Discrete fracture network and equivalent hydraulic conductivity for tunnel seepage analysis in rock mass

摘要

Proper evaluation of groundwater inflow into tunnel face during and after construction is very important at tunnel design stage. Conventional seepage analyses in porous media have been preferred for design purpose, but flow characteristics is quite different for tunnels in rock mass because groundwater mainly flows through natural fractures such as faults, joints and cracks. Discrete fracture network (DFN) model can be an alternative for tunnel design in this case. Recently, the DFN model has been widely applied for the problems of groundwater flow in fractured rock masses at near-field scale because fracture network provides major pathways for fluid flow while the conductivity of the intact rock matrix is generally very low. In larger scale problems, however, explicit representation of large numbers of fractures is less efficient, and the continuum model using equivalent properties is more attractive. In this case, proper characterization of the equivalent conductivity of fractured rock mass is important because this property is used for input parameter in the larger scale analysis such as regional groundwater drawdown due to excavation.