Numerical Analysis Of Slope Stability With Dual Structure Under The Condition Of Reservoir Water Level Fluctuation

The occurrence of landslides has a very close relationship with water.There is a saying in the engineering field of "ten landslides and nine waters",which shows that water is an important inducement factor for landslides,and the effect of water on slopes is mainly the rise and fall of reservoir water levels and rainfall two forms.For reservoir bank slopes,a binary structure is common,that is,"upper soil and lower rock".The rise and fall of reservoir water level is the main inducement factor for landslides.Therefore,it is of great significance to study the stability of the binary structure slope under the condition of the reservoir water level rising and falling.In this paper,Geo Studio finite element calculation software is used to perform unsaturatedunstable seepage analysis on the bank slope of the binary structure under the condition of the reservoir water level rise and fall;Based on the limit equilibrium method,the effects of reservoir water level elevation rate,permeability coefficient,slope angle,soil-rock interface inclination angle and matrix suction on the stability of ideal binary structure slopes were studied;Study on the change law of stress field and displacement field of ideal binary structure slope based on finite element stress method;Finally,combined with actual engineering projects,the engineering geological conditions investigation and seepage characteristics and stability analysis of the right bank slope of the Yongbuluo Reservoir were conducted.The main research results are as follows:(1)When the reservoir water level drops,the stability coefficient decreases first and then increases.When the reservoir water level drops to about 30% of the variable band,the stability coefficient reaches the minimum value.The faster the reservoir water level rises and falls,the faster the stability coefficient changes and the larger the amplitude.The larger the permeability coefficient,the smaller the variation of the slope stability coefficient;When the reservoir water level rises,the smaller the soil permeability coefficient,the greater the stability coefficient;When the reservoir water level decreases,the larger the soil permeability coefficient,the greater the stability coefficient.The smaller the slope angle,the slower the potential slip surface of the slope and the more stable the slope.The larger the inclination of the soil-rock interface,the higher the stability coefficient,but when the inclination of the soil-rock interface is small,the stability coefficient is not sensitive to the inclination of the soil-rock interface.As the inclination of the soilrock interface becomes larger,the distance at which the slip surface coincides with the soil-rock interface increases.As the reservoir water level rises,the contribution of matrix suction to the shear strength of the entire sliding surface gradually decreases,and vice versa.Considering matrix suction is beneficial to slope stability.(2)When the reservoir water level rises and falls,the stress change within the slope mainly occurs at the leading edge of the slope.When the reservoir water level drops,the maximum principal effective stress and maximum shear stress of the slope increase,and the phenomenon of stress concentration in the area near the foot of the slope is obvious,which is not conducive to slope stability.According to the change law of the shear stress and shear strength at the bottom of the soil strip on the slip surface,the analysis shows that when the reservoir water level rises,the stability coefficient changes little in the early stage and increases in the later stage;When the reservoir water level drops,the stability coefficient decreases in the early stage and increases in the later stage.The stability coefficient analysis results agree with the calculation results.(3)When the reservoir water level rises,the slope vertical displacement is always greater than the horizontal displacement,so when the reservoir water level rises,the slope is dominated by vertical displacement;In the early stage of the decline of the reservoir water level,due to the unloading of the hydrostatic pressure on the slope and the dynamic water pressure pointing outside the slope,the slope is mainly dominated by horizontal displacement;In the later period of the decline of the reservoir water level,the infiltration line in the slope decreased,the pore water pressure gradually dissipated,and the dynamic water pressure directed outside the slope decreased,and the vertical settlement was the main type of consolidation settlement.(4)Under the conditions of water level rise and fall in the reservoir area and heavy rain and earthquake conditions,the slope of the Yongbuluo right bank may have the possibility of local collapse and instability.The local instability and collapse of the slope may affect the overall stability of the slope.Considering that a large-scale sliding occurred in the early stage of the slope,although it is currently in a stable state,the slope deposit is still in a relatively loose and underconsolidated state.In the case of rapid water level fluctuations in the reservoir area,this slope does not rule out the possibility of "re-sliding" again.