An Early-Stage Design Procedure for Circular Tunnel Lining under Seismic Actions

Abstract eng:
The increments of the internal forces induced by an earthquake in the transverse section of a tunnel lining can be ascribed to the ovalisation of the section, induced by soil shear straining in the vertical plane. They can be assessed with several procedures at different levels of complexity. In this paper, two kind of analysis were per-formed on idealised geometry and soil conditions, considered representative of soil classes specified by Euro-code 8: pseudo-static analysis, where the seismic input was reduced to an equivalent peak strain amplitude, computed through a free-field pseudo-static analysis of the ground and then considered acting on the tunnel lining in static conditions; and full dynamic analysis, where the soil and tunnel responses were mechanically coupled and modelled by using FEM. Both were performed considering the soil as an equivalent linear medium. On the basis of the comparison of the results of both approaches, modification factors of the usual pseudo-static formulae are proposed, which take into account the kinematic interaction between the tunnel and the ground during shaking. The method, based on the use of simple charts, can be easily adopted for early-stage design.

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