## 2 Methodology  
### Preparation of Rock Samples  
As shown in Figure 1a, the rock samples used in this study were sourced from the southern slope landslide area of the Wulagen Mine, Xinjiang (75 deg02'30'' E, 39 deg40'52'' N), Since the end of 2020, multiple wedge collapses have occurred on the southern ultimate pit wall steps of the open-pit mine. Figure 1b shows the specific landslide body within the landslide area; the landslide body is approximately 60 m in length and 75 m in height. Field investigations of the landslide area revealed a significant number of seepage points on the slope. The average measured seepage volume at the pit bottom was approximately 4600 m\({}^{3}\)/day, far exceeding the predicted inflow rate, and the rock's average moisture level in this area was measured to be 2%. This suggests that the landslide is highly likely caused by prolonged water saturation. To verify the impact of water saturation on slope stability, dry feldspar sandstone samples were collected from the study area near the landslide region (Figure 1b). The feldspar sandstone samples have a medium to coarse-grained sandstone structure with medium to thick bedding. The composition mainly consists of quartz, feldspar, a small amount of rock fragments, and filling materials. The particles are well sorted, sub-rounded, and the maturity is low. The filling materials include needle-like gypsum and carbonate rock. The sandstone has a cemented type of porosity with flow-through pores, and some particles are suspended or loosely accumulated, classifying it as weakly cemented sandstone. Regarding porosity, although it was not directly measured in this experiment, according to the literature, the porosity of weakly cemented sandstone is typically around 30% [34; 35]. According to the guidelines established by the International Society for Rock Mechanics, 18 feldspar sandstone blocks that met processing conditions were chosen. All samples were collected along the bedding direction to ensure the consistency and comparability of  
Figure 1: Sampling locations and some feldspar sandstone samples: (**a**) Wulagen lead–zinc mine; (**b**) localized landslides; (**c**) feldspar sandstone samples. the experiment and processed into 50 mm \(\times\) 50 mm \(\times\) 100 mm cubes, with surface errors within 0.3 mm and intact surfaces. Some of the processed feldspar sandstone samples are shown in Figure 1c. All feldspar sandstone samples were subjected to drying at a constant temperature of 105 \({}^{\circ}\)C for 48 h. This is a standard practice commonly used in the field for drying rock samples to ensure complete removal of moisture. After drying, the longitudinal wave velocity of the samples was measured using a ZT802 non-metallic ultrasonic testing analyzer. Fourteen samples exhibiting similar wave velocities were chosen for further physical and mechanical testing. The dried samples were then sealed in plastic wraps, and the masses were recorded of two dried samples, labeled A0-1 and A0-2, kept aside. As shown in Figure 2, the remaining twelve samples were placed in two desiccators, A1 and A2, with six samples in each desiccator. The samples were prepared using a saturated sodium chloride solution with a mass concentration of 26.4%. Figure 2(a) illustrates the variations in moisture content of each sample under different immersion times, while the variations in average moisture content over time in desiccators A1 and A2 are depicted in Figure 2(b). The moisture content showed a steady increase with longer immersion, which can be classified into three stages, beginning with a linear growth phase from 0 to 5 days with an average growth rate of 0.3% per day, a decelerating growth stage from 6 to 18 days, with growth rates ranging from 0.2% per day (6-9 days) to 0.55% per day (10-18 days), and a stabilization stage from 18 to 30 days, with the final moisture content of 2.4%. Figure 3: The moisture content–time curve for the rock samples: (**a**) Sample test values; (**b**) Mean value of samples. Figure 2: Schematic diagram of desiccator.