Research Of Intercepting Groundwater With Compressed Air For Landslide Treatment

Landslide is one of the major challenges of geotechnical engineering projects because of its complexity of geological conditions, the difficulty of prediction and expensive management fees. The storage and transport of groundwater which is supplied by the trailing edge water and slope water is one of the major natural factors affecting the slope stability. Currently, the cut drainage method which has the merit of high efficiency and low cost is widely used in slope engineering. The existing cut drainage method is based on the water gravitation, therefore, its drainage efficiency can not be guaranteed. It is know that rapid treatment for a landslide is significant in engineering projects, therefore, great contribution will be make if a new drainage method can rapidly and effectively drain groundwater in slope.In this research, a new drainage by compressed air method is proposed to deal with drain groundwater in soil slope. This thesis investigates the feasibility of using compressed air to drain groundwater in the soil mass. The main research outcomes are as follows:(1)When the inject pressure is higher than the trigger pressure of the saturated soil, the use of compressed air can effectively drain water in soil. However, when the inject pressure is too high, it can result in soil failure. It is also found that when the compressed air is injected from the seepage path of saturated soil or at the bottom of dry soil, the seepage of soil will decrease than inflatable before.(2) In order to prove the feasibility of using compressed air to drain groundwater in the soil mass, the process of drainage by compressed air in soil mass is analyzed by using the theory of capillarity at a meso level. It is found that the effective of draining water using compressed air depends on the capillarity of the soil and the phenomenon of preferential flow because of the speed of airflooding water is faster in bigger pore channel. The soil mass has three seepage regions (air, air-water and water regions) at a macro level when inflating.(3) Based on the Darcy criterion which can be used to describe the water movement in the soil, formulas for calculating inject air rate are proposed. The analysis results show that the water in the soil can be drained in some ranges of bigger pore size, and the greater the air pressure is, the greater the influence range and the speed of airflooding water become, it is also found that the optimal air pressure exist in the process of air drainage.(4) Based on the theoretical analysis, it is found that the starting air pressure is equal to the water head plus the intake value. In order to make sure the soil mass is not damaged by compressed air, an empirical model which can be used to calculate the upper limit air pressure is proposed based on the Terzaqhi theory. However, analysis results show that the intercepting groundwater method by compressed air can only be used for soil with pore size>5μm.(5) A soil slope model is designed to test the feasibility and efficiency of drainage by compressed air. Test results show that the proposed compressed air method can drain groundwater effectively and can reduced infiltration rate above40%. Comparing with the natural seepage condition, the water level decrease around32～37%in the region after the inject tube and moisture content of the soil affected by compressed air decrease around32～46%.(6) It is found that the water table has no changes when the inject pressure is equal to the initial water pressure, which means there is a trigger pressure when the inject air pressure under the water table. Water in the back of the slope will go through the surface of the slope when the compressed air is injected in the slope.(7) Numerical modeling is performed to simulate the process of drainage by compressed air. The effect of different permeability coefficient, porosity and air pressure on drainage is compared. The results show that the effect of drainage can be significantly influenced by the inject air pressure; however, the permeability coefficient and porosity have slight effect on the drainage. The lower the permeability is, the greater the air pressure of draining groundwater become. The barrier occurred later than the inflating time in soil mass. The air pressure is greater, the time of starting to prevent infiltration is shorter.