Some features of rock failure under thermal cycling effects

Thermal cycling effect is a promising method for creating a developed system of fractures in rocks. In mining, it can be utilized for effective rock mass fracturing to facilitate subsequent mechanical destruction or to enhance the filtration capacity of the rocks. In nature, large-scale consequences of rock failure under thermal cycling loading are observed in the form of geological structure such as columnar jointing. The research purpose is to assess the influence of thermal cycling effect on the physical-mechanical and fracture properties of rocks and glass models. Additionally, the research aims to demonstrate the potential application of thermal effect under heating-cooling scheme in technological processes, such as the formation of boiler cavities, the creation of disturbed zones around advance wells, and the development of extensive fracture systems in large rock volumes using thermal waves. The research is based on experimental tests of changes in the compressive and fracture strength of rock samples and glass models under various thermal cycling treatment modes. It also includes an analysis of the application of thermal cycling effect in selected technological processes for mineral extraction. The findings are presented as parameters of changes in the compressive and crushing strength of glass, coal, and granite under different thermal cycling treatment modes. It is shown that the reduction in strength and an increase in fracturing of the studied materials depend more significantly on the temperature gradient ΔТ between heating and cooling rather than on the method of achieving this gradient. Shifting the temperature range to higher values enhances the thermal cycling effect. Generating thermal waves in large rock volumes can increase rock mass fracturing and improve reservoir collectability through repeated heating and cooling cycles. The research has revealed that a single cycle of heating and cooling in ordinary water with a temperature gradient of ΔТ = 300°С results in a reduction in compressive strength by 7.14% for granite, 49.11% for coal, and 45.45% for glass. When cooled in boiling water under the same temperature gradient, these values change to 12.38% for granite and 46.81% for glass. The efficiency of surface thermal cycling is shown to be limited by the low thermal conductivity of rocks. However, the generation of thermal waves within the rock mass enables the involvement of larger mass volumes in the fracturing process.