Although the main tunnel is now completed, construction of the high-speed line between Bologna and Florence is far from being terminated. Indeco breakers continue to take an upfront role during these phases of the project.
With over 72 kilometres in course of completion, the excavation works and lining of the main tunnel of the high-speed rail linking Bologna and Florence are coming to conclusion right on schedule. Despite the fact that construction of the major part of the new section has now entered its final stage, the works for the definitive completion will still require enormous effort.
In addition to the excavations at the Bologna and Florence railway stations, other important works critical to the start-up of the line must still be realised. Among these are connections between the main tunnel and the old alignment.
These back-up lines, while being relatively short, play a very important role in terms of operation and safety. Thanks to them, the convoys can go from one line to the other, or can be separated to follow different routes. The connecting tracks allow freight trains to cross the junction of Bologna by transiting the old line above ground, whereas the passenger lines will be able to run on the new line and stop in the underground station soon to be built.
The project entails that the two tunnels - designed to accommodate a single-track line for each direction of travel - stretch about four kilometres. To create the connection, one line will run along a section parallel to the high-capacity line, while the other will pass it from above, then flank it from the opposite side. The two branches will depart from a chamber accessed by means an access tunnel located in Pianoro. From a structural standpoint, the tunnels differ from the main tunnel in their narrower width and the different configuration of the polycentric section.
To optimise resources and accelerate the excavation, three fronts were opened, one on the North (Bologna) side, and two on the South (Florence) side. The two sides differ in consistency, which in turn affect the methods adopted for their excavation. The Bologna side is characterised by formations of the chaotic system, which require consolidation. The fronts on the Florence side contain sandstone formations dating back to the Pliocene epoch. On this side the consistency of the mass proved the use of explosives a suitable alternative; however the existence of pockets of gas, while constantly monitored by a system of sensors, discouraged the use of this technique.
The unique conditions on the Florence side indicated the use of a breaker on both fronts of the South side and promised excellent results from a production standpoint. The sub-contractor of the works, Sbaraglia, employed Indeco 5000 HP breakers, which enabled production of over 30 m3per day while excavating a section of about 85 sq. m.
Their high level of productivity considering the difficult conditions, and the breaker's adaptability in a difficult application, confirmed the level attained by the HP series. The breakers of the new series, in fact, feature innovative solutions designed to improve output and reduce wear and maintenance.