Road Tunnels Manual

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6.1. Relation between construction method and cross section

For road tunnels the cross sectional shape is typically rectangular or circular and depends mostly on the method of construction. In table 6.1-1 some typical cross sections and corresponding construction methods are indicated.

The dimensions of the shapes employed are dependent on the dimensions of the cross section necessary for traffic. These vary due to:

  1. Traffic volumes and the importance of the tunnel
  2. Design speeds, safe stopping distances and sight distances
  3. Space for in-tunnel equipment such as: signs, traffic and environment monitoring
  4. Cost of the facility balanced against the required safety standards
  5. The traffic management required to respond to an incident in the tunnel
  6. The usual local norms and the financial possibilities.

Internationally the response to the above differences varies greatly. In individual countries the response to the different situations has varied and evolves with time.

Table 6.1-1: Cross Sections and Typical Construction Methods
Cross Section Typical Construction Method Comments
1 Circular Tunnel Boring Machine (TBM) Recently extended in Japan for rectangular cross section
2 Rectangular Immersed tube tunnel In USA, circular cross sections are common
3 Rectangular Cut and cover tunnel Precast technology sometimes leads to circular cross sections
above the carriageway
4 Horse-shoe Blasting Applied in hard rock
5 Circular crown and elliptical invert Excavation sustainment methods In hard rock, horse-shoe shapes are usual
Reference sources

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