Tunneling in Rock

Tunnels in rock-masses are usually constructed by the bored tunnel technique. Both the conventional and the mechanized methods are used and the selection depends on the tunnel’s length and the rock’s characteristics.

In the conventional method, hard rock formations require the usage of blasting techniques and the support needed is usually minor. On the contrary, weak rock formations may be excavated by mechanical excavators and heavier support including shotcrete, anchors/bolts and steel ribs may be needed.

The strength of the excavating rock material is also a crucial factor when using a TBM. An open type TBM may be used in hard rocks, while single shield or double shield TBM may be used in fractured rocks and highly broken rocks, respectively.