Seismic analysis of long tunnel: Simplified or unified

Seismic analysis of long tunnel is important for safety evaluation of tunnel structure under earthquakes. Simplified models of long tunnel are commonly adopted in seismic analysis by structural engineers. Meanwhile, tunnel is usually modelled as a beam continuously supported by ground. Solving of the dynamic system is easy to get an overall response of tunnel structure. However, tunnels are not a tube with uniform cross-section. Road tunnel in mountain areas will be of varying section for emergence parking. Shield tunnel is assembled with segments to form a lining ring. Furthermore, the soil stratum, where a long tunnel is situated, is never at an identical geological condition. All of these would invoke non-uniform excitation if there be an earthquake. Tunnel engineers would like to know what it would be if a long tunnel subjects to earthquake, whether overall or locally, with the help of improved continuous-based or discrete-based dynamic analysis. This paper presents several examples to handle the seismic analysis with unified method, in comparison with simplified method. The proposed method developed a framework, with FDM and DEM, to compute both overall seismic responses of tunnel and damage in particular locations. A multi-domain analysis coupling discrete model and continuum model is proposed to reduce the computational cost and improve the accuracy, and a bridging scale term is introduced such that compatibility of dynamic behavior between the DEM-based and FDM-based models is enforced. To simulate the damage process of lining structure numerical method based on continuous mechanics and failure process by means of discrete method are hired to develop a coupled multi-scale method. Examples demonstrate the applicability.