## 3 Results and Discussion
### Analysis of Disaster Effects Caused by Different Types of Dynamic Loads
#### 3.4.2 Evolutionary Law of Stress Field Through Numerical Simulation  
Generally, the stress state at a point can be decomposed into isotropic tensile (or compressive) stress and anisotropic deviatoric stress tensor. The former mainly leads to volume changes, while the latter primarily induces shape changes. To further understand the distinguishing characteristics of the propagation of the three types of dynamic load waves, a numerical simulation analysis was conducted using the maximum principal stress, minimum principal stress, and their difference. The distributions of the maximum and minimum principal stresses in the 3310 working face in Gu Cheng Coal Mine, as well as the difference in principal stresses before and after perturbation, were simulated and are shown in Figure 15, Figure 16, and Figure 17, respectively. Figure 18, in turn, displays three loads difference in principal stresses before and after disturbance. From Figure 15 it can be observed that after disturbance by the three types of dynamic load waves, the maximum principal stress concentrates at the seismic source, as well as at the roof and floor of the roadway. Specifically, after disturbance, the maximum principal stress distribution for the roof-type dynamic load forms a funnel-shaped concentration pattern, with the maximum reaching approximately 53.0 MPa. For the fault-type dynamic load, the distribution of maximum principal stress undergoes significant changes, with a single elliptical concentration point forming at the seismic source, reaching a maximum of approximately 60.0 MPa. Compared to the unperturbed state, the range of stress concentration expands from 5 to 10 m below the roof and from 3 to 10 m above the floor of the roadway. Similarly, after disturbance by the coal pillar-type dynamic load, the distribution of maximum principal stress undergoes significant changes, forming a droplet-shaped distribution pattern at the seismic source, with the maximum reaching approximately 57.0 MPa, and the range of stress concentration expanding at the roof and floor of the roadway. Figure 15: Cloud map of maximum principal stress distribution before and after disturbance. (**a**) Unperturbed, (**b**) roof-type, (**c**) fault-type, (**d**) coal pillar-type. Figure 16: Cloud map of minimum principal stress distribution before and after disturbance. (**a**) Unperturbed, (**b**) roof-type, (**c**) fault-type, (**d**) coal pillar-type. Figure 17: Distribution of difference in principal stresses before and after disturbance. (**a**) Unperturbed, (**b**) roof-type, (**c**) fault-type, (**d**) coal pillar-type. Figure 16 illustrates that after disturbance by the three types of dynamic load waves, the minimum principal stress mainly concentrates at a distance of 10 m or more away from the seismic source and the roadway, while the maximum reaches approximately 32.0-34.0 MPa. For the fault-type dynamic load, the stress concentration position at the seismic source is located above the roof-type and coal pillar-type, further away from the top of the roadway. Figure 18 shows the principal stress difference curve before and after the disturbance. Combined with the principal stress difference Figure 17, it illustrates that within the range of 5-15 m from the top of the tunnel, the fault-type principal stress difference is the largest, within the range of 5-10 m, the roof-type principal stress difference is greater than the coal pillar-type, and in the area deeper than 10 m from the top of the tunnel, the coal pillar-type principal stress difference is greater than the roof-type. The results show that in the tunnel roof within 5 m above and below the source, the fault-type dynamic load has the most obvious effect on the change in the principal stress state of the tunnel. The action range of the roof-type and the coal pillar-type is similar. The principal stress state changes significantly within 3 m above and below the source, but the amplitude is small.