The T2D Project tunnels will be constructed using tunnel boring machines (TBMs), except for short lengths at each end of the tunnels where the roadway is too shallow for the effective use of TBMs.

For these short lengths, the tunnels will be constructed from the surface using cut and cover methodology.

Cut and cover areas are large open trenches that will be:

  • cut deep enough so that the TBMs can be launched or retrieved at the required gradient
  • reinforced with retaining walls to ensure stability.

The trenches will be approximately 120m long, 50m wide and 25m deep.

The TBMs will be assembled in the ‘cut’ trench – which will be located within both the northern and southern laydown areas – and will then begin excavating the tunnels. Once they have tunnelled far enough, work will start to build the ramp and ‘cover’ structure over part of the trench.

The structure covering the ‘cut’ trench will be made from concrete slabs and covered with soil. Some of the covered area will form the new motorway or surface roads, while some will also be used to house tunnel ventilation equipment and tunnel operations facilities, or converted into community space.

Using the land above the cut and cover tunnel section will minimise the land required to deliver the T2D Project.