Definition - What does Hydraulic Joints mean?
Hydraulic joints are engineered pressure transfer rings that safely transfer jacking forces from pipe to pipe.
These rings have predictable mechanical behavior and permit a proper understanding of stresses acting on the pipe. They also provide full-face transfer of pressure without a peak in stress even at large angles.
The hydraulic joints also minimize the eccentric loading on the pipe that is normally observed when transferring loads through articulated joints.
Trenchlesspedia explains Hydraulic Joints
Hydraulic joints allow tunneling with a much greater joint angle between the jacking pipes than conventional timber pressure transfer rings, allowing for much tighter radii.
Relevant measurements such as fluid pressure in the hydraulic joint and the joint gap width between jacking pipes are continuously recorded and monitored and help in documenting the stress states applied to the jacking pipe.
With the knowledge of the stress state, the jacking pressure can be used such that the limit values are not exceeded as excess stress can compromise the integrity of the pipe.
The hydraulic joints also provide a good seal against groundwater and soil even in the articulated state. The design of the joint is such that the area where the pressure is transferred is sealed against water and soil so that the behavior of the hydraulic joint is not adversely affected.
A good joint design will consist of an external steel band or collar cast into the concrete and a spigot end with the gasket in a groove on the outside of the pipe.