The Osek tunnel
OPTIMISATION OF THE BEROUN – ZBIROH RAIL LINE
The Osek tunnel
Project owner:
Railway Infrastructure Administration, state organisation
Contractor:
Skanska DS a.s. – consortium leader
Eurovia a.s.
Viamont DSP a.s.
Hochtief CZ a. s. – contractor for the tunnel
Designer:
Metroprojekt Praha a. s.
Construction period:
09/2009 – 03/2014
Technical data:
The Osek tunnel is a 324m long double-track cut-and-cover railway tunnel. It runs on curve with the radius of 747.805m (measured on the tunnel centre line). The height of the earth cover over the top of the reinforced concrete tunnel structure is 1.0m.
The work on the tunnel commenced by excavating the construction trench in mid September 2009; the total excavation volume amounted to 52,000m3. Slopes of the construction trench were stabilised by sprayed concrete reinforced with welded mesh and dowels. The biggest depth of the construction trench is 13m.
The tunnel lining (excepting the portal blocks) is a double-shell structure with an intermediate waterproofing membrane. The 300m-long outer lining (a false primary lining) is used as sacrificial formwork and provides protection for the waterproofing layer. The 300mm thick primary lining is in C20/25 sprayed concrete reinforced with steel lattice girders and welded mesh. The outer lining is supported by footings for the final lining, the width of which is increased.
The working procedure following after the completion of the false primary lining was identical with the procedure used in the execution of a mined tunnel, i.e. installing waterproofing layers, placing reinforcement of the final (secondary) lining and casting the concrete final lining by means of a traveller form.
The final (secondary) lining is in cast-in-situ C25/30 reinforced concrete with the minimum thickness of 350mm. The tunnel portal blocks with slanted front ends are cast into double-sided formwork; the minimum thickness is 500mm. The tunnel is divided into 25 casting blocks plus two portal blocks. The tunnel block is 12m long; the weight of concrete reinforcement for one tunnel block is about 11t. A safety recess is provided on both sides of every other tunnel block. The final lining will require the total volume of 3,565m3of concrete mixture.
The Osek tunnel – construction trench and installation of the false primary lining
The Osek tunnel – the traveller form and the final lining
The Osek tunnel in operation