STUDY ON LONGITUDINAL BENDING DEFORMATION BEHAVIOR OF SHIELD TUNNEL SEGMENTS REGARDING THE ACTION OF LONGITUDINAL FORCE

To investigate the longitudinal mechanical behavior of shield tunnels under the action of longitudinal forces, a longitudinal model test of a segment of the tunnel structure was carried out based on Wuhan Lianghu Tunnel (Donghu section). The vertical displacement and longitudinal strain of the tunnel are analyzed to reveal the influence of the longitudinal force on the longitudinal mechanical behavior of shield tunnels. The results show that: The longitudinal force can improve the longitudinal bending stiffness of shield tunnels, but the effect of the longitudinal force on the longitudinal bending stiffness increases first and then decreases with the increase of the vertical load. Taking the vertical loads of 3200 kN、9600 kN and 16 000 kN as an example, the maximum vertical displacement of the tunnel decreases by 45.5%, 56.8% and 62.7% respectively, when the vertical and longitudinal load ratio K is 0.56、1.67、2.78 respectively, but only decreases by 23.5% when the vertical load is 22 400 kN and K is 3.89. The longitudinal bending stiffness efficiency of the segment structure decreases with the increase of vertical load, which can be divided into three stages according to the reduction degree: The first stage is stiffness weakening, and the second stage is stiffness stabilizing, the third stage restores to the stage of stiffness weakening. Longitudinal bending stiffness efficiency is affected by both vertical load and longitudinal force. When the vertical load is constant, the smaller K is, the greater the longitudinal bending stiffness efficiency is. When the vertical load is 22 400 kN and K is reduced from 35 to 3.89, the longitudinal bending stiffness efficiency of shield tunnels decreases by 16.2%. Taking the midspan cross-section as an example, the neutral axis moves up with the deformation of the tunnel under the action of vertical load. Increasing longitudinal force can make the neutral axis move down and reach the position of the arch waist. The longitudinal bending stiffness efficiency obtained in this test is similar to the existing model test results in the absence of longitudinal force, but greater than the existing research results after considering the longitudinal force. The longitudinal bending stiffness efficiency should be considered with the influence of residual longitudinal force. and the recommended value is 0.218~0.696.