Overview Tunneling for transit projects is as much an art as a science. Variables affecting the design and construction of a project include predicting the behavior of ground mass during construction and the vagaries of ground-water hydrology.
Predictive models are only of some use because no two projects are the same.
The process of tunnel design and construction involves evaluation of geologic conditions, identifying and acquiring the appropriate tunnel boring equipment, ground modification techniques, environmental impact mitigation, utility and traffic protection, contractor selection and payment, and risk management. Research is needed in all of these areas. Many innovations have been made in tunnel technology. This information needs to be collected and reviewed to identify the range of options available to minimize the problems an initiator of a subway project may face. Lessons have been learned from projects completed in the U.S. and in other countries that should help identify ways to achieve greater efficiency in the design and construction of subway tunnels.