Effect of Flexibility Ratio on Seismic Response of Cut-and-Cover Box Tunnel

Equivalent linear time history analyses are conducted to calculate the seismic response of various types of cut-and-cover single box tunnels. A finite-element numerical model is calibrated against the results of centrifuge tests. The calculated tunnel responses compare favourably with the measurements. A validated model is then used to quantify the seismic response of box tunnels. The flexibility ratio (F) is illustrated to have a governing influence on the tunnel response. It is shown that the previously developed relationship betweenFand the racking ratio (R) is applicable for a wide range ofFup to 20. It is also shown that an increase inFaccompanies corresponding increase inR, the spectral acceleration in the tunnel lining, and the shear stress along the tunnel lining-soil interface. The thrust in the tunnel lining is also revealed to increase withF, although the calculated value is significantly lower than the pressure on yielding walls. Additionally, the surface settlement is shown to increase with an increase inF.

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