A mathematical model of heat conduction in surrounding rocks of the high geothermal roadway with thermal insulation layer was established in this paper, and its finite difference scheme was also proposed. On this basis, thermal insulation mechanism of thermal insulation layer was investigated. Results show that distinct regional temperature distribution exists in the thermal insulation layer. The temperature is continuous while the temperature gradient has a sudden fluctuation at the interface of different media. The wall temperature is lower and the inner surrounding rock temperature is higher in surrounding rocks with thermal insulation layer compared to that in surrounding rocks without thermal insulation layer. Moreover, the smaller the thermal conductivity of the medium in the thermal insulation layer, the larger the temperature gradient and the smaller the heat flux density. At the beginning of ventilation, thermal insulation of the gunite layer is better than that of the grouting layer. After three months, thermal insulation of the grouting layer is better than that of the gunite layer. Thermal insulation layer can reduce 29-40% of heat dissipation and the thermal insulation would be more significant if the thermal insulation layer was constructed earlier.

Experiments were conducted to study the mechanical characteristics of arkosic sandstones sampled from Pingyi, China. Rock samples were all thermally treated under the temperature ranging from room temperature to 800 °C. Results show that as the treatment temperature rises, the arkosic mineral composition does not change obviously, but the mechanical behaviors change regularly. Variation trend changes dramatically at 200 °C, 400 °C, and 500 °C. With thermal expansion of mineral particles being the dominant factor, mechanical behaviors barely change below 200 °C. When temperature ranges from 200-400 °C, it has an important effect on the mechanical properties because of the thermal fracture. From 400-500 °C, mechanical properties change dramatically as a result of the mutual influence of thermal fracture, fusion and re-crystallization, but the thermal fracture is the leading factor. Because of the fusion and re-crystallization, fractures are partly filled, which results in partial recovering of the mechanical strength. With the combined action of thermal fracture, fusion and re-crystallization after 600 °C, mechanical performance of arkosic sandstones degrades rapidly. Generally, the porosity and peak strain of arkosic sandstones increase with the temperature rising. However, the peak stress, elastic modulus and deformation modulus decrease simultaneously. Influenced by mineral particles' thermal expansion, thermal fracture, fusion, and re-crystallization and so on, the variation trend and amplitude are not the same at different temperature ranges, and the damage mechanism of sandstones also makes a difference.

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The rock mechanical properties under the effect of high temperature present a great significance on underground rock engineering. In this paper, the mechanical properties of sandstones, marbles, and granites under real-time heating were investigated with a servo-controlled compression apparatus. The results show that mechanical behaviours of all the three types of rocks are influenced by real-time heating to different degrees. Due to thermal cracking, the uniaxial compressive strengths decrease as the heating temperature rises from room temperature to 400°C. Above 400°C, the sandstone exhibits a significant increase in UCS because of the sintering reaction. The sintering enlarges the contact area and friction between crystal grains in the sandstone, which strengthens the bearing capacity. For marbles, the UCS continues to decrease from 400°C to 600°C due to thermal cracking. However, the carbonate in the marble begins to decompose after 600°C. The generated particles would fill the cracks in the marble and increase the strength. For granites, their UCS presents a sharp decline after 400°C because of thermal cracking. For all rock elastic modulus, they present a decreasing trend, and this indicates that the rock’s ability to resist deformation gradually weakens under the effect of temperature. In general, rock mechanical behaviours under real-time heating differ from those in normal situations, and use of the parameters presented here is important for underground rock engineering related to high temperature and can improve the precision in theoretical and numerical analysis.