交通荷载作用下局部塌陷区上覆加筋路基变形破坏机理研究

Reinforcement used to prevent localized subsidence under the subgrade can lower the cost and ensure the safety of operation．However，the theory lags behind engineering practice, especially lacks the study of the load transfer law of the soil and the mechanical and deformation characteristic of the reinforcement under the traffic loading. Meanwhile, the strength loss and modulus attenuation of the reinforcement can be caused by repeated loading and unloading, which is not conducive to the bearing capacity and stability of the subgrade. In this project, considering the reinforcement stiffness, reinforcement layers, embankment height, width of the subsidence area, plane strain model test in which the aluminum bar is used to simulate the soil, particle image velocimetry (PIV) and numerical simulation of discrete element are used to study the deformation law of reinforcement, the evolution of soil arch structure and the propagation of failure surface under the traffic loading. The influence of different amplitude, frequency and vibration number on the application of traffic loading is taken into account. The investigation aims to illuminate the interaction mechanism between the soil and reinforcement overlying the subsidence area and determine the key factors affecting the deformation of the subgrade. In addition, through cyclic tensile test to study the softening characteristics of reinforcement, the experiential model of softening is built, and the subroutine is programmed. The deformation rule of reinforced subgrade overlying the localized subsidence area under the traffic loading is analyzed by finite element software considering the softening characteristics of reinforcement. Finally, the deformation and failure mechanism of reinforced subgrade overlying the localized subsidence area under traffic loading is revealed. The research results of this project are helpful to further reveal the load transfer mechanism of the soil and the mechanism of the stress and deformation of the reinforcement above the subsidence area, so as to provide a theoretical basis for the improvement of the existing design theory.

采用水平加筋体防治路基下部局部塌陷可降低工程造价、确保运营安全，但其理论滞后于工程实践，特别是缺乏对交通荷载下土体荷载传递规律和加筋体受力变形特性研究。同时，筋材受到反复加卸载作用会造成强度损失、模量衰减，不利于路基的承载力和稳定性。本项目拟通过铝棒相似土平面应变模型试验、粒子图像测速技术(PIV)和离散元模拟，考虑筋材刚度、加筋层数、填土高度、塌陷区宽度等因素，对不同幅值、频率和振次的循环动载作用下筋材变形、土拱演化和破裂面扩展规律展开研究，阐明塌陷区上部土体和筋材相互作用机制，明确路基变形的关键影响因素。此外，通过循环拉伸试验研究筋材的软化特性，构建软化经验模型并编制子程序利用有限元软件分析交通荷载下考虑筋材软化影响的局部塌陷区上覆加筋路基变形规律，最终揭示其变形破坏机理。本项目的研究成果有助于深入揭示塌陷区上部土体荷载传递机理和筋材受力变形机理，为现有设计理论的改进提供理论依据。

采用土工加筋对空洞塌陷进行防治，能提高空洞上覆土层承载力，减小空洞塌陷导致地表塌陷程度。由于空洞的随机性，空洞位置、大小、形状等会对加筋效果产生影响，筋材变形传统监测方式存在精度低、效果差的局限性，静动荷载下土压力分布、筋材变形及路基破坏模式需进一步探索。本项目结合3D打印及光纤光栅（FBG）传感技术，研发了可测试变形的自感知土工格栅，基于静动载模型试验、有限元分析和离散元模拟研究了不同加筋层数、加筋间距下空洞上覆加筋路基的承载变形机理，结果表明：静载和循环动载下加筋均能提高空洞区上覆路基承载力，并有效减少路基沉降；加筋层数的增加和加筋间距的减小均能提高路基承载力；数值分析中筋材变形与FBG传感器所测值相吻合，格栅应变随着格栅埋深的增大而减少，顶层格栅的应变随着加筋层数和加筋间距的增加而减小；空洞的存在改变了上方土颗粒间的接触力链，空洞两侧土颗粒及上部一定距离的颗粒间形成了“拱状”的接触力链，土拱效应明显；由于筋材的限制，加载板下土体密实度高，接触力链粗广，防止局部土体强度超过抗剪强度而发生破坏，能承受更大的荷载，限制了空洞的塌陷变形。本项目进一步对上覆加筋路堤的极限承载力、土压力分布、筋材变形以及破坏模式展开了分析，提出了5种典型破坏模式：由空洞向上形成两条塑性滑移面贯通至堤顶，附近土体发生竖向剪切引起空洞上部土体塌陷；塑性区由空洞水平左侧与洞顶分别发展至堤顶；加载板下部与堤顶形成连续的塑性滑移面；塑性区从空洞底部贯通至堤顶，同时右侧顶角与坡脚形成塑性贯通面；空洞上部形成两条塑滑移带并通过加载板下部形成局部塑性滑移面贯通至堤顶。分析了关键影响因素的敏感性，依次为：空洞水平距离＞首层筋材埋深＞筋材层数＞筋材间距＞上覆填土厚度与空洞直径之比＞筋材强度＞加载板宽度与空洞直径之比。本项目的研究成果有助于揭示空洞上部土体荷载传递机理和筋材受力变形机理，为现有设计理论的改进提供理论依据。