Measurements of Coupled Normal Deformation, Permeability, and Heat Transfer in Rock Joints Using a Triaxial Test Facility

A description is presented of a rock-mechanics triaxial test facility capable of coupled testing of medium-sized cylindrical rock specimens at axial loads to 2.67 MN, confining pressures to 140 MPa, pore pressures to 105 MPa, and specimen temperature to 400°C. The test cell of the system is modified to carry out tests on fluid mass and heat transfer through rock joints/fractures and thermomechanical deformation of joints/fractures. Details of test procedures and techniques for conducting the coupled hydro-thermo-mechanical tests are described. Data on both natural joints and artificially induced extension fractures in the Carnmenellis granite are presented and discussed in order to illustrate the multifunctional capability of the testing system to cover the requirement for further understanding of rock joint/fracture and rock masses.

The study showed that joint/fracture permeability and mechanical aperture decrease with increasing effective normal stress. The relationship between the changes of mechanical aperture and permeability is influenced mainly by discontinuity surface characteristics. The permeability decreases with increasing temperature while measured mechanical aperture increases. Heat transfer coefficient measured during hydro-thermo-mechanical tests varies from 300 to 1200 W/m²-°C and is affected by flow velocity, temperature, and joint/fracture surface properties.