3D displacement and deformation mechanism of deep-seated gravitational slope deformation revealed by InSAR: a case study in Wudongde Reservoir, Jinsha River

• Published in: Landslides 2022-09, Vol.19 (9), p.2159-2175
• Main Authors: Ren, Kaiyu, Yao, Xin, Li, Renjiang, Zhou, Zhenkai, Yao, Chuangchuang, Jiang, Shu
• Format: Article
• Language: English
• Subjects: Agriculture; Civil Engineering; Cognition; Cracks; Deformation; Deformation mechanisms; Ductile-brittle transition; Earth and Environmental Science; Earth Sciences; Engineering geology; Escarpments; Fluvial deposits; Geography; Geological surveys; Gravity; Impoundments; Interlayers; Lithology; Natural Hazards; Original Paper; Parallel flow; Photogrammetry; Remote sensing; Reservoir water; Reservoirs; Rivers; Sliding; Slope stability; Slumping; Stability analysis; Substrata; Surveying; Synthetic aperture radar interferometry; Three dimensional flow
• ISSN: 1612-510X; 1612-5118
• DOI: 10.1007/s10346-022-01905-8

The deep-seated gravitational slope deformation (DSGSD) triggered by impoundment has attracted worldwide attention. After impoundment of Wudongde reservoir downstream of Jinsha River, China, Zaogutian DSGSD occurred with an estimated volume of 129 million m 3 , which provided an opportunity for in-depth analysis and cognition of its mechanism and risk. The DSGSD sits on a chair-shaped bedding bank slope with multi-weak interlayers at the bottom, forming a lithology structure of brittle cap overlying a ductile substratum. Based on the traditional engineering geological exploration, 3D observation of the DSGSD was carried out by UAV photogrammetry, and the cracks, discontinuities, and macroscopic deformation characteristics of different areas were identified. Combining the InSAR survey and surface-parallel flow assumption, the mm-level 3D deformation rate field and time-series displacement from December 2019 to December 2020 were reconstructed. Finally, the following conclusions were arrived at: according to the cracks and the boundary between rock mass and deposit, the DSGSD could be divided into four zones: the loose deposit near the bank, the scarp area in the front part, the major sliding area in the middle part, and the stable area. The loose deposits were deforming by uplifting with a maximum rate of 70 mm/year. The deformation rate in the western part of the major sliding area was the fastest, and the rates of the maximum settlement and southward deformation peaked at 100 mm/year and 250 mm/year, respectively, which were 2–3 times data in the scarp area. Under the soaking of reservoir water, the mechanical magnitude of the weak layer in the lower Dengying Formation and the Guanyinya Formation got reduced, which was the triggering factor of Zaogutian DSGSD. As a result, the major sliding area pushed the scrap area to creep along with the weak layer, and sliding accompanied by tensile fracturing is the instability mode in case of failure. The combination of InSAR and UAV observation provides a deeper insight into the deformation mechanism of DSGSD, which is not only conducive to slope stability evaluation but also demonstrates the role of remote sensing technology in the study of DSGSD.