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Author: Robbins
TBM Tunneling in Karst Conditions
France’s recently completed Galerie des Janots was the scene of some unforeseen challenges. During excavation with a Main Beam TBM, crews encountered a stalagmite studded 8,000 cubic meter cavern, and also a 4,500 cubic meter cavity directly under the bore path. In addition to the two large and uncharted caverns, there were also karst cavities of a multitude of sizes found throughout boring. What exactly did the crew do to beat the odds and power through?
For the answer, be sure to listen in as Detlef Jordan, Robbins Sales Manager Europe, goes into detail about the obstacles, lessons learned, and recommendations for future tunnels in karst conditions.
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48 Fault Zones and 26 Bar Pressure: Boring Turkey's Gerede Water Transmission Tunnel
Difficult ground doesn’t begin to describe the challenges overcome at a recent tunnel in central Turkey. The breakthrough of a 5.5 m diameter Robbins Crossover XRE TBM at the Gerede Water Transmission Tunnel was a feat of modern construction.
Robbins Main Beam carves out a win in Louisville
A 6.5 km (4 mi) long tunnel for wastewater storage below Louisville, Kentucky, USA has more to it than meets the eye. “At first glance, this seems like a straightforward project, but it turned out to be much more challenging,” said Shemek Oginski, Project Manager for the contractor, a joint venture of Shea/Traylor. The 6.7 m (22 ft) diameter Robbins Main Beam TBM and conveyor system had to cope with overstress in the crown that resulted in significant rock fallout in seven different areas, as well as methane gas in the tunnel. By the machine’s breakthrough on September 22, 2020, the crew had much to celebrate.
The machine was refurbished and consisted of older components as well as a brand new cutterhead supplied by Robbins and completely rebuilt electrical and hydraulic systems. “This was definitely an older machine—I actually operated it on the DART [Dallas Area Rapid Transit] tunnels in Dallas, Texas in the 1990s, but with many of the components being new we were confident in it,” said Oginski.
The original tunnel was expected to be 4 km (2.5 mi) long, but a change order added to the length by 2.1 km (1.3 mi). The extension was ordered by the owner, Louisville Metropolitan Sewer District (MSD), and its Engineer-of-Record Black & Veatch in order to eliminate four surface CSO storage basins. That included one basin originally located at the site of the TBM breakthrough, explains Oginski: “The original CSO site was located in close proximity to Beargrass Creek and had flooded multiple times. It was decided to extend the tunnel to that site in order to use the tunnel as storage instead, and connect it to the sewer system.” MSD installed a sheeting wall to protect the site from floodwaters while Shea-Traylor installed liner plate in the retrieval shaft, resulting in a site that is in much better shape.
It was in the 2.1 km (1.3 mi) extension, essentially a bifurcation of the main tunnel, where the crew encountered much of the crown overstress. “The longest section of overstress was 700 m (2,300 ft) and took two and a half months to get through,” said Oginski. The crew switched up the prescribed rock bolt pattern of four to six bolts at 1.5 m (5.0 ft) centers, and instead installed six bolts at 1 m (3 ft) centers. “It worked out to two rows per push. When that wasn’t enough, we installed wire mesh in the crown, mine straps, and channels. It definitely took extra time to install steel support, remove loose rock, and deal with the rock coming down so we could install rock support safely.” Overbreak varied from a few inches above the machine to 30 cm (1 ft) or more.
“We also had encountered natural methane gas in the tunnel just shortly before holing through,” said Oginski. The methane was discovered while the crew were probing out 150 ft ahead of the machine—something that the crew did continuously throughout the bore, using one, two or four probe holes depending on the geology. “We were down for about two weeks and were able to contain the methane within the cutterhead, where concentration spiked at 100% LEL. We were able to resume work after systematically ventilating, probing and grouting multiple times.”
Despite the challenges, the TBM was able to achieve up to 658 m (2,159 ft) in one month and 192 m (630 ft) in one week. The Robbins conveyor, including a 68.6 m (225 ft) long vertical belt, made this progress achievable, said Oginski: “The conveyor is definitely the way to go, especially for longer drives. There was quite a difference in performance between the extension tunnel, which we mined with lift-boxes, and mining with the conveyor. Our best month in the extension tunnel with the boxes was 221 m (725 ft), so that is a big difference.”
With tunneling now complete, Oginski is “definitely proud that we got to the end, as this is a challenging project.” The contractor is removing the components of the TBM to be stored in their yard in Mt. Pleasant, PA, and sees future applications for the equipment. “If the right project comes up then yes, it’s likely we would use this machine again.”
HYDRO 2020
Event Name: Hydro 2020
Dates: October 26-28
Location: Virtual Event
Register for the Hydro 2020 online event and get access to the latest information on all things hydropower, include Robbins’ innovative approach to small hydro tunnels at steep inclines using small diameter tunneling machines. Hear Robbins Civil Engineer and Cutter Product Manager Sindre Log speak on the use of three unique machines at up to 45 degree inclines in Norway.
Presentation Details:
Tuesday October 27
Session 22 – Tunnels & Underground Works – 2
11:00AM – 12:30PM CET
Title: Small but Powerful: Compact Hydro Tunneling offers Renewable Energy Solutions
Boring Through 48 Fault Zones and 26 Bar Pressure
Difficult ground doesn’t begin to describe the challenges overcome at a recent tunnel in central Turkey. The breakthrough of a 5.5 m diameter Robbins Crossover XRE TBM at the Gerede Water Transmission Tunnel was a feat of modern construction. The 9 km leg was the final section of the 31.6 km long water supply line bored through what is widely considered to be Turkey’s most challenging geology: from 48 fault zones to water pressures up to 26 bar, the ground put the machine and the crew to the test.
Listen in on the conversation with Robbins Vice President Doug Harding as we find out how the unique TBM design and experienced crew overcame a gamut of challenges.
Watch the Video
Hybrid TBM Excavation in Challenging Mixed Ground Conditions at the Mumbai Metro
Excavation in mixed ground conditions is always a challenge, but under a densely urban environment the stakes become even higher. At India’s Mumbai Metro, two 6.65 m hybrid-type rock/soft ground Single Shield TBMs are successfully boring parallel 2.8 km tunnels in basalt rock with transition zones of shale, tuff, and breccia below the city. They have made intermediate breakthroughs at the 1.2 km mark and overcome rock strengths up to 125 MPa UCS with significant water ingress, all just one year after factory acceptance, shipping, site assembly, and launch. The hybrid machines are optimized for abrasive rock geology using a robust cutterhead mounted with disc cutters and a reinforced screw conveyor at the centerline. The machines can also operate in closed or semi-closed mode using features designed to advance in soft ground with water inflows: dual ratio gearboxes to adjust cutterhead speed and torque to the geology, screw conveyors with bulkhead gates and discharge gates, ground conditioning with foam and polymers, and probe drills for pre-excavation grouting.
TBM Excavation in Himalayan Geology: Over 1,200 Meters per Month at the Bheri Babai Diversion Multipurpose Project
A Double Shield TBM achieved in 17 months what was projected to have taken 12 years with Drill & Blast: The 12.2 km long Bheri Babai Diversion Multipurpose Project (BBDMP). Bored in Himalayan geology including sandstone, mudstone, and conglomerate, the excavation was able to achieve over 1,200 m advance per month on multiple occasions. Crews achieved this while traversing a fault zone and getting through one section that required a bypass tunnel constructed in just five days. The success of this tunnel is not only in breaking through a historically difficult mountain range, but also in changing the notion, to the people of Nepal, that drill and blast is the way to excavate mountainous rock tunnels.
Tunneling through 48 Fault Zones and High Water Pressures on Turkey’s Gerede Water Transmission Tunnel
The December 2018 breakthrough of a 5.5 m diameter hybrid-type Single Shield/EPB TBM at the Gerede Water Transmission Tunnel in Central Turkey was a feat of modern construction. The 9 km leg was the final section of the 31.6 km long water supply line bored through what is widely considered to be Turkey’s most challenging geology. The project was originally started with the contractor selecting three Double Shield machines, which were procured and supplied without Robbins involvement. When two of the machines became stuck and were unable to continue, the solution of the hybrid-type TBM was developed to complete the rest of the tunnel. The TBM was assembled and launched more than 7 km from the tunnel portal and successfully navigated 48 fault zones as well as hydrostatic pressures up to 26 bar.
Overcoming Multiple Caverns: Successful TBM Tunneling in Karst Geology at Galerie des Janots
In April 2019, a 3.5 m diameter open-type, Main Beam TBM and its crew broke through at the Galerie des Janots Tunnel in La Ciotat, France after encountering two large, uncharted caverns. The 2.8 km long tunnel, excavated in limestone known to have groundwater, karstic features, and voids, took two years to complete due to the challenges encountered. Limestone and powdery clays made for slow going early on in tunneling, until a cavern measuring 8,000 cubic meters in size was encountered on the TBMs left side at the 1,035 m mark. The crew had to erect a 4 m high wall of concrete so the TBM would have something to grip against—a process that took about two weeks. The first cavern, while the largest, was not the most difficult void encountered. At the 2,157 m mark, crews encountered a 4,500 cubic meter cavity extending directly below the bore path. This cavern required stabilization, filling, six bypass galleries, and four months of work to get through.
Robbins Single Shield breaks through Turkey’s Hardest Rock
On July 24, 2020, a jubilant ceremony marked a milestone for southern Turkey’s arduous Bahçe-Nurdaği High-Speed Railway Tunnel. The first TBM-driven portion of tunneling using an 8.0 m (26.2 ft) diameter Robbins Single Shield machine is now complete. The 8.9 km (5.5 mi) long TBM tunnel was no easy bore, as it was excavated through some of the hardest and most abrasive rock ever encountered in the country.
“We are proud of the TBM crew who acted rapidly and were well organized to overcome the challenging ground conditions with a unique Single Shield TBM for the completion of the first tube of the Bahçe-Nurdağı Railway Project,” said Deniz Sahin, TBM Chief for contractor Intekar Yapi A.Ş.
Ground conditions during tunneling ranged from abrasive, interbedded sandstone and mudstone with quartzite veins to highly weathered shale and dolomitic limestone. The TBM encountered rock measuring between 136 and 327 MPa (19,700 to 47,400 psi) UCS. Water ingress with fines was expected in fault lines and shear zones affected by the East Anatolian Fault. “The TBM became stuck in three different fault zones, which we got through by building bypass tunnels. In smaller fault zones, we encountered excessive material flow and the TBM had to be stopped, while ground had to be stabilized with chemical injections while we cleaned the cutterhead,” said Sahin. Water inflows of 10 liters per second on average were removed using a dewatering system.
The majority of tunneling, said Sahin, was in metasandstone with quartz, with an average of 220 MPa (31,900 psi) UCS and a Cerchar abrasion value of 3.87. In such regions, the TBM’s 19-inch back-loading disc cutters had to be changed frequently and there was high vibration. Despite the challenges, Sahin was impressed by the machine’s overall capacity: “The Robbins Single Shield TBM’s motor power, hydraulic power and cutterhead torque were quite strong. The secondary ventilation and air suction systems inside the TBM were powerful. The connections between the gantries, scaffolding systems, walkways and working areas were good.”
The TBM ultimately achieved up to 456 m (1,500 ft) per month, a result achieved with the help of a Robbins continuous conveyor system for muck removal. “The electric motor and gearbox capacity of the conveyor system was quite enough for a 10 km (6.2 mi) tunnel and we had no failure on them. The conveyor performed well even under excess material and the whole system was quite robust,” said Sahin.
The owner, Turkish State Railways Directorate (TCDD), is aiming to overhaul the railway connection in southeastern Turkey by providing a shorter, faster route in one of the country’s busiest railway corridors. The new rail line between the towns of Bahçe and Nurdağı includes two parallel 9.8 km (6.1 mi) tunnels being excavated by both NATM (850 m / 0.5 mi) and TBM (8.9 km / 5.5 mi).