## 3 Results
### Pore-Water Pressure Changes  
Variations in pore-water pressure show a periodicity and strong correlation with the slope deformation [42; 43]. In our experiments, fluctuations in pore-water pressure mainly occurred during various stages of slope failure. In the initial stage of the testing, the deformation of the slope occurred due to creep caused by an increase in the slope's water content and erosion on the slope surface. During this stage, the pore-water pressure at the toe and middle part of the slope changes only slightly, with a small upward trend (Figure 4). In the second stage of the testing, continuous rainfall caused surface instability and a shallow slide in the slopes, and the pore-water pressure changed with these events (Figure 4). The pore-water pressure in given area had significant fluctuations during local failures in that area. When the sliding depth was shallow, only the surface pore-water pressure had significant changes, and when the sliding depth was high, the pore-water pressure at different depths had a significant response. The responses of pore-water pressure during local failure of slopes with different mitigation measures were slightly different, however (Figure 4). Specifically, the fluctuation of pore-water pressure on the slope without any mitigation measure mainly occurred in the shallow soil (5 cm), and the pore-water pressure variation in the deep soil did not change significantly. Combined with the deformation data, this indicates that when a local failure occurred, the pore-water  
Figure 4: Pore-water pressure changes for different slopes at different sites. pressure was mainly concentrated in the soil 5-15 cm deep from the slope surface, which means that the failure depth was concentrated at 5-15 cm as well. In the slope with step-by-step mitigation, the change in pore-water pressure was not significant, which indicates that at this stage, the response of the slope to rainfall was mainly concentrated on the surface. Although the water content in the deep soil increased, the pore-water pressure did not increase significantly, and the failure was mainly in the shallow soil. In the slope with a stepwise drainage channel mitigation, the pore-water pressure changed more rapidly, and the pore-water pressure in the deep soil (15 cm) was larger than in the other two types of slopes, indicating that the sliding surface of the slope was deeper than the other two types of slopes as well. In the last stage of the testing, the slope without any mitigation measures experienced overall failure along a sliding surface under continuous rainfall. Pore-water pressure at different depths and locations underwent rapid changes all at the same time as well. The most significant change in pore-water pressure occurred in the shallow soil, and the change in the deep soil was relatively small. Unlike the changes in the second stage, the change in pore-water pressure was nearly instantaneous. The trend in pore-water pressure changed at different positions and was a sudden increase within 1-2 s, followed by a rapid decrease prior to stabilization. This phenomenon is due to the rapid failure of the entire slope causing almost instant displacement of various parts of the slope and subsequent poor drainage that led to excess pore water pressure. This in turn caused a sudden increase in pore-water pressure in various parts of the slope [44; 45; 46]. The slope with a declining gradient mitigation also experienced shallow sliding, with a synchronous increase in pore-water pressure at all parts of the slope before eventually stabilizing. Compared to the slope without any mitigation measures, the changes in pore-water pressure in the slope with a declining gradient mitigation were more gradual, with a clear process of continuous growth and no pore-water pressure surges.