Model test investigation on the longitudinal mechanical property of shield tunnels considering internal structure

Reasonable evaluation of longitudinal mechanical property of shield tunnel is critical to the design and maintenance of tunnel structures. Traditionally, the internal structure has not been involved in the existing studies on the longitudinal mechanical properties of shield tunnels, of which the effect on the longitudinal mechanical properties of shield tunnels remains unknown. In this study, a series of physical similar model tests were conducted on homogeneous model (HM), non-homogeneous model (NHM) and non-homogeneous model with internal structure (NHMI), the effect of internal structure and longitudinal force on the longitudinal mechanical properties of road-metro shield tunnels were investigated. The longitudinal strain, displacement, curvature, and circumferential joint deformation of the tunnels were analyzed in depth. The experimental results show that the internal structure can reduce the longitudinal deformation of shield tunnels greatly, and the maximum displacement of tunnels with internal structure can be reduced by 70.58 %, the curvature radius can be increased by 1.73 to 2.36 times, the dislocation of the circumferential joint can be reduced by up to 70.4 %, and the opening of the circumferential joint can be reduced by up to 67.37 %. The longitudinal bending stiffness efficiency of tunnels ranges from 0.66 to 0.86 after taking into account the effect of internal structures. Increasing the longitudinal force from 0 MPa to 0.3 MPa significantly improves the longitudinal bending stiffness efficiency of tunnels, after which increasing the longitudinal force has no significant effect on the longitudinal mechanical properties of the tunnel.