Long precast elements with innovative seal

In renovating culverts, the focus as a rule is on one central objective: to disrupt rail service as little as possible, keeping rail-traffic possession times to a minimum. For this purpose, project engineers are constantly working on practicable solution alternatives to reduce the construction time. A good solution was found in the German state of Saxony-Anhalt for replacing a culvert in the area of the former Blumenberg Freight Terminal. Here, the engineers choose precast reinforced-concrete frame elements instead of in-situ concrete and, in this way, succeeded in significantly reducing possession times.

On the 59-km non-electrified railroad line 6404 from Magdeburg to Halberstadt, Germany, there is a culvert for discharging water at km 21.62, near a partly broken off ramp. The culvert was installed in 1843 and extended at the end of the 19th century. Since the culvert, approx. 97 m long, was badly damaged due to its age and usage, rehabilitation was no longer economically justified. The department Anlagen- und Projektmanagement of German Federal Railroad Network DB Netz AG decided to completely replace the culvert.

Erection in only two days

“To reduce track possession times as much as possible, we proposed a construction method with precast reinforced-concrete elements,” explained Alexander Bär of the company Königbau GmbH from Kesselsdorf, Germany. “The culvert passes under four tracks. Because only two tracks at a time could be closed off, two track possession times were needed – although exactly as would have been the case with in-situ construction, possession times would nevertheless have been significantly longer. All in all, it would be justified in saying that in-situ construction of the culvert would have taken more than double the time,” says Bär.

Erection of the complete structure from an assembly kit of precast elements took place in only two days. To prevent tilting, the culvert was stabilized with reinforced-concrete load distribution panels below the precast frame elements. These transmit the shear forces at the joints. A total of 33 elements from Kleihues Betonbauteile GmbH & Co. KG from Emsbüren, Germany, were placed in their final position by a heavy telescope crane. The elements had a maximum width of 1.90 m, maximum length of 5.1 m and an individual weight of up to 31 tons.

Innovation in the railroad sector

Tobias Janning, responsible for railroad projects at the manufacturer Kleihues, explains the complexity of the measure. “Because we were dealing with a covering here of less than 1.5 m, it was not possible for the precast elements placed near the tracks to have joints. For this reason, we developed a special solution for DB culverts. We manufacture individual frames with effective lengths of up to 5 m. The special feature: the frames are provided in the plant with a specific elastomer seal, similar to the one familiar from sewer construction – a genuine innovation never before used, especially not for railroad projects. The benefits are obvious: weak points encountered during implementation at the site, and the resulting damage, are minimized. Furthermore, this solution is very flexible – to adapt to requirements, we are able to manufacture precast elements of various cross-sections and effective lengths,” explains Janning. Alexander Bär continues: “A great advantage of this construction method was that we could backfill the precast elements immediately after erection and place the tracks on top. All the steps could be carried out immediately and consecutively. Complex provisional bridges and shoring were therefore not needed. In this way, we were able to reduce track possession time.”

Reduction of possible error sources

Paul-Martin Grosskopff mentions yet another benefit of precast construction: “Precast elements are manufactured under controlled conditions and are subject to continuous quality control in the plant. This results, in contrast to conventional processes, in generally better concrete quality that also offers optical benefits. Furthermore, the reduction of process steps, which is inherent to this construction method, leads to a simplification of the entire project as well as to reduction in possible error sources.” Alexander Bär confirms: “All in all, this process is a very clean solution and, technically, functions outstandingly well. With this method, we have had good experience also with numerous other construction measures.”

The construction company Königbau GmbH from Kesselsdorf performed rehabilitation of the structure, with assistance by an erection team from the company Kleihues in April 2024. The project was planned by consulting engineers GRE German Rail Engineering GmbH from Dresden. After short possession, trains could once again roll over the underpass.