Experiments and numerical simulation of the reinforcement effect of channel-steel-reinforced shield tunnel segments under unloading conditions

The increasing emergence of foundation pit excavations in dense urban areas has caused a series of adverse impacts on operating tunnels. Thus, the investigation of tunnel segment reinforcement is crucial and essential for geotechnical engineers. This article intends to investigate the reinforcement effect of the channel steel reinforcement method through a three-ring full-scale test and finite element simulation. The three-ring full-scale test is carried out by considering different confining pressures under the influence of different tunnel burial depths and different distances between the foundation pit and tunnel (clearance distances). In addition, a three-dimensional refined FEM numerical simulation verified by the full-scale model test is conducted to study the influence of foundation pit retaining structure deformation. The research results show that channel steel reinforcement can significantly improve the stiffness of the segment and its bearing capacity. The effect of the channel steel is more prominent in tunnels with a large burial depth. The stress and deformation of the segment are relatively uniform under the conditions of different clearance distances after the reinforcement of the channel steel. The top and bottom convergence of the segment and the bolt stress increase as the deformation parameters of the envelope structure increase; furthermore, the top and bottom convergence of the segment can be reduced up to 46.88% after the channel steel reinforcement.