## 3 A Comprehensive Monitoring System for Landslides in 'Space-Sky-Ground-Underground'
### Temperature distribution inside inclinometer tubes B1, B3, and B5
The effect of sunshine will cause a significant change in its temperature. With the increase in temperature, the viscosity of pore water in the soil decreases, and the permeability coefficient of the soil will increase with the temperature rise. Thus, the strength of the shallow soil of landslides will be reduced. The permeability of soil is influenced by lithology and burial conditions. Based on the previous research of the research group, the groundwater level in this area is about 13 m, and the permeability coefficient of the silty clay containing detritus in the shallow layer (<1 m) is 1.2107-1.377 \(\times\) 10\({}^{5}\) m/s; the permeability coefficient of sandy soil and sandstone below the groundwater table is 1.2107-5.817 \(\times\) 10\({}^{5}\) m/s [57]. In addition, data analysis shows that the rock and soil below 1.0 m of the landslide surface are less affected by climate, with a smaller annual temperature change amplitude than that of rock and soil at 0-1 m depth. Moreover, the further away from the surface, the more minor the temperature fluctuation. The maximum annual temperature difference between the rock and soil at 0.2 m of the surface exceeds 30 \({}^{\circ}\)C, while it is lower than 15 \({}^{\circ}\)C between the rock and soil at 2.0 m of the surface. Frequent rainfall events occurred in this area from July to September 2021, which led to an increase in pore water pressure. Meanwhile, it is important to consider the influence of temperature rise on the viscosity of pore water. At this time, the landslide rock and soil mass were in a state of poor stability. Therefore, the variation pattern of shallow temperature in landslides can also reflect, to some extent, the changes in climate such as sunshine and rainfall. Figure 19: On-site layout of landslide monitoring system. The deformation field of landslides is the main controlling factor affecting the evolution state of slopes, which is a coupled field generated by the joint action of temperature, seepage, and other multiple fields. Figure 21 clearly shows the strain changes in the deformation field inside the Xinpu landslide. Two sets of densely distributed grating strings with a spacing of 2 m were selected for the monitoring of strain changes at different depths (0-16 m and 16-32 m from the surface). According to the analysis of the cloud chart, the optical cable used for shallow strain monitoring of landslides broke at a depth of 7 m on October 7, resulting in a lack of subsequent monitoring data for rocks and soil between 7 and 16 m from the ground surface. It is inferred that the breaking of the fiber optic is a consequence of the landslide deformation rather than incorrect deployment. This assertion is strongly supported by three key observations: (1) The FBG in-situ inclinometer array suggests that the potential sliding surface is likely situated at depths of 5 m and 10 m. However, due to the limitation of the 5m spatial sampling interval of the inclinometer sensor, this array can only provide an approximate location of the sliding surface. (2) Highly detailed deformation (strain) data are obtained by FBG strain sensing cables with a 2 m spatial resolution in Figure 21. The potential sliding surface position identified through this strain profile aligns closely with the inclinometer findings, pinpointing it to approximately 7 m and 12 m depths. (3) Additionally, the stratigraphic material composition revealed by our drill core samples serves as further evidence to validate the location of the potential sliding surface [57]. The frequent rainfall from July to September 2021 led to an increase in pore water pressure and resulted in a decrease in the effective stress of the soil, which weakened its ability to resist deformation. In addition, the Three Gorges Reservoir Area begins to store water at the end of every September, and the rise in the reservoir water level also increases the buoyancy of the landslide slope angle, which significantly reduces the overall stability of the landslide.