OREANDA-NEWS. May 05, 2011. The lift to the surface of the first tunneling machine assembly began. The tunneling machine was used to build, in the “floating earth” zone, the missing section of the Main Sewage Collector in the Northern Part of the City.

The German Herrenknecht tunneling machine (shield) has passed the distance of 1.2km at the depth of 70m – from Arsenalnaya st. to Lenina Square. Having started off in February 2010, it completed the tunneling by 14 April 2011. It is on this day that the machine’s cutting head broke through the last centimeters of soil and reached a special shaft.

It took several days to install the last tunnel rings (liners) and prepare the machine for the lift to the surface. Today, the first assembly – the 4.5m diameter cutting head weighing 33 tons was lifted. Within this week, three more assemblies (head module, jacking module and off-jacking skirt) will be lifted by a powerful 300-ton crane. The tunneling machine will be taken to a special storage place where it will be preserved after the necessary repairs and maintenance.

During the construction of the Main Sewage Collector, the shield helped pass the floating earth similar to that near the underground station “Ploschad Muzhestva”. Actually, the floating earth is a gravel-and-pebble deposit saturated with water under the pressure of 6 bars. The tunneling machine can operate in two - normal and heavy-duty - regimes. The first part of the distance was passed by the shield in the normal operating regime, - the soil was transported to the surface by trolleys. And then, the shield was re-equipped for the heavy-duty regime to pass the floating-earth zone with the slurry lifted up through pipelines. In this way, the soil pressure could be compensated and equalized with the pressure in the drift to prevent the ingress of the floating earth into the tunnel which could waterlog the working. This could lead to the sagging of the road and destruction of the embankment and the buildings.

The shield passed 130 metres in 2.5 months in the heavy-duty regime, having overcome the floating-earth zone successfully. Then it was re-equipped again, and the remaining distance was passed in the normal regime.

The shield was purchased in Germany by the contractor – LLC STIS. The tunneling machine comprises the cutter and three assemblies. The total weight is 400 tons, diameter – 4.5m, length – 88m.