Experimental and theoretical study on longitudinal deformation and internal force of shield tunnel under surcharge

Abstract

The longitudinal behavior of a shield tunnel is essential for analyzing its deformation and internal forces under surcharge. This study involved the design and construction of a reduced-size indoor model of a tunnel to investigate its performance with various initial ovalities when subjected to different surcharges. Furthermore, a model was proposed to investigate the longitudinal deformation of the tunnel caused by rotation and dislocation, which was verified and compared. The results reveal that the longitudinal settlement of the tunnel follows a normal distribution. The maximum settlement occurs at the central ring and increases linearly with the applied load. The zone of strong influence extends approximately 1.6 times the load width, and an additional load of 20 kPa can be employed as a control value for the surcharge. Additionally, the study found that stress concentration typically occurs on the side of the tunnel waist under surcharge. As a result, the horizontal convergence at the central ring increases at a faster rate, leading to transverse elliptical deformation of the entire structure. The longitudinal curves of curvature and dislocation visually reflect that the dangerous sections of the tunnel structure are concentrated at the center and edge of the load. Moreover, the rate of deformation development and final deformation values differ among tunnels with varying initial ovalities, and there is no simple linear relationship between them. The oval shape of the tunnel exacerbates the progression of longitudinal deformation while inducing a three-dimensional coupling effect between adjacent segments. Ultimately, the plausibility of the experimental results is confirmed based on the proposed longitudinal model of the tunnel, thereby establishing a connection with practical engineering applications.