Construction sites, closures, narrowed lanes: Since the end of March 2020 the patience of drivers who use the Dortmund/Witten motorway junction is being tested. But the remediation work on the A44 is urgently required, says Cedric Kamgaing Kamdom: “ Most recently we detected and backfilled a hollow space, which was around 10 m high and 3 m wide – roughly as big as a single-family house. And it was just below the road surface”, explains Kamgaing Kamdom, who works as a project manager at the responsible engineering firm arccon -Ingenieurgesellschaft mbH, Gelsenkirchen/Germany. The experts have now piped around 800 t of concrete mix into the holey underground in order to secure it. This corresponds to around 30 full semitrailers.
The near-surface cavities originate from olden times: At one time the miners here mined the -Vereinigte Wiendahls-bank mine through the ground. The mine closed down in 1924. The available data is sparse.
“The plans for the deposits are over 100 years old. This does not make it any easier for us.” Apart from that, there is also the so-called illegal mining, which is not recorded anywhere. You cannot simply drill straight over it, explains Kamgaing Kamdom: “Our most important task is to optimally detect the suspected cavities in order to save time and costs.”
And the concrete mix needs to be carefully chosen, depending on the nature of the cavities and loose zones. At the beginning of such a project is a basic evaluation, during which old mine plans are also evaluated. They can provide guidance on surface openings, old tunnels or working areas of a mine. Following this basic research, if necessary exploration, safety and safeguarding works are planned, tendered and executed in the form of drilling and backfilling at extreme depths.
Specialist knowledge that Kamgaing Kamdom acquired in the course of his studies. Five years ago he came from Cameroon to Germany and decided to study at the TH Georg Agricola University (THGA) in Bochum. He acquired a fresh perspective in the master programme “Geological Engineering and Post-Mining”: “I was unfamiliar with the labour market beforehand, but did know that the coal mining sector in Germany was due to end in 2018 and that then certainly people who are knowledgeable in post-mining would be recruited”, says Kamgaing Kamdom, who already studied geosciences in his home country.
He turned out to be right. Experts at the interface between mining, surveying and geotechnical engineering are not only in demand here in Germany, but also internationally. Because the mining of raw materials leaves its mark worldwide (Figure 1). Special safety and restructuring measures are required in order to manage the risks at former mining sites. The master programme at the THGA, which is the only such programme offered in Germany, trains engineers to responsibly plan and execute the complex processes of mine closures and the aftercare. This also includes intelligent after-use in the affected regions.
For Kamgaing Kamdom the language was initially a little obstacle. “Especially in the lectures I had to be very attentive, but the good contact with other students and the lecturers made things a lot easier. The course is also very practical and you are out and about on the road a great deal”, says the graduate.
And what’s happening now on the A44? “We are currently on schedule. But there is still one part to come.” Here there may be more unexpected challenges hiding somewhere for the engineers, but Kamgaing Kamdom is confident: “When we have completed our work, probably in summer 2021, we are forever on the safe side.” Ideally, for drivers this means: For starters, peace and quiet on the A44. And for Kamgaing Kamdom: Off to the next construction site! Because the post-mining era is significantly longer than the mining era itself and brings full order books also in the future. (THGA/Si.)