Numerical simulation of Qiaotou Landslide deformation caused by drawdown of the Three Gorges Reservoir, China

Abstract

Landslides located beside reservoirs tend to be unstable or are characterized by large deformation during the drawdown process. This has been accepted by many experts. In this paper, we use Qiaotou Landslide, which is located beside the Three Gorges Reservoir (TGR), as a typical case study to investigate and predict the deformation mechanism during the drawdown process of TGR in detail. According to field investigation, the landslide mass is mainly composed of thick, loose silt and clay mixed with fragments of rock. Bedrock is mainly composed of silty sandstone. Field and laboratory tests indicate that the landslide mass has a high permeability coefficient. If the water level declines fast, intense seepage force may result. Based on these data, we establish a three-dimensional geological model of Qiaotou Landslide by FLAC 3D and perform a numerical simulation using the saturatedunsaturated fluid-solid coupling theory. For the simulation, we assume that the drawdown from 175 to 145 m takes place with a speed of 25 cm/day, which is based on the extreme water level regulation program of TGR. The simulation shows that this causes a significant deformation in the landslide mass and that the maximum displacement within the landslide is 24.2 cm. During the drawdown process, the maximum displacement zone is shifting from the upper part of the landslide where bedrock surface is steeper and thickness of loose deposits is less to the middle part of the landslide where bedrock surface is less steep and thickness of loose deposits is higher. The deformation mechanism indicates that in the early stage of the drawdown the deformation of the landslide mass is mainly caused by seepage and in the later stage mainly by consolidation.

Using wavelet tools to analyse seasonal variations from InSAR time-series data: a case study of the Huangtupo landslide

“…Because rainfall is a well-known triggering factor of landslides (Bittelli, et al 2012, He, et al 2008, He, et al 2010, Jiang, et al 2011, Jiao, et al 2014, Wen and Chen 2007, (Jiang, et al 2011), this section assesses the relationship between rainfall and the Huangtupo slope displacements through XWT and WTC analysis. The plots for the four different slumping masses are shown in Figure 7.…”

“…Water can act in several ways: (a) reducing shear strength of the weak zones due to the physical and chemical interactions between the slip zones' materials and groundwater (He et al 2008, He et al 2010, Jiao et al 2014, Wen and Chen 2007 or due to pore pressure increase (i.e. a rise in pore-water pressure causes a drop in effective stress reducing the shear strength of a slope); (b) increasing the hydraulic gradient and seepage force of a landslide mass during water level lowering (Jiang et al 2011); (c) reducing soil suction (Bittelli et al 2012, Cascini et al 2014; (d) increasing soil unit weight; and/or (e) causing soil consolidation-swelling due to the changes of effective stresses on the landslide mass (Jiang, et al 2011). However, these water actions are not independent from each other.…”

“…Many papers have discussed the above-mentioned effects on the Three Gorges landslides (Bin et al 2007, Cojean and Caï 2011, He, et al 2008, He, et al 2010, Jiang, et al 2011, Jin et al 2012, Wang et al 2004, Wang et al 2008, Xia et al 2013, Xie 2009.…”

The Monitoring-Based Analysis on Deformation-Controlling Factors and Slope Stability of Reservoir Landslide: Hongyanzi Landslide in the Southwest of China

“…Also, approximately 75% of triggered landslides were due to the revivification of ancient landslides [5]. In summary, the significant and instant reservoir water level fluctuations normally cause negative influences on the global stability of the reservoir slopes through influencing their hydrological conditions and reducing the slope strength [6].…”

“…The failure mechanisms and resulted chain of disasters (such as the impulse of wave) by reservoir landslides have been extensively studied in previous studies [5][6][7]. Erosions of loose debris at the slope toe by flow, instant pore water pressure generation in the slope by the drawdown of reservoir water level, and structural and strength reduction of the hydrofluctuation belt are the main reasons of triggering reservoir landslides [1,[4][5][6].…”