考虑组构影响的交通荷载作用下砂土变形特性试验及细观机理研究

The predictive long-term settlement is not accurate as the fabric of sand has always been ignored when calculating the permanent deformation in the sand of roadbed under traffic loading. In this project, the experimental tests combined with theoretical analysis and numerical simulations are employed to study the effect of fabric on sand deformation. Firstly, homemade device for sand preparation and resonant column test with torsional shear module are used to reveal the influence of fabric on dynamic shear modulus in three-dimensional direction and different strain levels. Then, a series of tests using GDS bi-direction dynamic triaxial apparatus and hollow cylinder apparatus are carried out under various stress levels, initial relative densities, stress amplitudes and stress paths to study the effects on the permanent deformation of sand with different fabric. Finally, based on Particle Flow Code (PFC) numerical simulation for sand with different fabric, the micro-parameters are obtained. By analyzing the experimental results and PFC results, the effects of fabric on dynamic shear modulus and cumulative permanent deformation under traffic loading are investigated with the method of macro-micro incorporation. The classic dynamic shear modulus model and the predictive model for permanent deformation under traffic loading are modified with considering the impact of fabric. This project will make great contribution to the study of sand properties and will improve the traffic design.

目前交通荷载作用下砂土路基变形计算理论忽略了砂土组构这一重要因素，无法准确预测交通荷载作用下砂土路基的长期沉降。本项目以室内试验、理论研究和数值模拟相结合的方式，深入探索组构对交通作用下砂土变形特性的影响。通过自制砂土试样制备装置和共振柱联合扭剪试验研究，揭示不同组构对三维方向和宽应变范围动剪切模量影响规律。通过GDS双向动三轴和空心圆柱系统分析应力水平、初始相对密实度、应力幅值、应力路径等因素对交通荷载作用下不同组构砂土变形特性的影响。通过不同组构砂土的颗粒流模拟，获取砂土的细观参数，综合分析试验结果和颗粒流模拟结果，采用宏细观结合的方式揭示组构对砂土动剪切模量及交通荷载砂土累积变形影响的细观机制，对经典动剪切模量模型进行考虑组构影响的修正，建立考虑组构影响的交通荷载砂土累积变形预测模型。本研究对深入认识砂土的基本特性、提高砂土路基设计和理论分析水平具有重要的科学意义。

本项目以室内试验、理论研究和数值模拟相结合的方式，深入研究了组构对循环荷载作用下下砂土动力特性的影响。（1）采用两种常用的重塑砂土制样方法得到不同初始组构的饱和试样，通过弯曲元测试系统和共振柱测试系统分别对不同组构的饱和砂土试样进行剪切模量和阻尼的测试并进行了对比研究；（2）利用变围压动三轴仪进行了一系列变围压和常围压应力路径下不同组构砂土动力特性的试验研究，同时利用弯曲元对试验过程中剪切波速进行测试，分析了不同应力路径下组构对剪切波速变化的影响；（3）利用空心圆柱扭剪仪对不同组构砂土在不同应力路径下进行了循环荷载试验研究，研究了在平均主应力p、循环应力比CSR和循环扭剪应力比η分别变化条件下不同组构对砂土轴向变形特性和体应变的影响；（4）采用离散元方法，利用半径扩展法和重力沉积法分别生成具有初始各向同性和各向异性内结构的试样，并开展循环荷载试验，研究不同制样方法产生的初始各向异性对砂土宏微观力学特性的影响；（5）分别建立了考虑变围压和主应力轴旋转的累积应变预测模型。