The influence of cooling methods on tensile properties and damage constitutive model of layered sandstone after undergoing high temperatures

To study the influence of different cooling methods on the stability of high-temperature layered tunnel surrounding rock after being subjected to a fire, direct tensile tests were carried out after natural cooling and water cooling methods using Sichuan sandstone as the subject of the research. The change laws of tensile strength and elastic modulus of square layered sandstone samples under direct tensile tests were studied, and the influence of the cooling method on the failure of the 3D morphology of the layered sandstone was also analysed. The statistical damage constitutive model of the layered sandstone under tensile action was established based on the statistical damage principle; a damage threshold is also introduced, which can be verified with experimental data. The results show that the elastic modulus and tensile strength of rocks with different bedding angles show an obvious anisotropy, and they all show a V-shaped trend. At the same bedding angle, water cooling causes more serious damage to rocks than natural cooling. The height differences of different bedding angles (0°, 30°, 45°, 60° and 90°) were 1.802, 3.254, 4.868, 3.047 and 1.758 mm, respectively. In addition, it is suggested that the calculated values for the statistical damage constitutive model fit well with experimental values, and the model parameters m and F 0 are related to the macroscopic elastic modulus and strength. This has a definite theoretical value when analysing and evaluating the stability of the tunnel surrounding rock after being subjected to the high temperatures experiences during a tunnel fire.