不均匀级配砂土渗蚀过程的细观数值模拟

Mesoscopic numerical simulation for suffusion process of gap-graded sandy soil

为了从细观角度研究不均匀级配砂土发生渗蚀的机理,采用离散元(DEM)与计算流体动力学(CFD)耦合模拟的方法,依据Kézdi判别准则,对9组不同颗粒级配的土样渗蚀过程进行数值模拟,分析内部稳定土体与易渗蚀土体在渗蚀过程中细观参数的变化,并探讨初始流速对渗蚀发展过程的影响。研究结果表明:土体的渗蚀过程可以分为起始、发展、过渡、延续4个阶段;土体的颗粒级配直接影响渗蚀的发展,间隙比越大,土体内部越不稳定,容易被侵蚀,当间隙比大于4时,土体渗蚀起始阶段时间短,发展阶段渗蚀速率大,延续阶段渗蚀率仍有稳定增长趋势;在相同间隙比的情况下,细粒质量分数不影响内部稳定土体渗蚀曲线的起始阶段和发展阶段,但细粒越多延续阶段的渗蚀率越大;流体边界条件是重要的外部因素,对于易渗蚀土体,超过临界流速,延续阶段的渗蚀率仍保持增长趋势,而对于内部稳定土体,流速对延续阶段渗蚀率逐渐稳定的趋势无影响。

To investigate the meso-mechanism of suffusion between gap-graded sandy soil,the discrete element method coupled with computational fluid dynamics was used to simulate the suffusion process of nine groups of graded soils based on Kézdi’s criteria.The changes of the meso-parameters of the internal stable soil and the unstable soil during the erosion process were analyzed,and the influence of the initial flow rate on the erosion process was discussed.The results show that the eroded process of soil can be divided into four stages,i.e.,initiation,development,transition and progression.The particle size distribution of soils directly affects the development of erosion.The larger the gap ratio is,the less stable the soil is,and it is easily eroded.When the gap ratio is greater than 4,the initiation stage of soil suffusion is short,the erosion rate in the development stage is large and has a steady growth trend in the progression stage.At the same gap ratio,the mass fraction of fine particles rarely affects the initial stage and development stage of the erosive curve,but the more the fine particles are,the greater the erosion rate is at the continuation stage.The fluid boundary condition is an important external factor.For easily erosive soils,when water flow rates exceed the critical value,the erosion rate still maintains an increasing trend in the progression stage.For the internal stable soil,the flow rate hardly affects the stable tend of the erosion rate in the progression stage.