Installation Manual - Future Pipe Industries

9.4. Subsidence
In order to allow for subsidence flexible rubber seal joints can be used (RSJ, RSLJ). There would be no sense in using
one joint in a pipe section (e.g. between two manholes), as these joints only allow angular deflection and no lateral
displacement.So they always have to be installed in pairs to create a rocker pipe. In this a way that one will be
placed at the beginning and the other at the end of the area where settlement will occur. The rocker pipe will then act
as a hinge.
Fig. 9.4.a.
The longer the rocker pipe, the bigger the difference in subsidence that can be accommodated. However, this will also
increase the loads on the joints. This can be avoided by using more rocker pipes.
Fig. 9.4.b.
intermediate part original position
flexible joint location of pipe after subsidence
intermediate part original position
flexible joint
location of pipe
after subsidence
Depending on the soil condition and foundation of the buildings, pumping stations, under piled manholes, etc.
to which the pipes are connected a minimum of 4 flexible couplers (RSJ) should be used between 2 manholes.
This accommodates possible settlement of the manholes. The branch connection of the manhole (provided with socket
or spigot end) should also be of a limited length to avoid excessive bending. Otherwise this may result in a break in
the pipe or the branch connection. The length of these connections is 1 x ID with a minimum length of 0.5 m.
Wavistrong Installation Manual
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settled profile after subsidence
settled profile
after subsidence
sag
sag