forms. The behavior of such a stratified rock mass can, in principle, be defined based on discontinuum modeling principles and the problem can be solved using numerical methods such as finite element methods or distinct element methods. In this approach, the intact rock layers are represented by a continuum material model and the joints are modeled as discrete entities. Such numerical methods include joint element models (e.g. Goodman et al. 1968) and the distinct element model (e.g. Cundall 1987). However, the process of defining each joint and each rock layer individually becomes a rather cumbersome and complex task when the spacing between the joints (i.e. the rock layer thickness) is substantially small in comparison with the length scale of the problem being considered. In another approach, if the jointing is reasonably persistent (i.e. they are spaced regularly and oriented in the same direction), the jointed rock mass can be idealized as a special continuum material with a special set of material properties.