Study on tunnel internal forces considering the excavation effect of shield tunneling during ground loading

In order to study the influence of ground loading on tunnel confining pressure and internal force, several circumferential load calculation formulas considering the stress release effect of tunnel excavation are derived. The influence of ground loading on tunnel is simplified into two stages: stress redistribution and transverse elliptization. The internal force calculation formulas of any ring segment are derived by introducing the shear dislocation and rigid body rotation collaborative deformation model. 34 groups of measured water and soil stress data of tunnels at home and abroad are collected and analyzed, and the empirical formula of stress release rate (σ) is proposed. Combined with indoor model test, the confining pressure and internal force of the tunnel are calculated and the reliability is verified. The results show that the magnitude and distribution of tunnel confining pressure under surcharge load obtained by the theoretical method are close to the experimental results. The confining pressure obtained by considering the stress release effect are closer to the measured values, and each internal force value decreases with the decrease ofσ. The effect of the additional confining pressure on the segment at the center of the ground loading is the largest, and it gradually decreases on both sides. While the additional bending moment, axial force and shear force will have maximum values near the central point of ground load and the reverse bending point of tunnel displacement.