## 4 Discussion  
The slopes of the three types of mitigation measures all underwent toe erosion, and formation and expansion of local failures, but the degree of slope changes at each stage were not the same. During the toe erosion stage, the main erosion and damage location of the three types of slopes were all concentrated at the toe. However, the slope with a declining gradient mitigation experienced the earliest erosion damage as well as the largest erosion at the toe. The step-by-step and drainage canal mitigation slope had the least amount of slope erosion (Figure 9). During the local failure stage, the slope without any mitigation measures formed steep lateral free faces after local failures, and the slope with a declining gradient mitigation collapsed rather than sliding; it experienced relatively little deformation. Furthermore, high and steep lateral free faces did not appear in the toe of the slope with slope down the slope step-by-step mitigation after local failure. The slope with a stepwise drainage channel mitigation was more prone to local failure and had deeper sliding surfaces due to the settlement cracks that occurred near the drainage channels (Figure 10). In the later stage of the experiment, both the slope without any mitigation measures and the slope with a declining gradient mitigation exhibited local failures. When overall failure occurred, the sliding back edge of the slope without any mitigation measure was located at the top of the slope, and the sliding surface was deeper. The sliding back edge of the slope with a declining gradient mitigation was located in the middle part of the slope surface, and the failure was shallow, with a thin sliding surface (Figure 11). Figure 10: Heights of local failures of different slopes. Figure 9: Erosion in the slope toe of different slopes. Based on the displacement data and observed experimental phenomena, we found the creep process of slopes with different mitigation measures to be different. During the experiment, tensile cracks appeared on all three types of slopes, and the appearance of tensile cracks on the slope without any mitigation measure had a clear chronological order. Tensile cracks first appeared at the toe of this slope, followed by a local failure at the toe of the slope. Tensile cracks then appeared at the middle and then the upper part of the slope. In contrast, the slope with a declining gradient mitigation had tensile cracks appearing simultaneously at different positions on the slope surface, with no clear chronological order. This indicates that the creep of the slope with a declining gradient mitigation occurred simultaneously at the toe, middle, and upper part of the slope, thus causing tensile cracks to appear at these positions simultaneously. The slope with a stepwise drainage channel mitigation had tensile cracks near the transverse drainage channels on the slope surface. For the slope without any mitigation measures, due to the influence of the erosion at the toe of the slope, the lateral stress at the toe of the slope was greater than at the bottom, and therefore the creep was more obvious at the toe of the slope [45,46]. As a result, tensile cracks appeared at the toe of the slope first, followed by the middle and upper parts as a consequence of local failures. The slope with a stepwise drainage channel mitigation experienced discontinuous creep, and cracks were prone to occur near the drainage channels due to differences in deformation. During the testing, slopes with different mitigation measures exhibited different characteristics in water infiltration and erosion, pore-water pressure, and slope deformation. However, there were also commonalities in the failure processes of all the slopes, such as erosion and failure at the toe of the slope being a prelude to subsequent slope failures. The toe of the slope is the most susceptible area to slope failure, so when carrying out slope protection, attention should be paid to protecting the toe of the slope to prevent failure caused by erosion.