## 3 Result
### Dynamic Response Characteristics of Disturbed Surrounding Rock under Impact Load  
#### 3.2.1 Stress Evolution Law of Disturbed Surrounding Rock under Impact Dynamic Load  
The stress values of each measuring point of the model were recorded after each impact dynamic load. Figure 4 shows the stress evolution of measuring points at different positions of the model after the impact dynamic load of different strengths. Figure 3: Deformation characteristics of overburden in the process of mining and excavation disturbance: **(a)** displacement marker survey lines; **(b)** mining 10 m; **(c)** mining 30 m; **(d)** mining 50 m; **(e)** mining 70 m; **(f)** mining 90 m.  
When the pendulum height is low, the input impact dynamic load strength is weak. With the increase in the pendulum height, the stress in the coal body on the left side of the heading face gradually increases, indicating that the roadway side of the heading face has considerable self-bearing capacity. The impact dynamic load makes the coal rock mass at the side further compact to a certain extent, and the surrounding rock strength improves. That is, when the height of the pendulum is 1.1 m, the dynamic load strength is about 3.60 \(\times\) 10\({}^{6}\) J, and the peak value of surrounding rock stress is about 3273 N. Subsequently, when the height of the pendulum further increases, the surrounding rock stress begins  
Figure 4: Stress response characteristics of disturbed surrounding rock under impact dynamic load: (a) 1#; (b) 3#; (c) 5#, 9#; (d) 12#; (e) 26#, 29#; (f) 37#, 39#. to decrease significantly, and the surrounding rock at the side has been destroyed, which corresponds to the imminent collapse at the site. As shown in Figure 4b, the surrounding rock stress at the left and right low roof of the roadway begins to decrease significantly when the impact dynamic load begins to act. With the increase in the input dynamic load strength, the roof stress continues to decrease, and the immediate roof also presents a state of cumulative damage. When the pendulum height is 0.7 m, that is, the dynamic load strength is about 2.29 \(\times\) 10\({}^{6}\) J, the pressure at the lower roof is about 328 N, and there is no significant change thereafter. Therefore, it can be considered that the direct roof of the heading face has completely collapsed and failed under the disturbance of dynamic load. The stress of the middle roof and the high roof in the driving face presents different response rules under the impact dynamic load. Similar to the lower roof, the pressure of the 5# sensor located in the 14 m thick siltstone gradually decreases with the increase in the pendulum height under dynamic load and fails only under the last dynamic load impact that causes the overall instability of the model. However, the pressure of the 9# sensor in the 34 m thick fine conglomerate has no significant effect on the increase in dynamic load strength, indicating that the upper key layer still has good stability. The pressure in the lower roof of the central coal pillar first slowly rises under the impact dynamic load of low energy. When the pendulum height exceeds 0.7 m, the monitoring results of the 26# sensor begin to decrease significantly, indicating that when the dynamic load energy reaches a certain level, the strength of coal and rock exceeds the limit, and the microscopic plastic deformation turns into the macroscopic fracture. However, the pressure in the lower roof of the goat in the working face rises slowly, which indicates that the working face still has good bearing capacity. To sum up, the stress response of the disturbed surrounding rock under the impact dynamic load has the following characteristics: (1) Under the impact dynamic load, the wave-facing side of the driving roadway (i.e., the left side of the roadway) is closer to the dynamic load source, with less energy attenuation, so it is greatly affected by the impact dynamic load.