Seismic analysis of underground tunnels by the 2.5D finite/infinite element approach: Fid-Bau Portal

Seismic analysis of underground tunnels by the 2.5D finite/infinite element approach

Lin, K.C. / Hung, H.H. / Yang, Judy P. / Yang, Y.B.

Abstract A procedure for the seismic analysis of underground tunnels using recorded free-field earthquakes based on the 2.5D finite/infinite element approach is presented. The near and far fields of the half space are modeled by finite and infinite elements, respectively. Using the 1D wave theory, the nodal force and displacement on the near-field boundary are computed for each spectral frequency of the earthquake. Then, equivalent seismic forces are computed for the near-field boundary for the earthquake spectrum. By assuming the soil-tunnel system to be uniform along the tunnel axis, the 2.5D approach can account for the wave transmission along the tunnel axis, which reduces to the 2D case for infinite transmission velocity. The horizontal and vertical components of the 1999 Chi-Chi Earthquake (TCU068) are adopted as the free-field motions in the numerical analysis. The maximal stresses and distribution patterns of the tunnel section under the P- and SV-waves are thoroughly studied by the 2.5D and 2D approaches, which should prove useful to the design of underground tunnels.

Highlights • A procedure for seismic analysis of underground tunnel using free-field earthquake data. • Demonstration of seismic waves transmission along the tunnel axis using the 2.5D approach. • Study maximal principal stresses of tunnel sections under P- and SV-waves by 2.5D and 2D approaches. • Show that SV-waves dominate maximal principal stresses of tunnel sections under P- and SV-waves. • Show that out-of-plane shear stresses of the tunnel section by earthquakes are non-negligible.