交通荷载作用下砂土非共轴变形特性及本构理论

The importance of non-coaxiality of sand has been widely recognised in the geotechnical engineering. Under traffic loading, the axis of principal stress will rotate with the change of deviatoric stress. The complication of traffic loading may induce significant non-coaxiality in the sand of roadbed. Without considering the non-coaxiality in the design will lead to an unsafe transportation structure. No study on the non-coaxial soil behaviours under traffic loading has been taken so far, which is of importance to be focused on. In this project, the experimental tests using HCA will be combined with numerical simulation to study the non-coaxial soil behaviours under traffic loading. Firstly, a series of drained and undrained HCA tests will be carried out under various deviatoric stresses, loading rates, stress paths and intial conditions of the materials to study the effects on the stress-strian behaviour and the non-coaxiality. Then, based on the experimental study, a constitutive model for soil deformation under traffic loading will be built up on the elasto-plastic theory and non-coaxial flow rule. By applying the new model in ABAQUS, a general 3D numerical calculation programme will be developed. After the back-check, the programme will be used to simulate the real project. Finally, the programme will be further validated by comparing the simulation result with in-situ monitoring data. This project will make great contribution to the study of the non-coaxial soil behaviour. The employment of new model will help to accomplish a more reasonable traffic design.

交通荷载是主应力轴连续循环旋转，偏应力值随之不断变化的特殊应力路径。对交通荷载下砂土的非共轴变形行为认识不清，是导致道路病害频发的主要原因之一。项目拟采用室内实验、理论研究和数值模拟等多种手段，深入探索交通荷载作用下砂土的非共轴变形特性。通过室内HCA三轴实验，研究不同初始状态、应力路径和加载速率的交通荷载对砂土非共轴性影响的基本规律，提出砂土非共轴塑性模量与各主要影响因素间的数学关系式。基于弹塑性理论和非共轴塑性流动法则，建立考虑主应力轴连续旋转条件下，应力路径、加载速率等因素影响的砂土非共轴本构模型。基于新建模型，在ABAQUS平台上编制通用的三维有限元软件，进行室内HCA实验的数值计算，反复校核程序和模型，并确定参数取值方法。对高等级公路试验段砂土路基工程进行数值仿真，结合现场监测数据，讨论模型的适用条件和应用效果。本研究对提高砂土路基设计和理论分析水平具有重要的科学意义和实用价值。

（1）采用空心圆柱扭剪仪(HCA)进行一系列排水试验，研究主应力轴旋转条件下砂土的变形特性。试验采用2种类型的加载路径，第一种保持偏应力不变旋转主应力轴，第二种在增加偏应力的同时旋转主应力轴。通过改变偏应力的应力水平，研究砂土的变形以及非共轴度的变化规律。同时，对同等试验条件、材料和加载路径下不同密实度试样的试验结果分析，研究密实度对于非共轴度的影响。另外，采用2 种材料进行对比试验(Portaway砂与LB砂)，研究砂土初始各向异性与非共轴性之间的关系。试验研究结果表明：砂土的变形随着主应力轴的旋转而累加，并体现出显著的非共轴特性。砂土的非共轴度与材料所处的应力水平、密实度及初始各向异性均存在一定相关性。.（2）对Portaway砂进行HCA排水试验，研究粗颗粒砂土主应力和主应变增量的非共轴性，以及应力路径（历史）对砂土非共轴性的影响规律。试验分两个系列，系列1 中试件在排水固结后直接沿着固定的主应力方向进行加载，系列2 中试件在排水固结后先进行轴向压缩，再沿着与系列1 同样的加载路径剪切。试验进一步验证了颗粒材料的非共轴特性。试验结果显示：非共轴度与材料的加载方向密切相关，加载历史对于非共轴度有一定的影响；随着试件接近破坏状态，主应力和主应变增量趋于共轴。