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Abstract 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.
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Received: 06 December 2010
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2011, Vol. 30 
