Evolution of permeability and pore structure of salt rock and its self-healing mechanism under coupled thermo-hydro-mechanical environment

Abstract

The self-healing characteristic of salt rock under the coupled thermo-hydro-mechanical (THM) environment is important for the safety assessment of underground repositories. In order to study the evolution of permeability and pore structure of salt rock and its self-healing mechanism under the coupled THM environment, the salt rock is treated with self-designed high-temperature and high-pressure THM coupled equipment. The pore/fissure evolution of the specimens is observed by computerized tomography (MCT) and metallographic microscopy and compared with the characteristic of salt rock after heat treatment only. The results show that (1) the salt rock after high-temperature treatment only does not have healing properties from 25 to 700 °C, and the salt rock damage increases sharply when the temperature is higher than 500 °C; (2) under the coupled THM environment, the pressure and temperature make some pores and fissures of the salt rock appear to heal. It is not that the higher the pressure and temperature, the stronger the healing effect, but there is an overall complex competing effect of damage and healing. When the temperature is 25–400 °C, the damaging effect is higher than the healing effect, so the overall microscopic parameters increase; when the temperature is 400–500 °C, the healing effect in the competing relationship is greater than the damaging effect, and the overall microscopic parameters decrease; when the temperature is 500–700 °C, the damaging effect dominates, the overall microscopic parameters increase sharply, and the damage is severe. The healing effect is best in the temperature range of 400–500 °C.