| Bank slope has been affected by the rise and fall of reservoir water level for a long time.Especially when the reservoir water level drops,the stability of bank slope changes significantly,which has attracted wide attention of scholars at home and abroad.This kind of landslide induced by water level decline will not only interfere with the construction and operation of water conservancy and Hydropower projects,but also greatly threaten the safety of life and property of downstream residents.Therefore,it is of great significance to study the influencing factors of slope stability under the condition of water level falling.In this paper,through the establishment of homogeneous soil slope model,analysis of homogeneous soil slope water level decline,sudden drop and unsteady seepage mode of seepage field and stability factors.Based on the fluid-solid coupling principle and Morgenstern-Price method considering the influence of matric suction,the seepage and stability of Shuping landslide during the process of reservoir water falling from 175 m to 145 m at different velocities,permeability coefficients,extreme rainfall rates and operating conditions of different water levels are studied.According to the law,a water level operation mode is proposed to increase the stability of Shuping landslide,which has a certain reference significance for the optimization of reservoir water level regulation scheme.In addition,the sensitivity of the factors affecting the stability of Shuping landslide was analyzed by orthogonal test,and the sensitivity of the factors affecting the stability of Shuping landslide was studied.The research results are as follows:(1)Under the slow descent mode,the infiltration line and pore water pressure in the homogeneous soil slope fall synchronously with the water level outside the slope;in the sudden descent mode,the infiltration line and pore water pressure in the slope are not affected by the change of the water level outside the slope;in the unsteady seepage mode,with the decline of the water level outside the slope,the infiltration line gradually convex upward,the smaller the soil permeability coefficient,the more obvious the upward convex characteristic;and the infiltration line in the slope lags behind the slope.Water level,the position near the slope is more sensitive to the hysteresis phenomenon,and the farther away from the slope,the weaker the response to the hysteresis phenomenon.(2)Analytical method is used to deduce the stability calculation formula of the homogeneous soil slope under the condition of slow drop and sudden drop,and the stability coefficients are compared with those obtained by finite element strength reduction method and Morgenstern-Price method.On this basis,dimensionless analysis is carried out,dimensionless parameter water level drop ratio L/H and revised stability parameter lambda are introduced.Slope,soil permeability coefficient and water level drop velocity are systematically discussed in five aspects: water level drop ratio,revised stability parameter lambda,slope gradient,soil permeability coefficient and water level drop velocity.The results show that the relative safety factor of homogeneous soil slope decreases linearly and sharply at first and then becomes stable with the increase of the water level drop ratio in the sudden drop mode,and decreases linearly with the increase of the water level drop ratio in the slow drop mode,and then increases slightly.? When the water level descent ratio is the same,the parameter lambda is positively correlated with the relative safety factor of the slope,while the slope degree is negatively correlated with the relative safety factor.In the unstable seepage model,with the increase of the water level descent ratio,the relative safety factor of the slope decreases approximately linearly,and then the change slows down.In the process of increasing the water level drop ratio from 0 to 1.0,the rate of water level decline is negatively correlated with the relative safety factor of soil slope.When the water level drop ratio is the same,the permeability coefficient is positively correlated with the relative safety factor.(3)The regional geological environment conditions,basic characteristics,formation mechanism,deformation monitoring and deformation characteristics of Shuping landslide are expounded and analyzed.(4)In view of the three GPS surface displacement monitoring points in the front,middle and rear edges of the main sliding area of Shuping landslide: ZG85,ZG86 and ZG87,the cumulative displacement curves of the three monitoring points under different downward velocities of Shuping landslide are simulated.It can be seen that the deformation of the front part of the slope body is large,and the results are consistent with the actual monitoring data.The faster the water level of Pingping Landslide Reservoir drops,the more significant the lag effect of saturation line is,and the faster the stability of the landslide drops.When the water level of the reservoir drops at 0.3m/d and 0.6m/d,the stability of Shuping Landslide changes from stable state to basic stable state.When the water level of the reservoir drops at 1m/d,the final stability of Shuping Landslide changes from stable state to unstable state.By comparing the extreme rainfall rate and the Extreme Rainstorm condition with the rainstorm condition,it can be concluded that the stability of Shuping landslide varies greatly with the increase of rainfall intensity;when the reservoir water of Shuping landslide decreases by 0.3m/d,the stability of Shuping landslide occurs under the condition of weakening soil strength,compared with before the weakening of intensity parameters.The stability coefficient of Shuping landslide decreases approximately linearly at first and then tends to be gentle when the speed of Shuping landslide drops to 145 m/d under different permeability coefficients,which is consistent with the law of homogeneous soil slope stability.(5)According to the actual dispatching plan of Shuping landslide from January to July 2012,simulating the actual decline of reservoir water level,we can draw the following conclusions: when reservoir water drops from 175 m to 163 m in 0.15m/d,the cumulative displacement rises steadily and the landslide creeps slowly;when reservoir water drops from 163 m to 145 m in 0.6m/d,it can be seen that obvious step phenomenon occurs when reservoir water drops from 163 m to 145 m,and cumulative displacement thereafter.The stability of the landslide decreases rapidly,which is consistent with the actual monitoring data of the cumulative displacement of the landslide.(6)According to the influence of water level rise on landslide deformation and the law of lagging deformation in Shuping landslide monitoring data,a new operation mode of reservoir water level is proposed,in which the water level decreases at 1 m/d speed and rises at 2 m/d speed,and is compared with that of water level decreases from 175 m/d to 145 m.It is concluded that the reservoir water level decreases from 175 m to 145 m first,then rises rapidly and then falls,and then circulates to 145 m.The operation condition is beneficial to the stability of landslide.(7)Through orthogonal experiment and using range analysis method and grey correlation analysis method,the sensitivity analysis of the influence factors on the stability of Shuping landslide is carried out.The sensitivity of four factors,cohesion,internal friction angle,permeability coefficient and water level descent speed,to the stability coefficient is studied.The results show that the sensitivity of various factors is as follows: internal friction angle > cohesion > permeability coefficient > water level descent.Speed.According to the sensitivity of the influencing factors of landslide stability,engineers can take corresponding engineering measures to prevent landslide disasters caused by slope instability in practical engineering.Therefore,further study on the sensitivity of influencing factors of landslide stability is of great significance to actual engineering slope control and disaster prevention. |
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