## 4 Results and Analysis
### Geoelectric Field Characteristics under Disaster Source Evolution in the Survey Line Area
The maximum apparent resistivity is 45 \(\Omega\cdot\)m, and the range (R) is 18 \(\Omega\cdot\)m. The apparent resistivity of section G from 0.105 m to the top of the slope suddenly increased and fluctuated after the 100 th rainfall event. The maximum apparent resistivity is 144 \(\Omega\cdot\)m, and the range (R) is 98 \(\Omega\cdot\)m. According to the observation results, obvious cracks could be observed in the area of electrodes No. 16-18 (near section E) at the top of the slope after the 100 th rainfall process. The Archie formula indicates that the resistivity (\(\rho\)) of water-bearing rock can be described by the porosity and saturation, as expressed in Equation (11) [36]. \[\rho=a\rho_{w}\varphi^{-\alpha}\ S^{-\beta} \tag{11}\]  
where \(\alpha,\ \beta\) and a are constants, \(\varphi\) is porosity and \(S\) is the volume fraction of pores filled with water, and \(\rho_{w}\) is the resistivity of the pore fluid. Under the same seepage medium conditions, the apparent resistivity was negatively related to the porosity and saturation within the slope. Therefore, the fluctuation in the apparent resistivity of section E after the 96 th rainfall event shows that the porosity and saturation within the slope constantly varied, the internal structure of the slope in section E area was damaged, and cracks were formed. According to the analysis of Figure 5 and fissure development in the slope top, the apparent resistivity data of each layer of sections B, C, D, E and F were selected, the apparent resistivity rainfall sequence diagram was generated, and the change characteristics of the apparent resistivity in the crack development process were analyzed, as shown in Figure 6.  
Figure 6a,b show that after the 96 th rainfall process, the apparent resistivity of sections E and F first increased and then fluctuated, and the maximum range (R) at the 0.035 m depth in section E reached 40 \(\Omega\cdot\)m. This indicates that cracks were first generated in the shallow slope near section E. Figure 6c-e reveals that after the 96 th rainfall event, the resistivity values of the other layers also exhibited sudden changes of different amplitudes, and the change amplitude decreased with increasing depth. Obvious cracks appeared at the measuring line at the top of the slope after the 100 th rainfall event. The results showed that corresponding areas within the slope had been damaged to varying degrees before the  
formation of cracks in the slope top. In other words, after the 96 th rainfall process, cracks were formed in the shallow slope and gradually developed towards the depths and surface of the slope. During the measurement (after rainfall cessation), under the action of water evaporation and seepage, the water content in the rock and soil mass above the critical depth continuously decreased, and the soil shrank and was deformed. When the tensile stress generated by shrinkage exceeded the tensile strength of the rock and soil mass and the lateral stress of the dead weight, the slope produced large shrinkage cracks, and the apparent resistivity dramatically increased. When rainfall again occurred, the rock and soil mass absorbed water and expanded. When the expansion stress exceeded the tensile strength and the lateral stress of the self-weight, shallow and short expansion cracks were generated, and the apparent resistivity value slightly increased. In the process of the drying and wetting cycle, crack development and water infiltration alternated along the cracks, reflected as the fluctuation in the apparent resistivity in the corresponding area. As the deep slope was less notably affected by water at the beginning of rainfall, the change form of the apparent resistivity differed from that in the shallow area, showing a slow fluctuation and decline. Figure 6f-i shows that after the 60 th rainfall event, the apparent resistivity of the slope below 0.21 m sharply decreased and gradually approached the apparent resistivity value in the saturated state.