# Numerical Modeling of Engineering-Scale Jointed Coal Mass and Confining Pressure Effect
## 6 Conclusions  
In this study, the discrete element software PFC2D was utilized to construct and calibrate engineering-scale parameters. The mechanical response was studied under biaxial loading conditions. The main conclusions are as follows:  
1. The bedding and cleats inside the coal seams of Honghui Coal Mine were counted, and they were negatively exponentially distributed and log-normally distributed, with an average spacing of 14.2 cm and 17.5 cm, respectively. A network joint model for the coal seam was established based on the statistical results.
2. The uniaxial compression test was performed to obtain parameters such as the uniaxial compression strength, elastic modulus, and Poisson's ratio of the coal specimens, while the direct shear test was conducted to gain parameters such as the cohesion and coefficient of friction of the joints. The calibration of the detailed parameters of the model was conducted by matching the numerical simulation with the experimental results, and the errors of the strength and the elastic modulus of the calibrated coal mass were within 5%. Further, an engineering-scale coal mass model was established with the step-by-step matching method.
3. Simulations of coal masses with varying fissure degrees were performed under different confining pressures. Based on these simulations, relationships were established between the strength, confining pressure, and fissure degree. The findings indicated that as the confining pressure increased, the load-bearing capacity of the coal mass improved, while the total number of fissures decreased. Meanwhile, the failure mode shifted from joint failure to matrix failure and the angles of the main fissure decreased.
4. The internal friction angle and cohesion of the jointed coal seam were determined through simulations involving confining pressure loading, across different fissure degrees. Using these parameters, the distributions of the abutment pressure and failure tendency coefficient within the coal seam were mapped. The results confirmed that the failure zone of the working face was obviously expanded when the fissure degree was increased.  
[PERSON] wrote the main manuscript text. [PERSON] presented the idea. [PERSON] and [PERSON] provided financial assistance and optimized the structure of the manuscript. [PERSON], [PERSON] and [PERSON] undertook the theoretical analysis and numerical simulations. All authors have read and agreed to the published version of the manuscript.  
Figure 15: Relationship between top-coal damage range and fissure degree.  
**Funding:** This research was financially supported by the National Key Research and Development Program of China (2023 YFC2907600, X.W.), National Natural Science Foundation of China (52174132, X.W.), Key Research and Development Special Tasks of Xinjiang Province (2022B01051, J.B.), Key projects of the Joint Fund of the National Natural Science Foundation of China (U21A20107, J.B.), and China Postdoctoral Science Foundation (2024M763556, F.Z.).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data is contained within the article.  
**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.