Category: Press Releases
In Spring 2022, a specialized Robbins 4.1 m (13.5 ft) diameter Main Beam TBM launched in St. Louis, Missouri, USA, to complete a critical infrastructure tunnel for contractor SAK Construction. The machine, named “Mrs. Vera”, is boring Phase 2 of the Jefferson Barracks tunnel, a 3,050 m (10,000 ft) long tunnel in karstic limestone. Designed to detect karst and other underground features, the unique machine comes equipped with enhanced 360-degree probe drilling capabilities, as well as versatile ground support options including McNally crown support, wire mesh, ring beam erector and roof drills.
“The overall design of the machine is a good fit for our project, not only for the mining aspect but also for the capability to run two probe drills in multiple locations around the TBM,” said Brotherman Bragg, Project Superintendent for SAK Construction. “The challenges I anticipate during tunneling are mostly related to ground conditions. The area that we are tunneling in has a potential for karst features. The probe drills are our lifeline and with the two probe drills on the machine, I believe that we will find out what’s in front of us before we get there, giving us the ability to take care of potential problems.”
During Phase 1 of Jefferson Barracks, a rebuilt 3.35 m (11.0 ft) diameter Robbins Main Beam TBM hit challenging conditions about 2,400 m (7,900 ft) into tunneling. The machine encountered a large vertical feature along with flowing and unstable ground that required the TBM to remain in place. While various options including ground freezing were considered, they were ultimately deemed infeasible.
A 62 m (205 ft) deep recovery shaft and 60 m (200 ft) long adit were built to stabilize the area and remove the machine in what would be an intensive and ultimately successful undertaking. After recovery of the machine, SAK Construction turned to Robbins for a solution to bore the remaining tunnel in what would become Phase 2 of the project.
SAK and Robbins agreed to do extensive in-shop testing of the new, larger TBM to ensure there would be no unnecessary delays on site. The TBM was ultimately delivered a couple months late due to both COVID-related matters and the additional in-shop testing. SAK operational personnel and Robbins personnel were heavily involved in final assembly and testing procedures.
After arriving in St. Louis, the TBM was swiftly assembled and launched from the recovery shaft. “The Robbins Field Service techs have been excellent in their support, helping us assemble the machine, and troubleshoot the machine. Our challenges during the assembly and launch from the shaft were minimal – this is the fastest and most efficient assembly we’ve ever had on a machine. We assembled the TBM in four weeks, which was a huge hurdle,” said Bragg.
“The overall design [of the TBM] is very functional and thus far in the early stages it seems to be mining very well,” continued Bragg. “So far, I’m very pleased with the machine and with the technicians.” Early indications were good, with the machine advancing 21 m (70 ft) in its first two shifts after launch.
The Jefferson Barracks project is a key component of MSD Project Clear, a massive USD $6 billion program undertaken by the Metropolitan St. Louis Water District to target water quality and wastewater concerns in the city and surrounding areas. The 5,400 m (17,800 ft) long, 2 m (7 ft) internal diameter Jefferson Barracks tunnel runs parallel to the Mississippi River and extends to the Lemay Wastewater Treatment Plant located at the confluence of the River des Peres and the Mississippi. The tunnel is slated for completion in Autumn 2023.
The breakthrough of an 8 m (26.2 ft) diameter Robbins Main Beam TBM at China’s Yin Han Ji Wei project is not only a cause for celebration, but also a triumph of technology and perseverance. The machine overcame 17.5 km (10.9 mi) of tunnel in some of the most difficult geology ever encountered, breaking through in the first quarter of 2022. The water diversion tunnel traverses the Qinling Mountains of Shaanxi Province, with up to 2,000 m (1.2 mi) of cover.
“Every day was full of challenges. We are most proud of our teamwork and unyielding spirit,” said a representative for tunnel contractor China Railway Tunnel Group (CRTG). The ground, consisting of mainly quartzite and granite, was estimated to have a rock hardness of between 107 and 309 MPa (15,500 to 45,000 psi) UCS, with high abrasivity and a maximum quartz content of 92.6%.
“This was in my opinion the most challenging project ever completed by TBMs, and it proves TBMs are up to overcoming even the most difficult conditions. I have great respect for the CRTG crews and management, and I thank them for moving TBM technology to a new level,” said Robbins President Lok Home.
During tunneling, crews encountered over 14,000 rock bursts, some with energy as high as 4,080 kJ. “Robbins’ overall equipment performance was excellent from the beginning to the end of breakthrough, and during seven years of excavation. This is despite the super hard rock with high quartz content, strong rock bursts, and substantial water inrushes,” said the CRTG representative.
Water ingress occurred a total of 69 times during the drive, with some inflows extremely high – exceeding 20,000 m3 (700,000 ft3) of water in one day from a single point. In-tunnel ambient temperatures peaked at 40 degrees Celsius and 90% humidity.
Throughout the challenges, the crew found ways to persevere. Rock bursting was controlled using steel slats in conjunction with the McNally crown support system, while zones of stress were predicted using a micro-seismic monitoring system. The micro-seismic system records rock stresses in a borehole 20 m (65 ft) ahead of the face and predicts the potential for rock bursting following comparative analysis with similar rockburst data from other projects, as well as from nearby sections of tunnel in the Qinling Mountains.
Water ingress was controlled by dramatically increasing pumping capacity in the tunnel to 41,000 m3 (1.4 million ft3) per day. Systematic probing ahead of the TBM was also used to detect water, as well as rock bursting. When ingress exceeded 70 percent of the in-tunnel pumping capacity, crews then carried out grout injections.
The abrasive, hard rock was another challenge, addressed by Robbins through the use of Extra Heavy Duty (XHD) 20-inch disc cutters that showed long cutter life and lower wear compared to standard 20-inch discs. The crew also optimized TBM operation with at times lower production rates where needed. “Especially with such a huge challenge, a strong cutterhead is required to ensure production. The quality of Robbins’ cutterhead has been proven. The cutterhead can still work properly after the tunnel breakthrough,” said the CRTG representative.
With TBM tunneling complete, the route will become part of two other sections of an altogether 82 km (51 mi) long tunnel that will link up the Hanjiang and Weihe Rivers in Shaanxi province. The completed tunnel, for owner Hanjiang-to-Weihe River Valley Water Diversion Project Construction Company, will secure a water supply for towns and agricultural areas in Central China, while also generating hydroelectricity.
On March 3, 2022, a 7.95 m (26.1 ft) diameter Robbins Single Shield TBM completed a record-setting run below Lake Ontario. The machine, for the Southland/Astaldi JV, bored 3.5 km (2.2 mi) in sedimentary rock for the Ashbridges Bay Outfall in Toronto, Ontario, Canada.
The machine launched in March 2021 from an 85 m (280 ft) deep, 16 m (53 ft) diameter shaft and began its bore in predominantly shale, with limestone, siltstone and sandstone. During its excavation, the TBM and its experienced crew bored a city-wide record of 30 rings in one day, or about 47 m (154 ft) of advance. The machine and crew surpassed a previous best day of 21 rings at a project with similar specifications. “We are proud to have completed another successful tunnel with Robbins and greatly appreciate their field service support,” said Joe Savage, Project Manager for Southland.
“This is a wonderful type of geology for our machines. During the entire excavation, a total of 7 cutters were changed. The wear behavior is incredible, between 2 and 5 mm, and everyone is amazed by the cutter performance,” said Alfredo Garrido of Robbins Field Service.
The crew had been operating the machine in two shifts of 12 hours from Monday to Friday. A Robbins continuous conveyor system including vertical conveyor transported muck behind the machine. “Every 25 machine cycles, it was necessary to stop the excavation to probe drill hole in front of the cutterhead to check for possible water. This drilling was done basically every day, stopping the machine for a few hours, but it was very necessary,” said Garrido.
The last kilometer of tunnel, bored below a series of 50 risers under Lake Ontario, was challenging but ultimately successful. “The team really worked together to overcome some tough ground conditions and high water inflows in the tunnel,” said Savage.
The success of the TBM is just one cause for celebration. The project won accolades from the Tunnelling Association of Canada (TAC) in late 2021 for its all-remote machine acceptance enacted due to the Covid-19 pandemic. The machine acceptance, the first of its kind, enabled communication and confirmation between the machine’s assembly location in Mexico, suppliers in the U.S. and those involved in Canada. “It was a challenge for all the people involved due the pandemic travel restrictions; however, due to good planning and communication we were able to go through the Acceptance Test successfully. I think this might become quite common in the near future,” said Robbins Project Manager Javier Alcala.
The completed outfall will connect to the 50 in-lake risers to enable efficient dispersion of treated effluent over a wide area of the lake, making it the largest outfall in the country. The project for the City of Toronto will improve the city’s shoreline and Lake Ontario’s water quality by replacing a 70-year-old existing outfall.
A Robbins 4.6 m (15.1 ft) diameter Crossover machine holed through in the Andes Mountains of Chile in the last quarter of 2021. The XRE TBM bored a 3.3 km (2.1 mi) long tunnel for Chile’s Los Condores Hydroelectric Power Project (HEPP) and project owner Enel.
A dedicated team, including three Robbins Field Service personnel, guided the machine to breakthrough in conditions including tuff, sandstone, breccia, and conglomerate with sections of high-pressure water inflows. Ground cover reached up to 450 m (nearly 1,500 ft) above the tunnel with rock strengths maxing out at 60 MPa UCS. “Robbins Field Service was an important part of the success of the excavation, evaluating continuous improvements in the machine and correcting faults,” said Ricardo Riveros Puratic, Project Engineer for Enel.
For Riveros Puratic, Crossover machines make sense despite the challenging conditions: “Towards the end, [the TBM] exceeded expectations. Crossover TBMs are suitable for Andean geology of sedimentary and volcanic type, where there is a great range of rock strengths and hydrogeological conditions.” Maximum advance rates topped out at 605.8 m (1,988 ft) in one month and 212.8 m (698.2 ft) in one week.
The Crossover machine featured a heavy duty, centrally mounted screw conveyor for the duration of the drive. The TBM remained in a hard rock configuration with muck chute installed, along with paddles, bucket lips, scrapers and disc cutters on the cutterhead. However, “75% of the excavation was performed using the main drive gearboxes in high torque configuration (EPB or low speed mode). We never physically changed the cutterhead or screw conveyor to EPB mode,” said Omar Alvarez, Robbins field service site manager at Los Condores.
High-pressure ground water inflows were the key challenge of the project. “When we started the excavation, we used dewatering hoses to reduce the water into the cutterhead during the excavation,” said Alvarez. Water pressures rose whenever the TBM stopped, however. “During the segment ring installation, we stopped the water from draining through the rear shield drilling ports and we closed the screw conveyor rear gate. We reached 7+ bar in the cutterhead earth sensors.”
“We bored in places with 5,500+ liters (1,500 gal) /min, making back-fill grout injection behind the concrete segments a challenge. We decided not to use the grout injection through the tail shield ports, but instead injected grout directly through the concrete segment with hoses. This approach was more flexible and reduced the need for reinjections,” said Alvarez.
With multiple triumphs and lessons learned during tunneling, Alvarez reflected on the breakthrough: “I’m proud to be part of a team that finished a tunnel in the Andes Mountains.” Once brought online, the Los Condores HEPP, located in the mountainous southern Maule region, will have an annual generating capacity of 150 MW.
In October 2021, the breakthrough of a Robbins Crossover XRE TBM was the cause of much celebration. A team of personnel from Kolin Construction, Turkish State Railways (TCDD), and Robbins field service gathered to watch the breakthrough of the world’s fastest TBM over 13 m (43 ft) in diameter.
The 13.77 m (45.18 ft) XRE TBM set world records three times over, beating its own records in May and June with a set of records over the summer, including a best day of 32.4 m (106 ft), a best week of 178.2 m (584.6 ft), and a best month of 721.8 m (2,368 ft). Launched in March 2021, the machine bored 3.05 km (1.90 mi) on the Esme-Salihli Railway Tunnel as part of the Ankara-İzmir High Speed Railway Project for the TCDD.
“When the strength, force and torque generated by our Crossover TBM are taken into account, we consider it to be a beast. It has performed extremely well in this tunnel,” said Onur Kansu, TBM Manager for project contractor Kolin Construction. He added “We are proud we have accomplished such high performance.”
The machine began its bore in altered gneiss, then passed through mélange consisting of gneiss, sandstone, claystone, mudstone, quartz, and silt. By the end of the bore the machine was excavating in mainly mudstone. Core drillings were taken every 200 m prior to boring so the crew felt confident with the geology—just one of several factors that contributed to the record rates. “A proper geological analysis, choosing the right TBM, a professional crew and a contractor who believes that they can break records are all key,” said Kansu. “Scheduled maintenance periods, an expert team, availability of sufficient spare parts, and good logistics also made it possible for us to reach our targeted advance rates.”
The project is particularly important for the Turkish tunneling industry, showing what is possible at larger TBM diameters. “We have disproved the idea that it is difficult to reach high advance rates while boring in EPB mode with large diameter TBMs. Crossover TBMs enable us to find quick solutions in changing ground, so we believe they will be the preference for future projects,” said Kansu.
With tunnel excavation finished, work will continue on the 508 km (316 mi) line that will connect Polatlı in Ankara Province to Izmir, the third most populous city in Turkey. Once complete, the Ankara-İzmir High Speed Railway will be the longest rail line in the country, conveying passengers at top speeds of 250 km/h (160 mph) in a railway journey of about 3.5 hours.
History has been made twice over at Turkey’s Eşme-Salihli Railway Tunnel where a 13.77 m (45.18 ft) diameter Robbins Crossover XRE TBM has set new world records for best day, week, and month in the 13 to 14 m (42.6 to 46 ft) diameter range. The machine broke all three records first in May with 25.3 m (83 ft) in one day, 117 m (383.8 ft) in one week, and 345.6 m (1,134 ft) in one month, then again in June with 28.5 m (93.5 ft), 133.2 m (437 ft), and 455.4 m (1,494 ft) respectively. The TBM, which sat in storage for seven years before being newly upgraded for this project, proves the robust durability of Robbins machines.
The Crossover TBM surpassed all previous performance rates by a machine in its size range. The closest another 13 to 14 m (42.6 to 46 ft) machine has come to these numbers was a 13.7 m (45 ft) diameter mixed ground TBM that achieved a 7 m (23 ft) average per day and a best day of 12 m (39 ft) at the Eurasia Tunnel project.
Onur Kansu, TBM Manager for project contractor Kolin Construction, attributes the machine’s success to the team operating it: “The most important reason for achieving fast advance rates is that we have an experienced and qualified team. If we open it up even further, such a team allows us to anticipate the malfunctions and to go to the solution in a very short time. In addition, all necessary maintenance is carried out on time, and the appropriate consumables are selected to increase the performance.”
The machine launched on its 3.05 km (1.90 mi) bore at the end of March 2021 as part of the Ankara-İzmir High Speed Railway Project for the Turkish State Railways (TCDD). Thus far the machine has encountered a mix of mainly mudstone with gneiss. “When we look at the overall tunnel geology,’ said Kansu, “we are excavating in complex and weak ground. In this geology, the advantages of the Robbins XRE TBM are highly favorable. The Robbins XRE TBM shows high performance in both complex and weak ground. It should also be noted that the TBM is very strong when looking at parameters such as torque and thrust.” To get through the challenging conditions, the large diameter XRE has a number of unique features. The large diameter design enables both a screw conveyor and belt conveyor to remain in place, enabling swift conversion between modes, and operation in full EPB and hard rock modes.
Regarding the future of the Turkish tunneling industry, Kansu is optimistic about the effects these new records will have: “It has been seen how well the engineers and application teams in Turkey have excelled in complex geologies and the large-scale tunneling industry. At the same time, it has shown to the whole world, especially Turkey, that with the right choices, it is possible to carry out excavations of this scale and complex geology without any problems and quickly. This project will be a pioneer in the Turkish tunneling industry, showing that faster and more economical tunnels can be built.”
In Spring 2021, the second of two 6.65 m (21.8 ft) diameter Robbins Crossover XRE TBMs made its third and final breakthrough for India’s Mumbai Metro Line 3. The first machine made its final breakthrough for the project in late April. The tunnel drives were a triumph for joint venture contractor Larsen & Toubro and the Shanghai Tunnel Engineering Company (L&T – STEC), as the crew and equipment overcame unpredictable terrain, high-pressure water ingress, and government-imposed lockdown orders during the Covid-19 pandemic.
The two custom-built machines were selected to bore parallel 2.9 km (1.8 mi) tunnels between the Cuffe Parade station and CST stations, breaking through into several station sites along the way. “It is the first time in India that Dual Mode, Crossover type TBMs equipped with a horizontal screw conveyor and high torque / high speed (two-speed) cutterhead drives were used. Overall, the performance of the Crossover TBMs was found satisfactory and we are in the process of shifting these TBMs for the L&T Chennai Metro project,” said Mr. Palwinder Singh, Head – Tunnel Construction for the L&T – STEC JV.
In another first for India, the Crossover TBMs employed a unique technique in a 554 m (1,820 ft) long section from Hutatma Chowk to CST stations. They were used in the benching of the NATM Platform tunnel through basalt rock (removal of the bottom section of rock remaining in the station after conventionally removing the top section). “This requires fine control on the operational parameters of the TBM because only 25% of the cutterhead is excavating the rock mass, while the remaining 75% of the cutterhead has no contact with rock or soil. In addition, the TBM was relaunched without using a reaction frame, instead taking reaction from half segments erected during the benching of the NATM Platform Tunnel. These innovative concepts were accomplished for the first time in India at Mumbai Metro Line-3, Package 1, and I therefore have many reasons to feel proud on the completion of tunneling,” said Singh.
L&T – STEC made impressive progress throughout tunneling despite the many exacting circumstances surrounding the scope of work. Above ground, the joint venture not only had to navigate the restrictions of working within an urban environment, such as limited work hours and the slow removal of muck due to minimal space and traffic, but also faced concern for major structures such as the Mittal Towers and the historic Bhikha Behram Well located along the tunneling route. The Crossover TBMs excavated with only 15 to 20 m (49 to 65 ft) of cover separating them from these important structures, which had to be instrumented to monitor vibrations, movements, and potential settlement.
Underground, L&T – STEC faced a complex geological mix of fresh greyish basalt, soft volcanic tuffs, shale, and breccias—consolidated rocks of angular fragments of disintegrated volcanic rock. One of the biggest concerns, however, came from the tunnels’ proximity to the coastline of the Arabian Sea. During one point, TBM 1 was only 25 m (82 ft) from the coastline, with the invert level of the tunnel running approximately 22 m (72 ft) below mean sea level. As anticipated with circumstances such as these, the Crossovers faced a significant amount of groundwater with up to 300 liters/min during their excavation.
Despite these obstacles, the TBMs were still able to maintain impressive rates. TBM 2 even completed one push in a swift 14 minutes. “In fact, the boring rate of the Crossover TBMs was never an issue for us. It was only limited by the rate of muck removal and we could have finished the tunnels much faster,” said Singh.
L&T engineers were highly involved in the specifications and designs of the machines and worked closely with Robbins to prepare for the challenges the project presented. While L&T had extensive tunneling experience, tunneling with a Crossover machine was entirely new to them. To remedy this, Robbins provided a team of key personnel to train L&T in all aspects of the machines’ design and operation. “Working with Robbins field service was more than satisfactory. Even during the Covid-19 pandemic times, Robbins field service was available 24 hours a day, 7 days a week. What else can one expect?” said Singh.
Each milestone reached on this project is another step closer toward significantly improving the lives of Mumbai residents. As the financial capital of India and one of the most populated cities in the world, Mumbai is faced with an excessive amount of road traffic. It currently takes up to two hours to drive the 25 km (15 mi) distance from Cuffe Parade to the airport—the same trip on the finished metro will take a mere 50 minutes. The completion of Mumbai Metro Line 3, which is expected in 2025, will not only save residents transit time, but is expected to initially decrease road traffic in the area by 35%, reducing daily fuel consumption by 460,000 liters.
A Robbins 13.77 m (45.18 ft) diameter Crossover XRE TBM launched recently in spring 2021 in Eşme, Turkey. The large machine is boring the 3.05 km (1.90 mi) Eşme-Salihli Railway Tunnel through mixed conditions including sandstone, gravelstone, claystone, and siltstone. Contractor Kolin Construction expects some occasional groundwater and weak rock between 5 to 9 MPa (720 to 1,300 psi) UCS, with the potential for a gassy environment.
The titanic TBM was launched after more than seven years in storage, and following a few upgrades to systems to ensure they meet the newest safety and efficiency standards. “I am very happy that the TBM has been launched. Up to now, the machine has bored nearly 500 m (1,600 ft) in gneiss and mudstone. This is an opportunity for Robbins to prove that large diameter TBMs can bore in such tunnels, even in very complex geology and difficult ground conditions,” said Yunus Alpagut of ATES, Robbins’ Turkish subsidiary. Alpagut went on to explain why the project is so important: “Recently, there have been large diameter, non-Robbins machines that have failed at projects such as the high-speed railway in Bilecik, so this is very important to show the Turkish tunneling industry that large machines are up to the challenge.”
To get through the challenging conditions, the large diameter XRE has a number of unique features. The large diameter design enables both a screw conveyor and belt conveyor to remain in place, enabling swift conversion between modes, and operation in 100% EPB and hard rock modes.
In EPB mode, the screw conveyor operates as in any typical EPB machine. The screw features a replaceable inner liner and replaceable carbide wear bits for abrasion protection. A mixed ground cutterhead is fitted with knife bits that can be switched out with disc cutters in harder conditions. The machine design includes a man lock for cutterhead inspection and changes, and mixing bars inside the mixing chamber.
To convert to hard rock mode, the mixing bars and initial portion of the screw conveyor can be optionally retracted. EPB knife bits are then replaced with disc cutters on the cutterhead, and the EPB scrapers on the cutterhead are replaced with bucket lips. Muck paddles are installed in the cutterhead to allow the muck to fall into the muck chute. A hydraulic muck ring allows a chute attached to the bulkhead to move forward and down at a diagonal angle, allowing rock chips to be deposited in the chute and through the screw conveyor onto the TBM belt conveyor. To keep up production rates in both modes, the Robbins Torque-Shift System is used: a two-speed gearbox that enables efficient tunneling in hard, mixed, or soft ground.
The Eşme-Salihli Railway Tunnel is part of the Ankara-İzmir High Speed Railway Project for the Turkish State Railways (TCDD). The 508 km (316 mi) line will eventually connect Polatlı in Ankara Province to Izmir, the third most populous city in Turkey, surpassing the Istanbul-Ankara High-Speed Railway as the longest rail line in the country once complete. The double-track railway system will convey passengers at top speeds of 250 km/h (160 mph), completing the journey between the two cities in 3.5 hours—a journey that would normally take 6.5 hours by car.
Global TBM Company, newly established by industry veteran Lok Home, is proud to announce the recent purchase of substantially all the assets of The Robbins Company. The company will operate as Robbins and with Mr. Home as the President and CEO. The acquisition will result in a seamless transition for a number of ongoing projects throughout the world, as Robbins renews its commitment to service, quality underground equipment, and top-notch support that its customers have come to expect. For a brief message from Lok Home, view the video here.
Home said the company has a bright future as a result of the transaction. We are starting off the new year with a respectable backlog of orders,” he noted. “In 2021 and beyond, our clients can depend on Robbins to deliver high quality machines, and technically superior machines for very difficult projects,” said Home. “That’s where Robbins really stands out.”
Home went on to say that Robbins is starting 2021 with no significant bank or institutional debt. “We have many projects to look forward to,” he continued. “Robbins is currently delivering Crossover machines and TBMs equipped for challenging geological conditions in many countries including the U.S., Norway, India, China and Canada.” The company’s conveyor and small boring machine divisions will also continue to deliver equipment worldwide.
Home emphasized that Robbins has always been focused on building the best and strongest machines. He pledged that they will continue to do that. “We still have our strong engineering team and we plan to continue our many industry involvements including the International Tunneling Association (ITA) and its associate member organizations. We’re glad to be a part of this community and this industry,” Home added.
The company expects to continue with exciting new developments as well, including a soon-to-be-unveiled non-circular rock boring machine. Robbins remains focused on creativity and innovation to solve the industry’s greatest challenges.
Robbins is one of the world’s foremost developers and manufacturers of advanced, underground construction machinery. Headquartered in Solon, Ohio, USA, Robbins is a total supply firm offering customized Tunnel Boring Machines, conveyors, cutters, and more, as well as knowledgeable field service personnel and technical support. The company has been an active industry participant and innovator for nearly 70 years.
From the first modern Tunnel Boring Machine built in 1952 to recent innovations such as the Crossover TBM for varied ground conditions, Robbins engineering and innovations have made a success of the world’s most difficult tunneling projects.
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.”
- Robbins TBM takes on Karstic Limestone below St. Louis
- Robbins Main Beam Triumphs on Challenging China Drive
- Robbins Single Shield completes Canada’s Largest Outfall
- Robbins Crossover holes through in the Andes
- Robbins Crossover XRE is World’s Fastest TBM over 13 Meters in Diameter