Soft ground tunneling in urban areas-proximity effects

Transportation and lifelines play a crucial role in maintaining living functions of people in/around urban areas. Due to progressive development of major cities, bored tunneling has become one of the commonly adopted methods for constructing transportation and lifeline facilities. As ground deformation would inevitably be induced by tunneling, buildings or structures in the close proximity are subject to various levels of risk to damage. The soil/groundwater conditions as well as their interaction with tunnels and substructures have further made the situation of each case unique and full of challenges. This paper discusses 4 cases in the Taipei Rapid Transit System (TRTS) projects, where tunnels were bored in close proximity to or even in conflict with existing substructures and/or substructures to be constructed in the future. In addition to a review of possible consequence caused by the construction, numerical simulations are introduced to characterize important features and obtain insights of the problems. Engineering judgment and decision-making process to the ground deformation control and protection strategies are further presented for resolution of each case.