Imagine the challenges of building a tunnel in an urban setting - for example, to construct a metro system in a big city such as London, New York, or Montreal. This article is about about building tunnels underground in cities and towns, or urban tunneling.
Civil engineers design, develop and build different types of structures. The increasing need for rapid and effective ways to move people and goods has led to a new and exciting field in civil engineering: transportation systems. Transportation can be done by systems built over the surface- streets, highways, and train lines- or underground (tunnels, mines, metro systems, etc).
Why Urban Tunneling?
The population in cities around the world is constantly growing, and this trend is expected to continue according to different studies. Cities considered small or medium sized twenty or thirty years ago are now considered big. Space in cities is always a limited resource, and as they grow, it becomes a challenge to use it appropriately. In addition, as cities expand the need to move people from one part of the city to another increases because people live farther from their place of work or places of activities (shopping, banking, etc). So, the limited space and the increase in the need of transportation make urban planners authorities and politicians to seek alternative means of transportation. Building transportation systems underground (metro, railways, etc) is one of those alternatives that leads to the challenge of doing urban tunneling, that is constructing underground urban tunnels
Urban Tunnels Construction
Building urban underground tunnels poses a great challenge for civil engineers. To start with, building underground in an urban setting is based on uncertainty of the main variables needed for building structures. The geotechnical and geomechanical behavior of the ground is unknown. So, there is a need at the start of project design to use a probabilistic approach and to proceed to construction with an iterative process “mind set" of building and measuring the response of the construction and adjusting accordingly as the project advances. This process must be repeated periodically and frequently to manage, mitigate, or reduce risks associated with this activity.
Building underground tunnels is not new. However, the way they are built today is very different. Tunnel construction today is now totally mechanized. The excavation environment is not like mining, but more like a factory with high levels of safety and comfort for workers. The excavation of underground tunnels today generate little disturbance on the surface (noise, vibration, dust, etc) and overall has a lower cost than traditional non-mechanized methods.
Vittorio Guglielmetti, Ashraf Mahtab, Shulin Xu. 2007. Mechanized tunnelling in urban areas: design methodology and construction control. Routledge.