Pipejacking

Pipe Jacking, generally referred to in smaller diameters as Microtunnelling, is a technique for installing underground pipelines, ducts and culverts.  The method provides a structural, watertight, finished pipeline as the tunnel is excavated.

Powerful Hydraulic jacks within the drive shaft are used to push specially constructed jacking pipes through the ground.  A steel tunnelling shield at the head of the pipeline is used to provide support for the excavation process and to provide directional control for the pipejack.  Excavation techniques cover a wide range, from simple hand mining to backhoe and roadheader machines through to sophisticated full face earth pressure balance shields.  Current safety legislation ensures that mechanical excavation techniques are used where possible.

Open face Tunnel Boring Machines (TBM’s) such as backhoe or roadheader shields are suited to dry stable soils and soft rock.  Full face Earth Pressure Balance TBM’s may be used when ground conditions are more difficult and where the pipeline is to be constructed below the ground water table.

An accurate alignment is maintained by following a laser set to line and grade.  The shield is steered to the laser line with adjustments made to the on-board steering jacks.  Pipeline materials are typically pre-cast concrete, although GRP may be used in specific circumstances.  Drive lengths vary depending upon excavation technique, ground conditions and pipe diameter.  The use of a lubricant injected through ports in the jacking pipes and the provision of intermediate jacking stations enable long drives to be carried out.