Reactivation characteristics and hydrological inducing factors of a massive ancient landslide in the three Gorges Reservoir, China

Abstract

With the construction of the Three Gorges Reservoir (TGR), water impoundment began in 2003. The reservoir water level (RWL) has been annually adjusted to a fluctuation level between 145 and 175 m above sea level (a.s.l.) since 2008. Numerous large scale ancient landslides have been reactivated in the region. This paper focuses on the reactivation characteristics and influence of hydrological inducing factors on deformation of a massive ancient reservoir landslide. The Taping landslide is taken as an example, and its geological setting, material composition, structural characteristics and spatiotemporal deformation characteristics of the landslide are presented. According to the surface deformation characteristics, the Taping landslide can be divided into three subzones. Then, an attribute reduction algorithm based upon neighborhood rough set theory is used to quantitatively analyze the influences of key hydrological factors on the movements within the three subzones of the landslide. Long-term monitoring data are used to identify the key threshold values that induce fast movements within the three subzones of the landslide. Finally, the reactivation mechanism of the Taping landslide is proposed. The results show that the Taping landslide is in a state of periodically consistent creep deformation. The movements within the three subzones of the Taping landslide are affected by different hydrological factors. For the leading section, the hydraulic gradient is the most important hydrologic factor affecting the slope movement, and 0.07 is the key hydraulic gradient threshold for fast movement. For the middle section, rainfall and hydraulic gradient are the two most important hydrologic factors affecting the slope movement. The average daily precipitation over the last seven days and hydraulic gradients of 10 mm and 0.15 are the threshold values that induce its fast movement. For the rear section, the slope movement is mainly affected by the ground water level (GWL), and a GWL of 185.5 m a.s.l., is identified as the key threshold value that induces its fast movement. The findings in this study can help in managing reservoir landsides and designing landslide reinforcements in the regions of the world with geological settings similar to that of the TGR region.