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Incredible India: Machines on the Move in Agra and Delhi
India’s metro network has undergone extensive growth in recent years, and is showing no signs of slowing. Multiple Robbins machines are part of tunneling work in cities across India, including Agra and Delhi.
Agra Metro: From First Site Acceptance…
On February 16, 2023 the Robbins crew and contractor SAM India celebrated the site acceptance test for the first of two 6.65 m diameter EPB TBMs at Agra Metro. The machine began boring a 1.3 km long tunnel in soft soils, for Uttar Pradesh Metro Rail Corporation Ltd.
To Second Site Acceptance…
With the first TBM well into tunneling, a second 6.65 m Robbins EPB underwent site acceptance on April 13, 2023 to bore a parallel 1.3 km long tunnel in soft soils. The crew gathered for a ceremony before sending the TBM on its way.
To First Breakthrough!
Just a few days later on April 26, 2023 the first machine made an intermediate breakthrough into a station site, completing the Jama Masjid to Agra Fort stretch of the metro. The machine bored a total of 345 m in sand and clay, and broke through to a celebration by the crew and project teams.
New Delhi Metro: Machines Ramping Up
On February 27, 2023 the first of two 6.65 m diameter EPBs for the Delhi Metro (owner is Delhi Metro Rail Corporation) was completed in the Robbins Gurgaon, India facility. The mixed ground machine will bore a 3 km long tunnel through rock with some gravel, sand, silt and clay for contractor Afcons Infrastructure Ltd.
A second machine factory acceptance followed in April 2023. Both machines are scheduled to launch on parallel tunnels this summer.
Notice of Retraction and Apology
To all Visitors of our Site: I declare that our website contained information that was inaccurate, and in retrospect, was offensive and disrespectful to our longtime Customer and highly qualified construction Client, Obayashi Corporation of Japan, along with their Joint Venture (JV) Partners, Taisei Corporation and Kosei Corporation. The referenced Project Site name is Hiroshima Expressway 5 Shield Tunnel Project and the Robbins Technical Article titled https://www.robbinstbm.com/grout-or-not/, which states as if the JV selected the wrong type of TBM for the Hiroshima Project.
We retract the statements made in our article such as, “Contractors who are used to tunneling in soft ground may not realize that when using a Slurry TBM in rock, inspections must be frequent due to increased cutter consumption. We have seen this borne out on recent projects such as the Hiroshima Expressway Line 5 in Japan” because these statements were not based on facts and were incorrect. This statement reads as if the contractor did not review other optional TBM types, when in fact, the JV did indeed study all TBM types and methods to excavate this Express Tunnel.
There were additional incorrect statements made in the Article as follows:
- The same paragraph of the Article continues,”…, and they (contractor) were expecting up to 13 bar water pressure. This high pressure water zone was only in a small section of the overall tunnel length, about 5 percent.“
- The Article further states, “The contractor in Hiroshima had grouted off from the surface a planned safe zone in which to inspect the cutterhead without requiring a hyperbaric intervention, but this strategy did not go according to plan. The abrasive rock damaged the cutters and cutterhead before they could reach the safe zone, resulting in unplanned delays“.
- The same paragraph of the Article continues, “…grout off from the surface a planned safe zone…“.
The reason for choosing a Slurry type TBM was not solely based on the high water pressure but was also a result of the JV’s extensive review of all aspects of the tunnel requirements.
There was no plan to grout a “safe zone/safe haven” from the surface as other plans for cutter changes were in place and such plans have proven to be effective over numerous cutter change events.
Robbins commits to have more peer review and where a Client is involved, to have the Client review prior to presenting such data on our website.
The Latest Updates: Records in Toronto, the News from Nepal, and More
Much like the face of a TBM, tunneling’s wheels of progress are always turning. Join us as we check in on projects across the globe—including a breakthrough in Japan, record setting progress in Canada, and a new project ramping up in Nepal.
Setting Citywide Records in Toronto
Exciting progress is being made deep below Lake Ontario. The 7.95 m (26.1 ft) Single Shield Robbins TBM boring the 3.5 km (2.2 mi) long Ashbridges Bay Outfall tunnel is seeing record setting progress for the City of Toronto, ON, Canada. The machine, operated by contractor Southland Holdings, has recently completed 30 rings in a single day, at 1.5 m (5 ft) per ring, equating to 45 m (148 ft). With this accomplishment, the machine and crew surpassed a previous best day of 21 rings at a project with similar specifications. The Ashbridges Bay Outfall is anticipated to be the largest wastewater outfall in Canada and will improve the city’s shoreline, beaches, and Lake Ontario’s water quality.
A Third Set of Records in Esme, Turkey
If two sets of records weren’t enough, the 13.77 m (45.18 ft) diameter Robbins Crossover (XRE) TBM boring Turkey’s Esme-Salihli Railway Tunnel has just set another precedent. In July and August 2021, the speedy machine outdid its previous records in the size class of 13 to 14 m (43 to 46 ft), boring 167.4 m (549.2 ft) in one week and 651.6 m (2,138 ft) in one month. The rates are the fastest ever recorded for any TBM over 13 m (43 ft) in diameter! They even surpass those set over a decade ago at the Niagara Tunnel Project by a Robbins 14.4 m (47.5 ft) diameter Main Beam TBM. Check out the records here.
Breakthrough at Tamagawa
In June, JV contractors Obayashi & Kumagai celebrated their final breakthrough at the Tamagawa HPP #2, Lot 2 project in Yamagata Prefecture, Japan. During the bore, the crew faced unpredictable soft ground conditions and other challenges. To surmount these issues, an airborne electromagnetic survey was conducted for predicting soft ground conditions ahead of the tunnel surface and tunnel face stability was improved by using forepiling. The project, completed with the use of a Robbins 4.5 m (14.7 ft) Main Beam TBM, will supply 14,600 kw of renewable power to the region.
Double Shield to Bore Second Nepalese Tunnel
A record-setting 5.09 m (16.7 ft) Robbins Double Shield TBM is currently being rebuilt to tackle its second project for Nepal. The machine, which set multiple records and finished a year early at the Bheri Babai Diversion Multipurpose Project, has been chosen to bore the 13.3 km (8.2 mi) long Sunkoshi Marin Diversion Tunnel. Upon completion, the structure will divert part of the flow of the Sunkoshi River into the Bagmati river to irrigate farmland in the Tarai district. The project has been awarded to contractor China Overseas Engineering Co (COVEC), who will be bringing their expertise and experience from the Bheri Babai tunnel to this new endeavor.
Most Momentous: 2021 Global Project Updates
From China’s largest Crossover TBM launch to an epic 13.77 m diameter XRE that began boring recently in Esme, Turkey, we’ve compiled the year’s most momentous events thus far. Read on to find out about Robbins machines embarking on tunnels large and larger.
Twin Crossover TBMs for Chongqing
Two 6.91 m (22.6 ft) diameter XRE machines are currently boring sections of the Chongqing Metro Phase 2 in ground conditions ranging from weathered mixed granite to weathered pegmatite and adamellite. The twin machines are the first of their kind in China, and are part of a trend towards more geologically challenging tunnels in China. To date, the machines have achieved up to 365 m (1,197 ft) advance in one month, with rates expected to ramp up as the machines progress.
An Epic XRE Launch in Esme
In Esme, Turkey, a massive 13.77 m (45.2 ft) diameter Crossover XRE TBM began its bore for contractor Kolin Construction. Launched in late March 2021, the unique TBM is designed to tackle mixed ground conditions including sandstone, gravelstone, claystone and siltstone along the 3.05 km (1.9 mi) Esme-Salihli Railway Tunnel. The XRE can swiftly convert between hard rock mode using a belt conveyor and EPB mode using a screw conveyor, as both remain in place inside the machine.
Tunneling below Lake Ontario
A Robbins 7.95 m (26.1 ft) diameter Single Shield TBM launched recently on March 26th from an 85 m (280 ft) deep, 14 m (46 ft) diameter shaft. The machine, for the Ashbridges Bay Outfall with contractor Southland Holdings LLC in Toronto, ON, Canada has the task of boring a 3.5 km (2.2 mi) long tunnel below Lake Ontario. The completed tunnel will connect up to 50 in-lake risers to enable efficient dispersion of treated effluent over a wide area of the lake.
China’s Largest Crossover TBM
The largest ever Crossover (XRE) TBM in China launched in late March 2021 in Guangzhou for contractors Sichuan Jinshi Heavy Equipment Leasing Co., Ltd and CREC Bureau 2. Onsite First Time Assembly (OFTA) was utilized to build the 9.16 m (30 ft) diameter Robbins TBM, taking just four months from contract signing to machine launch. The hybrid machine is boring the 2.5 km (1.6 mi) long Pazhou Line Lot PZH-1 of the Pearl River Delta Intercity Railway Project, which will offer better commutes for Guangzhou residents traveling to and from University City.
Tunneling in Karst: Your Questions Answered
On November 18, 2020 we held a webinar on a unique recent project, France’s Galerie des Janots. Crews utilized a 3.5 m diameter Robbins Main Beam TBM to bore a 2.8 km long tunnel through limestone with karstic features, with some surprises: Two uncharted caverns up to 8,000 cubic meters per size in the bore path of the TBM. To find out how the crew overcame the challenges, watch the video here:
We held a question and answer session during our event that was not recorded and wanted to share some selected Q & A with you below.
Question and Answer Session
Q: What type of karst was predominant along the alignment?
A: The karst was a kind of weak limestone formation. Very soft with a tendency to get pasty – like chalk in water.
Q: Could another type of TBM have been used in the geological conditions (limestone with karst)?
A: It was a rather small diameter tunnel and the less structure you have with the machine, the better. A shielded machine with segments at this diameter can work – but when in bad rock and you need to do something, the shield can become an obstacle to access the rock. We think the Main Beam machine was the best option and provided full access to the tunnel walls and strata.
Q: Do you think an EPB or Slurry machine could have been used in this tunnel?
A: I do not think so. When in rock, you will struggle with EPB or Slurry TBMs–producing conditioned muck or building up a filter cake and pressurizing the chamber will be very difficult to make happen in these conditions. However, our Crossover type machines do provide for operation in various modes and can run from rock into soft material.
Q: One of the typical challenges faced with karst is high water ingress. Can an open face machine deal with that?
A: Here we did not have water ingress, and did not have karstic aquifers either, so it was sufficient to employ normal water pumping. An open machine provides full access to the tunnel walls and the face. So, you can inject and fight the water ingress better compared to a shielded machine.
Q: In the Middle East, we had a project that, during pilot tunnel drilling in front of the cutterhead, resulted in sudden inrush of water ,which led to flooding inside the TBM. What types of mitigations measures do you recommend to overcome flooding risk?
A: A TBM can be furnished with doors and chutes at the relevant points to stop water ingress. A very appropriate tool is a so-called Guillotine Door, which is assembled to the muck chute above the TBM conveyor and allows for quick closing. Also, TBM conveyors can be furnished with a water-tight plug door, which can seal the machine when pulling back the conveyor. For sure, submersible pumps are needed, and to stop the water ingress, injection grouting should be used.
Q: What is BEAM Technology and was it able to successfully predict any real detected cavities before the TBM excavation?
A: BEAM Technology stands for Bore-tunneling Electrical Ahead Monitoring. BEAM is a ground prediction technique using focused electricity-induced polarization to detect anomalies ahead of the TBM. Yes, they were able to predict a cavity using BEAM on this TBM, see drawing below courtesy of Geo Exploration Technologies. The red spot spot in the colored band clearly indicates the location of the cavity, and the picture verifies that it was found at that location.
Q: What type of material did you use to fill the cavities?
A: It was mainly concrete reinforced with steel mesh and wood structures.
Q: How did they move past the first cavern and did ground support change during tunneling?
A: To cross the cavern space, crews erected a 4 m high wall of concrete so the TBM would have something to grip against (see picture below). The TBM was started up and was able to successfully navigate out of the cavern in eight strokes without significant downtime to the operation. Shotcrete was also employed – as long as necessary. Rock conditions changed often in this tunnel.
The Next Push: Robbins TBMs on the Move Around the Globe
Robbins machines continue to advance in 2020, with essential projects ongoing and starting up the world over. From a proven Main Beam starting its fifth tunnel in Switzerland to a triumphant small diameter breakthrough in Norway to continued Crossover success in India, we’ve got all the tunneling highlights below.
ASSEMBLY UNDERWAY IN TORONTO
Assembly is underway on a Single Shield TBM for the Ashbridges Bay Treatment Outfall in Toronto, ON, Canada. The 7.95 m (26.0 ft) diameter machine and Robbins continuous conveyor will bore a tunnel to replace a 70 yr old existing outfall. The video below shows the machine acceptance in Mexico before being shipped to Canada. Due to coronavirus protocol, this was the first all-remote machine acceptance that Robbins has conducted.
SMALL DIAMETER TRIUMPH IN NORWAY
On June 16, 2020, crews wrapped up tunneling at the Salvasskardelva Hydroelectric Power Project (HEPP), located far above the Arctic Circle at 68.7 degrees north latitude near Bardufoss, Norway. The site may well be the world’s northernmost TBM-driven tunnel. The 2.8 m (9.2 ft) diameter specialized Main Beam TBM known as “Snøhvit”, or “Snow White”, was provided to contractor Norsk Grønnkraft for use on several of their hydroelectric tunnels. A continuous conveyor was also provided. The small hydro tunnels featured moderate to steep positive gradients up to 25 percent. The TBM was able to achieve rates of up to 44 m (144 ft) in 24 hours.
PROVEN MACHINE RAMPS UP FOR 5TH BORE
In Oberwalden, Switzerland a 6.50 m (21.3 ft) diameter Robbins Main Beam TBM, originally built in 1993, is ramping up to begin boring in December 2020. The machine, rebuilt by Swiss contractor Marti, will bore the 6.4 km (4.0 mi) long Sarnen Stormwater Relief Tunnel through hard rock. As the bore proceeds, wire mesh, shotcrete, and invert segments will be installed.
UNIQUE CONVEYOR SYSTEM FOR NEUTRINO FACILITY
In Lead, South Dakota, a unique Robbins conveyor system is gearing up to begin hauling muck. The conveyor system will be used to build the Long Baseline Neutrino Facility (LBNF) for Fermilab. Contractor Kiewit will renovate a disused gold mine into a world-class neutrino research facility. Two caverns will be excavated by drill & blast and roadheader deep below the surface. Rock will be transported by cable hoist up a 1.5 km (0.9 mi) deep mine shaft to a rock crusher at the surface using much of the original but refurbished mining equipment, and from there will be transported via conveyors. The Robbins conveyor systems are designed for the unique application, and include the longest overland conveyor Robbins has ever provided (550 m/1,800 ft), which travels over a main road and city park and near a residential area.
CROSSOVERS CONTINUE BELOW MUMBAI
Tunneling continues on the Mumbai Metro Line 3, where two 6.65 m (21.8 ft) diameter Crossover XRE TBMs are on their third drives for the L&T/STEC JV. TBM 1 has bored 2,178 m (7,146 ft) with another 765 m (2,500 ft) left to bore. TBM 2 has bored 2,352 m (7,716 ft) with another 592 m (1,942 ft) left to bore, and is scheduled to bore fourth drive later this year. Two 6.65 m (21.8 ft) Robbins Slurry TBMs are also boring for the Dogus-Soma JV with one machine starting its second drive after boring 2,181 m (7,155 ft), and the other being reading for its second drive after boring 2,100 m (6,890 ft).
On the Move: Robbins TBMs Around the World
At any given time Robbins TBMs are operating in dozens of countries around the world at all project stages. Thus far, 2020 has been no exception to the rule: From an icy visit to the world’s northernmost TBM to breakthroughs across the U.S. to a vast hydropower project on the verge of completion in China, we’ve got the latest updates from Robbins tunnels around the globe.
TBM Tunneling Above the Arctic Circle
Robbins engineers paid a visit to what is likely the northernmost TBM ever to operate in the world, at the Salvasskardelva HEPP near Bardufoss, Norway, 68.7 degrees north latitude. Robbins personnel and the contractor, Norsk Grønnkraft , have been braving frigid winter temperatures, ice and snow to excavate the 2.8 km long tunnel with a Main Beam machine at an upward gradient of 5.8 percent. As of the first quarter of 2020 they are nearly two thirds complete. Once breakthrough occurs the machine will be moved to bore a second tunnel 1.3 km long.
A Trio of U.S. Tunneling Breakthroughs
Meanwhile in the U.S. multiple machines ranging from 2.2 to 6.5 m in diameter broke through. First up is the Deer Creek Interceptor using a 6.5 m Main Beam TBM and continuous conveyor. The machine holed through on January 29, completing a 6.3 km long tunnel below St. Louis, MO for contractor SAK. Watch this great video from the owner, MSD Project Clear, below.
Also in January, the Turkey Creek Interceptor finished up: a project using a 3.0 m diameter Robbins Double Shield TBM to bore three short drives below Kansas City, MO. Contractor Radmacher Brothers bored a total of 220 m with the machine. Check out the video of the final breakthrough, and image of its first breakthrough several months earlier.
Lastly, in San Antonio, TX a 2.2 m diameter Robbins Double Shield TBM achieved a breakthrough at the SAWS Central Water Integration Pipeline, Segment 5-1. The tunnel, for owner San Antonio Water System, was excavated by contractor Atkinson.
A Massive Project Nears Completion in China
Two of three long-running Double Shield TBMs have completed their epic drives at China’s Great Hydro Network in Shanxi Province in recent months. The Great Hydro Network sprawls thousands of kilometers and is a feat of engineering. The Robbins machines at Tunnel 2 and Tunnel 4 bored from 15 to 23+ km in length. The machines overcame fault zones, water inflows and karst cavities to forge fast advance rates up to 865 m in one month.
What it’s Like to Live at a Jobsite for a Year (or More): An Interview
Debbie Swival, Robbins Field Service Support, is no stranger to tunnel sites. Over her last 12 years at The Robbins Company she has worked on TBMs around the world, from the San Francisco Central Subway to the Moglicë Headrace Tunnel in a remote area of Albania to Turkey’s Bahce-Nurdag High Speed Railway and more. But her longest stay was in Newburgh, NY, USA for the Delaware Aqueduct Repair tunnel.
Swival remained on the jobsite from November 2017 until the TBM’s breakthrough in August 2019—a duration of 21 months. Her role in assisting the crew and troubleshooting issues was integral to the project’s success.
Boring Below the Hudson
The 6.8 m (22.3 ft) diameter Robbins Single Shield TBM for JV contractor Kiewit-Shea Constructors (KSC) bored a total of 3,794 m (12,448 ft) over 582 days with instantaneous penetration rates of 6 m (20 ft) per hour. The unique machine was designed to statically hold up to 20 bar pressure as it bored below the Hudson River to repair a section of the Delaware Aqueduct, the world’s longest continuous tunnel (137 km/85 mi long).
The New York City Department of Environmental Protection (NYCDEP), project owner, discovered that a section of the aqueduct below the Hudson River was leaking up to 75 million liters (20 million gallons) of water per day. On average the aqueduct—built in the 1930s and 1940s—supplies about 50 percent of the water consumed by 8.6 million residents of New York City and an additional 1 million residents in four counties north of the City. A swift repair of the tunnel section was essential.
The tunnel depth—ranging from nearly 270 m (900 ft) deep where the TBM was launched in Newburgh, New York to over 180 m (600 ft) deep at the exit shaft—the water volume, and pressure were all challenges. Probe drilling was mandatory ahead of the TBM and required the use of down-the-hole water hammers for accurate boring under pressure.
What was it like to be at the jobsite for 21 months?
Swival: Being on site for that long was a fantastic experience. I typically stay on a jobsite for 6 to 8 weeks so I do not see the machine in full production. Staying for the boring of the length of tunnel allowed me to see the way that the machine is actually used, as opposed to the theoretical understanding of how different operations should be done. This has given me new insight for programming the machines to better meet the customer’s needs.
Being there for that long also gave the opportunity to create a strong working relationship with the customer. I was part of the team, with everyone working together to get the job done safely and successfully.
What were your main roles at the jobsite?
Swival: Initially I worked with the crew on the machine’s electrical systems and PLC (Programmable Logic Controller) programming changes. Other members of Robbins Field Service conducted training on hydraulics and machine operation. We had three operators at the jobsite who needed training, so I also spent time afterwards reinforcing that training they received. Much of it was on-the-job style training.
As the job continued my role shifted to supporting the machine for any issues that came up. I assisted with troubleshooting hydraulic and mechanical issues as well as continuing to work with the electricians for any problems that arose there. I worked with the customer to implement changes that they requested to the PLC program and to the HMI (Human Machine Interface) screens. I also assisted the customer with interfacing with Robbins engineering to obtain information that they needed.
What was a typical day at the jobsite like for you?
Swival: My typical day started with a 7:30 am meeting with the engineers and supervisors to go over the plan for the day and address any technical issues that had occurred since the previous day. At 8:00 am, a quick safety meeting with the crew, then head to the cage where we all got to be up close and personal during the 6-1/2 minute ride down the shaft. Once at the bottom we got on the mantrip to ride in to the machine. Near the end of the drive it took around 20 minutes to get to the TBM.
Once in the machine, it was time to tie in with the night shift for information on what had happened during the night and where they were in the mining process. At that point it was time to start troubleshooting any problems that had occurred. If all was well I went through and checked the machine for any signs of something getting ready to fail such as wear marks on hoses or cables, low tank levels, loose mounting on sensors and other things that could be fixed before they broke and caused an issue. I spoke with the mechanics and operators to see if there was anything they needed assistance with and also got feedback from them on what they liked as well as what could have been done differently to make their job more efficient.
Conditions in the tunnel were as you would expect – loud and dirty, although there were only a few times when dust was an issue and respirators needed to be worn. The crew often said it was hot in the tunnel, but I love the heat so I didn’t really notice it. We ate lunch on the machine. Since we did not leave the tunnel until the next shift came in, something that is normally overlooked is the need for the crew to relieve themselves. On this machine there was a really nice toilet that was kept cleaned, which made life there so much better! Around 4:30 pm “Mantrip coming in!” was announced over the mine phones as the next shift started their way in to relieve us. We got back to the surface a little after 5 pm and it was so nice to be back in the fresh air!
How important are knowledgeable field service personnel for the success of a project?
Swival: It’s absolutely imperative to have knowledgeable personnel. At the Delaware Aqueduct site they had me there because I knew the equipment well and could solve problems quickly. For example, it’s beneficial to have a PLC person on site because it’s a specialized piece of equipment. Although after commissioning there are not many problems with the PLC, when there is an issue it requires the code to be changed. Some PLC hardware failures or changes can also require that the program is modified. When an electrical or hydraulic issue occurs on the machine, I can use the program as a troubleshooting tool, find out what physical device isn’t working then describe the problem to the crew and educate them on how to fix it. This shortens downtime from 12 hours for a crew without PLC personnel on site, to around two hours.
What are some other examples of challenges that you were able to overcome at the site?
Swival: I helped to optimize the boring parameters, such as reducing thrust pressure, adjusting ring build procedures, and fine-tuning articulation cylinder pressure to avoid downtime and keep the machine moving. There was a section of the tunnel where the rock transitioned from shale to granite, and the difference in rock strength meant we had to set new limits for the thrust pressure to extend the life of the disc cutters.
There was an issue with the segment unloaders where the forward unloader was in the lowered position and the rear unloader was raised. The setup didn’t provide any clearance for when the train moved out. Typical sensors were not able to be mounted in the location. I worked with the mechanical team to find a solution for sensing the positions of the unloaders and prevent this from happening in the future. Lights were added to give a visual indication to the operator of the fully raised and lowered positions, and I changed the logic to incorporate the modifications. Those are just a few examples of what I helped with.
What is your favorite memory from the project?
Swival: It was amazing to be able to climb through the hole in the cutterhead and stand in front of the machine when it broke through. The support from everybody throughout the project was incredible. Everyone worked together, and the level of community on the job was exceptional. It was simply a great place to work.
Video courtesy of NYCDEP (www.nyc.gov/dep).
For more on the unique tunneling operation at the Delaware Aqueduct Repair, check out these resources:
White paper: https://www.robbinstbm.com/managing-high-water-inflows-2/
Press release: https://www.robbinstbm.com/delaware-aqueduct-repair-breakthrough/
3 Ways to Bore More Efficiently in Extremely Hard Rock: Maximize your TBM Advance through Minimized Downtime
When the rock seems unbreakable, stresses are multiplied: The cutters must be stronger, the TBM more durable, and the operation optimized to keep equipment running smoothly. Once rock hardness rises beyond 180 to 200 MPa UCS, the limits of cutting tools are put to the test.
Given the clear risks of excavating massive, hard rock, how can tunnellers set themselves up for the best possible chance of success? The combination of knowledgeable personnel, properly designed equipment, and rigorous TBM operation and maintenance are making excavation of hard rock—even extremely hard rock strengths of 300 MPa UCS or more—possible.
1: Consider your Cutting Tools
Cutters are a significant factor for efficient excavation when rock is extremely hard. To that end, Robbins has developed Extra Heavy Duty (XHD) rings for projects where Heavy Duty (HD) rings are close to their design limit in terms of the thrust force required to break the rock. The XHD rings resist chipping, mushrooming, and other damage that can occur in very hard rock conditions. Enhanced heat treatment gives the discs increased hardness and strength without the normally-associated reduction in fracture toughness.
The rings have a proven track record: they’ve been put to the test at several jobsites, including Norway’s Røssåga headrace tunnel bored in rock from 200 to 280 MPa UCS. Initially, HD cutters mounted on the Main Beam TBM’s cutterhead experienced low cutter life in the range of 100 to 150 cubic meters bored per cutter. XHD rings were gradually introduced onto the cutterhead to determine what, if any improvement in cutter life could be obtained. It is likely that the performance in the very hard sections was improved by a minimum of 25%. The benefits of the XHD are also likely to explain the superior cutter life for the remainder of the project, even in the relatively softer ground.
2: Optimize Penetration Rate
Harder rock requires equipment that can stand up to high stresses. Penetration rate and thrust are exponential functions. The first rule is: Push as hard as you can. The more thrust the better. A machine with a robust steel structure is needed to take the higher loads without damage.
But penetration rate is trickier: The overall goal in hard rock should be to operate TBMs as efficiently as possible to maximize production. This means increasing penetration per revolution as much as possible. Consumption of cutterhead wear parts is related to the number of revolutions of the cutterhead, so it follows that increased penetration per revolution will result in fewer total revolutions of the cutterhead, reduced consumption of wear parts and fewer cutter changes for the duration of the tunnel.
The TBM Operator should therefore be looking for the best advance at the lowest RPM, because lower RPM reduces wear on the outer cutters and periphery of the cutterhead. Robbins has conducted site tests at multiple sites over several years showing that a lower RPM achieves the same and often better penetration rates than a higher RPM in hard rock. This can be clearly seen in the data: For example, on an 8 m diameter cutterhead, the circumference is 25.12 m. At 10 RPM during TBM operation, this would mean 251.2 m of travel in one minute. If the speed is reduced to 8 RPM, the distance would be 200.9 m of rotation—a full 50 m less in one minute. That is 3000 m less per hour, reducing wear substantially.
Malaysia’s Pahang Selangor Water Tunnel was a good example of this phenomenon. What is now the longest tunnel in Southeast Asia, at 44.6 km, required excavation using three 5.2 m diameter Main Beam TBMs mounted with 19-inch disc cutters. The machines operated in abrasive granitic rock exceeding 200 MPa UCS, up to 1,200 m below the Titiwangsa Mountain Range. RPM trials were conducted on the three TBMs, showing that an increase in penetration rate per revolution of 15 to 20 percent could be achieved by decreasing the RPM from between 11.5 and 12 to just 9.5. While the overall advance rate was lower because of fewer revolutions, downtime was decreased and cutter changes were reduced by as much as 19%. The overall time savings more than made up for the decreased advance rate.
3: Your Crew is the Key
Knowledgeable operators are key in hard rock: there needs to be a balance between cutterhead speed and thrust force. An experienced TBM Operator will be able to identify when ground conditions change and react accordingly. In addition, knowledgeable operators know how to react if varying rock strengths are present in the excavation face. The most effective way to prevent impact loading in such conditions is to reduce cutterhead speed and penetration rate per revolution.
Maintenance is another key point and is especially important for extremely hard rock conditions. At the start of a project it is recommended to set a maintenance period for each day, say four hours out of each 24-hour period, which enables the crews to become familiar with the maintenance regime. This equates to approximately 24 hours of maintenance in a 6-day working week. Cutter change time can take up substantially more than four hours per day in hard rock tunnels, so once the crews are familiar with the maintenance tasks they are best carried out concurrently with cutter change operations.
Cutterhead inspections should be carried out on a regular basis to enable worn, damaged or blocked cutters to be replaced as soon as possible. Boring with even one blocked cutter can result in a cascading type wipe-out, which will progress rapidly in a chain reaction effect through multiple cutters if not immediately recognized. In hard rock this can also result in damage to the cutterhead over the course of just a couple of boring strokes. The same applies to the inspection of the bucket lips—these should be performed regularly and the bucket lips kept in good condition.
Overall, ensuring success in some of the most difficult rock in the world requires pre-planning with proper machine design, good cooperation by all parties involved, a knowledgeable crew, and dedicated maintenance. More than that, it also takes some experimentation on the part of the contractor or those overseeing the TBM operation. Contractors can look at different cutter types and test the parameters of TBM operation, do regular penetration tests, vary the RPM, and vary the thrust to see what gets the best cutter life and the best TBM performance. Taking the time to do such testing can make all the difference between a successful project and an unsuccessful one.
Lastly, new and innovative cutter designs and housing designs exist for extremely hard rock. Consider XHD cutter rings, cutter mountings with hardened replaceable seats, and other designs that may be in development or available for testing.
A Bevy of Breakthroughs: The Robbins Jobsite Roundup Featuring 6 Epic Projects
Dozens of Robbins TBMs are normally in operation at any given time in countries around the world, but this month’s breakthrough extravaganza is exceptional. No less than six breakthroughs occurred during April 2019, and more are on the way. We take a look at these epic completions in pictures below.
Galerie des Janots, France
On April 3, 2019, a Robbins 3.5 m diameter Main Beam TBM broke through into open space, completing its 2.8 km long water tunnel. It was not the first time the machine had encountered open space: twice during tunneling, the machine hit uncharted caverns, the largest of which measured a staggering 8,000 cubic meters in size.
On April 8, 2019, the first of two 6.5 m diameter Robbins Double Shield TBMs completed its bore for Austria’s Gemeinschaftskraftwerk Inn (GKI) project. A second Double Shield TBM will break through later this year. The 22 km long headrace tunnel near the alpine town of Pfunds was bored under high cover (maximum of 1,200 m) in schist rock.
DigIndy Tunnel System, USA
On April 10, 2019, a Robbins TBM completed the White River and Lower Pogues Run Tunnels, part of the DigIndy project in Indianapolis, Indiana, USA. The 36-year-old, refurbished 6.2 m diameter Robbins Main Beam machine was launched in 2013 in Indianapolis, and has done exceedingly well. Multiple world records in the 6 to 7 m diameter range were broken on the job, including “Most Feet Mined in One Day” (124.9 m), “Most Feet Mined in One Week” (515.1 m), and “Most Feet Mined in One Month” (1,754 m). Over the course of the project the TBM will bore more than 40 km of tunnels.
Bheri Babai Diversion Multipurpose Project, Nepal
On April 16, 2019, the Prime Minister of Nepal and other government officials, contractor COVEC and Robbins gathered to celebrate the breakthrough of the first ever TBM in Nepal. The machine holed through months ahead of schedule after excavating in excess of 1,000 m per month.
Mumbai Metro Line 3, India
On April 18, 2019, the first of two 6.65 m Robbins Crossover XRE TBMs made its first intermediate breakthrough at the Mumbai Metro Line 3. The TBM completed its 1.2 km long tunnel drive from Cuffe Parade to Vidhan Bhawan station, and will now be readied for its second section on the 2.8 km lot.
Los Condores HEPP, Chile
On April 25, 2019, a 4.56 m Robbins Double Shield TBM completed tunneling a 12 km intake tunnel for the Los Condores HEPP in Region del Maule, Chile. Contractor Ferrovial Agroman overcame challenging mixed face conditions and high water inflows to break through into an underground chamber. A second machine—a 4.56 m Crossover XRE TBM—will be launched to bore another section of tunnel later this year.
- Incredible India: Machines on the Move in Agra and Delhi
- Notice of Retraction and Apology
- The Latest Updates: Records in Toronto, the News from Nepal, and More
- Most Momentous: 2021 Global Project Updates
- Tunneling in Karst: Your Questions Answered