Abstract
Forty-six ancient Tibetan star-shaped towers and a village are located on a giant slope, which would be partially flooded by a nearby reservoir currently under construction. Ground survey, boreholes, and geophysical investigations have been carried out, with results indicating that the slope consists of loose deposit with a mean thickness of approximately 80 m in addition to an overlying bedrock of micaceous schist and phyllite. Ground survey and Interferometric Synthetic Aperture Radar (InSAR) indicated that the slope is experiencing some local deformations, with the appearance of cracks and occurrence of two small landslides. Through using borehole logs with the knowledge of the regional geological background, it can be inferred that the loose deposit is a result of an ancient deep-seated translational landslide. This landslide was initiated along the weak layer of the bedding plane during the last glaciation in the late Pleistocene (Q3) period, which was due to deep incision of the Dadu River at that time. Although it has not shown a major reaction since the ancient Tibetan star-shaped towers have been built (between 200 and 1600 AD), and preliminary studies based on geological and geomorphological analyses incorporated with InSAR technology indicated that the landslide is deformable. Furthermore, these studies highlighted that the rate of deformation is gradually reducing from the head to the toe area of the landslide, with the deformation also exhibiting relationships with seasonal rainstorms. The state of the toe area is very important for stabilizing a landslide and minimizing damage. It can be expected that the coming impoundment of the reservoir will increase pore pressure of the rupture zone at the toe area, which will then reduce resistance and accelerate the deformation. Future measures for protection of the slope should be focused on toe erosion and some bank protection measures (i.e., rock armor) should be adopted in this area. Meanwhile, some long-term monitoring measures should be installed to gain a deep understanding on the stability of this important slope.
Highlights
Landslides triggered by the impoundment of reservoirs have been widely reported in the literature [1,2,3,4,5,6,7,8]
River deeply incised and the weak layer of the slope composed of micaceous schist was exposed; (2) the landslide occurred, resulting in its toe moving into the Dadu River and covered on the glaciofluvial deposits; (3) part of the toe was eroded by the river, with river facial sediments being deposited on the landslide toe; (4) the first river terrace was formed and covered on the toe of the landslide
(1) The slope investigated is covered by loose deposit, which has a thickness of 70–90 m
Summary
Landslides triggered by the impoundment of reservoirs have been widely reported in the literature [1,2,3,4,5,6,7,8]. Stability problems of partially submerged slopes are of great concern [10,11,12,13,14] Studies in this field of research can be roughly grouped into three categories: designing engineering geological models [2,5,8,15,16,17,18], material property studies [19,20] and formulating mathematical models [21,22,23,24,25]. We focused on an important slope in the southwestern part of China, which would be partially submerged by a reservoir under construction nearby This slope has 46 Tibetan star-shaped towers and a village with 40 inhabitants located on it. Based on the investigation and the regional geological analysis, we discovered the existence of an ancient landslide and presented its geological model, before giving a preliminary stability assessment and some countermeasures to prevent a major reaction
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