Seismic response of shield tunnel subjected to spatially varying earthquake ground motions

The subway shield tunnel of Sanyang Road in Wuhan, China, is a Yangtze River-crossing tunnel project with a mega diameter of 15.7 m, which crosses several soil layers with sharply different properties. To investigate the seismic characteristics of this special subway tunnel under spatially varying earthquake ground motions (SVEGMs) with high efficiency, the concept of response displacement method was utilized and realized with a refined free-field model and a simplified soil-tunnel model. Two sets of borehole accelerograms, denoting near-field and far-field ground motions, respectively, were selected and taken as the reference to generate fully non-stationary SVEGMs. A lot of responses along the longitudinal direction under multi-support excitation (MSE), including intersegment opening width, inner forces, and acceleration, were observed and compared with those under identical support excitation (ISE). The comparative results showed that the responses of subway shield tunnel under MSE are generally higher than those under ISE. The longitudinal distributions of intersegment opening width and bending moment response of lining are dominantly affected by the site conditions. Excitation methods, spectral characteristic and PGA of input earthquake can also have effect on the longitudinal distribution of tunnel response. The results can contribute to revealing the difference between seismic response characteristics of shield tunnel under MSE and those under ISE and predicting the underlying location of seepage or severe damage of shield tunnel. The analysis procedure established in this paper possesses highly potential for application to the aseismic design of practical shield tunnel project.