Effects of heating rate on physical and mechanical properties of layered limestone

In the process of sustainable energy, such as geothermal energy extraction and utilisation, the surrounding rock of the underground geothermal wellbore often involves the influence of high-temperature thermal and heating rates. Meanwhile, the deterioration of rock physical and mechanical behaviour due to heating rates can seriously affect the stability of the geothermal wellbore surrounding rock passing through layered rock masses. Physical and triaxial mechanical tests on layered limestone with different heating rates were carried out to analyse the variation of parameters of the rock in this research. Meanwhile, cracks and holes at the microscopic level of the rock were tested. Based on the coupled damage generated by heating rate and load, an improved statistical damage model is proposed, and the model is validated using test data from limestone with different bedding angles. The study reveals that taking the 45° specimen as an example, the corresponding wave velocities at 5, 110, 175, and 240°C/min rates are 5214, 4538, 3752, and 2984 m/s, respectively. As the heating rate increases, the mechanical properties of layered limestone progressively decline, accompanied by a rise in pore and fissure formation.