土体非共轴各向异性对城市浅埋土质隧道诱发地表沉降的影响

当前用于隧道工程数值模拟的本构模型,大多局限于土体各向同性框架下的共轴假设,难以充分反映隧道周围土体力学响应的复杂性。针对典型砂土和软黏土,建立考虑初始强度各向异性和非共轴特性的二维平面应变、理想弹塑性的土体本构模型,并编制用户材料子程序(UMAT),嵌入非线性有限元软件ABAQUS中,对城市浅埋土质隧道开挖施工进行二维数值模拟分析。结果表明:开挖面附近土体应力主轴可能发生明显旋转;同等地层损失率下,考虑土体初始强度各向异性预测的地表归一化沉降槽的形状与离心机试验结果更加吻合;同一程度荷载衰减下,考虑非共轴各向异性影响后沿中轴线的最大地表竖向位移明显偏大。因此可以认为,如忽略土体的非共轴和各向异性特性,可能会导致相关的设计方案偏于不安全。

Effects of non-coaxiality and soil anisotropy on tunneling-induced subsurface settlements

Nowadays, constitutive models for soils used for numerical modelling of tunnelling are normally restricted to the assumption of soil strength isotropy and coaxiality. A plane strain, elastic-perfectly plastic non-coaxial soil model with an anisotropic yield criterion is proposed. The non-coaxial soil model developed is then implemented into the commercial finite element software ABAQUS via the user-defined material subroutine (UMAT). Numerical simulations are performed on two-dimensional city shallow earth tunnel excavations using the newly proposed non-coaxial soil model. A case study is performed to compare the numerical results with the centrifuge test ones. The results show that the representative soil elements around tunnel experience severe principal stress orientations. The prediction of normalized subsurface settlement trough can be improved by considering the initial soil strength anisotropy. A larger value of the non-coaxial coefficient results in a larger magnitude of the maximum vertical displacement. It is concluded that no consideration of soil anisotropy and non-coaxiality may result in unsafe design in tunnelling.