# Risk Assessment of Compound Dynamic Disaster Based on AHP-EWM
## 2 Analysis of Main Control Factors of Compound Dynamic Disaster
### Geological Factors  
With the increase in mining depth, the self-weight stress and the accumulated elastic energy in the coal and rock mass increases. According to domestic and foreign research and statistics, when the depth is h \(\leq\) 350 m, the compound dynamic disaster will not occur. When the depth is 350 \(<\) h \(\leq\) 500 m, the risk will gradually increase to a certain extent. From 500 m onwards, with the increase in mining depth, the risk of compound dynamic disaster will increase sharply. When the mining depth is 800 m, the risk of compound dynamic disaster will increase 14 times compared with that at 500 m [38].  
Stress concentration is easy to form near the fault. Research shows that, when the mining of the working face is close to the fault, it will affect the distribution range, distribution form and stress peak value of the advanced roof pressure of the working face, the fracture tendency is different from the advancing direction of the working face and the influence on the roof pressure is different [39]. When the working face moves from the footwall of the fault to the fault, the coal pillar between the working face and the fault will be pressurized, resulting in high stress concentration, generating strain and thus accumulating a large amount of elastic energy. As the working face advances, the accumulated energy will continue to increase, and the risk of compound dynamic disasters of rock burst and coal and gas outburst will be greater.  
The suspended roof of the goaf is formed for mines with thick and hard roofs, as the roof is hard and does not easily fall. With the advance of the working face, the area of the suspended roof in the goaf increases, the roof will bend and sink under the action of its own weight and the load of the overlying rock strata, and a certain tensile stress will be generated in the center of the suspended roof in the goaf. Once a part reaches tensile strength, the roof will instantly form a macro crack and the tensile stress will transfer rapidly, forming an avalanche chain reaction causing the roof to suddenly break. In addition, when the roof rock layer is hard, complete, dense and impermeable, the gas in the coal seam is not easy to escape and continues to accumulate, resulting in high gas pressure, high content and high outburst risk. Therefore, when the roof is dense and the roof thickness is large, the possibility of rock burst and gas outburst is very high.  
The change of coal seam thickness is often more important than the thickness itself to form a compound dynamic disaster. At the place where the thickness suddenly becomes thinner or thicker, the stress concentration phenomenon is easy to occur in the coal body due to static load [40]. When the mining face is close to these areas, it is easy to create stress superposition, which may lead to the occurrence of compound dynamic disasters.  
The fold structure is formed by the bending deformation of coal bed due to the compression and torsion of vertical and horizontal stress. It is the most basic tectonic type in the process of crustal movement. In coal mining, there is a large tectonic stress in the fold area. [PERSON] et al. [41] studied tectonic coal and in situ stress, and identified that in situ stress of fold structures is the main controlling factor of coal and gas outburst. Under the influence of mining disturbance in the working face, it is very easy to induce coal and rock dynamic disaster accidents.