Author: Desiree Willis
This blog was originally published in 2017 and updated in 2022.
While probe drilling and pre-grouting have a long and successful history in drill and blast applications, their adoption for TBM technology has been more tenuous. Continuous probe drilling and pre-grouting was first pioneered in Norwegian hard rock D&B tunnels, where they have since been used with great success to detect ground conditions and consolidate weak rock ahead of the excavation face. If these methods have great potential to allow TBMs to excavate in difficult conditions, then there must be a knowledge gap. Here, we highlight four key things to know in order to get the most out of probe drilling and pre-grouting.
Number 1: There are always Pros and Cons
Much of the reluctance to adopt probing and grouting is based on a belief that the overall impact on the project schedule and TBM advance does not usually make up for the benefits provided. However, the benefits can be dramatic when compared to alternatives such as stuck TBMs, bypass tunnels, and other costly delays to the project schedule. The ability of a grout curtain to cut off or reduce water ingress and stabilize weak zones is unique to the method. This result has also been proven on hundreds of D&B projects over decades. When tunnel projects such as India’s Tapovan-Vishnugad Hydroelectric Project are considered, where a Double Shield TBM was brought to a halt following a massive influx of mud and water, the benefits seem clear.
There are other barriers towards industry acceptance besides time, however, and that is the perception of cost (both of course being related). In particular, in mountainous conditions or when tunneling downhill, probing may be the only practical approach towards risk mitigation, and pre-grouting may be the best possible option to control water inflows. When the cost of a stuck TBM is considered as the alternative, continuous probe drilling is looking pretty good.
Number 2: The Right Program and Machine Design can make all the Difference
Though the industry view of probing and pre-grouting tends toward the conservative, there are multiple ways to reduce impact to time and budgets while maximizing the benefits:
Plan and optimize the downtime for maintenance and cutter changes to minimize the downtime caused by probing and grouting
Proper scheduling may be one of the easiest ways to reduce downtime compared with current industry standards. To efficiently perform probe drilling and potentially pre-grouting in a TBM process, it is essential to plan the interventions and remove them from the critical path of the TBM process. Detailed planning should be done to coordinate the maintenance and cutter changing stops to the probing intervals. As an example a daily maintenance shift could be sufficient time to complete a grouting umbrella, with the correct TBM set up.
Analyze the drilling performance in detail
To get the most out of probe drilling and pre-grouting, detailed measurements of the advance rates of the probe drilling and the grouting pressure should be done. These measurements enable proper prediction of the ground ahead of the TBM. The drilling could be measured manually or automatically with Measurement While Drilling (MWD) systems, which are commonly used in D&B applications. The MWD system is used to analyze the rock in detail (hardness, water content, rock mass properties, etc.) and can be used to generate 3D-models of the rock mass in order to decide on the rock support or for documentation purposes.
Choose the right TBM Design
Ultimately, choosing the right TBM type can significantly cut time and cost. A customized machine, whether shielded or open-type, can be designed for accurate and continuous probe drilling. While it might seem that a shield machine would have limited drilling trajectories, machines like the Single Shield TBM for New York’s Delaware Aqueduct Repair offer 360-degree probe drilling paths using multiple drills, as well as probe drilling under pressure using down-the-hole hammers through ports sealed with ball joints. No matter what is needed, planning during the TBM design phase will most certainly cut downtime and costs later on.
Number 3: It has been Successful on Difficult TBM Projects
Though 100% probe drilling and pre-grouting has not yet been used extensively on TBM projects, successful examples can be found worldwide. At Canada’s Seymour Capilano Water Filtration Tunnels, using two Robbins Main Beam TBMs, 100% probe drilling (with minimum overlap) and pre-excavation grouting were specified as part of the twin down drives of the Seymour Capilano tunnel project. This was due to the down gradient of the tunnel under high cover where there was a moderate risk of encountering significant inflows. Fortunately the actual groundwater inflows were much less than originally anticipated and so very limited pre-excavation grouting was required. Probe drilling was continuously carried out during TBM excavation, and while it had an impact on progress in the early days, once the crews became familiar with the equipment and procedures the work activity became efficient, and was successfully implemented with minimum impact to progress. Success stories like this are common in deep rock tunnels around the world.
Number 4: Knowledge Level is Key to Success
As with many developments in the tunneling industry, probe drilling and pre-grouting are seen from the view of risk sharing. Risk sharing could entail clearly defined specifications and payment provisions that allow for fair compensation to the contractor so they will not be reluctant to accept the approach, for example. Clear design and environmental criteria need to be established, so the execution of probe drilling and pre-excavation grouting involve the opinion of the contractor, the design engineer, and equipment supplier. In some cases, for example, the contractor may choose to accept moderate inflows that are manageable and do not impact excavation progress.
Training in the operations of probe drilling and pre-grouting will also necessarily lead to greater acceptance. While there is some training available at colleges that offer mining and tunneling degree programs, much of the training for such operations is necessarily hands-on and experience based. With an experienced workforce, the negatives of probe drilling and pre-grouting are greatly reduced. Such hands-on training is currently being provided by Robbins on several projects using a combination of classroom instruction and jobsite operation for crews who are not familiar with the methods.
Ultimately, the adoption of probe drilling and pre-grouting on TBMs is something that must be recognized as an overall benefit to the industry in difficult ground conditions. The technology is well developed in D&B tunneling, and it has been field-tested for decades. It is, in our opinion, the best method of accurately detecting and treating poor ground conditions in front of the TBM.
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.
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).
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.
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.
In Nepal, the greeting ‘Namaste’, while pressing both palms together in front of the chest, signifies both ‘hello’ and ‘goodbye’. It implies a circular concept of time that I rather like—I certainly think I will be coming back to this country of high mountains, valley forests, and yes, tunnels.
The Adventure Begins
When I first learned that I would be visiting Nepal to see a swift-moving tunnel project making an impact in a local community, I was pretty jazzed. I also took it upon myself to overpack. The Bheri Babai Diversion Multipurpose Project (or BBDMP for short) is a 12 km long tunnel that travels below protected forest considered part of the Bardia National Wildlife Reserve. This is an area home to tigers, rhinos, Asian elephants, leopards, and more. And, most worryingly for me, mosquitoes.
Mosquitoes love me. I’m not entirely sure why they love me so much, but let’s just say that if there’s a mosquito within a 2 km radius it will find me. Thus, I decided to be prudent and go all out when packing. I purchased a whole new set of safari clothes, the most potent bug spray I could find in copious amounts, and much, much more. I stuffed everything into two suitcases and set off on my journey.
A full 24 hours of traveling later (the journey from Seattle, USA to Kathmandu is no joke, folks), and I arrived in the Kathmandu airport…with no checked luggage. Through a gross miscalculation (what a way to learn a lesson!) I also had not packed hardly anything in my carry-on bag. I had no clothing with me, and more importantly, no bug spray. What was I to do?
Rolling with It
After discovering that my bags were several days away, I decided to forego any hope of reuniting with them during my trip. Instead, I rolled with it. After a one-hour local flight from Kathmandu to Nepalgunj, we arrived at our destination. Nepalgunj is a frenetic, dusty town located around 8 km from the Indian border and one hour from the BBDMP site. The culture is heavily influenced by India, and we had many meals of delicious spicy curry and fried bread. The streets were lined with small shops and marketplace stalls, but to my dismay, no department stores.
After a quick Google search my coworkers and our guests with us for the site visit headed to the nearest approximation, known as Rani Mart (Rani means ‘queen’ in Hindi). To my surprise, I purchased a whole new wardrobe and everything I needed for 1/10th of the price I would have paid for it in the U.S. (though the sizing on the tags was quite a bit larger!) I was feeling very pleased with myself.
A Little Perspective
The next day we were ready to visit the jobsite. I couldn’t help but notice the rolling blackouts that plagued the city and the vast stretches of farmland requiring huge water resources. The people in the surrounding area make do with limited resources in ingenious ways—I was intrigued to see, for example, that every outlet requires you to flip an on-switch before the current becomes available. Perhaps we Americans could save significant energy if we made a setup like this a national standard. Local hotels, including one we stayed at, use solar panels for their power and air conditioning, and harvest rain water in order to reduce their usage.
All of this made me realize how much the BBDMP will impact the surrounding areas. This was confirmed in a meeting we had with Nepal’s Department of Irrigation (DOI), the project’s contractor China Overseas Engineering Group Co. Ltd. (COVEC), and consultant Geodata. The tunnel is sourcing water from the Bheri River to the Babai River, traveling through mountainous Himalayan geology known as the Siwalik Range. The water, as the project’s name suggests, is for multiple purposes. The estimated annual benefit in Nepalese Rupees is $2.9 billion for irrigation, and $4.3 billion for hydropower, making a total of $7.2 billion in benefits once the project becomes active.
The completed tunnel will irrigate 51,000 Ha of land and provide 48 MW annual generating capacity. That’s not to mention the environmental benefits: The Babai River currently swells each monsoon season and then runs extremely low in drier seasons. It is connected directly to the groundwater table, which is being aggressively depleted. With a regulated flow during all seasons, the groundwater table will see less depletion year-round.
The impact, in other words, is huge. Learning all of this made my obsession with my missing luggage seem inconsequential in comparison. I had my bug spray and some clothes. That was all I needed.
The First Nepalese TBM
With such a landmark project for the region, its proponents were willing to look to the latest technology during the planning phase. Our local representatives, MOSH Tunnelling, had been working since the 1990’s to bring a TBM to Nepal, a country known for its Drill & Blast tunneling. While TBMs had been considered multiple times, each time conventional tunneling had been chosen.
When the BBDMP was fast-tracked as one of the country’s “National Pride Projects” feasibility studies showed that Drill & Blast excavation could take as long as 12 years. The DOI needed a faster option, and they found it in TBMs. They began working with MOSH Tunnelling and Robbins to bring what would be the first Nepalese TBM ever into the country—a 5.06 m diameter Robbins Double Shield. The process for the DOI to acquire funding for the project and select a contractor through international competitive bidding took seven years, spanning from 2007 to 2015, when project commencement officially began.
Fast forward to our site visit in November 2018 and the project is far exceeding expectations. Tunneling has topped out at 1,202 m in one month with an average of around 740 m per month. The knowledgeable COVEC team have traversed a major fault zone, the Bheri Thrust, with no problems, and overcome a stuck TBM shield with a bypass tunnel constructed in just five days. Overall, the TBM is far ahead of schedule and the results are of national importance.
The local community, national media, and government are all watching how the TBM excavation plays out at BBDMP. Given the strong performance, they are now considering TBMs for a host of future multipurpose water projects. It’s the kind of result that opens up a whole new marketplace.
Into the Forest
After a great site visit, we chose to relax for one day at a spectacular local lodge that offered jeep safaris into the Bardia Wildlife Reserve. Currently home to nearly 90 tigers (a number that is rapidly increasing through conservation efforts) we were hopeful of perhaps seeing one of the striped cats in the forest. Our guide was knowledgeable, our jeep sturdy and our driver adept as we traversed bumpy roads and forded a few streams on our safari drive. We saw mischievous macaques, tree-dwelling langurs, a host of brightly colored birds, and various deer. We saw several enticing tiger prints…but the tiger itself remained elusive. Obviously, this means that I must go back!
A Lesson Learned
After traversing a tunnel, traipsing through the forest, and some swift sight-seeing in Kathmandu on our last day, I felt I had come full circle. I was ready to head home, but with an eye towards future opportunities to return to Nepal, whether for business or vacation. I will be back. But next time, you can rest assured, I will only bring what I can fit in my carry-on.
At any given time, Robbins TBMs are operating at dozens of jobsites around the world. Our dedicated Field Service personnel take video and pictures of the TBM progress often, so we’ve decided to offer a periodic roundup of what’s going on in a picture-based blog–from machine assembly for India’s Mumbai Metro to extremely hard rock encountered in Vietnam. Read on to found out the latest.
SIMULTANEOUS BUILDS FOR MUMBAI METRO
Mumbai, India’s massive Metro Line 3 project requires multiple TBMs on various contracts. A total of four Robbins TBMs will bore on two separate contracts–two 6.65 m (21.8 ft) Crossover (XRE) TBMs for contract UGC-01, and two 6.65 m (21.8 ft) Slurry TBMs for contract UGC-03. Assembly of the first Crossover TBM and the first Slurry TBM on each contract are occurring simultaneously, and are being overseen by our experienced Field Service crews.
EXTREME HARD ROCK IN VIETNAM
Robbins Field Service crews operating the Main Beam TBM at Vietnam’s Thuong Kon Tum HEPP have encountered granitic rock exceeding 300 MPa UCS and high water inflows. Despite the challenges the tunnel is more than 85% complete.
AN EPIC PROJECT IN MEXICO
With one of three Robbins lots completed at Mexico City’s massive 62 km (39 mi) Emisor Oriente tunnel, Field Service efforts are focused on completing Lots 4 and 5 in difficult mixed ground conditions. The customized EPB TBMs are boring through some of the most challenging conditions in the world, from abrasive basalt to watery clays and boulders.
A JOB WELL DONE IN ALBANIA
TBM assembly and breakthrough is often discussed, but disassembly can be just as complicated. Following the recent breakthrough of the Crossover (XRE) TBM in Albania (the first machine of its kind in Europe) for the Moglicë Headrace Tunnel, Field Service crews are working to disassemble the machine in an underground launch chamber.
At any given time, Robbins TBMs are operating at dozens of jobsites around the world. Our dedicated Field Service personnel take video and pictures of the TBM progress often, so we’ve decided to offer a quarterly roundup of what’s going on in picture and video format–from deep TBM assembly in New York, USA to an epic TBM launch in the Himalayan mountains of Nepal. Read on to found out the latest.
TBM Assembly in a Deep Shaft in New York, USA
A 6.8 m (22.3 ft) Robbins Single Shield TBM, designed for water pressures up to 20 bar, is undergoing assembly and testing at the Delaware Aqueduct Repair Project. The TBM will be launched from a starter tunnel at the bottom of a 274 m (900 ft) deep shaft.
TBM Assembly Time Lapse
Epic TBM Launch in the Himalayan Mountains
In the Siwalik Range of the southern Himalayan Mountains of Nepal, a 5.06 m (16.6 ft) Robbins Double Shield embarked to bore the Bheri Babai Diversion Multipurpose Project (BBDMP). The TBM launched on October 14. See the drone footage taken by our own Field Service TBM Mechanic Thomas Fuchs:
Crossover Machine Startup in Akron, Ohio
On October 19, a Robbins 9.26 m (30.4 ft) diameter Crossover (XRE) TBM launched below Akron, Ohio, USA to bore the OCIT tunnel. The machine is excavating in soft soils that will transition into mixed face and then full face shale. Before its launch, personnel at the jobsite filmed the cutterhead testing in a unique way. Watch the video below for more:
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.
Difficult Ground Solutions (DGS) is a suite of options that can be added to a shielded hard rock machine or Crossover machine to better enable advance when conditions are unknown or difficult conditions are anticipated. While each of these items is not new, the concept of installing them on a machine from the start, and of using them in concert to provide better visualization and performance in the most challenging ground, is. The uses and advantages of DGS are various and wide-reaching.
Number 1: DGS can act like risk insurance.
Yes, risk insurance. While one can argue that risk insurance is not needed—and of course if a tunnel were in entirely homogeneous, medium strength, self-supporting rock, under a medium amount of cover, I would tend to agree—there is a problem with this argument. That scenario exists only very rarely. At Robbins, we are seeing more tunnels being planned in mountainous, remote regions where an accurate GBR cannot be obtained. More tunnels planned through multiple fault zones and mixed face conditions. More tunnels planned in suspected karst conditions and in rock where large water inflows may occur. It is a trend we’ve observed arcing upward, and with these high-risk projects it seems prudent that an equipment manufacturer should strongly recommend risk insurance. We’ve done that the only way we know how: by calling on our extensive experience to develop, test, and provide various solutions that can be added to a TBM at the beginning of the project. These features mitigate the risk of getting stuck in unforeseen (or foreseen) challenges that might come up in a tunnel drive.
This risk insurance works like any other type of insurance—it must be purchased before the actual event happens. Waiting until a machine encounters a given challenge—where it may become damaged, stuck, or irretrievable—is not an adequate plan for difficult conditions. Sure, some of these options can be added in the tunnel, but such an operation is far from ideal. Risk insurance is best purchased during the TBM design phase, long before the machine is built and launched.
Number 2: DGS can get your TBM through a fault zone or squeezing ground where it might otherwise become stuck.
If fault zones or squeezing ground are known or suspected, or if there is even a possibility of encountering them, this can greatly affect your TBM operation. Shielded hard rock machines protect your crew from the surrounding ground, and they can bore and line a tunnel efficiently, but in fault zones and converging material they need some of the features of an EPB machine to keep advancing. Avoiding a stuck machine is paramount to project success. Luckily, DGS uses several ways to avoid the problem of a machine becoming stuck. The first of these is multi-speed cutterhead drives. These drives effectively give the machine multiple modes of operation—high speed, low torque for hard rock, and low speed, high torque for difficult ground. Designing a machine with high-torque, continuous boring capabilities allows that machine’s cutterhead to restart with break-out torque in difficult ground. The net effect is that the machine can keep boring in the event of a face collapse and can effectively bore through fault zones and running ground where the potential for cutterhead jamming exists. Going one step further, multi-speed gearboxes give the machine the ideal EPB-type torque if larger sections of soft ground are anticipated.
Secondly, TBMs can get through squeezing ground and faults using Continuous Shield Advance. This design utilizes a stepped shield configuration—where each successive shield is slightly smaller in diameter—to avoid becoming stuck in converging ground. External shield lubrication is an added insurance against becoming stuck, using a series of radial ports that can pump Bentonite into the annular space to act as a lubricant in squeezing material.
As a last effort, if a machine has already become stuck the TBM can utilize augmented, or “super” thrust. Additional thrust jacks can be added to supply an extra boost in a short stroke, generating enough force to break loose a trapped shield.
Number 3: DGS can keep your crew safe and save your TBM in the event of a massive inrush of water.
Water is an ever-present part of tunneling underground, but unexpected large inflows can damage a machine and grind a TBM operation to a halt.
In the event of a large inrush of water, a guillotine gate on the muck chute can effectively seal off the muck chamber of a Single Shield TBM to keep the crew safe as well as keep the machine from becoming flooded out. This system is termed “passive” water protection because the TBM is stopped in place (not actively operating). During that time the crew can then work to grout off water inflows and dewater the chamber to control the flow before they begin boring again. The grouting crew also have the added assistance of back pressure to assist in grouting.
Number 4: DGS can improve your visualization of the ground around the TBM.
Probe drilling is an essential part of visualization, and, combined with grouting, it can also fall under the heading of water control. We’ve learned that, in difficult ground, more is better. Multiple probe drills, and more drill ports in a 360-degree radius, are always going to give an advantage. We’ve taken this lesson to heart, and have installed multiple probe drills on many of our new shielded machines, with ports to provide probing patterns in a 360-degree radius. High-pressure grout injection can be done through these same ports to stabilize ground up to 40 m ahead of the face (or more if using specialized drills). The type of grout injected can also be specialized—for example chemical or polymer grout can be used to seal off groundwater. Lastly, a rotary forepole drill can be installed behind the cutterhead support to allow for ground consolidation around the shield periphery. The forepole drill is of particular use in fractured rock and fault zones. These drills are the mainframe of a visualization plan that can ultimately create an in-tunnel GBR as the machine advances: of particular use when no accurate GBR can be created due to topography, high cover, etc.
But what if you suspect the ground around your TBM is converging? What if you want to get a look at the actual rock face in the safest possible manner? There are DGS options for these types of visualization as well. For squeezing ground detection, a hydraulic cylinder can be mounted on top of the shield and connected to the TBM’s PLC. It measures the shield gap in the tunnel crown, so that if squeezing or collapsing ground is detected the crew can take countermeasures. These measures include using bentonite lubrication, crown or face rock conditioning, or planning ahead to use another system in the area before the machine can become stuck. For getting a better look at conditions ahead of the machine, a cutterhead inspection camera can be used to remotely inspect the boring cavity without intervention, and to check water levels ahead of the TBM. While these cameras have been used to monitor mixing chambers and perform cutterhead inspections in soft ground TBMs, their use in hard rock machines has been much more limited. In the new ground investigation system, the probe and injection holes in the cutterhead and front shield are specifically designed to accept these cameras.
Number 5: DGS can save you time and money.
The old adage “the best-laid plans can go astray” applies particularly well to tunneling. There are many unknowns, even with an adequate GBR in hand. Making an initial investment on DGS features when your TBM is still in the shop is far less costly than installing them in the tunnel after a major stoppage. These features can mean the difference between a successful operation and a stuck TBM requiring a bypass tunnel or worse. TBMs with DGS features also produce better advance rates in adverse conditions such as fault zones (see our recent projects Kargi and TEP II as good examples of this). Better advance rates mean your project is more likely to stay on schedule and on budget. And who wouldn’t want that?
Want to find out more about DGS and its successful use in the field?
Check out these white papers:
- Tunneling in Turkey: The Esme Salihli Railway
- Incredible India: Machines on the Move in Agra and Delhi
- Notice of Retraction and Apology
- Four Things You Need to Know about Probe Drilling and Pre-Grouting
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