## 4 Geomechanics Modelling Establishment of Different Lithologies
### Numerical Model Parameter Matching  
Since the collected rock samples are detached from the environment in which the rock mass exists and are limited by the structural characteristics and size effect of the rock samples, the rock strength determined by laboratory rock mechanics tests is generally lower than the strength of the rock mass in the field [29]. Therefore, it cannot be used directly for numerical simulation calculations. Accordingly, the Hoek-Brown strength criterion was used to correct the rock's mechanical parameters. The deformation modulus of the rock mass was modeled as the correlation between the modulus of the rock mass and the modulus of the intact rock by using the geological strength index (GSI) based on many years of research on the strength criterion of the rock mass by [PERSON] et al. The expression of the calculation is shown in (1) [30], and the strength of the rock mass was calculated using Equation (2) [31]. The calculated mechanical parameters of the rock mass after reduction based on the Hoek-Brown criterion are shown in Table 4.  
\[\frac{E_{\text{rm}}}{E_{i}}=\left(0.02+\frac{1-D/2}{1+e^{(60+15D-GSI)/11}}\right) \tag{1}\]  
\[\sigma_{\text{cmass}}=\sigma_{ci}\frac{(m_{b}+4s-a(m_{b}-8s))}{2(1+a)(2+a)} \left(\frac{m_{b}}{4+s}\right)^{s-1} \tag{2}\]  
\[m_{b}=m_{i}\exp(\frac{GSI-100}{28-14D}) \tag{3}\]  
\[s=\exp(\frac{GSI-100}{9-3D}) \tag{4}\]  
\[a=\frac{1}{2}+\frac{1}{6}\left(e^{-\frac{GSI}{15}}-e^{-\frac{20}{3}}\right) \tag{5}\]  
where \(GSI\) is the geological strength index of the rock mass, determined by the field investigation; \(D\) is the mining disturbance coefficient; \(m_{\text{b}}\), \(s\), \(a\) are the material constants of the rock mass; \(\sigma_{\text{cmass}}\) is the uniaxial compressive strength of the rock mass, MPa; \(\sigma_{ci}\) is the uniaxial compressive strength of the intact rock, MPa; \(E_{\text{rm}}\) is the modulus of the rock mass, GPa; and \(E_{i}\) is the modulus of the intact rock, GPa.  
A Mohr-Coulomb constitutive model is assigned to the block elements, and a Mohr-Coulomb slip model is adopted for the contact elements. The behavior of the rock mass is controlled by parameters that are assigned to different models and can be divided into the following two groups: (1) Block element model parameters: density, bulk modulus, shear modulus, cohesion, angle of internal friction and tensile strength. (2) Contact model parameters: normal stiffness, shear stiffness, cohesion, internal friction angle, and tensile  
Figure 8: Schematic diagram of the actual working condition and numerical model establishment.  
strength. Based on the rock mechanics parameters calculated from the laboratory tests, \(K\), \(G\), \(K_{n}\), and \(K_{s}\) were calculated using the following equations  
\[K=\frac{E}{3(1-2\mu)} \tag{6}\]  
\[G=\frac{E}{2(1+\mu)} \tag{7}\]  
\[K_{n}=10\left[\frac{K+\frac{3}{4}G}{\Delta z_{\text{min}}}\right] \tag{8}\]  
\[K_{s}=0.4K_{n} \tag{9}\]  
Other parameters required in 3 DEC can be obtained from simulated rock mass compression tests. The mechanical properties of the rock mass exhibit a size effect and tend to stabilize when the size of the rock mass increases to a certain extent. This minimum size is called the representative elementary volume (REV) [32]. In this study, we refer to the REV dimension selected by [PERSON] et al. [33]. Based on a series of uniaxial compression tests for numerical simulation, the other parameters required for numerical simulation were inverted, as shown in Table 5.