Stability Analysis Of Bank Slope Based On Coupling Of Seepage And Stress Fields

Landslide is one of the disasters induced by reservoir impounding. With large water conservancy project being constructed, the distribution of landslide expanding, and the stability problem of the bank slope under the conditions of reservoir level changing is of more and more concern in academics and geotechnical engineering. At present,many research works of slope, seepage analysis and stress analysis are calculated separately, but as long as there is water, stress field and seepage field will affect each other, will be in a complex dynamic process, and form a coupling relation.Based on the summary of previous research results, this paper uses the limit equilibrium method and seepage and stress field coupling theory for stability analysis of a ancient landslide which is near the dam area of reservoir under construction. First,using the limit equilibrium method for stability analysis, and then establishing the mathematical model and obtain the finite element solution based on the seepage and stress field coupling theory. By making a numerical analysis based on the coupling theory of the slope stability under various conditions, this paper analyze stable state of slope when the water level changes, and the reinforcement program is put forward according to the results of the analysis.The calculation results show that, the slope after reinforcement can deal with all kinds of design condition, meet the stability requirements. The main research contents and results are as follows:(1) Prediction of slope stability under the condition of the first impoundment of reservoir.Reservoir impounding will improve the underground water level of the landslide, change seepage field, increase seepage area, and the dynamic water pressure along direction of flow push the slope. In addition, if the slope toe is submerged, the shear strength of soil under water will decrease, and anti sliding force drop down, then the front of slope is in danger. The results of analysis shows that, the part in front of slope grows a large displacement tends to the direction of the reservoir during the rise in water level, the formation of sliding zone is obvious,and lead to local instability of slope. According to the calculation results, the bank slope is in an unstable state during the first impoundment.(2)The influence of the slope toe sliding to the stability of the bank slope. Analysis shows that the water level rise lead to slope toe sliding, and then the equilibrium state of slope is broken,the stress field will be re distributed. Due to the loss of support, the upper slope soil may be declined along the ancient sliding zone where raised the risk. The analysis of this paper reveals that during the process of water level rise, in the central and at the bottom ofancient sliding zone, the shear deformation area expanding through the foot of the slope, and the slope trend to slide along the direction to the reservoir. The overall safety factor of slope stability drop down from 1.759 to 0.992 due to the slope toe sliding. Therefore, if the front of slope slide, the upper part of the slope will decline along the ancient sliding zone because of the loss of support, and a tractive landslide will form.(3) The effect of slope toe reinforcement on the stability of the slope. In order to prevent the formation of retrogressive landslide, the numerical analysis model about the slope toe reinforcement is established in this paper. The calculation results show that, whether the reservoir or water level drawdown, the displacement of the slope are significantly reduced,and the slope sliding area has not formed, no local sliding tendency. Although the ancient sliding zone appear local, small sliding shear deformation zone, but did not cause significant adverse effects for the overall and local stability of the slope. Therefore, the slope reinforcement measures can effectively enhance the shear strength of slope material, enhance slope anti slide force,and prevent the formation of the traction type landslide. The slope is in a stable state after reinforcement.(4) The study of the early warning system based on the slope deformation monitoring. Due to the restriction of actual components, the slope monitoring content is general for the displacement monitoring points, and there are few monitoring for material strength.But the slope stability model and method is generally based on the strength of the material, there is not a clear connection. In view of this situation, this paper, according to the principle of the simple application, based on the method of limit equilibrium which the current standard recommended, established the early warning system of slope stability considering the strength and strain softening relationship. Then, taking a simple slope as an example to show the warning process of stability based on deformation monitoring data. On this basis, this early warning system platform is extended by combining with the finite element technique, in order to accommodate more geotechnical professional research like fluid-solid coupling. And now the system is expected to form a warning system based on deformation monitoring and strength-strain softening theory, which are more suitable for reservoir management and slope sliding control.