The thermo-hydro-mechanical coupling has significant effect on the macro mechanical properties of granite, and understanding the meso mechanism of the macro mechanical response is important for ensuring the safety of the disposal systems. In this study, the varied macro mechanical properties of granite subjected to thermo-hydro-mechanical (T-H-M) coupling were investigated, and the meso mechanism was fundamentally revealed from the evolution of the meso pore characteristics. The saturated granite samples were first subjected to different T-H-M couplings on the mechanical testing system, and the permeability of granites was simultaneously tested under coupled temperature (25-125^oC), pore pressure (0-12 MPa) and confining pressure (15 and 20 MPa) conditions. Second, the evolutions of meso pore characteristics, including pore size distribution, pore quantity and pore aperture were studied on the THM-treated granite via NMR test and image processing. Finally, the uniaxial compression tests were conducted to investigate the coupled T-H-M effects on the macro mechanical properties of granites, and the meso mechanism of the varied macro mechanical properties was further analyzed and discussed based on the relationship between macro mechanical responses and meso pore characteristics. Results show that the weakening effect of pore pressure on the uniaxial compressive strength (UCS) appears as the pore pressure increases to 4 MPa, while the strengthening effect of moderate temperature on the UCS is weakened by the application of confining pressure and high pore pressure. The meso mechanisms for the varied macro mechanical properties of the granite subjected to T-H-M coupling can be revealed from the coupled positive and negative contribution of the confining pressure, temperature and pore pressure to the large pore percentage and pore aperture.

thermo-hydro-mechanical coupling,NMR test,mechanical properties,meso pore characteristics