## 4 Results and Analysis
### Development Trend of Disaster Sources in the Survey Line Area  
According to the detection results of the high-density resistivity method, the resistivity change diagram of the rock and soil mass under the survey line was obtained by inversion, which describes the trends of water migration and crack formation in the slope. Typical time inversion results of the sections depicted in Figures 5 and 6 are shown in Figure 8, and the external changes in the slope at the corresponding time are shown in Figure 9.  
Before the test, the resistivity of the slope was measured. The model material layer is uniform, the slope soil is relatively dry, and the slope showed a high resistance value. After the 5 th rainfall event, the accumulated rainfall is 10.5 mm. The resistivity distribution in each layer within the slope survey line was obvious, and the resistance of the same horizontal layer was consistent. The depth of the wetting front is approximately 7 cm, and the resistance is approximately 65 \(\Omega\cdot\)m. The shallow slope contained an obvious low-resistance area, with the lowest resistivity of 19 \(\Omega\cdot\)m, as shown in Figure 8a. In Figures 5 and 6, the resistivity of the shallow slope experienced the first significant sudden change. After the 76 th rainfall process, the accumulated rainfall was 159.6 mm, and preferential flow seepage was formed inside the slope, as shown in Figure 8b. After the 85 th rainfall event, the accumulated rainfall was 178.5 mm, and several low-resistance areas were formed in the shallow slope of the survey line area, with the lowest resistance of 19 \(\Omega\cdot\)m. The abscissa ranged from 0.49 to 0.77 m, 1.07 to 1.29 m and 1.47 to 1.78 m, forming three obvious low-resistance areas. The low-resistance areas inside the slope moved downwards as a whole and showed uneven changes. The low-resistance area at the middle rapidly expanded, with a wetting front depth of 33.6 cm, as shown in Figure 8c. The resistivity of the deep slope showed a sudden change, as shown in Figure 6. After the 96 th rainfall event, the accumulated rainfall was 201.6 mm, and the soil mass from the slope surface to a depth of 5 cm was saturated, with a minimum resistance of 19 \(\Omega\cdot\)m. The three low-resistance areas formed during the 85 th rainfall event developed downwards. The low-resistance area from 1.07-1.29 m showed a low-resistance zone in the middle of the slope, indicating that serious water accumulation occurred in the slope and that the weak planes were well developed, as shown in Figure 8d. After the 100 th rainfall process, the slope surface area at the abscissa from 1.14-1.19 m exhibited a relatively high resistance, with a resistance value of 61.5 \(\Omega\cdot\)m, and obvious cracks could be observed in electrode areas 16-18 along the corresponding slope surface measuring line. The sections from 0.63-1.05 m and 1.26-1.47 m showed relatively high resistance values, indicating that cracks were formed in corresponding areas inside the slope, as shown in Figure 8e. After the 111 th rainfall event, the slope showed a low resistance as a whole. The resistance at several locations within the depth range of 5.3-17 cm was higher than that of the soil at the same depth, indicating that cracks had formed in the slope, as shown in Figure 8f. The resistivity curves in Figures 5 and 6 show significant fluctuations. Figure 8: Inversion graph of apparent resistivity at typical time. To observe the development process of cracks in the slope top, according to the change characteristics of the apparent resistivity and the development of fissures in the slope top, the resistivity from the 96 th to 100 th rainfall processes was selected for time-lapse resistivity inversion, as shown in Figure 10.  
The residual value (\(\Delta\rho\)) was selected as an index to describe the change in the resistivity during crack development. A positive \(\Delta\rho\) value indicates the development of cracks, while a negative \(\Delta\rho\) value indicates water accumulation inside the slope.