| Numerical models are developed to quantify the impact of underground mining on strata deformation and the pre-mining hydrogeological regime. The models conceptually represent mechanisms of hydraulic conductivity enhancement and drained and undrained behavior in both single porosity and dual porosity continua. The finite element technique is used for all three models.;The first model is structured to represent strata deformation and concurrent steady fluid flow in a porous fractured medium as a result of underground mining. The model is based on a coupled finite element formulation where elastic deformation controls changes in fluid hydraulic conductivity of a fractured medium idealized as a porous equivalent. Coupling is steady state and neglects the influence of seepage forces. Verification of the model has been made using a case study which reveals that changes in strata conductivities are strongly related to the intensity of the mining effect on the overlying strata. The greatest modification of the hydraulic conductivities occurs within the caving or severely fractured zones.;In the second model, a transient poroelastic formulation based on Biot consolidation theory is presented to study the impact of underground mining on strata deformation and subsequent modification of hydrogeological properties. The important parameters in this model are identified as pore pressure ratio, ;A third model, a dual porosity poroelastic model, is introduced to determine the effect of interaction between fractures and the porous matrix on the change in fluid pressure and solid deformation. In comparison with the single porosity poroelastic model, the analysis reveals that the dual porosity model generates larger deformation, and produces a substantially different fluid pressure profile in the initial period. The poroelastic behavior of the porous media is strongly affected by fluid exchange between fractures and matrix blocks, which may be approximate either by a quasi-steady transfer or a analytical transfer, and consequently results in a delayed pressure dissipation history. |
