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  Numerical Analysis on Settlement Behavior of Shallow Box Tunnel Widening

  Utility tunnels jointly accommodate various infrastructure such as electric and communication lines, gas, water and sewage pipes in the ground, so the aesthetics of urban areas are improved and traffic flows can be well maintained. In Korea, Utility tunnels was first installed in 1978 to supply electric power, water and heating in Seoul. After several repairs, they are still being used. But about 70% of the utility tunnels were installed over 20 years ago (Table 1) and there are now some problems due to their aging. In the case of electric power equipment, more space capacity is required to accommodate high voltage electric lines. Additionally, the heat from high voltage electric lines causes concrete structures to deteriorate. And so, to avoid deterioration, a cooling system is needed, but existing utility tunnels cannot afford that due to scarcity of space. At the same time, there are regulations for interval spacing between the lines, and of minimum width depending on the different voltages (Table 2). As a solution to these problems, reconstruction is suggested. For reconstruction, both open cut and excavation widening methods are possible. In order to avoid traffic problems with the open cut method, such as cut and cover, an excavation widening method can be adopted. In this study, an excavation tunnel widening method has been simulated by the numerical method to investigate the extension of internal space of a box shape shallow utility tunnel. Korean utility tunnel design criteria and utility tunnel standard specifications were used for the tunnel modelling. Depth of cover, soil properties, thickness of lining, tunnel type and construction stage were used to perform a safety analysis of the reconstruction target. FEM numerical analysis were conducted to estimate settlement and plastic failure in sandy soil. Table 1. Utility tunnel total time-length in Korea (km) Table 2. Cable interval regulations depending on voltages (mm)

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