OREANDA-NEWS. April 15, 2011. On 14 April, 2011, the tunneling of the extension of the Northern Tunnel Collector was completed: the tunneling machine passed the latest section of the second collector line, which is located in the flow earth zone.

The collector tunnel section from Arsenalnaya Street to Lenin Square – 1.2 km long – was the most complicated: it is here that a wash zone is located, which is similar to the flow earth in the area of the Ploschad Muzhestva metro station.

Conventionally, tunnels are constructed with using tunnel shield machines. The machine consists of a metallic shell, under the protection of which the ground is dug. To tunnel the missing section the contractor company STIS bought a unique shield from Herrenknecht, Germany, which is able to operate in two modes: in the first case the ground is transported to the surface by a conventional method with using trolleys and in the second case, when tunneling a flow earth, a water and sand mixture is transported upwards to the surface through pipelines. The tunnelling machine consists of a cutting unit and three sections. Total weight is 350 tons, diameter – 4.5m, length – 12 m (with transport platforms that follow the shield through the tunnel – 80m).

The shield was delivered to St. Petersburg from Germany in summer 2009, on 28 trailers. On the night of 14/15 December, 2009, it was transported on four trailers accompanied by the road police to Arsenalnaya Street. Here the shaft is located, where shield sections were descended to a depth of 70 m by a 300-ton crane on 15 December, 2009. First, “the cutting unit” was descended, then “the head” and “the jack” shield sections, then “the jack skirt” (four main parts of the case) were descended.

After descending, the shield in the shaft was assembled gradually, as the length of the underground infrastructure (a site in the base of the shaft) is only 35m. After “the cutting unit” had been grounded, it was moved forward, having made room for the next section. Builders assembled the shield, having connected two out of ten trolleys to it, and then “the separate startup” took place – the shield started operating in the incomplete form, and later (after tunnelling 70 m), the other platforms were connected to the shield. In February 2010, the collector tunnelling started.

The collector will be fully constructed in 2012. Currently, next to Grenadersky Bridge the construction of another very important and complicated collector facility is going on – the URS Pumping Station.