## 4 Analysis of Influencing Factors of Long-Distance Drilling Blasting  
### Numerical Model Establishment and Scheme Design  
#### 4.1.1 Numerical Modeling  
According to the layout of the 2412 working face in the mine site, combined with the ZK5-3 drilling data in the working face, a UDEC numerical calculation model with a length (x) of 570 m and a height (y) of 260 m was established. UDEC is the abbreviation of Universal Distinct Element Code, which is a computational analysis program based on the theory of discrete element method. Compared with other numerical simulation software, the main advantage of UDEC is that it can simulate the behavior of discontinuous media in geotechnical engineering more accurately and provide more accurate and effective analysis results. Therefore, this paper chooses UDEC as the main simulation method. By referring to the commonly used constitutive model of UDEC in mining engineering [34; 35], and considering whether the model can more intuitively reflect the failure mechanism of rock and the computational efficiency, the Mohr-Coulomb failure criterion is used to simulate the rock stratum. The elastic-plastic contact model of the relay zone with Coulomb slip failure was used at the joint of the model block. The \(X\) axis was the advancing direction of the working face and the \(Y\) axis was the mining depth direction. The buried depth of the model working face was 705 m and the mining height was 15 m. The calculation model was divided into 763,822 grids and 941,184 nodes. The survey line was arranged at the height of 230 m, and the pressure relief effect of long-distance drilling blasting was evaluated by comparing and analyzing the \(Y\)-direction subsidence and stress change of overburden rock at the survey line position. The initial model and the division of rock blocks are shown in Figure 4. According to the field measured data, the physical and mechanical parameters of the rock block are shown in Table 1.  
The 'engineering rock mass classification standard' stipulates that the integrity coefficient of rock mass should be measured when calculating the basic quality index of rock mass. When the measured values are obtained unconditionally, the rock mass integrity coefficient \(K_{v}\) can also be determined by the volume joint number \(J_{v}\)[36; 37].  
\[\mathrm{K_{v}}=(\mathrm{V_{pm}}/\mathrm{V_{pr}})^{2} \tag{1}\]  
In the formula, \(\mathrm{K_{v}}\) is the integrity coefficient of rock mass, \(\mathrm{V_{pm}}\) is the P-wave velocity of rock mass, and \(\mathrm{V_{pr}}\) is the P-wave velocity of original rock mass.  
The simulation realizes blasting through the joint encryption division of the blasting layer and the weakening of the rock parameters below the blasting rock layer. The weakening method uses the number of volumetric joints in the original rock mass as the initial base. The integrity coefficient of the rock mass after long-distance drilling and blasting can also be determined by the number of volumetric joints \(\mathrm{Jp}\) in the rock mass after blasting. The corresponding relationship between the two and the relationship between the integrity coefficient of the rock mass and the number of volumetric joints of the rock mass are the same. A comparison between the two is shown in Table 2.