Research on the Optimal Clearance Distance of Super-Large-Diameter Shield Tunnel Underpassing the Existing Metro Tunnel

Abstract

With the accelerating urbanization in China and the constant development of underground space, shield tunnels have been extensively applied to underground roads in central urban areas. However, the central areas are featured with complex surroundings, such as numerous subways, bridge pile foundations, basements, pipelines, and other structures and buildings. Therefore, it will be an unavoidable engineering difficulty for the construction of shield tunnel in the central urban area to cross at a close range buildings (structures) such as existing tunnels, underground pipelines, underground passages and basements. At present, there are remarkable research results for the crossing of subway shield tunnel with an outside diameter of 6.0 m, and rich research results for the crossing of shield tunnel with an outside diameter of 10-14 m. However, there are relatively few studies on the shield tunnel with an outer diameter of 15 m and above crossing existing buildings (structures). Based on Shanghai Beiheng super-large-diameter shield tunnel (outside diameter 15.0 m), the Midas_GTS finite element analysis software was used herein to study the relation between the underpassing clearance distance h and the peak settlement of existing metro tunnel S. The optimal clearance distance of the super-large-diameter shield tunnel underpassing the existing metro tunnel in the soft soil area h was drawn to be 7.0∼8.0 m. Through analysis, it was found that the ground loss rate ρ and the tunnel peak settlement S of the existing tunnel was linear, with the slope = 2.795 > 1. It proved that the tunnel peak settlement S of the existing tunnel was significantly influenced by the ground loss rate ρ. Therefore, it’ s quite reasonable to take the ground loss rate ρ as the evaluation indicator and control requirement for crossing construction.