| It is of great practical significance to study the instability mechanism of soil slope under the fluctuation of water-level to improve the operational benefit of reservoir and prevent the occurrence of geological disasters.In this study,a water-air two-phase flow model is established to investigate the seepage behavior during the water-level fluctuation process.The pore-air pressure,pore-water pressure,capillary pressure and water pressure are all considered during the simulation process.The safety factors can be obtained using the simplified Bishop method,and the main contents include the following sections:(1)First,a water-air two-phase flow model is established to investigate the seepage behavior.Based on the water-air two-phase flow model,the behavior of the seepage in the soil slope under the water-level drops or rises are simulated,respectively.During the water-level drawdown process,in the unsaturated zone,the capillary pressure and the pore-water pressure increase gradually,but the pore-air pressure decreases;in the capillary fringe,the capillary pressure and pore-water pressure decrease,and the pore-air pressure equals to 0.During the water-level rise condition,the capillary pressure,pore-air pressure,pore-water pressure and water saturation increase.(2)Furthermore,the influence of fluctuation rate of the water-level and the permeability of the soil on the seepage behavior are both analyzed in depth.The results show that,the faster the water level rises or drops,the faster the soil seepage changes;the greater the soil intrinsic permeability is,the faster the soil seepage changes.(3)Based on the seepage behavior in the water-air two-phase flow model,the safety factor of the soil slope considering the contribution of the pore pressure,capillary pressure,the pore-air pressure,the mass weight of soils and water pressure outside the slope is calculated,and the contributions of pore pressure,capillary pressure and water pressure outside the slope on the safety factor are all analyzed in details.During the water-level drawdown process,the safety factors decrease first and then increase,and after the water-level drawdown the safety factors keep steady.During the water-level rise condition,the safety factors first decrease and then increase,and after the water-level rise,the safety factors decrease gradually.The capillary pressure and the water pressure outside the slope are beneficial to the slope stability,but the pore-air pressure has an unfavorable effect on the slope stability.(4)At the same time,a single phase flow model is established,and the seepage behavior under water-level drawdown is analyzed.The effect of air phase on seepage behavior and slope stability is analyzed by compared with the water-air two-phase flow model.The results show that: the safety factor which not considers the contribution of pore-air pressure in the water-air two-phase flow model is larger than the safety factor in the water single phase flow,and the safety factor which not considers the contribution of capillary pressure is smaller than the safety factor in the water single-phase flow model.(5)During the simulation,the zone in the two-phase flow model is divided into three parts: saturated zone,capillary fringe and unsaturated zone,while in the single-phase flow model there are only two parts: saturated zone and unsaturated zone.In the capillary fringe,the pore-water pressure is negative,but the water saturation equals to 1.0,and the capillary pressure disappears,hence the pore-air pressure is negative and it has a beneficial effect on the slope stability. |
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