Laboratory Simulation of Flow through Single Fractured Granite

Laboratory simulation on fluid flow through fractured rock is important in addressing the seepage/fluid-in-rush related problems that occur during the execution of any civil or geological engineering projects. To understand the mechanics and transport properties of fluid through a fractured rock in detail and to quantify the sources of non-linearity in the discharge and base pressure relationship, fluid flow experiments were carried out on a cylindrical sample of granite containing a ‘single rough walled fracture’. These experiments were performed under varied conditions of confining pressures, σ ₃ (5–40 MPa), which can simulate the condition occurring about 1,000 m below in the earth crust, with elevated base pressure, b _p (up to 25 MPa) and by changing fracture roughness. The details of the methodologies involved and the observations are discussed here. The obtained results indicate that most of the data in the Q verses b _p plot, fall on the straight line and the flow through the single fracture in granite obeys Darcy’s law or the well-known “cubic law” even at high value of b _p (=4 MPa) and σ ₃ (=5 MPa) combination. The Reynolds number is quite sensitive to the b _p, σ ₃ and fracture roughness, and there is a critical b _p, beyond which transition in flow occurs from laminar to turbulent. It is believed that such studies will be quite useful in identifying the limits of applicability of well know ‘cubic law’, which is required for precise calculation of discharge and/or aperture in any practical issues and in further improving theoretical/numerical models associated with fluid flow through a single fracture.