## 5 Conclusions  
This article examines the effects of mine water immersion time, loading rate, and bedding direction on the fracture mechanical properties of coal through experiments in fracture mechanics. The following key conclusions have been drawn.  
The fracture toughness (\(K_{IC}\)) values of coal samples immersed in mine water for 30 days, 60 days, and 120 days were 4.39 MPa\(\cdot\)mm\({}^{1/2}\), 3.51 MPa\(\cdot\)mm\({}^{1/2}\), and 3.10 MPa\(\cdot\)mm\({}^{1/2}\), respectively, indicating decreases of 44.45%, 55.68%, and 60.87% compared to non-immersed samples, which had a fracture toughness of 7.91 MPa\(\cdot\)mm\({}^{1/2}\). After immersion in mine water for 120 days, the fracture modulus (\(E_{S}\)) and absorbed energy (\(U_{T}\)) of coal decreased by 53.38% and 63.21%, respectively, compared to the unsaturated coal  
Figure 11: Typical fracture trajectory of coal. (**a–f**) are six typical fracture trajectories, respectively.  
samples. The most significant weakening of mechanical properties occurs after 30 days of immersion. However, with prolonged immersion times, the degree of weakening in mechanical properties tends to stabilize.  
In a mine water environment, the physical and chemical interactions between various substances can compromise the structure of coal, leading to damage, the initiation of micropores and cracks, and the growth of existing cracks and pore sizes. Consequently, pores and cracks become interconnected, ultimately forming a fragmented structure. The ongoing evolution of these fragmented structures weakens the coal's ability to resist fracture.  
The fracture toughness, fracture modulus, and absorbed energy of coal exhibit a positive correlation with the loading rate; that is, as the loading rate increases, these fracture mechanical parameters also increase. This phenomenon occurs because the damage caused by load application requires time, and a higher loading rate reduces the likelihood of activating holes and cracks. The slopes of the fracture toughness curves for the three types of coal samples across varying loading rates are essentially the same, indicating that there is no significant difference in the degree to which loading rates influence the fracture resistance of different sample types.  
The orientation of bedding significantly affects the fracture toughness of coal. The Crack-divider type exhibits the highest fracture toughness and demonstrates the greatest resistance to fracture, while the Crack-splitter type displays the lowest fracture toughness and is most susceptible to unstable fracture. The fracture toughness of the Crack-arrester type lies between the other two types. This variation is attributed to the fact that the strength of the bedding plane in weak coal is lower than that of the matrix. Furthermore, when combined with the immersion effects of mine water, the mechanical properties of the three coal sample types differ markedly.  
[PERSON] and [PERSON]: provided the concept and idea and conducted the experiments. [PERSON] and [PERSON]: conducted the literature review, experimental data analysis, and wrote draft manuscript. [PERSON] and [PERSON]: conducted experiments, illustrated the pictures, and revised the manuscripts. [PERSON] and [PERSON]: analyzed the experimental results, and conducted theoretical analysis. [PERSON]: completed the writing--review and editing. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (Grant No. 52374099; 52404109), the open fund of the State Key Laboratory of Water Resource Protection and Utilization in Coal Mining (Grant No. GJNY-21-41-01), and the Natural Science Foundation of Sichuan Province, China (Grant No. 2025 YFHZ0323).  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors declare no conflicts of interest.