Transient groundwater flow in a single fracture

Abstract

Understanding the water flow behaviour in a single fracture is essential for investigating groundwater flow and solute transport in fractured crystalline rock formations in the context of water supply, remediation of dissolved contaminant or projecting long-term nuclear waste repositories. Numerical modelling was used as a tool for studying the geometrical and hydraulic properties of a single fracture. Two computer codes were developed for this purpose. The first one simulates the fracture-free space geometry and the other one solves the transient flow equation. The fracture geometry simulation consists of defining the contact zones where the fracture is closed for the water flow, and of generating the aperture values in zones of water flow. The distribution of contact areas within the simulated fracture is governed by principles of percolation theory. The positive values of aperture in water-flow zones were distributed according to the knowledge of real fracture data. Transient flow simulation is based on principles of fluid mass balance in the fracture space and on locally valid cubic law that quantifies flow rate through the fracture profile. The problem is solved numerically by means of the discretization in time and the finite element method. The percolation theory approach makes it possible to get a faithful evaluation of the fracture permeability and the transient form of the flow equation enables us to simulate the flow and pressure field propagation in accordance to laboratory or field test conditions.