Southern stretch is treating the soil to continue TBM excavation
Augusto Diniz – Rio de Janeiro (RJ)
On July 1st, 2016 subway line 4 is expected to start commercial operations linking the southern area of Rio de Janeiro to Barra da Tijuca. An insignificant delay may bring about a strong blow to one of the main projects of the city for the Olympic Games. That is so because one month later thousands of people will be arriving in the city to attend the mega-event whose main Olympic cluster is in the Barra da Tijuca district. Today, some 50% of the construction is already complete.
An unforeseen event in May this year made the construction consortium of the southern stretch, composed of Odebrecht Infrastructure, Queiroz Galvão and Carioca Engineering start to treat the soil around the tracks where the TBM (tunnel boring machine) has to ride, including those on streets Barão da Torre and Visconde de Pirajá (Ipanema) and avenue Ataulfo de Paiva (Leblon).
The TBM started its ride at the end of last year on General Osório station, the last one of Line 1 and future spot of connection between lines 1 and 4 – different platforms will interconnect them. But after moving ahead for 400 m, there were problems.
Marcos Vidigal, contract director of the consortium’s construction work explains that when the TBM passed between rock and sand, the compacted soil did not resist. “We had been doing blocks of soil contention, but as one face of the rock was fractured, it affected the blocks and destabilized the soil”. “Thus, we had to make an additional low-pressure injection of micro-cement in order to consolidate the soil”.
That engineer explains that the area is a “sand deposit” with a high water table. And that even before starting the work, an extensive geological and geotechnical investigation had been conducted. “We then defined that the best choice would be using the TBM at the southern stretch”, says he. Resuming the work with the TBM has been scheduled to the second semester this year. Marcos says that the priority now is to inform the population that the job is being done under strict control.
Marcos tells that there are other difficulties ahead related to the TBM. One of those is to prepare the machine to its arrival in the future stations Nossa Senhora da Paz, Jardim de Alah, Antero de Quental and Gávea. “At the southern stretch there is significant interference of operators and sensitive soil”, he states. According to him, experts already deem the construction of Line 4 one of the most difficult to implement in the world.
The director mentions that in the past he had to put together a strict plan to conceive, approach, plan and detail logistics in the southern area, a region highly populated in Rio, with a number of interferences.
Rio’s subway line 4 is composed of two stretches of construction work. The southern stretch, 4.5 km long, which is already being excavated with the TBM, encompasses stations Nossa Senhora da Paz, Jardim de Alah, Antero de Quental and the tracks as far as Gávea. The western stretch, 10.3 km long, includes stations Jardim Oceânico, São Conrado and Gávea
– at that stretch the work has been done according to the NATM method with disassembling done with explosives. The construction consortium of the west stretch is composed of Queiroz Galvão, Odebrecht Infrastructure, Carioca Engineering, Cowan and Servix. All stations of that line are being constructed. Four of them are being done with the cut and cover method (Nossa Senhora da Paz, Jardim de Alah, Antero de Quental and Jardim Oceânico), one with the wells method (Gávea) and the last one, with NATM – drill and blast (São Conrado).
The TBM, branded Herrenknecht, used in Line 4 jobsites is 120m long, including accessories, has a 11.53m diameter, weighs 2.7 thousand t, has a 250m curve radius and 4% superelevation (cant).
At the southern stretch an 8 km long double-tunnel is being constructed with walls and domes’ lining consolidated with fasteners, screen and projected concrete. A part of that stretch, which crosses Pedra da Gávea, between stations Jardim Oceânico and São Conrado, is already receiving its tracks. Excavations are being now done at the part connecting São Conrado to Gávea, crossing Morro Dois Irmãos. Still at that stretch, a stayed bridge over the Barra canal, where the tracks passes before entering the tunnel drilled into Pedra da Gávea, is having the foundation work done.
A plant of lining springers for the subway’s tunnel has been assembled at the yard of former Leopoldina train station. There 3 thousand rings are being manufactured for 7 km of tunnels. Each one of them has an 11.13 m external diameter, is 1.80m long and 40 cm thick. More than 90% of the springers have already been produced.
There are 8,500 workers at the jobsite among contractors and subcontractors. The undertaking is worth R$8.79 billion. Rio Barra operator, composed of Odebrecht, Queiroz Galvão and Carioca, have a 25-year concession of the subway and, in addition to the construction work, it includes implementing rolling material. Line 4 is expected to carry 300 thousand passengers/day. The construction started at the beginning of June 2010.
Knowledge Transfer Program
The Knowledge Transfer Program, prepared by the Consortium of the subway Line 4 develops with engineering students at the four main universities in the State (UFRJ, UFF, UERJ and PUC-Rio) the transfer by means of courses of techniques applied in the project related to the essential activities of equipment logistics, environmental actions, relationship with the community involved, among other subjects. Later, students will present papers on the knowledge acquired.
“Those students will arrive in the work market much better prepared; they will understand the challenges and the logistics to carry out a large undertaking”, explains Marcos Vidigal, contract director of the constructions and one of the creators of the program.
Fonte: Revista O Empreiteiro