EVALUATION OF FULLY-COUPLED STRATA DEFORMATION AND GROUNDWATER-FLOW IN RESPONSE TO LONGWALL MINING

A finite element poroelastic model is presented to evaluate fully-coup led strata deformation and groundwater flow resulting from underground longwall mining in variably saturated fractured geologic media throug h an equivalent porous elastic continuum representation. The explicit coupling between the groundwater flow field and the solid skeleton def ormation field is achieved by simultaneously solving the governing equ ations for groundwater flow and solid skeleton deformation. The implic it coupling between these two fields is also accomplished by consideri ng the effects of both unsaturated water flow and solid skeleton defor mation on the hydraulic properties such as water content and hydraulic conductivity. In addition to the implicit coupling caused by unsatura ted water flow, the other implicit coupling caused by solid skeleton d eformation is also important because it may produce hydraulic heteroge neity and anisotropy in a geologic medium affecting the groundwater fl ow field even when the system is in a fully saturated condition. A phy sically based constitutive model is proposed to account for the deform ation (strain)-dependencies of porosity and saturated hydraulic conduc tivity of the fractured media. To evaluate the impacts of longwall min ing and to understand their hydrogeomechanical nature, the numerical m odel is applied to a well documented case study with satisfactory resu lts. Although the numerical simulation results presented in this paper will not apply to all underground longwall mines because of differenc es in site-specific hydrogeological and geomechanical settings, the me thodology described herein may find some useful applications in many l ongwall mining projects. (C) 1998 Elsevier Science Ltd.