The ZÜBLIN Pipe Jacking Division team is helping to build the new sewage system in Singapore. For the pipes, which are laid underground, the team managed to come up with a special idea for fixing the elements.

The Deep Tunnel Sewer System in Singapore consists of a main sewer 50 km long, 11 of which are constructed by ZÜBLIN, together with three separate link sewer systems to the main sewer. Each of this link sewers is approximately 5 km long, with varying diameters of 1.2 meters up to 3.0 meters. These link sewers are being installed using pipe jacking method.

As the subsoil is very soft in various sections, the ZÜBLIN’s Pipe Jacking Division team had a non-trivial problem to solve: Possible push back of the installed jacking pipes into the jacking shaft since the pressure from the front on the pipe elements laid in the ground is higher than the force of friction on the side walls.

To overcome this challenge, the team devised an inhouse solution: a steel pipe brake that is attached on both sides of the last installed jacking pipe. Together with hydraulic jacks, that were already available on the construction sites, the pipe bracket holds the pipe string in place until the next jacking pipe is installed.

Step 1: The special jacking pipe is lowered down and pushed by the hydraulic jacking rams until the created space is sufficient to lower down the next jacking pipe. Then the stopper steel brackets are inserted into the prefabricated holes on both sides of the pipe.
Step 2: The hydraulic strutting rams are extended against the mounted stopper steel brackets until the system is stabilized.
Step 3: The pipe is now fully supported, allowing the main push rams to be retracted to create space for lowering down the next pipe.
Step 4: The next pipe is lowered down.
Step 5: Once the next jacking pipe is installed, the push ring is extended and pushed against the pipe. Then the hydraulic strutting rams are retracted, the stopper steel brackets are unmounted and the pipe jacking operation can be resumed.

Complex statics

The solution is as simple as it is ingenious. All necessary materials and equipment can be found on the construction site and the staff already has a routine in handling hydraulic presses, steel parts and concrete pipes. Only two small steel plates with conical pins on both sides of the concrete pipe are needed in addition. The conical opening is left in the concrete pipes at the appropriate place – and is, shortly before advancing further, closed again until watertight with prefabricated conical concrete plugs.

The pre-produced cones are waiting to be put to action.

Compared to other conventional methods such as pipe clamps which not only take up a lot of space but are also expensiveand limited to larger diameter shafts, the pipe bracket is a simple, cost-effective and easy-to-use method.

‘To me, a technical innovation does not necessarily have to be high-tech. If the idea allows us to achieve the optimum with simple means, if we keep everything in our own hands, if we are not dependent on others and if the building materials and equipment can be found on the construction site anyway, then it is, to my understanding, a serious innovation.’

Oliver Chen
ZÜBLIN Pipe Jacking Division

The challenge behind the bracket idea was mainly the calculation of the necessary stability. Fortunately, a structural engineer was found who, like the team, was open to new challenges and highly motivated to calculate this completely new idea.

Design & Engineering
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