Effect of Soft Ground Tunneling-Induced Displacements on Railway Embankments

With the rapid development of urban infrastructure, certain transportation lines, utilities and pipelines are needed to be excavated under operating railway lines. When a tunnel under a railway is excavated, it will inevitably cause disturbance to the track structures, and the disturbance could influence the safety of railway operations. Consequently, the alleviation of ground surface displacement is of great significance to ensure the safety of both railway operations and tunnel construction. This thesis is a fundamental study of the surface displacements due to the construction of both shallow (near-surface) and deep (away from the surface) tunnels. The analysis of displacement along the surface of railway embankments is performed via two-dimensional finite element modeling. The freight train operating speed, tunnel diameter and tunnel depth are the three key factors that affect the surface displacement. The results illustrate that a 3 m diameter tunnel at depths greater than 3 m or a 4 m diameter tunnel at any depth greater than 16 m can be constructed beneath an existing railway without significantly affecting the safety of railway operations by considering subsidence control standards. Thus, this thesis contributes to determination of the maximum displacement of railway embankments induced by tunnel excavation as a function of various factors considered. Also, the findings of this thesis can help to guide future tunnel design and displacement control measures for excavations under operating freight railway lines.