3D Discrete Element Method Modelling of Tunnel Construction Impact on an Adjacent Tunnel
Closely-spaced side-by-side mechanized twin tunnels are commonly used in urban metro transit systems. The aim of this paper was to investigate the influence of tunnel construction on an adjacent existing tunnel using the 3D discrete element method (DEM) and propose a new method to protect the existing tunnel. The first tunnel at the left side was initially included in the DEM model. The construction of the second adjacent tunnel at the right side was then modelled in phases. Displacement, stress variation, porosity variation, and coordination of surroundings of the first tunnel were investigated. The results showed that the excavation of the second tunnel had a great negative impact on the existing tunnel surroundings when the distance of twin tunnels was less than the diameter of the tunnel. The maximum horizontal displacement occurred at the angle of 45° and was equal to 103 mm. The influenced area of the existing tunnel is the surroundings between the tunnel crown and the spring line on the second tunnel side near the tunnel lining. The composite reinforcement method consists of pasted fiber reinforced plastic (FRP) sheet method and grouting in a specific area; thus, the structure safety and the normal operation of the existing tunnel nearby can be guaranteed. The protective method can give reference for similar project.