Mechanism And Stability Of Landslides With Step-like Deformation In The Three Gorges Reservoir

Since the first impoundment of Three Gorges Reservoir, sharply rising and periodic variation of reservoir level have worsen the geological environment of reservoir area. A large number of old landslide showed the sign of revival. The displacement-time curve of most landslide presented step-like changing. The displacement of them jumped disconnectedly and with a large value. It was hard to judge the stability of this kind of landslide. And the landslide forecast wound be very difficult.The landslide with step-like deformation is the object of study in this paper. And the deformation features, deformation mechanism and the influence factor of deformation of this kind of landslide are the main topic. The main research contents include: according to the monitoring data of deformation, rainfall and reservoir level, chapter 2 analyze the deformation behavior, failure mode and influence factor of deformation; Taking the No 1 landslide of Tangjiao village as example, chapter 3 research the deformation mechanism of landslide and the influence factor under rainfall condition; Taking the Bazimen landsliding as example, chapter 4 research the deformation mechanism of landslide and the influence factor during the changing of reservoir level; Taking the Taping landsliding as example, chapter 5 analyze the deformation mechanism of landslide under coupled effect of rainfall and changing of reservoir level. The main results of this study are as follow:After analyzing the slope condition, external factors and deformation features of three typical landslides with step-like deformation in the Three Gorges Reservoir, following conclusions have been reached: when reservoir level changes around the front of landslides, the landslides may behave as a pull-type deformation and rainfall will be the main factor of deformation. When reservoir level changes around the middle part of landslides, the landslides may behave as a push-type deformation and rapidly change of reservoir will become the main factor of defamation.Taking the No 1 landslide of Tangjiao village as example for studying rainfall factor, and found: With the same intensity of rainfall, the higher the precipitation, the greater the decrease of safe factor of landslides. And with the same amount of rainfall, the larger the intensity of rainfall,the greater the decrease of safe factor. Under the same rainfall condition, the bigger the saturation permeability coefficient of landslides, the shorter the lagging effect of rainfall. And the safe factor will have a smaller decrease during the rainfall, and a faster rise after rain. When the landslides saturated water content are bigger, the safe factor will draw down later and smaller during the rainfall, and have a slower rise after rain.Taking the Bazimen landslide as example for studying reservoir level factor, and found: When reservoir level changes within the range of locked segment of landslides, the higher the water level, the worse the stability of landslides. When reservoir level changes within the range of sliding segment of landslides, the higher the water level the greater the stability of landslides. Safe factor of landslides increases and decreases while the reservoir rise or draw down. And the faster the reservoir changes the greater the safe factor changes. The bigger the saturation permeability coefficient of landslides, the smaller the safe factor changes during reservoir level rising or falling. The larger the landslides saturated water content, the greater the safe factor changes during reservoir level rising or falling.Taking the Taping landslide as example for studying the coupled effect of rainfall and changing of reservoir level, and found: Two secondary landslides called H1 and H2 are there formed In the front of Taping landslide. Rainfall is the main inducing factor of deformation in H1 landslide. And the changing of reservoir level is the main factor of deformation in H2 landslide. The step-like deformation of landslide is the result of periodic variation of ground-water seepage field under the coupled effect of rainfall and changing of reservoir level. And the landslide will present the progressive failure feature. Rising and falling of reservoir level will cause the local deformation around the water level changing area, and form a pulling effect to the rear part of landslides. Rainfall will cause the local deformation in the rear part of landslides and form a pushing effect to the front part of landslides. During the periodic rainfall and changing of reservoir level, repeatedly “push-pull” effect will lead the plastic zone in the landslides jointing together and form a large deformation.