## 2 Materials and Methods  
### Water Softening Test of Rock  
Through the study of the engineering geological conditions in the Yili mining area, it has been revealed that the coal-bearing strata in the Yili area are primarily composed of Jurassic and Early Precambrian mudstones, sandstones, and sandy mudstones. Due to their relatively young diagenetic age and low degree of cementation, these rock formations are considered typical weakly cemented strata [19; 20; 21]. The main mechanical parameters of weakly cemented sandstone specimens in their natural and saturated states were determined. The specimens were 100 mm in height and 50 mm in diameter. Uniaxial compression tests were conducted using displacement-controlled loading at a loading rate of 0.1 mm/min, and axial deformation of the specimen was monitored throughout the loading process. Tensile strength was determined using the Brazilian splitting method. Multiple measurements were performed for both saturated and natural rock states to obtain the average values. The measured mechanical parameters are listed in Table 1.  
To study the effect of water on the failure mode and strength degradation of weakly cemented sandstone, it was found that the mechanical parameters of weakly cemented sandstone in its natural state are relatively lower compared to conventional rock types [22; 23; 24]. The stress-strain curves of weakly cemented sandstone in its natural and saturated states are shown in Figure 1. In its natural state, the stress-strain curve exhibits different stages of compaction, elasticity, yielding, and post-peak deformation. It can be observed that with the increase in axial stress, the specimen in its natural state rapidly loses strength after reaching the peak, displaying distinct brittle characteristics. The failure modes of the two rock types are different. From the stress-strain curve, it can be seen that during the pore compaction stage, the curve is convex, and the convex part of the rock significantly reduces before and after water saturation. After water treatment, the internal friction angle and cohesion of the rock noticeably decrease, leading to a different rock failure mode. Figure 1 also depicts the failure mode of weakly cemented sandstone, characterized by a single inclined shear failure plane. The uniaxial compressive strength decreases by 63.5% after saturation. Under saturated conditions, the maximum uniaxial compressive peak strength of weakly cemented sandstone is 4.5 MPa. It is evident that water has a significant weakening effect on the strength of weakly cemented sandstone. To construct the numerical computational model, this research employed the UDEC 7.0 (Universal Distinct Element Code) software [25], which is founded upon the Discrete Element Method (DEM). UDEC possesses the capacity to simulate the mechanical behavior of rock masses under both static and dynamic loading conditions, encompassing phenomena such as block separation and rotation. The use of DEM allows for an effective analysis of the propagation patterns of internal fractures, and UDEC relies on these internal fractures to form predominant fluid pathways [26]. If finite element simulation is employed, it will be unable to accurately represent the fluid migration resulting from the presence of large-scale fractures. The sample is composed of numerous individual blocks and joints, with fluid percolating through these joints. [27], and the pore pressure difference is used as the basis for fluid migration\".