The Hydraulic Joint

Function

The safe transfer of the jacking force from pipe to pipe up to the tunnel boring machine (TBM) and tunnel face is essential in microtunnelling and pipe jacking. The possibility of being able to transfer high jacking forces is indispensable for an efficient way of driling.

Pressure transfer media made of wood materials prove their worth on straight tunnels. However, with larger joint angles and / or tighter curve radii, they reach their limits, i.e. only significantly smaller jacking forces Q can be transferred from pipe to pipe without damaging the pipes. Consequently, the admissible jacking force Q for articulated pipe joints and thus the jacking performance is significantly reduced. Articulation angles between jacking pipes occur not only as a result of planned alignment curvature, but also as a result of steering movements of the TBM, as a result of changing geological conditions and also as a result of manufacturing tolerances in the jacking pipes. The characteristic, irreversible material behaviour of a conventional pressure transfer ring made of timber results in stress concentrations on the inside of the curve when the pipe joint is articulated, which can exceed the strength of the pipe wall even at apparently small angles, while the joint on the outside of the curve is gaping and thus no jacking force is transmitted there.