Abstract: The experiment of hydro-mechanical coupling rheological damage is an important means to reveal the catastrophic mechanism of soft rock. However, the limitations of this experiment are in the lack of large-scale experimental apparatus that can simulate the actual engineering environmental conditions and its multi-scale measurement technology for accurately tracking the entire process. Hence, a pressure chamber was designed by applying high-strength transparent materials, according to the principles of mechanical control and intelligent optimisation. Combining with servo control, non-contact 3D measurement and synergetic integration technology, a multi-scale mechanical testing system was developed for studying the hydro-mechanical coupling rheological damage of soft rock. This system mainly includes the full transparent chamber with high dynamic/static water pressure, the multi-phase synchronous-loading triaxial system, a real-time measurement system embedded the fiber optic sensing technology under high confining pressure, a multi-scale three-dimensional imaging system for the observation of internal and external rheological damage and a synchronous and rapid system for processing the spatial measurement data. Thus, a prototype machine was successfully developed using the integration of hardware and software. This system can simulate the whole process of hydro-mechanical coupling soften damage of soft rock under the conditions of high pressure dynamic/static water and other working fluids. Besides, it also can carry out a variety of soft rock rheological damage tests with different solutions, pressures and rheological stages. Thus, both high-precision non-destructive measurement and multi-scale observation were achieved in the same period. The stress-strain curves, internal damage evolution, surface strain changes and surface damage evolution of soft rock were obtained through application. Internal and external damage evolution processes were reconstructed, and their reconstructed images were further compared with the changes of actual rock samples. The results indicate that the reliability of the testing system was verified. This study provides experimental technical support for the capture of the whole process and in-depth study of soft rock disaster.

Key words: soft rock, hydro-mechanical coupling, rheological damage, multi-scale, mechanical experiment system