| Ever since the operation of hydraulic engineering,the reservoir water level fluctuates periodically,which disturbs the inherent geological environment of the reservoir bank.The hydraulic boundaries of reservoir landslides undergo a series of shifts.These lead to the damage of previous balance and promote the revival of an amount of ancient and new landslides,and that may result in great potential threatens to life and property of people near the reservoirs.It is very important to avoid or reduce the damage of reservoir bank landslides scientifically and effectively to ensure the sustainable development of social economy in reservoir area.Many of the ancient landslides come into shape by going through times of slides.The landslide has several sliding masses and sliding surfaces.The deformation of the landslide is determined by several these sliding masses and sliding surfaces.Different areas tend to perform differential deformation due to the fluctuating of water level and rainfall.The research on the deformation mechanism,failure mode,stability and displacement prediction of this type of landslides under the reservoir operation has become one of the leading topics in both academic and engineering fields.This essay takes Outang landslide in the Three Gorges Reservoir area as a research object.It is a giant bedding ancient landslide which is composed by three landslide masses(the first sliding mass,the second sliding mass,the third sliding mass).The first sliding mass is approaching to the river which makes its leading edge covered by water.The leading edge of the second sliding mass lies on the top of trailing edge of the first sliding mass.The leading edge of the third sliding mass lies on the top of trailing edge of the second sliding mass.There are many prominent indications of revival of Outang landslide after Three Gorges Reservoir impoundment.In this essay,a lot of geologic investigation data and monitoring data about Outang landslide were collected in conjunction with a great amount of field geological investigations,which clearly defined the characteristics of the geological structure and spatial pattern of the landslide.The analyses about the geotechnical minerals and chemical ingredients,microstructure,hydrochemical characteristics of the landslide were carried out with the help of X-ray diffractometer.X-ray fluorescence spectrometer,scanning electron microscopy and other instruments and equipment.The physical and mechanical parameters of landslide rock mass were obtained by physical and mechanical tests.A research about deformational characteristics of the landslide was generated according to the indication of surficial deformation and the data analysis at the scene.Grey correlation method was used to quantitatively study the correlation degree between the ground displacement of the landslide and the fluctuation of reservoir water level and rainfall.A physical model of characterized landslide structure was created to cater for the model test of Outang landslide under the condition of both fluctuating water level and rainfall in order to find out the evolution mechanism of landslide deformation and failure mode.A numerical model of Outang landslide was established,and the seepage field and stability coefficient of the landslide were analyzed by numerical simulation and limit equilibrium method under the action of reservoir water level fluctuation and rainfall in a natural year.At the same time,based on the orthogonal design method,the sensitivity of each sliding mass in Outang landslide to the influence factors of stability was studied.Finally,according to the research results of deformation characteristics,mechanism and stability variation characteristics of Outang landslide under the fluctuation of reservoir water level and rainfall,the CEEMDAN-GRU coupling prediction model of landslide displacement was proposed.Below are the relevant research outcomes and conclusions:(1)Study on mineral composition,chemical component and microstructure characteristics of the sliding zone,hydrochemical analysis of landslide,physical and mechanical properties of the landslide rock mass.The main ingredients in sliding zone soil are quartz,feldspar and clay mineral,and the amount of clay mineral remains outstanding among the rest,hydrophilic clay mineral swells up as long as it gets in contact with water,water softening is one of the main factors which leads to the decline of landslide stability;electron microscope scanning test manifests that the sliding zone soil of Outang landslide is equipped with apparent linear scratches and the clay mineral is in a characterized microstructure of oriented alignment,microstructure of laminated particles of sliding zone soil makes its micromechanical property noticeable with a directional preference;the chemical ingredients of the flowing water of Yangtze river and rainfall within the landslide area and the underground water of the landslide mass are in a big difference,the rain drops descend into the sliding mass and then work with the rock soil mass to generate a complicated water ion chemical reaction which renders a variation of water quality;a laboratory based physico-mechanical property experiment is conducted on a sample of sliding zone soil,and some relevant physical mechanism parameters are collected.(2)Study on the correlation between deformation of landslide and water level fluctuating-rainfall.Outang landslide as a whole stay in a constant creep slippage process.The main sliding direction of each phase sliding mass is consistent.But the displacement of each phase sliding mass is different.The third phase sliding mass displacement > the second phase sliding mass displacement > the first phase sliding mass displacement.The displacements of these three sliding masses perform a step growth.It takes bigger move during May to September and it keeps a minor move for the rest of time.The time of a rapid displacement perfectly matches the period of water level rapid decline and rainy season.The first phase sliding mass deformation is more affected by rainfall water decline.The second and third phase sliding masses deformations are more affected by rainfall.(3)Study on deformational evolution mechanism and failure mode of Outang landslide.(1)There is not an obvious effect of the fluctuating water level on the stress field of the second and third landslide.The influence of the fluctuating water level mainly targets on the first sliding mass area.Deformation and instability of the first sliding mass will cause the variation of stability for the second and third sliding masses,which eventually generates modification.Landslide will not come across a big deformation at the times water level goes up in a speed of 1m/d,2m/d,3m/d,only a tiny crack appears on the lower foot slope,the faster the water goes up,the greater buoyance there will be,hence a more distinct tiny crack.In contrast to the impact of rising water level,there is a much greater influence of declining water level on the stability of the first sliding mass.A bigger landslide deformation will occur under the condition of a faster declining water level,when the water level in the reservoir experiences a sharp fall,there is a big risk of traction landslide in partial lower foot slope from the first sliding mass.Outang landslide is a hydrodynamic pressure type landslide.(2)Landslide gains no significant deformation under the effect of average rainfall.Strong rainfall has a remarkable effect on the lower foot slope of the first sliding mass and the stability of the third sliding mass.The main reasons for lower foot slope instability of the first sliding mass are combined with the softening effect of water,the seepage and flushing of rainwater;The main factor for an overwhelming creep deformation on the third sliding mass rather than the rock slip zone of the overall landslide is illustrated as the rainfall in a stepper slope creates a larger dead wight,the down sliding force from the seepage and the softening feature of contacting to water make the scene.(3)The leading condition for deformation of the first sliding mass is determined by the declining water level in the reservoir,the impact of a sharp decrease in water level on the first sliding mass outweighs it of a strong rainfall,and the latter imposes a bigger influence compares to a rapid increase in water level.Rainfall is the dominant factor for the deformation of both second and third sliding mass.(4)With the joint effect of both sharp fall in water level and strong rainfall,the slope instability mode is the combination of the partial slumping in the lower foot slope of the first sliding mass and/or the slip slope of the third sliding mass.The probability of the occurence of hazardous Integral slip along the bedrock surface remains low.(4)Stability and its impact factors sensitivity analysis of landslide.When there is no rainfall and the reservoir water level is 175 m,the stability of sliding mass which is controlled by sliding surface 1 > the stability of sliding mass which is controlled by sliding surface 2 > the stability of sliding mass which is controlled by sliding surface 3.Fluctuating water level in the reservoir is the crucial factor for the stability of sliding mass under control of sliding surface 1,as the water level shifts upward,there will be a stronger stability.While as the water level falls downward,a weaker stability will be generated.The stability of the sliding masses which fall under control of sliding surface2 and 3 is subjected to rainfall,it creates a severe impact on the stability of the sliding mass which is by charge of sliding surface 3.The ranking for the sensitivity level of the stability of sliding mass which is controlled by sliding surface 1 to its impact factors goes from strong to mild: internal friction angle,fluctuating water level in reservoir,cohesion,permeability coefficient and rainfall;the sensitivity level of the stability of sliding mass controlled by sliding surface 2 to its impact factors on a strength grade basis: internal friction angle,cohesion,permeability coefficient,rainfall and fluctuating water level in reservoir;in the case of sliding surface 3,the ranking is internal friction angle,cohesion,rainfall,permeability coefficient and fluctuating water level.For every single sliding surface,its stability and changing ratio are determined by internal factors,external factors(fluctuating water level and rainfall)impose minor effects on the stability of landslide,while if external factors induce a series of modifications on internal factors of landslide,that will lead to a significant influence on the stability of landslide.(5)Study on prediction model of landslide displacement.Aiming at the dynamic system nature of landslide evolution.This essay comes up with a dynamic forecasting model about landslide displacement which is based on CEEMDAN and GRU.At first,this model takes advantage of CEEMDAN technology and defines the accumulated displacement of landslide into two categories,the trend term and fluctuation term,predicts the trend term displacement by adopting single variable GRU model;by analyzing the mechanism and characteristics of landslide deformation in accumulation horizon which is caused by water level fluctuation,take appropriate deformation factors,achieve the prediction of the fluctuation term displacement by applying multi variable GRU model,in conjunction with a comparison to multi variable SVR model,multi variable BPNN model.The result indicates the superiority of the multi variable GRU model which takes inducing factors into account over SVR and BPNN models,especially in predicting step deformation.The great predicting feature of this model attributes to its state feedback,which better reflects the nature of dynamic system of landslide evolution.This model is also equipped with memorizing function.So the historical information of the landslide can be fully applied in order to enhance the accuracy of displacement prediction.Other than that,the unique design of the structure makes it possible to function without relying on the analysis of time-based training data. |
