Abstract: In order to study the long-term THM coupled behaviour of soft rock, a parallel-linkage triaxial testing machine for THM coupling in soft rock is developed. This machine is particularly applicable to study the mechanical properties of soft rock under different temperatures and various stress conditions. Using the technology of servo-control, this machine can automatically stabilize voltage and record experimental data. It can also achieve temperature gradient loading, pore pressure gradient loading and independent stress gradient loading. Furthermore, high-precision LVDT sensor is also implemented to measure the deformation. This machine can complete these tests including uniaxial compression test, triaxial compression test, triaxial rheological test, cyclic loading and unloading test, penetration test under steady state and transient conditions. It can simultaneously implement the mechanical tests of two samples with the same confining pressure, the same pore water pressure, different axial pressures and different temperatures, thanks to the unique design of this machine. It can save time because of this feature, especially for the long-term mechanical test. In addition, it can also reduce the system errors. The results of these tests during last year show that this machine is a convenient machine with complete functions, good stability and high precision.

Key words: soft rock, rheology, THM coupling, rock mechanics