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II line Construction

Technology

The central section of the second underground line constitutes, i.a.,  seven meters under the bottom of the Vistula river – 10 meters of bored tunnel during twenty-four hours (on average) – two tunnels – the deepest station is called Nowy Świat (30 meters under the ground).

Modern technique and technology are going to be used for the construction of II subway line. The central section of the second underground line will join seven stations: from Rondo Daszyńskiego to Wileński station. There will be bored two, single- track tunnels.

Geological section of the area requires machines and shields which overcome sand, limestone, loam, postglacial rocks and quicksand. It is assumed that three shields, or rather three 120 m. long tunnel boring machines (TBM) will be built. They will bore on average 10 meters of tunnel per day, creating an excavation of a round shape. The machine will be equipped with a shield, each shield will have a head, which will be specially designed for the needs of next created stations. On the revolving shield specially exchangeable knives will be placed. Each of them will weigh about 250 kilograms, and their wear and tear will be signaled by detectors.

For boring and building tunnels of the central section of the second underground line, we are going to use three machines constructed according to a pattern: a shield, space behind a shield where bored winning will be dropped, tight wall, operators’ room. The winning will be transported to the surface by conveyors. The space will be closed by a tight wall behind which operators of the machines will work. They will use a satellite navigation.   

A shield, or rather a huge unit is closed, which means that a human does not have an access to winning because a working chamber is separated with a large pressure wall from a machining head. Groundwater pressure and the external force of the ground need to be overcome, which determine the effectiveness of a longwall – a shaped ground wall. A modern machine overcomes variously geologically formed terrain without difficulties.

The bored tunnel will be at the same time protected by a concrete casing. Its elements will be delivered by specialized transport and built-in using a fully mechanized device which is a part of the TBM shield. We assume, that the average outer diameter of the tunnel will be 6.1 m. together with the casing.   

Each of the boring machines will cost about 13 million Euro. A modern mechanized shield, called TBM (Tunnel Boring Machine) weighs several thousands of tons, a trifle really. However, it builds several meters of ready tunnels per day. It is an exact opposite to so called manual shields which build 2 meters of tunnel per day and which were used during the construction of the first underground line in Warsaw.

Mechanized shields have been used in the whole world for many years not only for underground train constructions but also for boring road tunnels (e.g. nearby Łaba in Hamburg, on Moscow ring road). A TBM machine was used for the first time in 1964 during the construction of the underground train tunnel under the Thames in London.

At the construction of the central section of the second underground line, a hollow of the stations will be diverse. Subsequent stations from Wola to the Vistula river will be built deeper and deeper. It is required because of the necessity of boring the tunnel seven meters beyond the Vistula bottom and passing of the second line under the first line – the deepest, 30 meters under the ground, the new station Nowy Świat will be built.
    
A technical terms "shallowing of the stations" and their "deepening" help to understand the necessity of providing trains a route they can run through smoothly. It is worth reminding that when building the first subway line, similar difficulties had to be overcome. The tunnel joining Pola Mokotowskie and Politechnika stations was constructed under Trasa Łazienkowska, and the tunnel between Politechnika and Centrum stations, under the diametral railway.