On May 3, 2018 a 6.2 m (20.3 ft) diameter Robbins Crossover (XRE) TBM broke through into an underground chamber, marking the completion of the first TBM-driven tunnel in Albania. The TBM, operated by contractor Limak, was also the first Crossover machine to operate in Europe, and bored through geology including ophiolite, sandstone, breccia and siltstone flysch.
“The cutterhead and cutters have achieved outstanding performance,” said Engin Gur, TBM Manager for Limak. The TBM achieved rates as high as 648 m (2,126 ft) per month in April 2018, and as much as 37.4 m (122.7 ft) in one day. The Crossover TBM did not encounter high-pressure water and was thus used in hard rock Double Shield mode throughout tunneling.
“The TBM performed very well, as did a Robbins-supplied adit conveyor that operated in a 180-degree continuous curve. It was impressive,” said Max Walker, Robbins Field Service Superintendent. Several field service personnel remained onsite throughout operation of the TBM to provide guidance and trouble-shooting.
The machine was launched in November 2016 following Onsite First Time Assembly (OFTA), which enabled the machine to be initially assembled at the jobsite. The crew ramped up production slowly over the next 230 m (755 ft). “Ground conditions were good and we did very few cutter changes—only 20 cutters were used during the bore,” said Walker. Two-stage grouting was carried out as the TBM bored and lined the tunnel in three 8-hour shifts. “The personnel on this project have created a friendly work environment; they’ve made it enjoyable coming to work each day. They’re good guys to work with,” he added.
While the TBM did not need to be sealed, the unique machine design took into account a predicted high risk of water inflows. The Crossover XRE machine used a belt conveyor and not a screw conveyor for muck removal, so the muck chute needed to be able to be sealed off in the case of an inrush of water. The bulkhead was thus designed with a large sealing gate just above the belt conveyor. These pressure-relieving gates could also be used in a semi-EPB mode: As the pressure built in the cutting chamber, the gate would then be opened by the pressure, and material would spill onto the belt. As the pressure lowered, the gates would then automatically close, again sealing off the chamber. In extreme cases, the gates could be sealed and the probe/grout drills could be used to drill, grout, and seal off water. Additionally, the gripper shoes and inner telescopic shield were designed with inflatable seals to further protect against inrushes of water.
With the breakthrough now complete, grouting will continue behind the TBM segments. No additional lining will be added, and the tunnel is expected to become operational by May 2019.
The 6.7 km (4.2 mi) long Moglicë headrace tunnel is part of the Devoll Hydropower Project, a Build-Own-Operate-Transfer (BOOT) scheme to construct two hydropower plants along the Devoll River, named Moglicë and Banja. The project is owned by the Norwegian power company Statkraft AS. The completed Devoll Hydropower Project will increase Albania’s electricity production by 17% and will have an installed capacity of 242 MW.
A rebuilt Robbins 3.5 m (11.5 ft) diameter Main Beam TBM has yet another milestone to add to its storied career: an unexpected cavern, encountered and successfully passed through.
Contractor Eiffage Civil Engineering is operating the machine, which launched in 2017 for the Galerie des Janots project in La Ciotat, France. The cavern, studded with stalactites and stalagmites and measuring 8,000 cubic meters (283,000 cubic ft) in size, was grazed on the tunneling operation’s left side. The crew named the cavern “grotte Marie Lesimple” after their site geologist.
“We hit the corner of it. To cross it, we had to erect a 4 m (13 ft) high wall of concrete so the TBM would have something to grip against,” explained Marc Dhiersat, Project Director of Galerie des Janots for Eiffage. A small door allowed access inside the cavity, which formed naturally at a point 60 m (200 ft) below the surface. The TBM was started up and was able to successfully navigate out of the cavern in eight strokes without significant downtime to the operation.
“This is certainly unusual, to come across a cavern of this size and significance. It is somewhat related to the geology, with karstic and volcanic formations having the most potential for underground cavities,” said Detlef Jordan, Robbins Sales Manager Europe. Karst cavities were a known risk during the bore, but the cavern was not shown in vertical borehole reports conducted from the surface along the alignment.
A further 1.8 km (1.1 mi) will need to be tunneled before the 2.8 km (1.7 mi) tunnel is complete. “It is possible there could be more unknown caverns. We have a geotechnical BEAM system on the machine, and are conducting probe drilling, shotcreting, and maintenance in a separate shift,” said Dhiersat. The BEAM system, standing for Bore-tunneling Electrical Ahead Monitoring, is a ground prediction technique using focused electricity-induced polarization to detect anomalies ahead of the TBM.
The crew encountered difficult ground conditions early on in the bore, consisting of limestone with powdery clays. “When the machine is boring it does well. We have good production and it’s a good machine for hard rock. But sometimes it’s not hard rock that we encounter,” said Dhiersat. The weak rock and clay conditions necessitated ground support including resin-anchored bolts and rings in bad ground, topped with a 10 to 15 cm (4 to 6 in) thick layer of shotcrete. Despite five months of poor ground conditions, Eiffage is optimistic that conditions will improve and the tunnel will be complete in the next four to five months.
Galerie des Janots is one of the fourteen operations designed to save water and protect resources, which are being carried out by the Aix-Marseille-Provence metropolis, the water agency Rhône Mediterranean Corsica, and the State Government. The future Janots gallery will replace existing pipelines currently located in a railway tunnel—these original pipes have significant deficiencies with estimated water losses of 500,000 cubic meters (132 million gallons) per year.
The completed tunnel will pass under Le Parc National des Calanques, with cover between 15 and 180 meters (50 to 600 ft), in order to replace the pipes that are currently being utilized for the water supply networks. “The current pipes have a capacity of transit limited to 330 liters (87 gallons) per second, which is largely insufficient in the summer period. The objective of the operation is to secure the lines and increase capacity to 440 liters (116 gallons) per second,” said Dhiersat.
In Chicago, Illinois, USA Kenny Construction is nearing completion on the Albany Park Stormwater Diversion Tunnel. The project, owned by the Chicago Department of Transportation, will divert water from the Albany Park neighborhood, which has long been plagued by flooding. Plans for the tunnel began in 2013, after flood conditions became so severe that residents had to be evacuated from the area by boat. The tunnel is expected to be functional by April 2018.
A Robbins Main Beam Hard Rock TBM bored the tunnel and broke through at the end of August 2017, bringing the project one step closer to completion. The TBM, also known as “Keri,” has been owned by project contractor Kenny Construction since the 1990s and has been used on several projects prior. “The machine holed through into the inlet shaft,” said Clay Spellman, Project Manager for Kenny Construction. “We excavated the shaft as part of the project. The machine has since been disassembled and removed.”
For the Albany Park Project, Keri was rebuilt by Kenny Construction with size modifications designed by Robbins. Robbins took an existing cutterhead, repaired it, and then added segments, taking it from 5.2 m (17.2 ft) to 6.2 m (20.4 ft) in diameter. “Extensive modifications were also made underground to the machine to be able to install rock dowels and stand the ring steel under the roof shield,” added Spellman.
“Rebuilding TBMs has always been a core part of Robbins’ business. Most customers immediately recognize that a rebuilt machine with updated systems can offer exceptional value without increasing risk, and a rebuilt machine can usually be delivered faster,” said Robbins Engineering Manager Steve Smading. “While the financial and schedule advantages are obvious, the flexibility of used equipment may be less obvious. Boring diameters can be increased or decreased and machine configurations can even be changed. For example, a Single Shield can be reconfigured as a Double Shield or vice versa, and a Main Beam TBM can be reconfigured as a shielded machine. Soft ground machines can be configured for different geologies and can be set up as either Slurry or EPB.”
Over 50 percent of all Robbins Main Beams ever manufactured have been used on three or more projects. Incredibly, many Robbins TBMs that have been used on multiple projects are approaching over 50 km (31 mi) of use. Prior to its ownership by Kenny, Keri has successfully bored tunnels in the Dominican Republic, Saudi Arabia, New York, and Chicago—totaling at least 19.5 km (12 mi) of tunnel.
Due to the project location in a residential neighborhood, there were restrictions in place as to when the machine could operate and the frequency at which blasting would be allowed per day. Despite these limitations, the TBM achieved a best day of 39.5 m (129.7 ft) and a best week (5 days) of 146.4 m (480.4 ft). The machine bored through dolomite with an average compressive strength of 64 MPa UCS (9,300 psi). “During boring we encountered approximately 30.4 m (100 ft) of fractured ground that had to be supported with rolled channels, straps, and 19 full circle steel rings,” said Spellman.
The drainage tunnel starts in Eugene Park and extends for approximately one mile under Foster Avenue to the North Shore Channel. When the Chicago River’s water levels reach flood stages—exceeding 2 m (7 ft)—the tunnel will divert a flow of 65 cubic meters (2,300 cubic ft) of water per second, avoiding Albany Park, then deposit it into the Channel. The tunnel will essentially be transferring the water where it would have ended up, without damaging the residential area or adversely affecting the river’s wildlife.
In Jilin, one of the three provinces of Northeast China, a 7.9 m (26 ft) diameter Robbins Hard Rock Main Beam TBM has achieved a national record for 7 to 8 meter (23 to 26 ft) machines: 1,423.5 m (4,670 ft) in one month. The record tops a previously-set achievement on the same project from earlier in 2017, when the TBM advanced at a rate of 1,336.8 m (4,386 ft) in one month.
The world record for the size class is held by another Robbins machine, set more than 20 years ago at the Tunnel and Reservoir Plan (TARP) in Chicago, Illinois, USA, for 1,482 m (4,862 ft) in one month. However, given the differences in rock conditions this Jilin project record is very significant. At TARP the rock was relatively homogeneous dolomitic limestone averaging 145 MPa/21,100 psi with occasional rock bolts; at Jilin the rock types were rated from 35 to 206 MPa UCS (5,100 to 30,000 psi), and identified as tuff, granite, sandstone, and andesite with multiple fault zones—conditions requiring nearly continuous ground support.
Despite the difficult conditions, the Jilin machine has achieved an average monthly advance rate of 708.3 m since the start of boring in March 2015—more than three times the average monthly rate of a Drill & Blast operation on another section of the project. “It is now very evident that well-equipped, open-type Main Beam TBMs with specialized features for difficult ground can traverse faults and large water inflows much faster than conventional tunneling methods. This fact, coupled with the high performance capabilities as demonstrated at Jilin, lowers the cost and time to complete long tunnels in difficult ground,” said Robbins President Lok Home.
The Jilin Lot 3 tunnel, which is being bored as part of a water conservation project, will be 24.3 km (15 mi) long when complete. Under contractor Beijing Vibroflotation Engineering Co. Ltd. (BVEC), the machine has excavated 14 km (8.7 mi) of the tunnel as of January 2018.
Throughout its bore, the Main Beam is expected to traverse a total of 24 fault zones. The TBM was designed accordingly, and is equipped with four rock drills, McNally pockets in the roof shield for the ability to install McNally slats, a ring beam erector, and a shotcrete system. The McNally slats were used in difficult ground encountered in the tunnel.
The McNally Roof Support System was designed and patented by C&M McNally and licensed for exclusive use on Robbins TBMs in certain markets. By replacing the roof shield fingers on a Main Beam TBM, the McNally system prevents movement of loose rock in the critical area immediately behind the cutterhead support. The system has been tested and proven on projects worldwide—including the world’s second deepest civil works tunnel, the 2,000 m (1.2 mi) deep Olmos Trans-Andean Tunnel in Peru—to increase advance rates while still maintaining worker safety on Main Beam machines in difficult rock conditions.
The Jilin TBM’s first fault zone was encountered after just 87 m (285 ft) of boring, requiring cooperation between the owner, Jilin Province Water Investment Group Co., Ltd., contractor BVEC, and Robbins field service. Water inflows and collapsing ground in a section measuring 1,196 m (3,926 ft) long were resolved with a combination of McNally slats, grouting, and consolidation of the ground ahead of the machine. Ground support overall consists of wire mesh and shotcrete. Tunnel Reflection Tomography (TRT)—a method of ground prediction using seismic waves—is also being used to detect changing conditions ahead of the TBM.
Despite the initial challenges, the TBM is now achieving between 40 and 60 m (130 to 197 ft) advance per day. “My colleagues and I all feel that the Robbins TBM is very easy to operate. All components of the system work well during operation, which has ensured our good progress,” said by Tao Yong, BVEC Jilin Lot 3 TBM Site Manager.
The Jilin Lot 3 tunnel is part of the Jilin Yinsong Water Supply Project, which will convey water to the central cities of Jilin Province. The large-scale, trans-regional water diversion project is the longest water supply line, measuring 263.5 km (163.7 mi), with the largest number of recipients benefiting from it in the history of Jilin Province. The construction project will divert the water from Fengman Reservoir at the upper reaches of Di’er Songhua River to central regions of Jilin Province experiencing chronic water shortages. These regions include the cities of Changchun and Siping, eight surrounding counties, and 26 villages and towns under their jurisdiction. Tunneling is expected to be complete in late 2018.
On Tuesday, October 31, 2017, a 6.65 m (21.8 ft) diameter Robbins EPB TBM broke through at Chennai Metro, making this the third tunnel the machine has bored for the project and for contractor Afcons Infrastructure Ltd. The three separate bores for the EPB are part of an increasing trend, as many Robbins EPBs have been used on multiple tunnel drives with good performance. Robbins EPBs are built one third heavier than any other EPB on the market and are designed for 10,000 hours of usable life, making them ideal machines for use over many kilometers. “Robbins is known for designing resilient machines,” said Mr. Gopal Dey, Afcons Senior Manager. “For this project, we needed a machine that was specifically tailored to project conditions from soft clay to mixed ground with rock. Robbins EPB TBMs have unique design features that optimize the machine for the geology.”
After completing its original twin tunnels, the EPB was refurbished in preparation to bore its latest 1.8 km (1.1 mi) section. During refurbishment, the inner seal greasing system was changed from auto to manual mode and the foam nozzle system was modified. These changes optimized the machine for excavation in the highly variable mixed face conditions encountered in the first two tunnels.
The EPB was launched on February 3, earlier this year. According to contractor Afcons, the machine faced a major challenge right out of the gate. “When the TBM came out of the launching shaft, a few rings were erected and then the machine had to cross a live railway track, which meant there would be a possibility of ground settlement,” said Afcons Director, Mr. Manivannan. “At this stage, we had to closely monitor TBM face pressure and advance the machine at a uniform rate to ensure proper primary grouting.” The bore’s geology mainly consisted of clayey sand and about 60 meters (197 ft) of mixed ground.
“We [Afcons] chose this machine for this project due to the underground geology in Chennai, which continuously changes from soil to mixed ground,” said Mr. Dey. “We also liked that Robbins EPB machines are designed with active articulation to allow the machine to turn or steer with ease.” During active articulation, thrust cylinders react evenly against the entire circumference of the tunnel lining, even in a curve—a design that eliminates the problem of tunnel lining deformation. “This feature enabled the machine to negotiate through well-controlled conditions,” added Mr. Manivannan.
With all three tunnels, Robbins Field Service members were on location to assist and support as required. During the course of each bore, Robbins was there to advise Afcons on how best to maneuver through challenging ground and provide instruction for machine operation. The ability of the contractor and manufacturer to work well together, as Robbins and Afcons have throughout their contracts, was critical to the good advance rates. The result was a robust machine that advanced at rates of 80 mm (3 in) per minute in challenging conditions.
This latest tunnel connects multiple stations along the metro line, starting from Washermenpet through to Sir Theagaraya and to Kurukpet. The Chennai Metro Project will provide much needed transportation to a rapidly developing city.
On October 18, 2017, a Robbins 9.26 m (30.4 ft) diameter Crossover machine started up at the Akron Ohio Canal Interceptor Tunnel (OCIT) in Ohio, USA—but the startup wasn’t the only milestone. Running behind the Crossover TBM is the 100th Robbins Continuous Conveyor system supplied for muck removal. The side-mounted conveyor is a design standard, but the landmark is a significant one: “With this system we have provided more conveyors than any other TBM conveyor supplier,” said Dean Workman, Robbins Director of Conveyors, Cutters, & SBUs. Counting conveyor systems the company has on order but has not yet delivered, that number is now well above 100, Workman added.
The Akron OCIT conveyor system consists of the belt plus a main drive, splice stand, storage unit, and advancing tailpiece, operating through several curves requiring patented self-adjusting curve idlers that correct themselves based on varying belt tension and belt load. The system discharges onto a customer-supplied overland conveyor, which delivers the muck to a large storage yard near the portal site. The belt was designed to handle variable geology, from soft soils to partial face rock and finally full-face shale rock.
The 100th conveyor system has been refurbished and customized for the job in a process that Robbins has been perfecting for decades: “We design our conveyor systems to last for five to ten years, but many last for decades longer. We have systems utilizing components that have been in operation for 30 years. We haven’t reached a limit for many of our systems—for example we had a specialized conveyor system built more than a decade ago for the Parramatta Rail Link in Sydney, Australia. Those components were refurbished for a job in Atlanta, Georgia, and now they are being used at the Dig Indy tunnels in Indianapolis, Indiana. These are long and challenging tunnel drives and the components are up to it.” While the Akron OCIT conveyor is just beginning to haul muck, it is sure to be a benefit throughout the project’s varying ground conditions.
The conveyor in Akron is also part of a long history for Robbins conveyors—the first of which (not counted in the list of 100) was the first ever continuous conveyor system used behind a TBM. That prototype, developed by founder James S. Robbins in 1963, was successfully used behind the 11.2 m (36.7 ft) diameter Main Beam TBM at the Mangla Dam project in what was then known as West Pakistan. While conveyors would not be adopted as a standard method of muck removal for many years afterward, the project laid the groundwork for future success.
Today’s conveyor systems are capable of spanning dozens of kilometers and hauling 1,800 metric tons (2,000 US tons) an hour or more. It’s a legacy that Workman sees will continue to grow: “This is my 20th year with Robbins and I remember when we started our conveyor list. It is amazing to look at all of the jobs and things we’ve done. It’s amazing to see what these systems can do.”
The first of two Slurry TBMs, a rebuilt 6.65 m (21.8 ft) diameter machine, passed its factory acceptance on September 4, 2017 in Singapore. The machine, fitted with a Robbins cutterhead and outer shields, is destined for the Mumbai Metro Line 3 under contract UGC03 for the Dogus-Soma JV (DSJV), and will begin excavation in late 2017. The factory acceptance for a second 6.65 m (21.8 ft) diameter Slurry TBM will be conducted by the end of 2017.
The on-time delivery of the first machine is just the beginning of partnership that will span years. “There are few companies in the international arena that are as professional as Robbins. Robbins has been very helpful to DSJV since the inception of the project and will be our partners until the end of the contract. Robbins’ presence in India including field service crews will be a great help for us in future,” said Mr. DV Raju, Senior Vice President for SOMA.
The two machines will excavate parallel 3.5 km (2.2 mi) long tunnels between Mumbai Central and Worli station sites, passing through three intermediate cut and cover stations on the way. Ground conditions consist of fresh to weathered basalt and breccia up to 100 MPa UCS with water pressures up to 3 bar.
The JV selected Slurry machines for their contract due to the challenging ground conditions expected. “I have worked with Slurry TBMs on similar geology globally. Slurry TBMs have real power and will suit the hard rock geology of our Mumbai Metro contract 3. The water table and variable geology, especially basalt of higher hardness, can be easily tackled by Slurry TBMs,” said Mr. Tamay Sayin, Project Manager for DSJV. The cutterheads of the machines are fitted with wear protection, wear detection bits, and Robbins 17-inch disc cutters for the conditions. Grizzly bars will limit the size of boulders that can enter the cutterhead to 250 mm (9.8 in). The slurry systems includes rock crushers as well as abrasion-resistant plating in high-wear areas.
The two TBMs are the first of a total of four machines being provided by Robbins for the Mumbai Metro Line 3. Another two 6.65 m (21.8 ft) diameter Crossover XRE machines will bore parallel 2.8 km (1.7 mi) tunnels on a separate contract in 2018. “Mumbai Metro is one of the most prestigious metro works in the country, and Robbins’ involvement in providing suitable machines and associated services is an honor,” said Kapil Bhati, Managing Director for Robbins India.
The 33.5 km (20.8 mi) long Line 3 of Mumbai Metro being constructed by the Mumbai Metro Rail Corporation (MMRC) will consist of 26 underground stations and one at-grade station that will reduce heavy traffic and rail congestion between Bandra and Churchgate areas of the city. A total of 17 TBMs are being procured to bore various sections of the tunnels, which will be excavated at average depths of 15 to 25 m below the city. The entire line is expected to be operational by 2021.
Nepal will welcome its first TBM ever this summer, a 5.06 m (16.6 ft) diameter Double Shield machine for the Bheri Babai Diversion Multipurpose Project (BBDMP). The Robbins TBM underwent its Factory Acceptance Testing in July 2017 and is currently being shipped to the jobsite in the Siwalik Range, part of the Southern Himalayan Mountains. Pre-construction, including laying gravel onto rural roads and excavating wells for drinking water, has been completed to make way for the TBM and its impending launch.
The BBDMP is one of Nepal’s 11 National Pride Projects–prioritized plans sanctioned by the Government of Nepal to further develop the mainly rural country. This project will irrigate 60,000 hectares (almost 15,000 acres) of land in the southern region of Nepal, benefitting an estimated 30,000 households. It will divert 40 cubic meters of water (1,400 cubic feet) per second from Bheri River to Babai River under a head of 150 m (492 ft) using a 15 m (49 ft) tall dam, providing year-round irrigation in the surrounding Banke and Bardia districts. The water will also be used for hydroelectricity, with a generating capacity of 48 MW benefiting the country with NPR 2 billion (20 million USD) annually.
Contractor China Overseas Engineering Group Co. Ltd. Nepal Branch (COVEC Nepal Branch) is responsible for the headrace tunnel and is aware of the challenges associated with tunneling in tough geology. “The design of Robbins TBMs is good, and in particular Double Shield TBMs,” said Project Manager of BBDMP, Hu Tianran. The Siwalik range is projected to consist of mainly sandstone, mudstone and conglomerate, requiring a TBM that can withstand squeezing ground, rock instability, possibly high ingress of water and fault zones. Maximum cover above the tunnel is 820 m (0.5 mi).
Due to the challenges in the young geology of the Himalayas, Difficult Ground Solutions (DGS) have been incorporated into the machine’s design. A stepped shield has been designed to move through squeezing ground. Robbins Project Engineer Missy Isaman talked about the DGS features incorporated into the TBM: “There is a probe drill in the rear that probes through the gripper shield in 14 places. We added ports in the forward shield for drilling too. There are eight ports around the circumference for hand drilling. There are also six ports in the top 100 degrees of the shield for forepoling.” She further noted that no equipment was ordered for either of the forward shield drilling options, but it’s easier to add the ports to the shield now, in case more comprehensive drilling is needed later in the bore. Other machine modifications included 35 mm (70 mm on the diameter) of possible overcut for gage cutters, and additional ports in the forward shield for dewatering.
Muck removal will be achieved by muck cars. Robbins will provide Field Service to support the machine erection, testing, commissioning and boring of the first 500 m (1,640 ft). The tunnel will be lined with hexagonal precast concrete segments.
The project owner, the Government of Nepal’s Ministry of Irrigation (MOI), has chosen a TBM over the traditional method of Drill & Blast due to the faster mobilization and rate of advance offered by mechanized mining. “The reason a TBM was chosen for this project was because using D&B method could have taken at least 12 years for project completion. This was due to there only being one excavation heading with no possibility of launching multiple operations using adit tunnels,” said Robbins General Manager for Nepal, Prajwal Man Shrestha. More generally, Mr. Shrestha saw the project as a way to prove that TBMs can indeed take on complex Himalayan rock. “Since the Himalayan range has a young geology and not much has been surveyed yet, the use of newer technology is looked upon with slight apprehension. The first few TBM projects and additional surveys will show how suitable TBM technology will be for the Himalayan Range.”
The success of the BBDMP, a national pride project, is paramount for the country as well as the TBM industry. It is expected to help aide the food crisis in the mid-western region of Nepal by increasing agricultural yields and invigorating socio-economic development in the region. The Robbins TBM for the 12.2 km (7.5 mi) tunnel is scheduled to launch in November 2017.
El 8 de julio de 2017, un selecto grupo de autoridades responsables del proyecto, incluido el presidente de México Enrique Peña Nieto, celebró el cale final de un titánico proyecto de construcción de túneles. La TBM Crossover Robbins de 8,7 m de diámetro es la primera de este tipo de máquinas híbridas que se utiliza en Norteamérica y puso el broche final al Túnel Emisor Poniente (TEP) II. La tuneladora, del tipo denominado XRE —un cruce o crossover (X) entre TBM para roca (R) y EPB (E)— logró sortear zonas de fallas, terrenos variables y bajas coberturas, entre otros obstáculos, para lograr un récord nacional de 57 m en un día, así como avances máximos de 231 m en una semana y 702 m en un mes.
«La XRE presenta la gran ventaja de estar diseñada para trabajar en modo abierto o cerrado (EPB), lo cual le permite excavar túneles tanto en suelo como en roca. Hemos comprobado que su rendimiento ha sido muy eficiente», afirmó el ingeniero Juan Alberto Herrera Moro y Castillo, responsable en el TEPII de la Conagua, la Comisión Nacional del Agua, propietaria del proyecto.
Se empleó el método de montaje in situ OFTA para ensamblar en la misma obra esta singular máquina y su sistema de cinta transportadora Robbins, que fueron diseñados para un consorcio contratista formado por Aldesem, Proacón y Recsa. La TBM XRE Robbins incorporaba componentes tales como una cabeza de corte convertible con herramientas de corte intercambiables, transportador de cinta y de tornillo intercambiables y reductoras de velocidad variable para aumentar el par con el fin de perforar túneles en terrenos difíciles. «Las ventajas del diseño residen en su excepcional potencia de empuje y en lo sencillo que resulta variar el par de la cabeza de corte, lo cual facilita mucho el proceso en el caso de que la máquina se quede atascada en un terreno dificultoso», comentó Alberto Martínez, jefe del departamento de construcción de túneles de Recsa.
La tuneladora XRE entró en servicio en agosto de 2015 para perforar el túnel de aguas residuales de 5,8 km de longitud. La máquina estaba configurada para roca dura y montaba cortadores de disco de 20 pulgadas (51 cm) de diámetro. A principios de 2016, la TBM la primera de varias zonas de contacto, una falla de 30 m de anchura de roca fracturada y en bloques. Si bien la excavación se ralentizó al atravesar la zona de contacto, el ritmo de avance se recobró en la roca andesítica, que presentaba una mayor competencia. Tras llevar a cabo un cale intermedio en marzo de 2016 para desembocar en un pozo de 80 metros de profundidad, seguido de un proceso de inspección y mantenimiento, la TBM siguió adelante.
En otoño de 2016, mientras excavaba en roca andesítica fracturada, la TBM se encontró con una caverna natural que, presumiblemente, se había originado por un desprendimiento de rocas en una zona de transición o por un lago subterráneo que había erosionado el material rocoso. La caverna tenía un tamaño estimado de 90 metros cúbicos e incluía una zona de suelo inestable de 57 metros cúbicos. Se detuvo la tuneladora y se adoptaron medidas inmediatas para estabilizar el terreno situado frente a la máquina con espuma de poliuretano antes de rellenar la caverna con una mezcla de gravilla y lechada.
A finales de octubre de 2016, la tuneladora alcanzó un trecho final de 900 m de longitud en terreno blando, donde se pasó al modo EPB. En este último tramo de túnel con baja cobertura, la distancia desde la parte superior del túnel a los cimientos de las viviendas llegaba a reducirse hasta los 4 m y el terreno presentaba la consistencia de un suelo reconsolidado. Para estabilizar los suelos blandos y minimizar el riesgo de que se produjera un asentamiento bajo la zona residencial, el personal de construcción de túnel perforó desde la superficie e instaló 890 micropilotes a intervalos de 1 m. «Fuimos capaces de lograrlo sin causar daños en las propiedades de los vecinos de las zonas aledañas al trazado del TEPII, ni en la carretera, ni en las infraestructuras urbanas instaladas en dicha zona», explicó el ingeniero Francisco Miguel López, jefe de obra en el TEPII del contratista Aldesa.
Con las excavaciones ya concluidas, se procederá a aplicar en el túnel un segundo revestimiento de hormigón con un espesor de 35 cm antes de que entre en servicio. El túnel de aguas residuales servirá para modernizar la actual infraestructura en zonas del extrarradio situadas al oeste de la Ciudad de México y para evitar las periódicas inundaciones en Valle Dorado. El túnel beneficiará especialmente a las ciudades de Cuautitlán Izcalli, Tlalnepantla y Atizapán de Zaragoza, que en conjunto albergan a 2,1 millones de habitantes.
Una TBM Crossover (XRE) Robbins con un diámetro de 9,26 m se sometió a las pruebas de aceptación en fábrica el 30 de mayo de 2017. La gigantesca tuneladora fue presentada en la sede central de Robbins en Solon (Ohio, EE. UU.) durante la jornada de presentación a la prensa celebrada el 25 de mayo, antes de ser enviada 40 km al sur para la construcción del Ohio Canal Interceptor Tunnel (OCIT) en la ciudad de Akron. Entre los presentes se hallaban el alcalde Daniel Corrigan, el ingeniero jefe de Robbins Dennis Ofiara y David Chastka, ingeniero de proyecto del contratista, el consorcio Kenny-Obayashi.
La TBM, que aúna características de las máquinas de tipo EPB y las de escudo simple para roca dura, es la primera de tipo Crossover que se utiliza en EE. UU. Se pondrá en marcha desde una embocadura a una profundidad de 12 m y construirá los primeros 68 m en terreno blando para pasar más tarde a un tramo de 183 m de lutitas en frente mixto antes de volver a cambiar al modo de roca dura para el resto de la perforación en lutitas a sección completa. Se realizan continuos sondeos mediante dos perforadoras de sondeo para determinar el modo que debe adoptar la TBM. «Estamos convencidos de que el robusto diseño creado por Robbins será capaz de lidiar con todas las dificultades que plantee la perforación del túnel del proyecto OCIT», apuntó Chastka.
Entre los aspectos distintivos de la máquina se incluye una versátil cabeza de corte que se configurará teniendo en cuenta tanto el tramo en terreno blando como el tramo más largo (alrededor del 65% del túnel) en roca dura. Se empleará una combinación de cortadores de disco y se recurrirá a útiles de corte sacrificables en el caso de que un cortador se quede bloqueado. El par de rodadura exigido para los cortadores de disco se ha reducido en un 25% para favorecer una rotación suave en terrenos blandos. Los motores de la máquina XRE se han readaptado a partir de una configuración original de EPB para permitir una mayor velocidad del motor a un par reducido para los tramos de perforación en modo abierto.
La retirada de escombros se llevará a cabo con un transportador de tornillo de larga vida útil, cuya primera sección está recubierta con placas de desgaste soldadas. El eje del tornillo sinfín está revestido con un recubrimiento duro con una trama cruzada, mientras que la carcasa del transportador ha sido revestida de manera similar con placas de desgaste y recubrimiento duro. Se ha elaborado un plan de supervisión del desgaste para toda la perforación con el fin de aumentar al máximo la eficiencia en el tramo de roca más abrasiva. El jefe de proyecto de Robbins Pablo Salazar se muestra orgulloso de haber empleado profesionales locales durante el proceso de construcción y diseño de la TBM: «Hemos construido buena parte de la máquina en la zona nororiental de Ohio. Muchos de los componentes fueron fabricados en la región con subcontratistas, así como en nuestro propio taller».
La máquina recibió el nombre de Rosie en honor a Rosie la remachadora, un icono popular que representa a las mujeres estadounidenses empleadas como mano de obra en factorías y astilleros durante la II Guerra Mundial. Centenares de «Rosies», entre ellas Rose May Jacob, vecina de Akron, trabajaron en las fábricas que producían material bélico y armamento para el bando de los Aliados. La TBM se enviará al lugar de la obra en camiones, con la cabeza de corte separada en cuatro partes. «El proceso de montaje ha permitido al contratista seguir muy de cerca las pruebas realizadas con la tuneladora, por lo que a estas alturas ya están bastante familiarizados con la máquina. En la obra también ofreceremos un apoyo inmediato tanto en materia de repuestos como de personal», explicó Salazar. Los supervisores de obra de Robbins ayudarán en el montaje de la TBM y en la excavación de al menos los primeros 1000 m. El túnel se empezará a perforar en agosto de este año.
El proyecto OCIT para la ciudad de Akron consiste en la construcción de un sistema de túneles de transporte y retención para controlar los reboses de alcantarillado unitario (o CSO, por su sigla en inglés) para varios reguladores de la zona centro de Akron. El proyecto, exigido por la agencia de protección medioambiental EPA, incluye el túnel de transporte y almacenamiento de 1,89 km, así como pozos de caída, estructuras de desvío, colectores y otras estructuras complementarias. El decreto de consentimiento especifica que el túnel debe estar operativo para el 31 de diciembre de 2018.
- Robbins TBM breaks through nearly One Year Early in Nepal
- Galerie des Janots Main Beam completes Arduous French Drive
- Robbins EPB and Conveyors complete complex Lot 5 at Emisor Oriente
- Robbins Crossover TBM completes Turkey’s Longest Water Tunnel
- Tough TBM and Team Overcome the Odds with Atlanta Breakthrough