No abstract

Lining structures are subjected to three-dimensional stress transferred from the overburden soil and rock formation and usually encounter external sulfate attack; permeability and mechanical properties of cement materials are significant for the stability of underground engineering. Geotechnical testing methods were adopted to analyse the evolution of gas permeability, ultrasonic P-wave velocity, uniaxial compression and splitting tensile strength of cement mortar specimens subjected to sulfate attack. With increasing confining pressure, the gas permeability gradually decreased, and the rates and amounts of decrease for the attacked specimens and non-attacked specimens were different. The gas permeability of attacked specimens was greater and more sensitive to the variation of confining pressure ranging from 5 to 20 MPa. Under high confining pressures ranging from 20 to 30 MPa, the rate of decrease in gas permeability was reduced. The ultrasonic P-wave velocity of attacked specimens was visibly lower than that of non-attacked specimens, while their open porosity was higher than that of their counterparts. Both the splitting tensile strength and uniaxial compressive strength decreased after sulfate attack, and the deterioration of the former one was more severe. The experimental results can provide reference material for establishing the long-term stability of concrete structures in a high-sulfate environment.

No abstract

The mechanical and permeability properties of rocks under unloading stress path and high temperature are critically important for hot dry rock. A series of unloading confining pressure and gas permeability tests were conducted on granite samples after heating and rapid cooling treatment. Five levels of temperature and three levels of confining pressures were used. The stress–strain curves of unloading confining pressure were obtained. The strength parameters and deformation parameters were further discussed and analysed. When the heat treatment temperature is higher than 600°C, the granite samples experience a significant degree of thermal damage. With the increase in heat treatment temperature and the decrease in confining pressure, the gas permeability increases. Beyond 600°C, the gas permeability of the samples increases significantly. With the increase in temperature, the internal friction angle decreases slightly from 25 to 400°C, while it increases beyond 400°C. The cohesion exhibits an inverse evolution. The initial unloading elastic modulus and deformation modulus decrease gradually during relief of confining pressure. The decrease rate of the deformation modulus increases with the increase in heating temperature. The experimental results could improve knowledge about the effect of thermal shock and stress on the physico-mechanical properties of granite.