Three-dimensional analysis of displacements resulting from tunneling in soft ground

Due to increasing demand for basic infrastructure and habitation in many modern cities worldwide, tunneling has become a strong alternative solution for delivery of public works, especially transportation in densely populated areas. Ground displacements generated by tunneling construction are one of the most important aspects in any tunneling project, since existing infrastructure and high-rise structures in the urban environment can be very sensitive to any ground movements. Because ground displacements are inevitable, geotechnical engineers need versatile and accurate techniques to model and accurately predict the ground displacements. To accomplish this, the concepts of tunnel construction, which comprise complex three-dimensional situations including different construction processes, variable geological settings, complex soil properties, etc., are needed. The available conventional displacement prediction methods are based on empirical studies, which have limitations and lack the flexibility to include influences from many basic factors such as stages or non-proportional features of tunnel construction. By using a general purpose nonlinear three-dimensional finite element method (FEM) geotechnical software tool, this dissertation summarizes the methodology and suggests a way to create a FEM tunnel model that accounts for many realistic tunneling construction details. Two of the leading tunneling techniques, the Shield Tunneling Method and New Austrian Tunneling Method are investigated in this study, with focus on the behavior and performance deriving from differences in these construction methodologies. The Heathrow Express Trial Tunnel project and the Airside Road Tunnel project in the United Kingdom are used as case studies. The results from FEM simulations show good ground displacement predictions when comparing to the real measurement data. The model also shows the potential to simulate influences deriving from important construction-related variables such as in-situ stress states, fluctuations of shield pressure, and changes in construction sequences.