A new true triaxial apparatus with pore fluid system for rock deformation under representative crustal stress conditions.

We have developed a new true triaxial apparatus for rock deformation, featuring six servo-controlled loading rams capable of applying maximum stresses of 220 MPa along the two horizontal axes and 400 MPa along the vertical axis to cubic rock samples of 50 mm side. Samples are introduced into a steel vessel, allowing rock specimens to be subjected to confining pressures of up to 60 MPa. Pore fluid lines connected to two pump intensifiers enable high-precision permeability measurements along all three principal stress directions. Experiments are conducted at room temperature. We present a suite of finite element method models implemented to determine the conditions and loading configuration that minimize the loading boundary effects during true triaxial loading. These observations are generic, and we expect they will contribute to the development of true triaxial loading systems generally. Finally, we validate our experimental configuration by presenting results on permeability measurements along the three axes on cubic samples of three types of well-studied rocks: Darley Dale sandstone, Crab Orchard sandstone, and Etna basalt.