坡体充气过程中气水两相流数值模拟

Numerical simulation of air-water two-phase flow in inflatable slope

依据多相渗流和非饱和土理论,提出在潜在滑坡区后缘进行充气形成非饱和区,截排斜坡后缘来水向潜在滑坡区入渗,以降低潜在滑坡区的地下水位,提高边坡稳定性。采用长边坡二维有限元数值模拟方法,研究充气过程中坡体非饱和区气–水两相流运动特征和地下水位变化规律,为充气截排水技术运用于实际工程提供理论指导。通过分析充气点下游边坡地下水位的变化规律,论证充气截排水方法具有可行性;基于充气过程中非饱和区的扩展过程分析,将充气截排水分为3个阶段,即充气点附近非饱和区形成与扩展阶段、充气形成的非饱和区局部越过地下水位线的不稳定两相流阶段和充气形成的非饱和区基本稳定的截排水工作阶段;发现了充气过程中非饱和区孔隙气压力、孔隙气流速度、孔隙水渗流速度和体积含水量会随时间发生波动性变化,且四者的变化具有良好的相关性,当孔隙气压力随时间增大时,孔隙气体流速也随时间增大,孔隙水渗流速度和体积含水量则随时间减小,反之亦然,此规律的形成主要是气-水的流动性差异和相互驱动作用的结果。

Based on the multi-phase porous flow theory and unsaturated soil theory,a new method was proposed to improve the stability of the slope. 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. 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;（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.