网格状带齿加筋体筋-土界面特性及其三维细观机理研究

The interface behavior of geosynthetics and soil is a premise for structure design of reinforcement. The intriguing mechanism of reinforcement and how it will affect the general behavior of reinforced soil have been investigated by many researchers, and most of these work focused on the macromechanical properties. Considering the fact that soil is granular material, initialization and development of contact interface is also affected by the microstructural properties. As the result, in order to shed more light into the mechanism of the interaction between geogrid and soil, it is necessary to find the links between mechanical behavior and microstructural properties. However, only the macromechanical properties and deformation of boundary region can be achieved through conventional experiments, and the microstructural properties can not be obtained. The problem can be resolved by the transparent soil experimental technique because transparent material with geotechnical properties similar to those of natural soils can be used to study deformation using non-intrusive optical visualization techniques. So the transparent soil will be adopted in the research as a substitute for natural sand. The proposed study will focus on the interface behavior of soil reinforced with denti-inclusions. Pullout tests are carried out on dry silica gel, and the internal displacement are measured by the laser speckle technique. The 3-D deformation fields of a pull-out process are obtained by combining 2-D deformation fields of multiple cross-sections. Based on the reconstructed 3-D digital volumes, a series of 3-D characterizations and analyses will be conducted. In addition to the image analysis based reconstruction and characterization, the 3-D discrete element method (DEM) code, PFC3D, will be used to explore the interface behavior at the global and particulate scale. Local variation of microstructural properties as well as global stress and strain responses will be investigated and analyzed. Finally, all the characterization and analysis results will be summarized, an advanced mechanism model of interface behavior will be established.

筋-土界面特性是加筋土结构设计的基础。对界面特性进行合理预测的一个关键点是如何揭示筋-土界面内局部变形场的变化特征，而目前的研究方法无法测得内部的三维变形特性。申请者首先提出了一种新型网格状带齿加筋体，其不仅汲取了传统水平网格状筋材的优点，而且由于齿筋的存在可增加侧阻力，能有效改善筋-土界面特性。为此，本项目拟采用试验、数值模拟和理论分析三种方法对其界面作用机理进行研究。主要内容：以透明土为试验介质，借助拉拔试验分析筋-土界面的力学特性，采用三维图像分析技术揭示筋-土接触面内局部变形场的形成规律；应用离散元方法系统分析筋-土接触界面效应的形成和发展规律；结合试验和数值模拟结果，将三维细观特性与力学行为相结合，进一步揭示筋-土间的相互作用机理，并建立网格状带齿加筋体的界面力学模型。研究成果将拓展和丰富加筋体系，对阐明筋-土作用机理及指导加筋结构的工程设计，具有重要的理论意义和工程实用价值。

土工合成材料可以有效的解决工程边坡稳定、沉降变形等问题，因此在工程中应用非常广泛。网格状带齿加筋是一种新型的土工加筋技术，汲取了传统网格状与条带式带齿加筋的优点，其筋土界面特性是加筋结构设计的基础。对界面特性进行合理预测的一个关键点是如何揭示筋-土界面内局部变形场的变化特征。本项目针对网格状带齿加筋体的筋-土界面特性开展了系统研究。借助平面应变试验，分析了齿筋效应对加筋体的强度的影响，并借助颗粒流模拟揭示了齿筋的细观作用机理。针对网格状加筋体的动力变形特征，探讨了围压、循环荷载条件及加筋间距对残余变形的影响。开展了网格状带齿加筋体拉拔试验,分析了法向应力、砂垫层厚度、齿筋高度、横肋间距四因素对加筋体极限拉拔力的影响，从宏观角度揭示了筋-土界面间的力学特性。应用以离散元法为基础的颗粒流软件来模拟网格状带齿加筋体的拉拔试验，并进行二次开发，建立了加筋体拉拔界面作用细观模型。通过对拉拔过程颗粒位移、接触力、孔隙率、配位数等参量的监测，从微观角度分析了网格状带齿加筋体筋-土界面的力学特性和接触面变形场的发展规律。依据数值模拟结果得出齿筋的受力特点，并在考虑了齿筋侧阻力与筋材应变关系的基础上建立了极限拉拔力模型。