基于三维数字图像相关技术钙质砂颗粒运动行为试验研究

桩基附近土颗粒的运动行为与宏观力学表现密切相关，对揭示界面剪切机制具有重要意义。利用自主研制的大型直剪仪，结合三维数字图像相关技术（3D-DIC）全场位移测量分析系统，开展了钢?钙质砂界面循环剪切试验，研究了界面附近砂颗粒的运动行为演化规律。结果表明：界面峰值剪切应力和发挥的界面摩擦角随循环次数的增大而增加，体变特性以剪缩为主；钙质砂颗粒左右移动的幅度与距界面的垂直距离成反比，钙质砂颗粒的位置随循环次数的增大逐渐向正剪切方向移动，试验结束时上剪切盒左侧区域的钙质砂颗粒向正剪切方向移动的距离最大；钙质砂颗粒在单个循环内出现有规律的上下移动，向下移动的幅值更大，位于上层的钙质砂颗粒向下移动的位移值大于下层；钙质砂颗粒的运动速度在沿单方向剪切时，呈现出慢?快?慢的变化规律，位于上剪切盒右侧区域的钙质砂的体变特性较左侧区域更显著；网格位移值和缺失数量随循环次数的增大而增加，在试验后期趋于稳定，试验结束时的破碎带厚度为 6.21 mm。

Experimental study on movement behavior of calcareous sand particles based on three-dimensional digital image correlation technology

The movement behavior of soil particles near pile foundation is closely related to the macroscopic mechanical performance, which is of great significance to reveal the interface shear mechanism. By using the self-developed large-scale direct shear instrument and the 3D-DIC full field displacement measurement system, cyclic shear tests of interface between steel plate and calcareous were carried out to examine the motion behavior of sand particles near the interface. The results show that the peak interface shear stress and the developed friction angle of interface increase with the number of cycles, and shear shrinkage is the main characteristic of volumetric deformation. The range of left-right movement of calcareous sand particles is inversely proportional to their vertical distance from the interface. The position of calcareous sand particles gradually moves to the positive shear direction with the number of cycles. At the end of the test, the calcareous sand particles in the left area of the upper shear box move a large distance towards the positive shear direction. Calcareous sand particles move up and down regularly in a single cycle, which is mainly characterized by downward movement. The downward movement displacement of calcareous sand particles far from the interface is greater than that closer to the interface. The movement speed of calcareous sand particles shows a slow-fast-slow change law when shearing along the single direction. The volume deformation characteristics of calcareous sand on the right region of the upper shear box are more obvious than those on the left region. The displacement value of the grid and the number of missing grids increase with the number of cycles, and tend to be stable in the later stage of the test. At the end of the test, the thickness of the breakage zone is 6.21 mm.