考虑各向异性和非共轴塑性的土体本构建模及城市浅埋隧道土体变形机制研究

It is well acknowledged that most of the constitutive models that are applied to analyse tunnelling are restricted to the framework of soil isotropy and coaxiality. Hence, the corresponding mechanism of the soil behaviour around the tunnel crown cannot be fully understood. This project will be performed through the method of theoretical analysis, centrifuge testing and numerical modelling. A three dimensional non-coaxial soil model within the framework of strength anisotropy subjected to complex stress paths will be developed. The newly developed non-coaxial soil model will be numerically implemented into a finite element software by using an explicit/implicit integration method. Closed-form solutions of the displacement around the tunnel crown will be developed based on the cavity expansion theory. The subsurface settlement and deformation around the tunnel crown will be obtained through centrifuge testing. By comparing the results from the numerical modelling, analytical solutions and experimental results, the variation of the stress path and principal stress rotation will be investigated in terms of a representative soil element. The influences of degree of soil anisotropy and non-coaxiality on the subsurface settlement and deformation around the crown will be obtained. This project will deeply reveal the mechanism of the soil deformation around the tunnel crown, and provide a common fundamental for the controlling of the subsurface settlement and lining support. Overall, this project is meaningful both in theoretical aspect and engineering application.

当前用于隧道工程数值模拟的多数本构模型，局限于土体各向同性框架下的共轴假设，难以充分反映实际隧道周围土体力学响应的复杂性，本项目拟通过理论分析、模型试验和数值模拟对此开展系统研究。针对典型砂土和软黏土，考虑土体强度各向异性和流动方向沿屈服面切向加载效应，建立适用性强的复杂应力路径下的三维土体非共轴本构模型，提出与之适应的高效弹塑性有限元解法。在此基础上，基于小孔扩张理论，推导隧道周围土体位移场；采用离心机试验，研究相应的地表沉降和开挖面周围土体变形；通过与数值模拟结果综合比较，从单元尺度探究不同静止土压力系数下隧道土体应力路径及应力主轴旋转的变化特征，揭示新建本构模型中控制土体各向异性和非共轴性的各参数对隧道土体力学响应的影响规律。本研究可深入探明开挖引起的浅埋隧道地表沉降及周围土体变形机制，为城市浅埋土质隧道沉降变形及支护稳定性控制，提供共性的理论基础，具有重要的理论意义和工程应用价值。

本项目针对当前用于城市浅埋土质隧道模拟的本构模型多基于土体各向同性、共轴假设的事实，从宏观角度构建了一系列二维、三维，参数物理意义明确的考虑非共轴各向异性的本构模型，所建立的本构模型通过材料用户子程序（UMAT)嵌入非线性有限元软件平台ABAQUS中。通过有限元数值模拟、离心机模型试验以及小孔扩张理论确立了非共轴各向异性对地表沉降槽及涉及明显地层位移的塑性区的影响规律；从土单元性质出发揭示了浅埋隧道开挖施工致开挖面土体应力主轴明显的旋转现象。新建本构模型在条形基础承载力、边坡稳定性问题中也得到了广泛的应用。以上研究得出了在应力主轴这一特定加载条件下，不考虑非共轴各向异性的影响的岩土工程问题的设计将是偏于安全的结论。负责人基于本项目以第一或通讯作者已发表SCI论文7篇，EI论文2篇，在审发明专利1项。