Mechanical properties of coal and rock mass under thermo-mechanical coupling

Abstract

The properties of coal and rock mass in coalfield fire areas require investigation because both coal and rock can become deformed by impact or under high temperatures. Thermo-mechanical coupling forms interconnected channels in the air and can produce a combustion center along a coal seam which can further promote unwanted spontaneous combustion. This paper uses a MTS880/25T electro-hydraulic servo material test system to conduct uniaxial compression experimental tests on coal and rock samples from Huojitu coal mine located in Yulin City, Shaanxi Province, China. Various mechanical parameters were recorded for the samples at different temperatures. Results indicate that temperature has a significant effect on the strength of coal and rock mass. As temperature increased, peak strain, elastic modulus, and peak stress of coal and rock mass decreased at first, then rose, and eventually decreased. From 25 to 200 °C, the elastic modulus and peak stress of the rock samples gradually decreased with an increase in temperature, showing a decrease of 31.45% and 34.07%, respectively. Above 200 °C, they gradually rose to their maximum and promptly dropped until the temperature exceeded 400 °C. Peak strain of the rock samples was slightly different from the elastic modulus and peak stress in the same temperature stage. At 300 °C, peak strain increased to its maximum value. Above 300 °C, peak strain began to drop. The peak strain, elastic modulus, and peak stress of the coal sample were less affected by temperatures below 100 °C. They gradually increased until temperatures exceeded 100 °C. The maximal values for peak strain, elastic modulus, and peak stress corresponded to temperatures of 140, 200, and 200 °C, respectively. After the temperatures corresponding to the maximal values were exceeded, the peak strain, elastic modulus, and peak stress of the coal samples decreased.