Study On Stability Of Bank Slope Under Reservoir Water Fluctuation

In addition to the damage caused by general slope instability factors,the more important and special reason is that the reservoir water level rise and fall may cause the bank slopes instability.Due to the wide distribution of mountains and hills in China,besides the natural reservoir bank slopes,some dams have been built to promote development of the economic and society,resulting in the emergence of many new reservoir bank slopes.The bank slope is in a stable state before the reservoir drawdowns.During the drawdown of the reservoir water level or a period of time after reservoir drawdowns,landslide appear,which makes it very important and urgent to study the stability of the bank slope under the condition that reservoirs drawdown.In the traditional methods of analyzing of the stability of slope,the stability analysis of the bank slope stays at the level of two-dimensional,which is quite different from the actual situation,and stays at the qualitative analysis,not in-depth to the level of quantitative analysis.This paper focuses on the analysis of the influence of the drawdown speeds,the height of the drawdown,permeability coefficient,aquifer thickness,cohesion and internal friction angle on the stability of the bank slope during the reservoir drawdowns.Through theoretical analysis,the method to determine the seepage force is first deduced,and then the three-dimensional rigorous limit equilibrium method which suitable for the soil bank slope is derived,the derived seepage force is introduced into the method,so as to analyze the influence of the drawdown speed,the height of the drawdown,permeability coefficient,aquifer thickness,cohesion and internal friction angle on the slope stability in the process of reservoir drawdowns.The SEEP/W module of GeoStudio software is used to simulate and analyze the seepage field in the bank slope under different drawdown speeds and height.In this paper,SEEP/W module and SLOPE/W module of Geo-Studio software are used to analyze the seepage field and stability of the bank slope during the rise of reservoir water level.Conclusions:(1)In the process of reservoir drawdowns,the seepage force points to the outside of the slope,which increases the instability of the bank slope,which will reduce the safety factor of the slope,and may activate the ancient landslide,making the safe slope unstable,which is not conducive to the stability of the slope.(2)The drawdown speed,the height of the drawdown,permeability coefficient,aquifer thickness,cohesion and internal friction angle all affect the stability of slope.The safety factor of the bank slope decreases with the increase of the drawdown speed;decreases with the increase of the height of the drawdown,with a slight increase at last;increases with the increase of the permeability coefficient;increases with the increase of the aquifer thickness;increases with the increase of cohesion and internal friction angle.(3)With the increase of the rising height and rate of the reservoir water level,the stability of the reservoir bank slope increases gradually,and the rising height of the reservoir water level has a greater impact on the reservoir bank slope,while the rise rate of the reservoir water level has no significant impact on the stability of the bank slope.The innovation points of this paper:(1)Applying the seepage force to the rigorous limit equilibrium equation,a three-dimensional rigorous limit equilibrium method for soil bank slope is derived.(2)Based on the proposed method in this paper,the most critical slip surface can be determined.(3)The influence of the drawdown speed,the height of the drawdown,permeability coefficient,aquifer thickness,cohesion and internal friction angle on the safety factor of the bank slope is quantitatively analyzed,which provides theoretical basis and evaluation method for the analysis and prediction of the stability of the bank slope during reservoir drawdowns.