M85: this is the solution to speed up concreting in the northern tunnel of the Sopron tunnel

According to our newspaper, all the counterbolting in the southern tunnel of the M85 motorway is now complete. The 780 m long tunnel is being built by SDD Konzorcium (Dömper Kft., Subterra-Raab Kft., Pannon-Doprastav Kft.) on section V of the M85, which is being built from the Fertőrákos junction to the border by Építési és Közlekedési Minisztérium (ÉKM).

How the tunnel tunnels are made

As explained in our previous articles, the east-west tunnel will be created by a northern and a southern tunnel, crossing the Vienna Hill near Sopron.

After the successful completion of the excavation in the shafts, the final structure of the tunnel will be made of 35 centimetres of reinforced concrete in both shafts, with the help of a four-man machine chain.

The latter consists of the insulation wagon, the ironwork wagon, the 130-tonne formwork wagon and the aftertreatment structure.

The concreting of the tunnel, including the open sections, will be completed in 64 blocks per tunnel. The construction of the final structure, designed with the BIM programme, will begin with the cleaning and fine profiling of the tunnel in both passages, followed by the installation of the counter-bolt and the concreting of the counter-bolt. Then the 35 cm thick reinforced concrete vault will be insulated, reinforced and concreted by a formwork carriage in succession, with a 2-3 block backlog, in parallel work streams. The concreted vault already contains all the fittings and junction boxes and protective tubes for the internal installation, in order to allow the installation and operation of the subsequent tunnel management and operating systems.

This was a key step in the tunnel project

During the construction of the Sopron tunnel, the southern tunnel was also excavated and punched well ahead of schedule, so the concreting is also well ahead of schedule compared to the northern tunnel. Attila Kerékgyártó, the project manager of SDD Konzorcium, told us at the time of our enquiry that the main concreting work on the southern tunnel had been completed at block 61, the sealing had already been completed and only the two open sections remained to be completed in terms of iron installation.

An important step in the works was the assembly of the second formwork carriage during the spring, which will allow two formwork carriages to work in the northern tunnel. "When we have two shuttering carriages in one tunnel, they will both run from east to west"

- added the project leader. "Before this phase of work, of course, the counter-bolt has to be built, and the ironwork and insulation have to be done. It was therefore also an important moment that we had another ironworking trolley delivered, in order to complete the machine chain before both formwork trolleys."

Both shuttered wagons are diverted from the southern to the northern route

Turning to the organisation of the formwork trolleys, Attila Kerékgyártó said that as soon as the first formwork trolley reaches the west side in the south tunnel, it will be diverted to the north tunnel. "Then it will first concrete the open blocks on the west side of the north tunnel, then it will be set to work in block 42, standing back, and from there it will move westwards." (At the time of our conversation, the first formwork car in question was still working in block 61 in the south tunnel, from where it was heading west, with three blocks still to go - ed.)

The second formwork truck has completed the construction of the open blocks in the southern passage and we have successfully built the first open block vault in the northern passage, a slower task that requires careful work.

As a prelude to the above work, the counter-blocks of the open section on the eastern side of the northern corridor have already been completed, this section consisting of two and a half blocks.

One day it's one formwork truck, the next day it's another

In response to our question, the specialist explained that when the two formwork carriages were transferred to the northern tunnel, from then on there will be a main concreting operation every day: "One day with one formwork carriage, the next day with the other.

This will require a lot of organisation, but it will also allow us to complete the concreting in the northern tunnel by the end of November."

He added that the concreting of the southern corridor is scheduled to be completed by mid-August.

When asked about the specific challenges, he explained that paving open blocks is different from what he has done before. "This is because the tunnel is built backwards: there is no cover over it, no shotcrete over it, instead we use a counter-block. It is a more complex, slower job, but also an exciting challenge. For this reason, it is a significant achievement that several open blocks have already been completed."

He concluded by saying that, in parallel with the above, the internal works have already started in the southern corridor, including the construction of the fire protection system, the protective piping and the concreting of the pavement.