土钉拉拔接触面的细观模型试验研究与数值模拟

 利用数码可视化跟踪技术和土体变形无标点量测技术，通过室内模型试验，从细观层面对密砂中粗糙土钉拉拔时，钉土接触面的位移场、砂颗粒运动轨迹及剪应变规律进行研究，发现接触面颗粒先竖向运动，而后水平运动，且发生剪胀作用；土钉周围土体剪应变逐渐以径向为主，作用区域上下对称。以室内模型试验为基础，建立土钉拉拔的三维颗粒流模型，从细观力学角度验证室内模型试验中接触面砂土位移场规律，并进一步发现拉拔过程中土钉周围的孔隙率随着与土钉距离的增大逐渐减小，土钉端部处的土体孔隙率等值线为由一点逐渐向外扩散的同心的不规则圆；颗粒接触数在接触面处最小，然后向外逐渐增大等细观发展变化规律。研究成果对于进一步明确土钉拉拔的机制和接触面的发展规律都具有意义。

MESO-MODEL TESTING AND NUMERICAL SIMULATION OF NAIL-SOIL CONTACTS DURING PULL-OUT

Using technique of image visual tracing and non-target measuring，the meso-model tests of the rough nail-soil during pull-out in dense sand were carried out. The displacement field of the nail-soil contacts，trajectories of the sand particles，and shear strain of sand particles of contacts were analyzed during the process of pull-out of nail-soil. The result shows that in the first instance，the displacement motion of the particles is vertical and then was horizontal；also the particles have shear expansion action. The soil shear strain around the nail-soil changes in radial and regional role from top to bottom of the nail is symmetry. Based on the model test，the particle flow code in 3D(PFC3D) method was introduced to simulate the pull-out process of nail-soil，Firstly，the law of displacement field of contacts between soil and nail in model test was verified in meso-scale. Then，the PFC3D method is used to discover some changes regular of meso-mechanism，such as the porosity and coordination numbers during the process of the pull-out of nail-soil. It is revealed that the porosity of the sand around nail-soil reduced with the increase of the distance to the nail-soil；and the porosity contour of the sand in the end of nail-soil was gradually outward proliferation，which was irregular concentric circles；coordination numbers were the smallest around the nail and soil contacts，and gradually increasing to the outside. The study is expected to contribute to disclose the mechanism of soil nail pull-out and the development of contacts.