Prefabrication in-house of tunnel lining segments: the case of the of Warsaw Metro Line 2 
The Central section of Metro Second Line in Warsaw, recently completed by AGP Metro Polska with Astaldi SpA Leader, provides among the construction of approximately 10 km of natural tunnel executed by mechanized method. The final lining involved the installation of nearly 7,000 prefabricated rings to be placed in the course of the advancement of 4 EPB used machines. The precast of all the elements casing the tunnel has been adopted by mean of a separate pre-casting factory; the production has been initiated early in advance from the commencement of the TBM drilling so far. Indeed, the“back up” of segments has carried out 6 months before commencing the TBM works, in order to have safe continuity granted for the sake of excavation schedule. The Precast segment production was been organised into 2 warehouses and the outdoor yard by 19000 m2 area was utilized as the first temporary storage. The system is composed by a carousel plant with 8 complete sets of six elements moulds each one for a total of 48 moulds. The steel moulds for segments are mounted on Summary of: Prefabrication in-house of tunnel lining segments: the case of the of Warsaw Metro Line 2 special trolleys devices that travel along the production line until to enter in the curing chamber, equipped with steam dispenser points, in order to make the temperature be subjected to full monitor.All positions the trolleys cover along the operating line were subjected to the operations of dismantling, cleaning, laying the reinforced iron bars, positioning the insert, pouring the concrete and polishing the surface just performed. After the curing time (8 hours), the segment was removed out from the moulds by special vacuum crane, then moved to the tilting system, in order to upside down the segment ready to be shifted to second building by a special trolley.The production line was arranged inside the first warehouse by 2800 m2 area, where the preparation of steel cages was arranged as well in order to have the magazine of all the steel cages to be moved directly inside the moulds by means of a 8 ton gantry crane. The concrete was produced by an external batching plant, equipped by 1,5 m3 mixer, able to produce 50 m3/hour, 500 m far away from our factory. The second shed, instead, having a 2400 m2 area, was organised as temporary storage indoor, equipped by 15 ton gantry crane to load trucks and move the segments to the outside storage yard. The ring design foresees both of the pins connection to join the rings during the advancement and the sealing of the EPDM gasket with base dimension equal to 26 mm with the aim to reach the hydraulic sealed waterproofed of 7 bars with 15 mm offset and 4 mm gap. The design stage requires in addition the supplement of an amount of polypropylene fibers to add into the concrete, in order to limit the concrete spalling in case of fire in the tunnel. With the exception of the phase of learning curve that lasted 3 weeks time, the daily production has always reached the constant number of 16 rings meanwhile, in the periods of peak demand, it has been calibrated on 24 rings. The quality of the products and the satisfatcted confirmation of the Client affirm the outcome of the good in – house work performed, since it also has been subjected to the rigorous and careful system of Quality Control, which has included the checks of all equipment and all utilized products during the production.