## 3 Results
### Active Controlled Landslides Areas  
Some evident deformation was detected in the Dazhou landslide, which is a landslide group consisting of five individual landslides named from Zone A to Zone E. Situated in Dazhou town, the total length of these five landslide bodies stretches over 1370 m. Extended from south to north, Zones B, C, and D are separated by gullies and maintain their own boundaries (Figure 8). The trailing edge of them is in a gentle area on the west side of the highway, and the leading edge has a steeper slope and is permanently submerged into the Yangtze river. Figure 7: (**a**) PSInSAR deformation rate map of the Dadiping landslide. (**b**) InSAR time-series analysis result of persistent scatters at site P1. (**c**) Cracks observed at the floor of a nearby house. (**d**) Anti-slide piles in front of the highway. (**e**) Crack observed in a nearby slope protection wall. Previous field investigations suggested that significant deformation was found for Zones C and D, including clear signs of sliding caused by tensile rupture, such as cracks on the buildings and ground, collapse, and distortion on the road (see Figure 9). A strong deformation zone between Zones C and D is highlighted in Figure 10.  
The engineering remedial work for the Dazhou No.2 landslide was designed in a segmented form and the main engineering countermeasures are anti-slide piles, combined with drainage ditches and modification of the slope geometry. Based on the calculation of the slope thrust and the design load, the pile spacing was initially drawn to be 5.5-6 m, and the pile length was 15.5 m. In total, 29 piles were planted into the bodies of Zones B, C, and D. No obvious deformation was detected in engineering the countermeasure structures of slides B and D, while some damages occurred in three anti-slide piles on the left edge of slide C (Figure 9). In total, three anti-slide piles were inclined on the left edge of slide C.  
Figure 8: Photos of the Dazhou landslide: (**a**) Aerial photograph of the Dazhou landslide. (**b**) Shear crack at the front edge of the Dazhou landslide. Figure 9: (**a**) The PSInSAR deformation rate map of the Dazhou landslide, with the strong deformation area circled in red. (**b**) The soil slip between the anti-slide piles observed at the circled area at site P1 (shown in a); (**c**) Damage to the anti-slide piles at the circled area at site P2 (shown in **a**). (**d**) An anti-slide pile shifting towards the sliding direction at site P3 (shown in **a**); (**e**). Crack observed in a nearby house at site P4 (shown in **a**). Soil in front of the anti-slide piles moved down significantly. An evident crack, about 30 cm length, was observed on the second pile of the left edge of slide C. Another crack about the same length was found on the left edge of slide B. Except for the different level of soil slips in front of the piles, the pile structures were basically intact. The information indicates that the slope is unstable at a certain depth, and the damage of engineering project could influence the overall stability of slide C; to assess the exact deformation of the underground pile section and the depth of the sliding surface subsurface data are needed. As the Dazhou landslide is one of the few controlled landslides that was still carefully monitored, more sources of monitoring data could be introduced to verify its deformation. The positions of the monitoring devices are shown in Figure 10; all of the monitoring points were arranged along the three cross sections of Zones B, C, and D. The position of the piles was also depicted in Figure 10. The most significant deformation occurred between Zones C and D, where no piles were designed to protect this area. This deformation could also be verified with InSAR surface monitoring: PSs with relatively high deformation rates were located exactly at the same place between Zone C and D.  
Figure 11 shows the inclinometer data of the Dazhou landslide, showing that a significant movement was detected in 2017.