循环荷载作用下根土复合体的强度及变形特性研究

With the rapid development of Chinese public transport, more and more artificial slopes with ecological slope protection were established during highway or railway construction. Thus, the stability of slopes is essential for the normal operation of public transport and avoiding loss of life and property. Study on the strength and strain behavior of Root-Soil Composite under cyclic loading can provide significant theoretical basis for the mechanism of slope stability. This study focuses on a series study of dynamic properties of Root-Soil Composite under cyclic loading. Triaxial tests, Dynamic Triaxial tests, Mercury Intrusion Porosimetry tests (MIP) and Scanning Microscopy tests (SEM) will be carried out with the aim of analyzing the strength behavior, strain behavior and microstructure change caused by dynamic loading. Firstly, the changes of shear strength and dynamic strength due to adding roots will be investigated. Further, the study will focus on the relationship between strain and stress under cyclic loading, and a reliable dynamic constitutive relationship model will be proposed. Finally, the third aspect deals with the response of microstructure characteristics induced by deformation. The results could be helpful to the study on the nature of strain behavior under dynamic loading. In addition, the application of MIP and SEM will provide a new research approach for research on the soil properties.

随着国家公路铁路网覆盖范围不断扩大，道路沿线形成大量的人工边坡，生态护坡技术也应用广泛，边坡的稳定性是交通顺利运行和人民生命财产安全的重要保障。明确循环荷载作用下根土复合体的强度及变形特性，可以为研究交通循环荷载长期作用下的边坡稳定性提供重要的理论支持。本项目拟以根土复合体为研究对象，结合三轴试验、动三轴试验和微观试验手段，首先探究植物根系对土体强度和动强度的影响规律；然后结合土动力学理论，进行根土复合体在循环荷载作用下的变形特性研究，并构建累积塑性变形模型和动本构模型；最后从微观研究视角揭示循环荷载引起根土复合体微观结构的响应规律，建立变形特性与微观结构的量化关系，研究有助于深入了解根土复合体在循环荷载作用下土体特性变化的本质。

随着国家公路铁路交通网不断发展扩大，生态护坡措施应用广泛。边坡土体除了受到静荷载作用外，还长期受到周期循环荷载作用，其引起的土体变形会对边坡稳定性造成威胁。本项目以根土复合体为研究对象，选取不同根系排布方式，运用三轴压缩试验、动三轴试验、压汞试验和扫描电镜试验，探究循环荷载作用下加根土体的强度及变形特性，对土体在动荷载作用下的加筋作用进行分析，主要获得以下几方面重要结论：.1）根系的加筋作用在不同荷载条件下有所差异，静荷载作用下混合根系排布方式能有效提高土体强度，而在动荷载作用下，交叉根系排布方式更有利于提高土体的抗变形能力。.2）在低动应力幅值循环荷载作用下，土体产生塑性变形和弹性变形，植物根系能有效降低塑性变形产生，并且提高土体的回弹模量和阻尼比。交叉排布产生的抗变形能力更为优越。.3）在高动应力幅值循环荷载作用下，根土符合体会发生液化，植物根系能有效提高土体抗液化能力。研究提出的孔压模型，能有效预测根土复合体的孔隙水压力变化趋势。.4）循环荷载对土体微观结构的产生影响，主要体现在孔隙体积减小，但孔表面积没有明显变化，孔隙度降低，土体形状系数减小，加载后土体颗粒变得更为尖锐，概率熵降低，土体颗粒分布方向性增强，混乱度降低，不均匀系数增大，土体粒径分布范围有所扩大。.研究结果表面植物根系的加筋固土作用会在不同荷载形式下有所差异，混合排布根系能提高土体强度，但交叉根系更有利于抵抗动荷载作用下变形。循环荷载作用下土体的孔隙颗粒都发生响应变化，而孔隙体积变化率可以用于预测土体的累积塑性变形。研究结果可以为边坡土体变形控制及生态护坡设计提供一定的理论支持。