THREE DIMENSIONAL NUMERICAL ANALYSIS OF DYNAMIC RESPONSE OF UNDERGROUND UTILITY TUNNELS DURING EARTHQUAKE

As underground utility tunnels are buried at shallow depths, the effects of Rayleigh waves should be considered in relevant seismic analysis. To investigate the dynamic response characteristics of utility tunnels subjected to Rayleigh waves and bottom earthquake acceleration, a three dimensional(3D) finite element(FE)numerical model for double-cabin utility tunnels was built. An advanced constitutive model characterized by hysteresis loops(HSS model) was used to simulate the soil mass. Rayleigh waves were generated by multiple pulse loads at the boundary. Upland waves, Kobe waves and Taft waves were applied horizontally at the bottom of the model. The results were compared with those derived from the conventional time-history analysis where only transverse force was taken into account. The research results showed that the transverse dynamic response of utility tunnels was mainly influenced by transverse seismic waves, while the longitudinal dynamic response was affected by Rayleigh waves that were incident along the axial direction of the structure. The dynamic response to the input of Rayleigh waves plus bottom seismic waves was more significant than that to the input of bottom seismic waves alone. When different earthquake acceleration time histories were input, the dynamic response rules of tunnels were similar but the impacts on them varied, which implied that the compatibility between bottom seismic waves and Rayleigh waves exerted a certain influence on the dynamic response of the structure. The research findings are expected to provide a reference for the fine numerical analysis of the dynamic response of earthquake-excited underground utility tunnels as well as their seismic design.