Characterization of Groundwater Flow in a Fractured Crystalline Rock Mass Using Taiwan’s Reference Case Data

In this study, fracture data known as ‘Taiwan’s reference case’ were used for numerical simulation of discrete fracture network (DFN) and subsequent groundwater flow and particle tracking simulations. Borehole fracture data helped to classify the rock body into two rock domains with a total of nine fracture sets. Analyzing fracture trace data with scales covering three orders of magnitude concluded that fracture size in the study area follows a power law distribution. Ten DFN realizations were generated. For each realization, regional scale groundwater flow simulations were implemented by upscaling the DFN into an equivalent porous medium. Simulation results demonstrated the importance of viscous and gravity instability on brine migration. A small simulation domain containing the hypothetical deposition plane was used to investigate the characteristics of transport pathway. It was found that large fractures tend to form the major transport pathway. Particle breakthrough curves (BTCs) obtained by considering advection only exhibit distinct characteristics in terms of first arrival time, mean/variance of travel time, and the impedance/acceleration of particle migration. If dispersion is taken into account, however, the resulting BTCs become more smoothed with pronounced spreading, resulting in faster first arrival and prolonged breakthrough time.