Horn- Bad- Meinberg-based Beton Tille GmbH originally started its pipe coupling line of business for the repair of defective seam tubes. In the early years of the Federal Republic, non-reinforced concrete pipes were largely the standard in sewer construction. One end of the pipe had a narrowing, a fold, it was pushed into the groove of the following pipe. Both were made of concrete, the seal was made of tar - if at all - a tarred cord. Since they were unreinforced, often made of lean concrete and only slightly compacted, the pipes quickly tended to crack, especially at the rebate, where tilt caused slight tension. Pipelines are generally plugged together, which is a simple principle that, however, poses challenges when it comes to maintenance because it is not possible to move buried pipelines by just a few centimeters in order to lift a single pipe segment out of its socket or to insert it again.

Squared and ring-shaped coupling
The basic design Beton Tille came up with includes the clean removal of the damaged pipe segment complete with its adjoining socket using a cut-off wheel. In the next step, the socketless replacement part is inserted so as to ensure perfect fit. It is then sealed using a ring-shaped element previously pushed onto the pipeline. This element includes two EPDM seals and is 25 cm wide in its standard version. After putting the new pipe in place, this ring-shaped coupling is moved along the pipeline by mechanical means until it covers the butt joint formed by the old and the new pipe segment. In the manufacture of pipe couplings, concrete provides the advantage of ensuring maximum flexibility and stability at the same time, irrespective of the materials the incoming and outgoing pipe segments consist of. This method permits shifting from any cross-section to another, including from egg-shaped to round or from steel to concrete pipes. Friedrich- Wilhelm Reineke, managing director of Beton Tille GmbH & Co. KG, adds that the company previously also manufactured couplings with tips. Its range basically includes custom products that can be inserted into a standard socket.
The outer, rectangular shape of the coupling is the pragmatic outcome of the company’s response to specific production needs because this is the easiest way to fabricate the form and to fill it with concrete. The corresponding openings are prepared with pinpoint precision in a manual work step, mostly using wooden blockouts. The edges and grooves in which the EPDM seals (mostly wedge seals) are placed are secured against breakout by steel angles embedded in the concrete. This precaution is necessary because the couplings are subject to enormously high loads when being shifted using hydraulic presses. Cracking and tearing-apart of the concrete in this moment would require a complete restart of the work.

Sleeve pipe in the track bed
In the Frankfurt/Main metropolitan region, two new tracks are currently being added to the S-6 local railway line. The network operator, Netzdienste Rhein- Main GmbH – NRM, intends to accelerate train speed in order to shorten the time required for traveling from Bad Vilbel to Frankfurt Main Station by 5 to 21 minutes.
In the Eschersheim district, a DN 500 underground water main crosses the existing dual-track railway line in the Maybachstrasse/Eschersheimer Landstrasse area. A DN 800 concrete sleeve pipe was laid around the pipe segment underneath the track bed in order to protect it from the enormous dynamic loads of passing trains. In the event of failure of the water main, the water would flow only into the sleeve pipe and onward into a dedicated manhole structure installed beside the railway line because flooding of the soil below the rail tracks must be prevented at all times.
A 10 m extension had to be added to this sleeve pipe during construction of the two new rail tracks. The NRM and Deutsche Bahn experts decided in favor of installing a steel sleeve pipe extension with a diameter of 864 mm and a wall thickness of 18 mm.
In May 2017, the project managers asked Reineke if he could supply a pipe coupling suitable for this diameter and type of changeover between materials. This coupling had to provide sufficient capacity for absorbing the expected dynamic compressive loads generated by rail traffic. This additional static load was taken into account in the design by including additional reinforcement. Reineke also performed a complete survey and high-precision laser measurement of the existing concrete sleeve pipe in order to push on the required coupling piece as tightly as possible.

Quick completion
It took almost two years to go through the design, engineering, and permitting stages, which is why Beton Tille was able to start up production of the coupling only in the second half of 2019. The element was finally delivered to the client in November last year. The pipe was installed using an open-cut method in February 2020 because the new tracks had not been laid yet at this point. While the lead time was very long, the work as such was completed within a single day, not least because cutting an entire district off the water supply for an extended period should be avoided.
In the next step, the DN 500 water main was cut apart and the new sleeve pipe was pushed onto it. The pipe coupling was then completely pushed onto the end of the concrete pipe, followed by welding the steel water main together again, approaching the new steel sleeve pipe to the existing pipe, and pushing the pipe coupling supplied by the Lemgo precast plant over the resulting butt joint. This is why the coupling piece had to be initially pushed onto the existing pipe segment exhibiting a comparatively rough surface, rather than placing it on the smoother steel pipe, because the diameter of the latter was 64 mm larger than that of the old concrete pipe.
Robert Mehl, Aachen
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