Simulation Study On Mechanism Of Inflation Drainage Method In Slope

Landslide disasters,which cause quantities of economic losses and casualties,happen frequently in China.Especially because of the paroxysm and difficulty of prediction of the rainfall-type landslide,it is difficult to solve the problem of landslide rescue by traditional forecasting and control methods.As a kind of new technology of landslide rescue,inflation drainage method is based on the multi-phase porous flow theory and unsaturated soil theory.In this method,through filling the trailing edge of potential landslide area with compressed air,an unsaturated belt was formed.By cutting off water in seepage path,the underground water level was artificially lowered.Inflation drainage method has the characteristics of simple construction,fast interception and drainage,in accordance with the requirements of the landslide disaster rescue.To enhance the theoretical research,a two dimensional finite element model was employed to investigate the characteristics of air-water two-phase flow and study the law of groundwater level variation in unsaturated zone during the process of aeration.The results illustrate that it is feasible to intercept water with compressed air in a slope.An analysis on the expansion process in unsaturated zone indicates that the process of intercepting water can be divided into three stages:(1)The unsaturated zone near aeration point is formed and start to expand;(2)As the unsaturated zone extends over underground water level,an unstable two-phase flow is formed;and(3)The unsaturated zone expansion is terminated and water intercepting method works smoothly.In the unsaturated zone,it is found that the pore-air pressure,pore-air velocity,pore-water velocity and volumetric water content fluctuate locally and these variations are related intimately.As the pore-air pressure increases with the time,the pore-air velocity increases while the pore-water velocity and volumetric water content decrease,and vice versa.This phenomenon can be ascribed to the interaction and lag between air and water.In this paper,a laboratory experiment and numerical simulation are carried out to investigate the relationship between the air pressure and interception effect.Results show that for a given slope,the intercepting water process exists the start-up pressure and the optimal pressure;that means when the air pressure is greater than the start-up value,the water table can be lowered;when the pressure ranges between the start-up and optimal value,the water table decreases with the increase of air pressure;however,when the air pressure is higher than the optimal value,the water table increases with the increase of air pressure.