Tunnels of Prague Underground under the Vltava River Bed

Location | Praha 7, Line C, Sector IV, Holešovice - Troja
Designers | Jiří Růžička, Josef Kuňák, Metroprojekt, a.s. (route alignment), Jan L. Vítek (team manager), Stanislav Dostál, Jaromír Šob, Zdeněk Tobolka and others, Metrostav, a.s. (design and execution of the construction technology)
Investor | Prague Transport Corporation - Transport Construction
Costs | 350 mil. Kč
General contractor | Metrostav, a.s. - divize 6
Subcontractors | Zakládání staveb, a.s., VSL Systémy (CZ), s.r.o., TBG Metrostav, s.r.o.
Design | 1999-2001
Construction | 2000-2002
Technical characteristics |
Length of launched tunnels (both tubes) 168 m | Radius of horizontal alignment right track tube 750 m, left track tube 670 m | Radius of vertical alignment (both tubes) 3800 m | Weight of one tunnel tube 6700 t | Underwater tube weight right track tube 70 t, left track tube 57 t | Launching time right track tube 9 hours, left track tube 7.5 hours

The technology called "tunnel launching" represents an original technical solution in the location, where the standard driving technology was not applicable. The method minimizes the interference with river banks, reduces the excavations, accelerates construction, assures the quality and impermeability of the work by the use of impermeable concrete, dispenses with the additional waterproofing and reduces the costs as compared with the conventional procedure. The method is based on the following principle: the tunnel tube was concreted in a dry dock. Subsequently the dock was closed and flooded. After opening the sheet pile wall separating the dock from the river, the tunnel was pulled by means of a special mechanism into the trench excavated previously in the river bed. The tunnel had to be balanced for launching by means of water tanks installed in the tunnel tube. Its stability was assured by its three-point support: the front part was suspended from a pontoon, the heavy rear part rested on two sliding supports and moved forward along a track prepared in the dock. The pair of sliding supports secured the tunnel position also against overturning e.g. by water flow pressure. The vertical suspension on the pontoon controlled the height above the river bed. Two pulling suspensions proceeding from the opposite Holešovice river bank enabled the control of the direction of the movement by varying the tension velocity of hydraulic units. Another braking suspension fastened to the rear end of the tunnel tube pretensioned the whole rope system, thus assuring the required sensitivity of direction control of the movement and acting, moreover, as a brake, if required. After the tunnel tube had attained definite position the supporting bulwarks were concreted between the sub-base and the tunnel tube. Finally the tunnel was anchored in the river bottom by micropiles and the trench was backfilled. After subsequent sealing of dock walls and its drying the dock was used for the concreting of the second tunnel tube. After its launching into position the dock was dried for the second time and used for the concreting of the tunnels proceeding to Kobylisy. When the concreting has been completed, it will be backfilled, too.