基于虚拟元-有限元耦合的隧道内道床干缩裂缝细观研究

为解释道床与盾构隧道管片产生脱空的现象，研究新混凝土在浇筑后由干燥收缩产生的裂缝机理。基于虚拟元推导任意多边形骨料的刚度矩阵格式，利用UEL子程序实现有限元与虚拟元的耦合计算，纯弯梁数值试验结果表明耦合法较有限元法计算效率明显提升，且具有较好的稳定性。在此基础上，建立细观尺度下新老混凝土的干缩数值模型，并通过圆盘干缩模型验证了模型参数。研究骨料和砂浆的应力分布、内部湿度与裂缝发展的对应关系以及新老混凝土表面和界面的应力发展。结果表明：①收缩过程中，骨料主要承受压应力作用，砂浆沿骨料边界的切线方向受骨料约束作用易形成收缩裂缝，在新混凝土表面首先出现大量微小裂缝，随后界面两端发生剥离; ②受表面下骨料的约束作用，新混凝土表面拉应力呈现“驼峰”分布。开裂后表面被划分为多个收缩区，收缩区边界受拉应力，内部受压应力；③界面的拉伸和剪切应力由两侧开始增加，并且随着界面剥离的增加不断内移。在界面内部未剥离区域内存在由界面附近骨料约束导致的局部压应力和剪切应力增大。

Study on dry shrinkage crack of invert-filling in the shield tunnel at mesoscale based on virtual element-finite element coupling method

To explain dry shrinkage cracking phenomenon of invert-filling in the shield tunnel, the mechanism of crack formation caused by dry shrinkage of new concrete after pouring was studied. The stiffness matrix format of aggregate with the shape of arbitrary polygon was deduced based on virtual element, and the coupling calculation of finite element and virtual element was realized by UEL subroutine. The numerical test results of beams in pure bending show that the coupling method is more efficient than the finite element method and has better stability. On that basis, the dry shrinkage numerical model of new and old concrete was consequently established at mesoscale, and the model parameters were verified by the disk drying shrinkage model. The stress distribution of aggregate and mortar, the relationship between internal humidity and crack development, and the stress development of new and old concrete surface and their interface were studied. The results show that: ①during the shrinkage process, the aggregate is mainly subjected to compressive stress, and the mortar along the tangent direction of the aggregate boundary is subjected to the aggregate constraint so that shrinkage cracks are easily formed. A large number of micro-cracks appear on the surface of the new concrete first, followed by the debonding at both ends of the interface. ②Restricted by the aggregate below the surface, the surface tensile stress of new concrete presents a “hump” distribution. After cracking, the surface is divided into several contraction zones, the boundary and the internal of the contraction zone are subjected to tensile stress and compress stress, respectively;③The tensile and shear stresses of the interface begin to increase from both sides and move inward gradually with the increase of the interface debonding. The local compressive stress and shear stress may increase due to aggregate constraint in the bonding region inside the interface.