Robbins Double Shield Launches in Nepal
In October 2022, China Overseas Engineering Group Co. Ltd and China Railway No. 2 Engineering Group Co Ltd launched a 6.4 m diameter Robbins Double Shield TBM. The TBM is boring the 13.1 km headrace tunnel for the Sunkoshi Marin Diversion Multipurpose Project (SMDMP) located in southern Nepal. The tunnel is connected to a new 28.6 MW surface powerhouse on the Marin River to alleviate the shortage of power supply in the area. It will also be used for farmland irrigation in the districts of Dhanusha, Mahottari, Sarlahi, Rauthat and Bara in the Terai Plain, diverting water from the Sunkoshi River to the Marin River. Since the TBM’s launch, it has bored over 500 m, with a best week of 224.6 m, and a best day of 36.6 m.
The headrace tunnel is being bored through granitic rock with maximum overburden of 1,320 m. Geological conditions may include squeezing ground, fault zones, and water inflows. In particular, a major fault zone is located approximately 4 km into the tunnel at Dhanamana Khola. The machine was customized for the conditions, explains Mr. Liu Fengfan, Project Manager for contractor B-2/COVEC: “The TBM shield is a tapered design to reduce the risk of becoming stuck in squeezing ground; there is an enclosed cutterhead design to reduce the collapse of surrounding rock as well. The TBM has overcut capabilities, and a high thrust. It has also been designed to be equipped with an extra high torque cutterhead drive, as well as strong auxiliary thrust to be used in squeezing ground or weak fault zones to keep the machine from becoming stuck.”
As for the major fault zone, to be reached in approximately June 2023, and other zones of concern, Mr. Liu’s plan is well-thought-out: “We have prepared the advance geology forecast along with technical measures and equipment to cope with the extraordinary geological conditions. These include advance drainage holes, pre-excavation grouting (both ordinary and chemical), and other methods based on our experience. When we reach the major fault zone at Dhanamana Khola we will go slow, with more probe drilling while in the fault zone.”
The tunnel is the machine’s second: on its 12.2km first tunnel (the Bheri Babai Diversion Multipurpose Project/BBDMP), the TBM finished nearly one year early and achieved 1,202 m advance in one month. “The Robbins TBM at BBDMP successfully broke through the 12.2 km tunnel and overcame extraordinary geological conditions especially in fault zones. Its stable and excellent performance and function have been verified very well. We have much confidence in the TBM to be used in SMDMP,” said Mr. Liu.
Landmark Breakthrough for Robbins TBM ‘Big Tex’
On July 25, 2022, a crowd gathered as a large Robbins Main Beam TBM, dubbed ‘Big Tex’, broke through in Dallas, Texas, USA. The machine and its continuous conveyor system, for the Mill Creek Drainage Relief Tunnel, successfully bored 8 km (5 mi) in chalk and shale at up to 498 m (1,634 ft) advance in one month. “I think when you step back and look at what was accomplished by this team as whole…the overall length and size of this tunnel, the TBM conversion, the everyday grind to keep moving forward…it truly is something to be proud of, professionally and personally. No single individual could reach this milestone. It took a great team of skilled individuals. I am fortunate to be a part of it,” said Nick Jencopale, Sr. Project Manager for contractor JV Southland/Mole.
Good advance rates were not the only cause for celebration: the unique project required a planned in-tunnel diameter change of the TBM from its original 11.6 m (38 ft) to a more compact 9.9 m (32.5 ft). The first-of-its-kind conversion process was undertaken 2.8 km (1.7 mi) into the bore and was not done inside a shaft or pre-excavated portal. “The TBM conversion was a unique challenge that we were excited about, and ultimately provided a more efficient method for the desired product compared to the alternative options. Hopefully the successful conversion proved that this option can be considered for future tunnel projects,” said Jencopale.
While there were many detailed steps to the conversion process, precision design of the machine was a key aspect. “We started with a smaller machine, then we made a kit or second skin that was slightly larger. And then when the time came, we just took that skin off. It was essentially that simple,” said Evan Brinkerhoff, Robbins Field Service Manager. The conversion took about four months and was completed in April 2021.
“The Robbins Main Beam TBM (‘Big Tex’) performed consistently throughout the duration of the tunnel excavation. There were very minor issues and little overall downtime as a result of the TBM itself,” said Jencopale. Due to the relatively favorable ground conditions in much of the tunnel, including low rock strength and low abrasivity, only eight disc cutters were changed during the length of tunnel bored at the larger diameter. At the time of diameter change the full dress of cutters was changed, and since that change only 14 cutters have needed replacing. Crews did encounter some fault zones, and installed rock bolts and wire mesh in the tunnel crown as needed.
With the TBM-driven portion of the tunnel now complete, work can commence to remove the machine from the tunnel and install a final lining. The tunnel is a designated critical infrastructure project for the City of Dallas, providing 100-year flood protection for areas of East Dallas that have experienced severe flooding in the past. Construction work is expected to be complete in late 2024/early 2025.
Robbins TBM takes on Karstic Limestone below St. Louis
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.
Robbins Main Beam Triumphs on Challenging China Drive
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.
Robbins Single Shield completes Canada’s Largest Outfall
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.
Robbins Crossover holes through in the Andes
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.
Robbins Crossover XRE is World’s Fastest TBM over 13 Meters in Diameter
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.
Robbins develops Rectangular Rock Mining Machine for Flat Invert
Robbins’ latest innovation is making good headway on a non-circular tunnel excavation in hard rock. The rectangular TBM, known as the MDM5000 (standing for Mine Development Machine with dimensions of 5.0 m x 4.5 m) is capable of excavating a flat tunnel invert for immediate use by rubber-tired vehicles. Employed by Mexico’s oldest silver mine, Fresnillo Plc, the MDM5000 is boring a mine access tunnel in andesite and shale with quartz intrusions that has defied earlier attempts using roadheaders. The successful operation is the result of extensive discussions between Robbins, who designed and supplied the machine, with TOPO machinery and Fresnillo Plc. View the video of the machine in action here.
“We decided to work with Robbins for their experience. A lot of people have tried to provide these kinds of machines but nobody has done it. Robbins used their experience and their skills to provide us with a rectangular profile machine,” said Fidel Morin, Projects Superintendent for Fresnillo Mine.
The technology is not only useful for the mining industry, but also for many applications in civil tunneling. While other machines have been developed for soft ground, the MDM5000 represents the first successful foray into rectangular hard rock tunneling. “We’re very pleased to add non-circular tunneling to our wheelhouse of solutions that continues to include TBMs, conveyors, cutters, and more. We see applications for the MDM wherever a rectangular profile is needed, such as train tunnels requiring a flat invert. In a traditional circular tunnel, the invert is filled or an invert segment is needed, but with the MDM 30% less rock is required to be removed from the profile,” said Robbins President Lok Home.
With more than 1,700 m of advance thus far at rates up to 52 m in one week and 191 m in one month, the MDM is significantly faster than drill & blast excavation. “We’re making history. Fresnillo is always looking for new technology, and we believe that the usage of the MDM5000 is going to be something extremely successful, not only for our company but also for the industry,” said Morin.
The MDM5000 has undergone major component enhancements during the course of its successful bore at Fresnillo mine. It was first transported to the -695 m level of the mine and underwent final assembly and launch in a cavern, where sections of the MDM were moved by crawlers and pieces were lifted by hoist. The machine is now boring a 270-degree spiral to end above the original tunnel. It will then be backed up to the original tunnel and continue driving straight ahead.
Developed for use in rock up to 200 MPa UCS, the MDM5000 utilizes disc cutter technology proven on traditional, circular TBMs. During excavation a reciprocating cutterhead and swinging cutterhead motion create a rectangular cross section tunnel.
The MDM offers a number of advantages over drill and blast. MDM tunneling has advance rates roughly twice those of a drill and blast heading, and results in smooth tunnel walls, less overbreak, and minimized ground support. The increased advance rates are partly due to the machine’s continuous progress, unlike drill and blast operations where crews must exit the tunnel during blasting for safety. In addition, simultaneous ground support installation further increases overall advance rates compared with drill and blast operations that must install ground support sequentially.
View the machine boring at Fresnillo mine: https://youtu.be/mgFopWaf220
Turkish TBM Records, Twice Over
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.”
Robbins XRE TBMs Cross the Finish Line in Massive Metro Project
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.
- Robbins Double Shield Launches in Nepal
- Landmark Breakthrough for Robbins TBM ‘Big Tex’
- 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