渗流管涌作用下松散堆积层结构演化规律

为揭示渗流管涌作用下松散堆积层结构演化规律,基于颗粒-孔隙尺度流固耦合方法,分别对密实、中密和疏松结构的松散堆积层开展渗流管涌仿真试验,从细观层面分析渗流管涌作用下松散堆积层颗粒迁移特征、颗粒流失量、颗粒间接触力链演化和骨架变形的结构演化特征。结果表明：渗流管涌主要以细颗粒迁移为主,存在局部“堵塞”现象,块石颗粒仅会在细颗粒迁移脱空后自由堆积。细颗粒迁移具有明显的“颗粒堆积”现象,主要集中在出口处,呈“上多下少”的特点。同时,渗流管涌发展过程中相同部位的孔隙率变化具有高度相似性,且结构越疏松愈加显著。管涌发展过程中,块石颗粒间接触承担主要的应力传递,力链演化的本质是堆积填料内部应力传递结构的改变。此外,下沉量和体应变均随时步增加,呈先急剧增加,后趋于平稳的态势,且随初始渗流速度越大,平稳时刻逐步提前。该研究成果可为从细观角度认识松散堆积层渗流管涌结构演化规律提供一定借鉴。

Evolution Law of Loose Accumulation Layer Structure under the Action of Seepage Piping

To reveal the evolution law of loose accumulation layer structure under the action of seepage piping. Based on the particle pore scale fluid-solid coupling method, seepage piping simulation experiments were conducted on loose accumulations with dense, medium dense, and loose structures, respectively. The structural evolution characteristics of particle migration, particle loss, indirect particle contact chain evolution, and skeleton deformation in the loose accumulation layer under the action of seepage piping were analyzed at the mesoscale. The results showed that the seepage piping is mainly dominated by fine particle migration, and there is a local "blockage" phenomenon, while the rock particles only accumulate freely after the fine particles migrate and become empty. The migration of fine particles has an obvious "particle accumulation" phenomenon, mainly concentrated at the outlet boundary, characterized by "more up and less down". Meanwhile, the porosity changes at the same location during the development of seepage piping are highly similar and become more significant as the structure becomes more porous. During the development of piping, the contact between rock particles bears the main stress transmission, and the essence of force chain evolution is the change of the stress transmission structure inside the packing. Besides, both the subsidence amount and the volumetric strain gradually increase at any time, showing a trend of rapid increase at first, and then tending to be stable. As the initial seepage velocity increases, the stable time gradually advances. This study can provide some reference for understanding the evolution law of seepage piping structures in loose accumulation layers from a mesoscopic perspective.