Mechanism of Landslides around China’s Three Gorges Dam

• Author / Creator

  Li,Yang

• In this research, a literature review is conducted for landslide reactivation and movement caused by reservoir water level fluctuation around the world and especially in China in the past decades. Based on the movement patterns and characteristics, landslides triggered by reservoir level fluctuations are broadly classified into two types based on their movement mechanism. Mechanism 1 refers to landslides which move or move faster when reservoir water level is decreasing. The soil in this type of landslide usually has low permeability and the combination of outward seepage force and lower hydrostatic pressure at the toe makes the landslide less stable when reservoir level is decreasing. Mechanism 2 refers to landslides which move or move faster when reservoir water level is rising. The soil in this type of landslide has high permeability and the increase in landslide movement is caused by decreased effective normal stress in the slip zone. These two types of landslides have been studied using a numerical model with a strain softening and strain rate dependent model adopting Drucker-Prager plasticity using the ABAQUS program. Three landslides around the Three Gorges dam reservoir have been studied. They are the Shuping landslide, Baishuihe landslide and Muyubao landslide. For Shuping and Baishuihe landslides, with low permeability soils, the calculated changes in groundwater table does not follow the fluctuation of reservoir water level closely and there is a time lag between movement and changes in reservoir water levels. The changes in the calculated factor of safety follows the expected trend on changes in reservoir water level which increases when reservoir level is rising and decreases when reservoir level is decreasing. In addition, the calculated landslide movement from coupled seepage/stress finite element model with Drucker-Prager constitutive model shows that movement accelerates when reservoir level is decreasing and decelerates when reservoir level is rising. These two landslides belong to Mechanism 1: low permeable landslide material, reservoir drawdown causes outward seepage force and less stabilizing hydrostatic pressure at the toe, which leads to movement acceleration; when reservoir level is rising, the increasing hydrostatic pressure at the toe helps stabilize the slope and decreases the rate of movement. For Muyubao landslide, which has high permeability material, the calculated groundwater table follows closely with the observed reservoir water level, which indicates that the fluctuating reservoir level has significant influence on the pore water pressure along the slip zone. The calculated factor of safety decreases when the reservoir level is rising and increases when reservoir level is decreasing. In addition, calculated landslide movement from the finite element model accelerates and decelerates when reservoir level is rising and decreasing respectively, which agrees with the observed movement from GPS stations. Hence Muyubao landslide belongs to Mechanism 2: with high permeable landslide material, fluctuations of reservoir water level induce changes in the pore water pressure and effective normal stress in the slip zone; the effective normal stress and shear resistance decrease when reservoir level is rising, which lead to movement acceleration; the effective normal stress and shear resistance increase when reservoir water is decreasing and decelerate the movement. Field permeability tests have been conducted on Shuping and Baishuihe landslides. Moreover, laboratory tests such as grain size distribution and Atterberg limits tests have been conducted on the landslide materials. It is recommended that further laboratory tests should be conducted to verify the strain softening and strain rate hardening parameters as well as unsaturated permeability parameters used in the numerical models.

• Subjects / Keywords

  • Landslides
  • Mechanisms
  • Three gorges
  • Cyclic reservoir fluctuation

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3K35MQ98

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.