交通荷载作用下格栅加筋三明治形混合填料挡土墙的变形机理研究

The backfill of the geogrid reinforced sandwich earth fill retaining walls consists of clay reinforced with geogrid encapsulated in thin layers of sand. The structure of clay reinforced with geogrid encapsulated in thin layers of sand looks like sandwich.The cost of this kind of reinforced retaining walls can be cut down by reducing the use of coarse soil . A series of cyclic direct shear tests ,considering the features of traffic loading, will be carried out using modified version of large direct shear apparatus. Influence of thickness of sand layers, cyclic shear rate and shear amplitude on interface cyclic shear behavior will be discussed. Then, a new dynamic constitutive model considering the effect of cyclic shear for the sand-geogrid interface of clay reinforced with geogrid encapsulated in thin layer of sand will be advanced. The new dynamic constitutive model will be incorporated into FLAC3D to set up a numerical analysis model for geogrid reinforced sandwich earth fill retaining walls subjected to traffic loading. After that，the deformation and failure mechanism of geogrid reinforced sandwich earth fill retaining walls under traffic loads will be studied through indoor model tests. The results from the numerical analysis will be compared with the results from indoor model tests. At last, the key factors affecting the deformation behavior of geogrid reinforced sandwich earth fill retaining walls will be studied by the validated numerical model.The methods for reducing the deformation of the reinforced retaining walls will be supposed.

格栅加筋三明治形黏土-砂混合填料挡土墙采用黏土与砂土分层间隔填筑而成，并在薄砂层中用土工格栅进行加筋，形成如三明治形的黏土夹加筋砂层的填土构造。这种新型挡土墙能减少粗颗粒土的使用，降低成本。本项目拟针对交通荷载的特点，采用改进的大型直剪仪对三明治形加筋土的筋土界面进行一系列长时间的循环剪切试验，分析黏土和砂土的分层厚度、剪切速率、剪切位移幅值、砂土密实度等对界面循环剪切特性的影响；提出考虑循环剪切效应的筋-土界面相互作用的理论模型，并将该模型编制成 FLAC3D 的用户子程序，采用FLAC3D 建立交通荷载作用下该类挡土墙的三维流固耦合分析模型；采用室内模型试验研究该类挡土墙在模拟交通荷载作用下的变形特性和破坏机理，并为数值分析模型提供验证依据；最后采用验证后的数值分析模型对该类挡土墙的变形机理和影响变形的主要因素进行分析，提出减小变形的方法。

格栅加筋三明治形黏土-砂混合填料挡土墙采用黏土层夹加筋薄砂层构造，既可以充分发挥砂土与筋材界面良好的相互作用特性，又减少了砂砾类填料的使用。本项目拟针对交通荷载的特点，采用改进的大型直剪仪对三明治形加筋土的筋土界面进行一系列长时间的循环剪切试验，分析黏土和砂土的分层厚度、剪切速率、剪切位移幅值、砂土密实度等对界面循环剪切特性的影响；然后采用室内模型试验研究该类挡土墙在模拟交通荷载作用下的变形特性和破坏机理，并为FLAC3D软件建立格栅加筋三明治形混合填料挡土墙的动力分析模型提供验证依据；最后采用验证后的数值分析模型对该类挡土墙的变形机理和影响变形的主要因素进行分析，提出减小变形的方法。研究结果表明：粗粒土粒径越大，界面峰值剪应力和残余剪应力越大，达到峰值剪应力和残余剪应力所需的剪切位移也越大；在遭受循环剪切后，界面峰值剪应力增加，残余剪应力变化不大，界面残余应力比降低，峰值后的软化现象更加明显；在一定竖向应力的条件下，随着薄砂层厚度的增加，筋土界面的峰值剪应力先增大后减小；在室内动力模型试验中，三明治形混合填料挡土墙挡墙面板水平位移均随着竖向循环荷载的幅值和频率的增大而增大；在薄砂层厚度逐渐增大到14cm的过程中，墙顶差异沉降和面板水平位移呈现出先减小后增大的趋势，混合式加筋土挡墙的薄砂层厚度存在一个最优值；本项目探索了减小该类加筋土挡墙在交通荷载作用下变形的方法，为工程实践提供理论基础和技术支持。