| Nowadays, many roads located in the riverbank or reservoir bank. The change of groundwater caused by the change of reservoir’s water table can cause roadbed deformation, and even lead to uneven deformation, causing the failure of pavement structure, and even landslides. However, for subgrade slope of reservoir bank, a considerable part of the displacement occur in the unsaturated soil area. Therefor, it is need to use saturated-unsaturated soil theory to analyze the influence of reservoir water level changes on the deformation and the rules of failure. The study has practical significance for understanding the deformation and failure mechanism of the reservoir bank and roadbed and the prevention and control of the disaster. For this purpose, the following work has been carried out in this paper:Firstly, the strength and deformation properties of unsaturated soil are studied. On the basis of collecting and analyzing the existing experimental study, the changes of various deformation and strength parameters of different types of rock and soil are summarized and the formular relationship between water content and deformation and strength parameters of rock and soil is established, this can provide the basis for the physical and mechanical parameters of unsaturated soil analysis in practical engineering.Secondly, based on the seepage theory of non-saturated soil, the two-dimensional saturated-unsaturated seepage mode is established by using the SEEP/W module in GEO-STUDIO finite element software. The evolution law of the seepage field of the slope under different working conditions is simulated and analyzed. The influence of reservoir water level fluctuation and different decrease rate of reservoir water level on the saturation hne and pore water pressure are mainly discussed. When the reservoir water level rises, the saturation line is gradually raised and it is lower convex curve. When the reservoir water level decreases, the saturation line is gradually reduced and it is upper convex curve. When the reservoir water level is gradual water level, the saturation line gradually tend to be gentle. The more the descending rate of reservoir water level is, the more obvious the hysteresis effect of the slope seepage is. In addition, the pore water pressure of the slope increases (decreases) with the rising (fall) of reservoir water level, and the more far from the slope, the more obvious the lag of the response of the pore water pressure to the change of water level.Thirdly, when the transient seepage field of the roadbed slope is obtained, based on the seepage-stress imperfectly coupled method, the evolution law of stress field and displacement field of the slope under different conditions of the reservoir level fluctuation is simulated by using the SIGMA/W module in GEO-STUDIO finite element software. And roadbed displacement caused by the water level fluctuation is calculated and analyzed. The results show that the roadbed deformation is related to the reservoir level fluctuation and its rate. The displacement of slope and roadbed closed to reservoir bank is greatly influenced by the reservoir water level fluctuation, and the displacement of slope and roadbed which is far away from reservoir bank is less influenced by the reservoir water level fluctuation. There is a positive correlation between the settlement of roadbed of the reservoir bank and the decrease velocity of reservoir water level.Finally, connected with the engineering example, the effect of soil physical and mechanical parameters on the deformation of the slope, the sensitivity of each parameter is analyzed, and the seepage and deformation characteristics of the high roadbed are analyzed. The results show that the elastic modulus is the most sensitive to subgrade settlement, Poisson’s ratio takes second place, saturated infiltration coefficient is not obvious. In addition, the lag effect of the clay is more obvious than that of sand, and it has a more great influence on the deformation of the subgrade settlement.
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