Mutual influence mechanism between soft soil interlayers and shield tunnels under seismic action: Laboratory tests and numerical simulations

Soft soil is widely distributed and has complex origins. Shield tunnels are inevitably constructed within soft soil interlayers, and under seismic action, tunnels may be subject to severe damages. On the basis of actual engineering, this study utilized dynamic triaxial testing to investigate the dynamic properties of soft soil. Using the PIMY constitutive model, the seismic subsidence characteristics of the soft soil were characterized, and a refined finite element model was established to study the mutual influence mechanism between the soft soil layer and shield tunnels via the open-source software framework OpenSees. The results demonstrate that soil exhibits a softening effect under dynamic loading; soft soil with better structural integrity is less prone to seismic subsidence; and the greater the inertial force acting on the soft soil, the greater the likelihood of settlement. Under seismic action, the presence of the shield tunnel exacerbates the settlement of the soft soil, as the surrounding soil experiences significant inertial forces from the tunnel structure, hindering drainage and accelerating the accumulation of pore water pressure; The soft soil itself has large deformation and displacement under the action of earthquake, which leads to the great stress, deformation, and displacement of the structure. The arch foot position of the tunnel is identified as the most vulnerable to damage.