列车振动下隧道与土体响应的双尺度耦合模拟

TWO-SCALE COUPLED SIMULATION OF TUNNEL-SOIL VIBRATIONS UNDER TRAIN EXCITATION

对于土体离散–连续耦合问题,给出通过强化边界耦合力在离散和连续模型中的相容性,将提取边界耦合节点力转化为寻优问题的新方法,并用Lagrange乘子法求解。将此方法嵌入离散–连续双尺度耦合动力模型,模拟列车振动下隧道与土体的动力响应。用相互作用的离散颗粒模拟隧道附近土体,远离隧道的土体用连续模型模拟,编写结构的动力有限元程序嵌入离散元软件中来模拟隧道。通过离散元软件PFC2D和有限差分软件FLAC2D的交互运算实现耦合过程。在耦合边界通过交换速度和力保证耦合模型的连续性,通过自振柱模拟使离散区域土体的宏观性质与连续土体模型一致。通过比较耦合方法与只用连续模型模拟得到的结果,说明提出方法的有效性。双尺度耦合模型可以有效描述动力响应中隧道附近土体的细观特性,并极大降低离散元的模拟规模,减少模拟时间,适用于振动在半无限体中传播时重点考察区域土体的细观分析。

A new method for picking up coupled nodal forces in coupled micro-macro model is presented. By enforcing the compatibility of coupling boundary nodal forces obtained from discrete and ,continuum models, picking up coupled nodal forces is converted to an optimization problem solved by Lagrange multiplier method. Based on two-scale coupled approach, tunnel and its surrounding soil under periodic train loading are simulated. Particle flow code in 2 dimensions（PFC2D）, which is based on discrete element method, is used to simulate sands near the tunnel, while the domain containing particles away from the tunnel is simulated as continuum media by FLAC2D. The motion of the tunnel is governed by a self-edited dynamic finite element program which is added to PFC. Coupling is achieved by interchanging data between the two softwares during each time step. The continuity between the discrete and continuum domains is fulfilled by interchanging velocities and forces; and a free-vibration column simulation is applied to obtain particle assembly＇s macroproperties. Through comparison between results from coupled model and continuum model, the effectiveness of the presented method is demonstrated. It is shown that, the coupled method can well depict the concerned zone around the tunnel on the micro-scale while efficiently reduce particle numbers, and is suitable for micro-scale dynamic analysis of concerned zone in a semi-infinite body.