Mechanism And Deformation Prediction Of Taping Landslide In The Three Gorges Reservoir Area

The rainfall and fluctuation of reservoir water levels often lead to reactivation of old instabilities in the Three Gorges Reservoir area.The number of colluvial landslides in the TGR area is about 3000 until 2002.The displacement-time curves of most colluvial landslides in the TGR area presented step-like changing.The displacement was not constant over time,but stepped or graded.These landslides have gone through several acceleration phases.So it is difficult to judge the stability of this kind of landslide and to make a judgment on warning.Taking the Taping landslide with step-like displacement as example,the mechanism of deformation and deformation prediction of colluvial landslides affected by the rainfall and fluctuation of reservoir water levels are studied in this paper.Based on the field investigations,monitoring analysis,numerical simulation and theoretical analysis,the deformation characteristics,triggering factors,kinematic evolutions and deformation prediction are analyzed in detail.Main researched work and achievements of this paper are as follows:(1)The deformation characteristics of Taping landslide was analyzed based on the field investigations and analysis of measurement results from a monitoring network.The spatial distribution of surface cracking in the landslide was found out and deformation characteristics of the landslide with obvious periodicity were expounded.The displacement of landslide was stepped or graded.During the stage of drawdown of the reservoir,the displacement increased rapidly.Then,the displacement developed into stable period(nearly 9 months).(2)The influence of rainfall and fluctuation of reservoir water levels on landslide periodical deformation was expounded based on the monitoring analysis and numerical simulation.Fluctuating water levels is the decisive trigger for the phase of slope acceleration.High slope velocities coincide with low water levels and high drawdown velocities.Rainfall promotes the acceleration of landslide.Fluctuating water levels has an effect on the stability of rock and soil mass on the foot of the slope.As the water level decreased,downslope flow tends to be dominant and fluid velocities and displacement increase towards the ground surface.Long-term impoundment is bad for the stability of the landslide.Rainfall has an effect on the mass above the reservoir water level.The weakening of strength parameters of rock and soil mass and the downslope seepage flows are the main factor responsible for the deformation during the rainy season.(3)Mechanism of the landslide with step-like displacement under the effects of fluctuating water levels and rainfall was revealed.Fluctuation of reservoir water levels causes changes in groundwater levels and erosion in fluctuation belt.The stability of the slope in fluctuation belt is weakened and local deformation is formed,which leads to the traction of the rear slope.Rainfall enhances seepage force and weakens strength parameter of mass above the reservoir water level.The stability of the mass is weakened and local deformation is formed,which pushes the front slope.The periodical variation of pore water pressure and seepage field in slope makes the landslide presented the progressive failure feature under the influence of repeatedly push-pull effect and displacement-time curves are presented step-like changing.(4)A method of displacement prediction of landslide with step-like displacement was proposed based on H-P Filter,ARIMA and VAR models.H-P filter is used to decompose the displacement time series into the sum of the trend displacement and the periodic displacement.ARIMA and VAR models are used to predict the trend and periodic displacement respectively.The overall predicted displacement is obtained by adding the predicted values of trend and periodic displacement.The predicted results compared with the monitoring data and one predicted by other forecasting methods show that the method proposed shows a good effect and can accurately reflect the development of landslide with step-like displacement.