考虑时间效应边界面模型在地铁工程中的应用

 为了真实刻画地铁移动荷载低振幅、高振次特征，准确计算软土地铁地基在运营期的长期沉降，需要提出能描述低应力水平下土体动蠕变特性的本构模型。据此，基于边界面本构模型，结合Mesri蠕变模型，建立考虑时间效应的边界面本构模型。随后，为了开发ABAQUS材料子程序，采用应力积分算法对本构模型进行推导，借鉴阻止应变法进行算法的优化，可以使计算间隔缩短，总迭代次数增多，更易收敛。采用提出的本构模型和南京软土GDS动三轴试验获得的相关参数进行数值模拟计算，并进行试验对比，验证本构模型的有效性。同时，将开发的本构模型嵌入数值模拟计算中，设置黏弹性人工边界，进行三维地铁有限元数值模拟分析。结果表明：(1) 基于阻止应变法的优化算法可以进行推广使用；(2) 考虑时间效应的边界面本构模型适合描述软土动蠕变特性，能有效预测软土在低振幅地铁移动荷载作用下的累积沉降。研究对理论研究和实际工程具有重要的指导意义。

Application of a time-dependent bounding surface model in metro engineering

In order to simulate realistically the characteristics of low amplitude and high vibration of the moving metro loads and to calculate accurately the long-term settlement of the soft soil foundation，a dynamic constitutive model was suggested to describe the creep behavior of soft soil under low stress levels. A time-dependent bounding surface model based on the theory of bounding surface model and Mesri creep model was established. In order to write the user-defined material subroutine in ABAQUS，the proposed model was deduced using the stress integration algorithm and further optimized using the prevent strain method. The model has advantages of shortening the computation intervals，increasing the total number of iterations and ultimately making the convergence much easier. The model was validated through the comparison of the simulation results with those from the GDS dynamic triaxial tests on normally consolidated Nanjing soft soil. Moreover，the 3D finite element analysis of a metro system incorporating the viscoelastic artificial boundaries and the proposed dynamic constitutive model was carried out. The results revealed that the optimization algorithm based on the prevent strain method is useful for the easier convergence of the simulation. The time-dependent bounding surface model is appropriate for describing the dynamic creep characteristics of soft soil and can predict effectively the accumulated settlement of soft soil under the moving metro loads of low amplitude.