## 3 Test Results
### Change in Compressive Strength and Elastic Modulus  
To more intuitively reflect the influence of temperature on the physical and mechanical properties of sandstone, this paper introduces the normalized value according to the mechanical parameters of sandstone obtained from the test. That is, the uniaxial compressive strength of bedding sandstone at room temperature (\(\sigma_{c0}\)), elastic modulus (\(E_{0}\)), internal friction angle (\(\varphi_{0}\)), and cohesion (\(c_{0}\)) is taken as the initial value, and the ratio of the corresponding physical and mechanical parameters of rock samples treated at different temperatures to the initial value is taken as the normalized value after high-temperature treatment to obtain the dimensionless uniaxial compressive strength (\(\sigma_{ct}\)/\(\sigma_{c0}\)), elastic modulus (\(E_{t}\)/\(E_{0}\)), internal friction angle (\(\varphi_{t}\)/\(\varphi_{0}\)), and cohesion (\(c_{t}\)/\(c_{0}\)). As shown in Figure 8a, the change trend of the compressive strength of sandstone at different bedding angles can be divided into three cases: (1) At \(\beta\) = 0\({}^{\circ}\) and 30\({}^{\circ}\), when \(T\) < 200 \({}^{\circ}\)C, the compressive strength of sandstone shows little change. When the heating temperature is between 200 \({}^{\circ}\)C and 600 \({}^{\circ}\)C, the compressive strength is higher than that at room temperature, and the strength of sandstone increases. When \(T\) \(\geq\) 600 \({}^{\circ}\)C, the compressive strength starts to decrease. When \(T\) \(\geq\) 800 \({}^{\circ}\)C, the strength deteriorates significantly, and the compressive strength decreases rapidly. (2) At \(\beta\) = 45\({}^{\circ}\) and 60\({}^{\circ}\), the compressive strength of sandstone under heating conditions below 800 \({}^{\circ}\)C is higher than that at room temperature, and the maximum compressive strength is at \(T\) = 200 \({}^{\circ}\)C, which indicates that the mechanical properties of sandstone have been strengthened under high-temperature conditions. A heating temperature of approximately 200 \({}^{\circ}\)C has the most obvious effect on sandstone strengthening. Although heating conditions of 400-600 \({}^{\circ}\)C caused obvious physical and chemical changes in the interior of sandstone, in general, the influence on the compressive strength of the sandstone with two bedding dip angles is benign. When \(T\) > 800 \({}^{\circ}\)C, the compressive strength of sandstone decreases rapidly at \(\beta\) = 0\({}^{\circ}\) and 30\({}^{\circ}\). (3) When the temperature is 90\({}^{\circ}\), the compressive strength of sandstone under heating conditions of \(T\) < 600 \({}^{\circ}\)C shows little change compared with that at room temperature, and it only decreases slightly when \(T\) = 400 \({}^{\circ}\)C, reducing by approximately 8%. When \(T\) > 600 \({}^{\circ}\)C, the compressive strength of sandstone starts to decrease significantly. When \(T\) = 800 \({}^{\circ}\)C, it decreases by approximately 20%. When \(T\) = 1000 \({}^{\circ}\)C, the strength of sandstone decreases rapidly. The influence of temperature on the compressive strength of sandstone with different bedding angles can be summarized as follows: a heating temperature below 800 \({}^{\circ}\)C will increase or keep the compressive strength of sandstones with different bedding angles unchanged, but when \(T\) > 800 \({}^{\circ}\)C, the strength of sandstone with all bedding angles decreases rapidly, and when \(T\) > 100 \({}^{\circ}\)C, the strength decreases to 40% at room temperature. Figure 8b shows the change trend of the sandstone's compressive strength with increasing dip angle under the same heating conditions. Under any heating temperature in this experiment, the compressive strength of sandstone at \(\beta\) = 45\({}^{\circ}\) was the minimum, and the maximum compressive strength generally occurred at \(\beta\) = 30\({}^{\circ}\) and 60\({}^{\circ}\)Compressive strength testing was conducted on high-temperature layered sandstone and the obtained parameters were normalized.