## 4 Influence Analysis by Simulation
### Discussion  
This study used UDEC to build two models based on the geology of the Huaibei Coalfield to analyze the impact of overlying igneous rocks on coal mining face advancement. In the in situ stress simulation, for vertical stress, Model 1 had stress concentration in the goat-surrounding rock and the lower igneous rock's arch angle side. As the face advanced, the vertical stress peak and influence range grew, with both igneous layers affected. The max vertical stress was 36.4 MPa, and the influence range reached 32.4 m. In Model 2, stress concentrated near the goat, with a max of 35.6 MPa and an influence range of 29.6 m. Model 1 had more extensive igneous rock stress concentration. For horizontal stress, in Model 1, stress evolved from local in the lower layer to widespread in both layers. In Model 2, the overlying rock's horizontal stress changed gently, showing igneous rocks' significant impact on horizontal stress. In the roof absc  
Figure 10: Simulation results of roof strata subsidence.  
Model 1, fissures developed in two igneous layers, with a max water conducting fracture height of 142.4 m (35.6 times the mining height). In Model 2, goat middle fissures compacted, and water-conducting fissures were near the open-off cut and face, with a max height of 90.4 m (22.6 times the mining height). Model 1 had a larger water-conducting fracture height. In roof strata subsidence simulation, Model 1's lower and upper igneous layer subsidence was about 2.78 m and 2.21 m, respectively, while Model 2's was 3.03 m and 2.58 m. Model 1's subsidence decreased by 8.25% and 14.34%. The subsidence of other strata was similar, indicating igneous rocks' control over upper strata subsidence. In short, igneous rocks greatly affect stress distribution, roof abscission layers, and strata subsidence in coal mining.  
The presence of hard-thick igneous rocks leads to a large-scale horizontal and vertical stress concentration in the upper and lower layers of the igneous rock. This stress concentration can serve as a major driving force for coal and gas outbursts or water intrushes. The roof abscission layer, which acts as a reservoir for gas or water and is formed under specific geological conditions, may trigger dynamic disasters once the hard-thick igneous rock fractures. The data published on the official website also confirm that the occurrence of igneous rocks is an important inducing factor for disaster accidents. For example, in Wolonghu Coal Mine, two coal and gas outbursts in Coal Seam No.10 both took place near the magmatic intrusion boundary. On 25 April 2009, a coal and gas outburst accident happened in Coal Seam No.10 in Haizi Coal Mine, which is located under an extremely thick igneous rock layer. Also affected by the extremely thick magmatic rocks, a major water intrusion accident occurred at the 745-working face of Haizi Coal Mine in 2005.  
Moreover, the igneous rock within the overburden exerts a certain degree of control over the subsidence of the upper strata. It has played a positive role in alleviating surface subsidence, which is of great significance for the sustainable development of coal mining areas.