Backfilling the Zollverein colliery

In the heart of the Ruhr area in Essen (NRW) are the grounds of the Zollverein colliery, a coal mine that was active until 1986 and is also unofficially known as the ‘Eiffel Tower of the Ruhr’. The Zollverein colliery has been a UNESCO World Heritage Site since 2001 and is therefore officially one of the most important cultural assets in the world. In the course of planning the backfilling of shafts II and XII at Zeche Zollverein, Thyssen Schachtbau approached Schwing in 2018 with a request for a concrete pumping concept.
The shafts were to be backfilled for reasons of stability. However, it also had to be possible to continue to separate the mine water from the groundwater permanently. For this purpose, cladding pipes are inserted into the shaft, which is backfilled with concrete all round. This means that the mine water can be pumped out of the shaft at any time using high-pressure pumps.

A total of approx. 95,000 m³ of concrete will be pumped, of which 55,000 m³ will be used for Shaft XII and a further 40,000 m³ for Shaft II. The backfilling of the shafts was to take place during ongoing museum operations, meet the highest safety requirements and fit into the landscape of the World Heritage Site as far as possible. This required numerous measures, which were realised over several years of planning by Thyssen Schachtbau and Schwing.
There were special requirements for the backfilling of Shaft XII in particular. Concrete was to be pumped above ground from the pumping station to the transfer station at the shaft using a stationary concrete pump via a 150 metre long delivery line.
An SP 2800 E, a stationary concrete pump with 132 kW electrical drive power and a maximum concrete delivery pressure of 108 bar, was installed in the pumping station. An SP 2800 E was also used for backfilling Shaft II.
The stationary pumps were fitted with sound enclosures for noise protection reasons for museum operations. The delivery line concept ensures that there is always redundancy in the event of any complications and that cleaning or concreting demolition concepts are also economically feasible with regard to returning the concrete to the pumping station. In addition, in the event of a defective or damaged delivery line, no escaping concrete should pollute the grounds of the World Heritage Site or endanger visitors.

This was realised with a 3-strand concrete delivery line and 2 supply lines for compressed air and water. The entire delivery line was enclosed in so-called ‘pipework troughs’ and made accessible for maintenance purposes with opening flaps. Insulating elements were also installed inside the pipework troughs for noise protection reasons. The pumping station was designed so that the electrically driven stationary concrete pump SP 2800 E can pump concrete through all 3 concrete delivery lines. This was a sensible solution to reduce wear on the delivery lines, which was realised by arranging a total of 4 pipe switches. As part of the overall project at Shaft XII, approx. 20,000 m³ of concrete is to be pumped through each line of the delivery pipeline.
An elaborate ‘concrete conveying circuit diagram’ was created, which covers all scenarios. This also made it possible to return the concrete to a delivery line gallows. This means that the concrete can also be pumped back into the concrete mixer in an emergency. 
The shafts are backfilled using self-compacting concrete (SCC), as it is impossible to place concrete at a depth of 1000 metres using externally supplied compaction energy from vibrators. The concrete should also not segregate during downward transport into the shaft and thus achieve the best possible installation result.

In the run-up to the realisation of this project, several pumping tests were carried out in the presence of all the companies involved, including the client Ruhrkohle AG.
The aim was to determine the pumpability and the individual coefficient of friction of the intended concrete. The coefficient of friction factorises the resistance of the concrete in the delivery line and enables the concrete pressure to be extrapolated to the dimensions of a concrete pumping project.
The pumping tests provided a great deal of information, allowing the concrete to be optimised further and further following these tests. The result is an elaborate self-compacting concrete (SCC) of concrete grade C30/37 with a maximum grain size of 8 mm. In terms of pumpability, the concrete achieved the best results after repeated optimisation. The concrete pumps pump the concrete at a speed of approx. 60 m³/h over a distance of 150 metres. Each concrete layer fills an average of 6.50 metres of the shaft. This corresponds to 31-33 truck mixers with 7.5-10 m³ of concrete each, totalling 232-247 m³. The concrete is supplied by BAV from Herne and AVG from Gelsenkirchen.

“We are proud to be able to participate in such an exciting project together with our partner Thyssen Schachtbau and all the other companies involved on behalf of Ruhrkohle AG and the state of North Rhine-Westphalia. For us as a local company from Herne, this is a reference project. We have short distances to the construction site and the cooperation symbolises the cohesion of the Ruhr region.”

Dennis Feldbrügge, project engineer


The Zollverein Colliery in Essen/ Germany - a UNESCO World Heritage Site
3-strand concrete delivery line