密实砂土蠕变的颗粒运动特征与微观力学机制研究

Although the creep of sand is smaller than that of clay, it still can cause harm and reduce the long-term stability of the infrastructures. The phenomenon, such as creep sliding of slope, settlement of foundation, deformation of tunnel and pile tip sinking of the high-speed railway, is closely related to the creep of sand. In this study, the improved experimental tests and the numerical simulations based on discrete element method (DEM) will be carried out on dense sand samples to examine the underlying mechanics involved during creep. The kinematic characteristics of particle movement, micro mechanism and the induced structure variation during creep will be revealed. The relationship and difference between three different creep stages (primary creep, secondary creep and tertiary creep) will be explored, and then the law of creep from quantitative change to qualitative change will also be dug out. Further, from the point view of kinematic characteristics of particle movement and micro mechanism, the essential difference between creep and shearing in dense sand will be examined, which can help to identify the specific characteristics during creep. The results can provide a theoretical basis for solving problems related to creep in sand in civil engineering construction.

砂土蠕变虽然较黏性土小，但同样会对工程造成危害，降低工程的长期稳定性。工程中常见的边坡蠕滑、建筑物沉降、隧道变形以及高速铁路桩基桩端沉降等现象，都和砂土的蠕变特性密切相关。本研究以密实干砂为研究对象，通过改进的模型试验和离散元数值模拟，研究密实砂土蠕变三个不同阶段（初始蠕变、稳态蠕变，加速蠕变）的微观特征，揭示密实砂土蠕变的颗粒运动特征与微观力学机制，以及内部结构的变化趋势；探求不同蠕变阶段的联系与差别，挖掘砂土蠕变特征从量变到质变的规律；研究砂土蠕变与常规剪切破坏的在颗粒运动特征与微观力学机制上的区别，阐明砂土蠕变的特殊性。研究成果可为工程中解决与砂土蠕变相关问题提供理论依据。

粗粒土，例如砂土蠕变虽然较细粒土小，但同样会对工程造成危害，降低工程的长期稳定性。工程中常见的边坡蠕滑、建筑物沉降、隧道变形以及高速铁路桩基桩端沉降等现象，都和砂土的蠕变特性密切相关。本研究以密实砂土为研究对象，通过基于自设计的高透明度试验箱、3D打印模拟杆件与粒子图像测速（PIV）技术和近景摄影测量技术进行模型试验，联合离散元数值模拟，从微观角度，揭示了砂土宏观蠕变的特殊性，阐释了发生蠕变破坏的内在机制。外部荷载主要由颗粒间接触力的强力链承担，变形主要受弱力链控制。颗粒间接触的不同运动形式对宏观蠕变变形的贡献不同，法向接触变形（与颗粒滑动相关）使得砂土体积减小，切向接触变形（与颗粒滑动相关）使得砂土体积膨胀，接触滚动与“颗粒对”刚体转动对宏观变形的贡献相对较小，即，内部颗粒的滑动控制宏观蠕变压缩变形。高蠕变应力下，蠕变过程中随着时间的增加弱力链比例增加，土内部颗粒运动能够产生类似剪切作用下的应变集中与应变条带状分布，该条带与剪切作用下的剪切带分布一致，进而形成蠕变破坏。中低蠕变应力下，蠕变过程中土内部颗粒运动相对均匀，未产生应变集中，蠕变变形相对均匀，蠕变最终稳定，不产生破坏。

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