Microtunnel
Carried out by tunnel boring machine (TBM), very accurate tunneling and able to undertake long tunnels in varied ground conditions. Can excavate tunnels in material that ranges from rock to flowing sands. Material is extracted from the face generally in slurry form by pipes. Tunnel is lined either with concrete or steel jacking pipes installed in sections.
Augerboring
Carried out by machine with flytes (augers). Very limited steering available so length of tunnel in our case is really limited to about 50m. Able to cope with firm ground and with a change of cutterhead can cut rock up to a certain strength. Lining is a steel enveloper which is pushed in as the ground is cut. We are installing 6m lengths of enveloper.
Pipe ramming
This is a solution for bad/soft ground. Enveloper pipe is push through the soft ground and then the material is excavated from the pipe. This is usually done by flushing the material out with water. In bad ground this is the best solution as the support is installed before any material is removed. This limits the risk of ground settlement.
