大型土与结构相互作用恒刚度直剪试验装置研究

已有的土与结构接触面室内剪切试验多集中在恒荷载和恒位移加载条件下接触面力学特性的研究,而预制桩基础沉桩过程中桩土界面受力条件与恒刚度加载类似,即桩土界面法向应力随桩周土体法向位移是动态变化的。针对目前黏性土中桩土界面大型恒刚度的试验手段比较缺乏,自主设计研制了一种大型恒刚度直剪仪用于桩土界面力学特性的测试。该直剪仪考虑了桩周土体变形特点,剪切过程中桩土界面接触面面积始终保持不变,能够准确模拟桩土界面剪切试验;采用弹簧组加载系统和数控电机控制系统,法向可提供恒刚度边界条件,水平切向可按位移控制,能够实现桩土界面上直线和循环剪切的加载路径。试验结果表明:该直剪仪能够很好地再现黏性土中桩土界面在恒刚度加载条件下直线剪切的力学响应,为静压桩沉桩过程的桩土界面力学特性的研究提供了基础。

Development of a Large-scale Direct Shear Test Apparatus with Constant Normal Stiffness for Pile-soil Interface

The existing laboratory shear tests on soil-concrete interface mainly focus on interface mechanical characteristics under constant loading and constant displacement. While the stress conditions of pile-soil interface during precast pile driving process are similar to the constant stiffness loading, which means that the interfacial normal stress changes with the normal displacement of soil around the pile dynamically. Due to the insufficiency of the methods on constant stiffness tests of large pile-soil interfacial, a large-scale constant stiffness shear device was self-designed to test the pile-soil interfacial mechanism properties. The shear device, taking the soil deformation around the pile into consideration and keeping the pile-soil contact area be stable during shear process, can accurately simulate the shear force on pile-soil surface. Loading system of cluster spring and control system of numerical control motor were adopted on the shear device, and normal direction could provide constant stiffness boundary conditions, and horizontal shear direction can be controlled by displacement. Then linear and cycle shear loading paths of pile-soil interface could be imposed. It was shown that this apparatus could be employed to represent the mechanical response of linear shear tests on the pile-soil interface under constant stiffness loading paths, but also could provide a foundation for the study on pile-soil interfacial mechanical characteristics of precast pile during pile driving process.