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Year: 2018
Europe’s First Crossover TBM breaks through at Moglicë Headrace Tunnel
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.
Excavating Turkey’s Most Challenging Project: The Gerede Water Transmission Tunnel
At the Gerede Water Transmission Tunnel in Central Turkey, a 31.6 km long water supply line has been designated a national priority due to severe and chronic droughts in the capital city Ankara. Drawing water from the Gerede River (and conveying to Çamlıdere Dam), it will be the longest water tunnel in Turkey once complete.
But completing the tunnel has been an obstacle in itself. The project has been called the most challenging tunnel currently under construction in Turkey, and with good reason. Out of three standard Double Shield TBMs originally supplied to bore the tunnel, two became irretrievably stuck following massive inflows of mud and debris. In 2016, a hybrid type “Crossover” machine was launched to excavate the final 9 km of tunnel, but to do so it would need to cross dozens of fault zones and withstand intense water pressures up to 20 bars.
To accomplish this, the machine was designed with a number of unique features including the ability to be sealed up to 20 bar pressure. In the event of a large water inflow, the stopped TBM would hold back the water/muck and allow time for pre-consolidation grouting. The machine is also equipped with a bottom screw conveyor and a unique cutterhead design that facilitates effective muck transportation in both hard rock and mixed ground, among other features. This paper discusses the performance of the machine in exceedingly difficult conditions, and outlines the challenges yet to be overcome and how they may be surmounted. The paper also covers the unique aspects of this urgent Turkish projects and the unique logistical requirements of assembling and launching a machine deep within an existing tunnel.
Excavating Mexico City's Mega-Tunnel in Mixed Ground at 150 Meters Deep: Emisor Oriente Wastewater Tunnel Lot 5
Mexico City, with its 19 million inhabitants, is one of the world’s largest cities, but much of its infrastructure is struggling to keep up. Between 1970 and 200 the population doubled and today it produces 40m³/sec of wastewater; however, capacity is only 10 m³. In addition, much of the city’s wastewater is untreated and flows through a network of open sewers and underground lines.
The National Water Commission, CONAGUA, has developed a critically designated plan to assuage health concerns and the potential for catastrophic flooding if a wastewater line should fail. The mainstay of their scheme is the country’s largest infrastructure project, Túnel Emisor Oriente (TEO). The 62 km long tunnel will be connected to the first wastewater treatment plant in Mexico City, and will alleviate flooding. A total of six TBMs are excavating the tunnel in some of the most complex geology on earth.
This presentation will look at the challenges of the TEO Lot 5, examining machine assembly at the bottom of the deep shaft, and modifications and performance in the exceedingly difficult conditions that challenge the limits of the EPB tunneling.
Recent Cutter Technology Advances to Efficiently Bore Through Extremely Challenging Conditions in Hard Rock
For TBMs in hard rock, two of the most important parameters to consider are the cutter performance and the penetration rate. These two considerations are highly dependent on each other, as the cutters are typically the critical components that limit the thrust of the machine—a critical variable that dictates the net penetration rate. In such conditions optimal cutter performance is extremely important, not only to optimize the net penetration rate, but also to minimize the time needed to change cutters and maximize the time available for boring. Over the last five years, massive investments have been made in cutter development to make cutters that can withstand even the most challenging conditions. This paper presents the developments and challenges that have driven the last years’ advances in cutter technology, as well as the results of those developments on recent projects.
Excavating Turkey’s Hardest Rock at the Bahce-Nurdag Railway Tunnel
Southeastern Turkey’s Gaziantep province is characterized by complex fractured rock within the Eastern Anatolian Fault, and it is now the location of an important railway tunnel project. With a population of nearly 1.7 million, the province is overhauling its public transportation with a rail line between the towns of Bahçe and Nurdağı. The Bahce-Nurdag Railway Tunnel consists of two parallel 9.75 km tunnels being excavated by both NATM (850 m) and TBM (8.9 km).
Contractor Intekar Yapi Turizm Elektrik Insaat San. ve Tic. Ltd. A Robbins Single Shield TBM, 8 m in diameter, was chosen to excavate two sections of tunnel. Mixed ground conditions prevail on the project, and range from abrasive, interbedded sandstone and mudstone with quartzite veins to highly weathered shale and dolomitic limestone. The TBM has thus far encountered some of the hardest rock ever tunneled in Turkey, measuring between 136 and 327 MPa UCS.
This paper will analyze TBM performance, as well as the performance and wear of disc cutters in the difficult ground conditions. It will discuss TBM design and project logistics including onsite TBM assembly in a remote area of Turkey. Finally, it will give recommendations as to proper TBM design and cutter usage in hard, abrasive rock based on the project results.
9 Things to Consider When Choosing a TBM: A Checklist
Purchasing a Tunnel Boring Machine is no small consideration. Many factors are equally important to the price, and they can mean the difference between project success and significant downtime. Download our complimentary checklist to learn about the nine most important things to consider:
Learn more! Download the checklist for choosing a TBM here.
Robbins TBM uncovers Spectacular Cavern at Galerie des Janots
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.
Complimentary Webinar: How to Get Through Squeezing Ground, Rock Bursting, and More
If you’ve ever faced mountainous tunneling conditions, then you know what it is to face the unknown. Most deep tunnels under high cover encounter some unexpected conditions, whether its fault zones, squeezing ground, or rock bursting. Without the proper planning, crew experience, and TBM design, these challenges can quickly halt a TBM in its path. From severe squeezing that can trap a shielded machine in place to highly pressurized rock bursts that can damage the TBM itself, mountainous tunneling can get serious fast.
So how do you keep your TBM moving when the going gets tough? Spend 60 minutes with our tunneling professionals and learn from the best in this complimentary webinar—the first in our 2018 series. Using real case studies, we’ll discuss some of the most difficult conditions encountered in our decades of tunneling in the field. Find out how to overcome obstacles while keeping your downtime to a minimum and your crew safe.
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BAUMA India 2018
Event Name: BAUMA India
Dates: December 11-14, 2018
Location: Delhi, India
Venue: HUDA Ground, Sector 29
Join the Robbins Company at BAUMA India from December 11 through 14 in Delhi. We look forward to seeing you there.
BAUMA China 2018
Event Name: BAUMA China 2018
Dates: November 27-30, 2017
Location: Shanghai, China
Venue: Shanghai New International Expo Centre
The Robbins Company will be exhibiting at the 2018 BAUMA China in Shanghai from November 27 through 30. We invite you to stop by booth E2.641 to learn more about how Robbins can help you save time and money on your next tunneling project.