## 4 Application: A Real Case
### Computational Model and Mechanical Parameters in the DEM Calculation  
In this section, the calculation model in the DEM calculation is established, which is used to analyze the deformation and failure of the open-pit slope.  
When using the discrete element modeling software 3 DEC to analyze the deformations and failures of jointed rock slopes, the essential step is to establish a simple but practical computational model. According to the project report of the open-pit slope, the actual geological conditions are simplified reasonably. The rocks of the slope are divided into migmatite in the southern subarea, ore in the middle sub-area, and phyllite in the northern sub-area. According to the geological and topographic map of the study area, the altitude of the ground surface is extracted; and the ground surface is generated by MIDAS/GTS software. Then, the initial geological model is established in the 3 DEC software according to the prisms generated by triangular surface meshes. Finally, simplified joints are added to obtain the required computational model.  
To be more specific, establishing the calculation model consists of two procedures: (1) an original geological model without joints is established; (2) establishing the final calculation model by adding key joints to the original geological model.  
The first procedure is to establish the initial geological model of the study area, which is completed by using MIDAS/GTS software. This procedure consisting of three main steps is as follows:  
(1) According to the geological and topographic map of the Yanqianshan iron mine, the elevation of the ground surface is extracted; a representative section is selected, and the ground surface is generated in MIDAS/GTS software;  
(2) The ground surface is divided into triangular surface meshes in MIDAS/GTS software;  
(3) An initial geological model is established according to the prisms generated by triangular surface meshes.  
The second procedure is to establish the final calculation model by strictly adding key joints, and the procedure is implemented by the 3 DEC software. This procedure consisting of three main steps is as follows:  
(1) The geological model established according to the prisms generated by triangular surface meshes is transformed from the MIDAS/GTS software to the 3 DEC software using a special interface program;  
(2) The excavated roof and ore body are established by using multiple planes to cut models and to divide regions, see Figure 10a;  
(3) The required calculation model is established by adding the key joints to the model by calling the command jet; see Figure 10b.  
The parameters are determined according to the project report of the open-pit to underground mining project of the Yanqianshan iron mine. Table 2 shows the physical and mechanical parameters of the rocks in the three sub-areas; and the mechanical parameters of the joints are shown in Table 3.  
Currently, the Mohr-Coulomb model is the most commonly employed for investigating the stability of rock slopes in numerical modeling [39, 40]. In this paper, the Mohr-Coulomb model is also employed as constitutive model.  
In Table 2, \(E\) represents the young's modulus; \(\mu\) represents the possion's radio; \(\rho\) represents the density; \(c\) represents the cohesion; \(\varphi\) represents the internal friction angle.