Launching of the construction of tunnels of the 4th line of the Metro

On April 3rd the tunnel building and tunnel boring machines set on their 106 week journey. That is to say, the 7.2 kilometre long tunnel of the 4th line of the Metro between the Kelenföld Railway Station and the Keleti Railway Station is planned to be completed in 106 weeks.

On April 3rd the construction of the tunnel on the left side is commenced. The
excavator wheel of the tunnel building machinery exceeding 100 m in length started its journey a few minutes before noon. Two tunnel boring machines will build the tunnels; the second tunnel boring machine is scheduled to be launched three weeks later. This delay is required due to reasons of logistics.
The tunnel boring machine responsible for driving the entire chain and rotating the excavator wheel is located at the beginning of the tunnel building machinery (behind the excavator wheel). Depending on the soil conditions 15 to 20 m length of tunnel may be built a day. The entire machinery is controlled from the control cubicle. The tunnel wall is assembled from rings built at the same time as the TBM proceeds along its route. Each tunnel ring consists of six segments called tubings made of reinforced concrete. Each tubing weighs 3 tons. The total number of rings built into the tunnels of the 4th line of the Metro is 6800.
Tunnel construction by the use of tunnel boring machines is the state-of-the-art technology used, among others, in the construction of the tunnel connecting France and England. The entire machine chain consists of hundreds of complex measuring instruments and appliances that need fine tuning for proper operation. For this reason the first few weeks of construction will, in fact, involve pilot operation when the tunnel boring machines will operate in a start-stop mode, In this period only a few meters length of tunnel will be built in order to proceed later with the construction in a much faster and smooth manner. This is a standard process for all tunnel projects where tunnel boring machines are used for construction.
In every country of the world the launching of tunnel construction is, by tradition, a ceremonial event, whether or not the tunnel is built for road, railway or metro traffic. The tunnel contractors and miners consecrate and put up at the tunnel entrance the statue of Saint Barbara, and elect the symbolic godmothers of the tunnel; they will “baptize” the tunnels and they will be the unofficial helpers of tunnel contractors and metro builders.
Some interesting details of the tunnel boring machines follow below.
Total length: 113 m
Diameter: 6,10 m
Electric power: 2 x 5 MegaWatt that is, nearly 1600 HP
Volume of earth excavated: 350.000 m3
The staff working in tunnel construction in each shift is 80-100.