The tunnel boring machine
The TBM that worked for making the deep tunnel of the city underground fell within the type of cutters called EPB (Earth pressure balance), generally used for excavation of land with no self-supporting features as in the case of the alluvial soils in Brescia.
Its task involved digging the ground causing, through a balance of the excavation volume, a pressure of soil capable of supporting the area itself, and installing the walls consisting of seven prefabricated elements fitted by making a closure ring.
The TBM used in Brescia was about 130 meters long, with a weight of 1300 tons and consisting of a cylindrical shield being 9 meters in diameter and 9 meters in length, followed by a series of service cars, the so-called backup. In the front part, the shield had a 9-meter diameter cutter whose rotation was ensured by 14 hydraulic motors that developed a power of 2,000 kW. The power supply occurred with an average voltage in the tunnel of 15,000 volts.
The machine that worked in Brescia is a product of the German technology, built by Herrenknecht in Schwanau and owned by Astaldi. Herrenknecht and Astaldi worked together with great care and even in the most relevant operating stages the German engineers always guaranteed advice and assistance so as for everything to be well tested and proven.
The TBM in the stations
The TBM did not constantly travel in the dark, in the depths of the city, in its cavities. At varying distances from 500 meters to one kilometer, the TBM met open stations and there the machine could work under the open sky and be visible to the public. In the six intermediate stages, before reaching the target being the Ospedale station, the engineers were thus able to intervene in the ordinary and extraordinary maintenance works.
The first stage was represented by Volta, with "rail level" being 17 meters below; a 20 meter wide huge box, 60 meters long and 22 meters deep. Then Lamarmora came, the station prepared for the "subdivision" in the Fiera direction, where the network path is ready to divide in half having already prepared the route that will be the second and future line.
The third stage along the underground journey of the boring machine took place in Brescia due, 27 meters deep. Then it was the turn of the Railway Station, near the city railway station and located across the railroad tracks with access oriented in the direction of the exit to facilitate passengers.
After "fully" crossing the central stations of Vittoria and San Faustino, due to the events related to the finding of the foundations of a medieval tower and the ancient Venetian walls, it was then the turn of Marconi and the Stazione Ospedale, the last stage before reaching, just a bit further ahead, the extraction well.
The times of translation in the stations where the "void" stages took place varied in relation to the need to carry out regular and especially extraordinary maintenance to the TBM itself. There were stations where the translation occurred in 20/30 days, others that took 40/50 days.
Brief history of the journey
The TBM began operating on 6th December 2005, when started off inside the inlet pit. About four months later, on 26th April reached the Volta station and started again on 19th June. On 22nd January 2007 entered the Lamarmora station, back from the chasm that opened in August and that required several weeks for servicing. From Lamarmora it started again on 21st March, with Bresciadue direction that reached on 28th May to start again on 28th June. On 25th September, the milling cutter disk showed in the pit of the Railway Station, the last stop before facing the path of the historic centre undertaken since 16th November. It reached Vittoria on 5th February 2008 and crossed S.Agata any without problem, assisted the Loggia and crossed the finish line of San Faustino on 9th July. It started from there on 1st September reaching Marconi on 20 October to start again on 26th November. On 16th February 2009 it reached the last station before the Civil Hospital to travel the last 200 meters toward the extraction pit.