Evaluating the pore characteristics of granite in disposal system under thermo-hydro-mechanical (T-H-M) coupling

Abstract

Evaluating the pore characteristics is of great importance to understand the thermo-hydro-mechanical coupled effect on the macro mechanical properties of granite in disposal systems. In this study, the pore characteristics of granite subjected to thermo-hydro-mechanical (T-H-M) coupling, which referred to the coupled treatment of temperature, pore pressure and confining pressure were systematically investigated, and the meso-mechanism of the varied permeability and macro mechanical properties was fundamentally revealed. Considering the coupled conditions in disposal systems, 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 with temperature (25–125 o C), pore pressure (0–12 MPa) and confining pressure (15 and 20 MPa) coupled treatments. Second, the evolutions of pore characteristics, including pore size distribution, pore quantity and pore aperture were studied on the THM-treated granite via nuclear magnetic resonance (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 quantitative relationship between macro mechanical responses and pore characteristics was further analyzed and discussed. Results show that the effect of high pore pressure on permeability is greater than that of moderate temperature, and the effect of low pore pressure is the weakest. 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 more pronounced with low confining pressure and pore pressure under T-H-M coupled conditions. The meso mechanisms for the varied macro mechanical responses of the granite subjected to T-H-M coupling can be mainly revealed from the coupled positive and negative contribution of the confining pressure, temperature and pore pressure to the large pore percentage and pore aperture. • The varied macro mechanical properties of granite subjected to T-H-M coupling were systematically investigated. • The evolutions of pore characteristics were studied on the THM-treated granite via NMR test and image processing. • The meso mechanism was analyzed based on the relationship between macro mechanical responses and pore characteristics.