Nonlinear Response Characteristics of Undersea Shield Tunnel Subjected to Strong Earthquake Motions

Ensuring the safety of undersea shield tunnels constructed in soft marine deposits that are subject to strong seismic motion represents a major engineering challenge. An example of one such undersea shield tunnel is the 2.70 km-long subsea highway tunnel crossing under the Gulf of Suai in the Rongjiang River Estuary in Shantou, China. Using the generalized response displacement method, the authors developed a nonlinear seismic response analysis of the segmental lining for the 2.7 km-long Suai tunnel. In the proposed longitudinal seismic response analysis, the engineering geology characteristics and nonlinear dynamic behavior of the Suai seabed soil, the nonuniform mesh layout of the free-field site, the artificial boundary conditions and nonuniform seismic input, simulation model, and the parameters of soil-tunnel interaction systems, are considered in detail. Special emphasis is given to the irregular unloading-reloading rules for the stress-strain hysteresis loop, the seismic input at artificial boundary nodes, and the spatial incoherency of ground motions in the seabed site. The opening width at the ring intersegment under simultaneous actions of longitudinal, transversal, and vertical seismic motions is critical for seismic safety. The proposed methodology was deemed conservative, as demonstrated by a comparison with dynamic transient analysis using the three-dimensional finite element method. The results of this pilot study should be of use in the construction of future long subsea shield tunnels in the high seismic intensity region.