Nell’ambito della realizzazione del Lotto 1 della Linea 5 della Metropolitana di Bucarest, la scelta di Impresa inerente il secondo impiego di due scudi TBM già utilizzati in precedenza si e’ rivelata tecnicamente e strategicamente vincente nonostante la necessità di eseguire in principio un importante ricondizionamento tecnologico a manutenzione delle macchine, al fine del successivo adattamento alla nuova situazione. Lo scavo delle gallerie in oggetto, tuttora in corso di avanzamento, è infatti compiuto mediante l’ausilio di due cespiti di proprietà e di provenienza da precedente positiva esperienza in altro cantiere, opportunamente inseriti nel nuovo contesto. La presente dissertazione intende perciò dimostrare come sia stato possibile, grazie ad una attenta cura nella realizzazione delle indispensabili modifiche, poi risultate in corso d’opera in perfetta sinergia con il progetto, raggiungere ottime produzioni di avanzamento, pur avendo a disposizione macchine TBM in precedenza progettate per differente destinazione d’uso.
The two full section second hand refurbished TBM machines from ready to bore to production record in Metro Bucarest Line 5The construction of the 5th Line of Bucarest Underground is certainly a further step in the development of the public transport system in the capital of Romania and it’s included in the vast expansion program of public infrastructure; the so-called “Magistrala 5” is in fact destined to become the main connection between West and East Zones of the city. Last April 2011, the works were assigned to the Consortium Astaldi from Rome (Group Leader) - FCC Construction from Madrid and it deals with the realization of nine stations and two more than 6 km tunnels. The excavations are actually involving the use of two TBMs EBP type, accurately refurbished as the machines were assets coming from another previously performed and successful project. The “second hand” drilling machines were in fact already used in the construction of Metro Istanbul, lot Kadikoy-Kartal. Since the basic technical characteristics allowed the re-use, with the exception of some essential modifications which were deeply taken under consideration for the successive “ready to bore”, it was studied to obtain a “hybrid” typological machine in accordance with the new characteristics and requirements to meet. Before of the restoring, the main peculiarities of Istanbul machines, to be adjusted for the scope to be once again launched in Bucarest, can be summarized as below: 1) Rated torque available lower than the one usually explicated by a TBM of similar diameter in standard soft ground. 2) Total pushing force available inferior if compared to the one usually explicated by a TBM of similar diameter in soft ground. 3) Backfilling mortar in traditional system and not by bi-component mixture. 4) Cutting wheel for rock face, that means as very “closed” with an opening ratio of only 18%, equipped by cutters and explicating a quite high RPM. 5) Rotary joint composed by only four lines to distribute the passage of soil conditioning foam. 6) Lack of bentonite restoration plant. 7) Absence of passive articulation between central shield and trailing one. 8) Electric power supply on 34 kV. 9) Minor “defects”, by the way needing few different interventions. For what above, later on the done refurbishment, the properly revised TBM no. S743 and S744 were installed on the construction site and achieved an excellent production till a daily peak of 30 advances and 30 rings on 24 hours, for total bored and lined 45 meters: this performance shows the goodness of the preparatory works on the basis of a strategic Company choice.
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