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