Triaxial deformation apparatus


Conventional triaxial deformation tests (σ1 > σ2 = σ3) with and without pore pressure are performed in a pressure vessel using oil as confining medium. Axial load, confining pressure, and pore pressure are servo-hydraulically controlled using double chamber pistons. Solid pistons (experiments on dry samples) and pistons capable of conducting pore fluid through a central bore (experiments on dry and saturated samples) are positioned on top of the sample to apply axial load with a constant displacement-rate. High-pressure tubing connects the piston to one of the two pressure intensifiers (pore-volumometer). Equivalently, the pressure vessel is connected to the bulk-volumometer.

Samples and pistons are jacketed by rubber tubes to prevent oil from penetrating the sample and to separate the confining pressure system from the pore pressure system. Pressure is measured by a pressure gage, the axial load is measured with an external load cell, the axial displacement with a coupled pair of displacement transducers and an additional single displacement transducer, and the position of the bulk- and pore-volumometer pistons with displacement transducers.

Two identical ultrasound transducers can be placed below and on top of the vessel in line with axial loading pistons and are connected to the ultrasound bench-top unit (LINK). Transducers are embedded in hollow steel cylinders to prevent them from carrying axial load. A spring and coupling medium (ultrasound gel or graphite lubricant) are used to provide constant coupling to the inner surface of the cylinder during an experiment.

- Triaxial deformation experiments at room temperature
- Confining pressure and pore pressure up to 200 MPa
- Axial load 5000 kN
- Optional true triaxial pressure vessel
- Optional ultrasound transmission measurements in axial direction
- Optional single-transducer acoustic emissions measurements