Cut and cover tunnels
‘Cut and cover’ is an approach used for constructing shallow tunnels in situations where all the ground above the tunnel can be cleared. The first step in the construction is the formation of retaining walls on either side. These are commonly diaphragm walls (see Structural elements/Foundations/ Diaphragm walls) or contiguous piles (see Structural elements/Foundations/ Contiguous bored piles/secant piles).
Once the concrete has gained sufficient strength, excavation can be carried out and the base slab cast. Temporary props will usually be required to stabilise the walls so they can resist the lateral pressure of the soil. The roof of the tunnel can then be constructed, either cast in situ or using precast concrete beams ( see Precast/Beams) and the cover to the tunnel reinstated.