# A Study on the Effects of Hob Temperature on the Rock-Breaking Characteristics of Sandstone Strata
## 2 Calibration of Mechanical Parameters  
The indoor test used calcareous sandstone from Fujian Province, mainly composed of silicon, silica, calcium, clay, and iron oxide. Rock was processed into direct 50 mm cylindrical test blocks with heights of 100 mm. The high-temperature damage experiment is mainly realized using the high-temperature horse fee furnace, with a maximum temperature of 1200 \({}^{\circ}\)C. High-temperature damage was performed at 300 \({}^{\circ}\)C, 600 \({}^{\circ}\)C, and 900 \({}^{\circ}\)C, with a heating rate of 10 \({}^{\circ}\)C/min and a constant temperature of 4 h, and the mechanical parameters at high temperatures were measured. The basic mechanical parameters at normal temperatures are also presented in the paper. The elastic modulus of sandstone at room temperature was 26.4 GPa, the uniaxial compressive strength was 58.72 MPa and the internal friction angle was 51.14 \({}^{\circ}\)C.  
[PERSON] et al. [21] showed that when the ratio of model height to mean particle radius \(\mathrm{L/R}\geq 125\), the particle size does not affect the macroscopic parameters. [PERSON] et al. [22] showed that when (\(\mathrm{L/Rmin}\)) [\(1/(1+\mathrm{Rmax/Rmin})\)] \(\geq 10\), the size and number of particles have less influence on the macroscopic mechanical parameters of the model, where \(\mathrm{L}\) is the minimum scale of the model and Rmin and Rmax are the minimum and maximum diameters, respectively. [PERSON] et al. [23] suggested that \(\mathrm{Rmax/Rmin}=1.66\) without considering the gradation, suggesting that the generated rock is more consistent with the physical properties of the rock. In the indoor experiment, the drill core sandstone sample with a diameter of 50 mm and a height of 100 mm is used. Therefore, according to the indoor experimental sample size, the numerical simulation model is established as a cylindrical sample with a diameter of 50 mm and a height of 100 mm. According to the influence of size effect, the minimum particle diameter is 1 mm and the maximum particle diameter is 1.66 mm. The numerical simulation model of uniaxial compression adopts the rigid wall in the PFC as the loading plate. The arrow is the loading direction and the loading ends when the test block is broken. The conventional three-axis compression numerical simulation model adopts the upper and lower walls and the cylindrical wall shape loading. The cylindrical wall controls the surrounding pressure through the servo and loads the upper and lower wall speeds until the test block is destroyed and the loading is completed. The loading diagram is shown in Figure 1 below. [PERSON] et al. [24] chose the elastic modulus \(E\), Poisson's ratio \(\
u\), and uniaxial compressive strength \(UCS\) to calibrate the model's fine-scaled parameters and then performed numerical analysis. [PERSON] et al. [25] pointed out that the model obtained using only these parameters as calibration indices cannot be used for the properties of rocks in a multidirectional stress state. Therefore, this paper considers these indicators on top of the strength indicators \(c\) and \(\varphi\) in the enclosing pressure state. For cracking parameters, [PERSON] et al. [21] proposed that the strength variation coefficient \(R_{\mathrm{sd}}\) has a significant effect on the cracking strength of rocks. So, in this paper, the strength distribution is taken to obey the Gaussian distribution, which in turn is used to calibrate the cracking strength of rocks. As for rock composition, [PERSON] et al. [26] responded to the denseness of rock composition by varying the coefficient of the adhesion ratio \(\theta_{\mathrm{b}}\). Therefore, the microscopic coefficients were selected as \(E_{\mathrm{p}}\), \(k_{\mathrm{p}}\), \(\mu_{\mathrm{p}}\), \(\sigma_{\mathrm{p}}\), \(C_{\mathrm{p}}\), \(\varphi_{\mathrm{p}}\), \(R_{\mathrm{sd}}\), and \(\theta_{\mathrm{b}}\).