Triaxial Deformation Machines
Triaxial Machine-Heard
This machine consists of an externally heated triaxial testing machine, with silicone oil as the confining medium, linked to logging and several pressure control systems. The main features of the apparatus are a main pressure vessel, containing the sample, a linked auxiliary pressure vessel, and a load transmitting yoke/piston assembly driven by a motor/gearbox/ball-screw system. Furthermore, the set-up is equipped with a pore fluid pressure control system plus sample dilatometry and permeametry systems (gas, transient step and liquid-steady state flow through). CO2 pressure control occurs via an ISCO 65D servo controlled pump system.
The Heard triaxial apparatus is suited for axi-symmetric compression testing of cylindrical samples at confining pressures up to 100 MPa, and temperatures up to 400 °C, either at constant stress (creep tests) or constant strain rate (10-4-10-7 s-1). In addition, it is possible to perform stress stepping and relaxation tests, as well as strain rate stepping tests. This machine has been used to study subsurface CO2 mineralisation and fault rock permeability.
Gas Apparatus
This internally heated machine can generate pressures up to 1 GPa and temperatures up to 1200 °C. Additional differential loading may be applied via an Instron loading frame to deform materials under lower crustal to upper mantle conditions. Typical applications involve studies of rock rheology and deformation mechanisms at high pressure and temperatures. Recently, it has been used to constrain the strain-dependent rheological behaviour of the lithosphere.
Triaxial Machine-Shuttle
This internally heated, 100 MPa confining pressure vessel, is mounted on a standard Instron 1362 loading frame with a servo controlled positioning system. This machine can be used to deform the sample at a constant piston velocity, ranging from 10-7 to 10-2 m/s. The displacement is measured outside the vessel using a (Instron standard) linear variable differential transformer (LVDT), with 2 μm resolution. The apparatus is equipped with two (internally and externally located) load cells, each of 100 kN capacity. The confinement on jacketed samples is done by silicone oil, with the pressure being controlled by a servo pump, which also serves as dilatometer to carefully monitor the compaction/dilation of the sample under study. It is also facilitated with an internal heating furnace to locally heat up the sample, up to a maximum temperature of 150 °C. Recently, a high resolution stress-relaxation method was developed for simulating rheology at in-situ conditions (strain rates down to 10-9 s-1).