A novel and versatile apparatus for brittle rock deformation

Abstract

This paper describes a new biaxial rock deformation apparatus within a pressure vessel, consisting of a stainless steel vessel with an internal diameter of 40 cm and six main access ports for electronics ( 100 pins), pore fl uids (three lines), and con fi ning oil. The apparatus has to ability to work on large rock samples, up to 20 20 cm 2 , with horizontal and vertical forces up to 1.5 MN. The maximum con fi ning pressure of the vessel is 70 MPa, and fl uid fl ow properties and permeability of large-samples can be tested using up to 8 L of fl uids that can be pressurized up to 30 MPa. Sliding velocity during experiments is in the range 0.1 μ m/s – 1.0 cm/s. The machine stiffness is 0.91 kN/ μ m and 1.3 kN/ μ m for the vertical and horizontal axes, respectively. Measurements on friction, velocity dependence of friction and healing properties of reference material like granite and talc replicate the values presented in the literature. Triaxial stress state tests with controlled con fi ning and pore fl uid pressure, and fl uid fl ow through the samples have been performed successfully. The machine is extremely versatile, as it works as a uniaxial, triaxial or true-triaxial apparatus, on rock samples with dimensions ranging from several to tens of centimetres. Due to the broad number of potential operating conditions, we decided to name the machine BRAVA: Brittle Rock deformAtion Versatile Apparatus