Category: Press Releases
In April 2017, a ceremony was held to celebrate the commissioning of the Dariali Hydropower Project in the Republic of Georgia. Many attended the ceremony marking the first carbon-neutral hydropower project in the world, including Georgian Prime Minister, Giorgi Kvirikashvili. The power station, an independent power project (IPP) developed through Dariali Energy Ltd, was a joint venture involving three other firms: Georgian private companies Peri Ltd and Energy LLC, and state-owned Georgian Energy Development Fund (GEDF). The Dariali HPP gathers water from the Tergi River and directs it through the headrace tunnel to the power house located near the Russian—Georgian border. Each year, the site will generate 500 GWhs of carbon-neutral energy, with 70 percent of power production occurring during the country’s summer months.
Robbins also invested in the project by gaining equity through supplying tunneling equipment and services in consortium with contractor Peri. “Robbins understood the risk in the tunneling portion of the project and we were compensated for taking on part of the risk. Peri is a long-time customer, as we supplied a TBM to them 15 years ago for a small project in Georgia. It was great to be invited to invest and risk share on this project, and to work together again,” said Robbins President Lok Home. The 5 km (3 mi) long headrace tunnel for the power station was bored with the use of a 5.5 m (18 ft) diameter Robbins Main Beam TBM starting in February 2012.
Due to the remote and mountainous location of the jobsite 160 km (100 mi) from the capital Tbilisi, the machine was shipped in pieces to contractor Peri’s workshop, where they were refurbished under Robbins supervision and then delivered to the site to be assembled. Each piece was transported by truck down narrow, winding roads that eventually gave way to dirt paths. Assembly at the jobsite was difficult, as the project site at a 1,700 m (1.0 mi) altitude was blanketed in snow and components arrived in December. Bone-chilling temperatures often reached negative 15 degrees Celsius (5ºF), and 40 below with the wind chill factor. Once the machine had launched, it encountered difficult ground including slate, sandstone, limestone and malms with fault zones.
“The main challenges we faced were boring the tunnel at a 6 percent incline and having restricted access to service the machine. There were also two major landslides that delayed the project for over a year,” said Home. After the first landslide, the access tunnel, which had allowed mud and water to enter the power station, had to be relocated at a higher elevation and facing away from the river valley. When the machine was nearing the end of its bore, a second landslide blocked the exit portal for the machine as well as access to the main highway. Despite these challenges, tunneling crews persevered and the machine successfully holed through in October 2014.
Throughout the construction process, careful steps were taken to minimize the carbon footprint. Although the plant’s energy production is carbon emission free, construction of the plant was not. To offset these emissions, 7,000 seedlings are being planted all around the area in a reforestation effort. In years to come, the trees will absorb enough carbon dioxide to compensate for the emissions produced during the construction of the hydropower plant.
Overall, said Home, there is much to celebrate as the project has immense benefits: “Not only does it provide affordable electrical power for the country with essentially no pollution effects, but it also provided jobs during construction and will continue providing jobs during its operation and maintenance.”
A Robbins TBM, recently christened “Augustine”, is being commissioned to undertake its eighth bore after being launched by contractor Eiffage Civil Engineering on March 3. The TBM, which was extensively modernized and upgraded during the rebuild for the Galerie des Janots project in La Ciotat, France, has previously completed seven other successful projects across Europe and Hong Kong. This time, it will bore the Janots gallery to improve access to water in the communities east of the Aix-Marseille-Provence metropolis (Cassis, Roquefort-la-Bédoule, La Ciotat and Ceyreste). “It’s a single machine 3.5 meters (11.5 ft) in diameter, 250 metric tons (275 US tons), and 135 meters (443 ft) long, that will work 24 hours a day for almost 10 months during this operation,” says Marc Dhiersat, Project Director of Galerie des Janots for Eiffage.
Currently, the machine is ramping up as back-up decks are being installed. As of April 2017, the machine has bored more than 51 m (167 ft), mainly encountering limestone. “Limestone is a rock easy to dig, but one can be confronted with the phenomenon of karst,” explains Loïc Thévenot, Director of Underground Works for Eiffage. “For this purpose, the tunnel boring machine is equipped with a probe drill. If the karst is small, we will fill it with concrete. If it is large, we will erect a small parallel gallery.”
Galerie des Janots is one of the fourteen operations designed to save water and protect resources, which are being carried out by the Aix-Marseille-Provence metropolis, water agency Rhône Mediterranean Corsica, and the State Government. The future Janots gallery will replace existing pipelines currently located in the railway tunnel that have significant safety and vulnerability deficiencies with estimated water losses of 500,000 cubic meters (132 million gallons) per year. According to Danielle Milon, Mayor of Cassis, “This is an investment of 55 million euros (USD $59 million) with 11 million in aid from the water agency. This project required 10 years of reflection and work to improve water supply. And water is essential for the development of each municipality, and for citizens’ well-being.”
Augustine is boring a tunnel 2,750 m (1.7 mi) long, and will pass under Le Parc National des Calanques, with cover between 15 and 180 meters (50 to 600 ft), in order to replace the pipes that are currently being utilized for the water supply networks. “[The current pipes] have a capacity of transit limited to 330 liters (87 gallons) per second, which is largely insufficient in the summer period. The objective of the operation is to increase to 440 liters (116 gallons) per second,” says Dhiersat. Once the project is complete, networks can easily be maintained in comparison to the old pipes currently running beneath the railway.
Robbins has completed the manufacture and testing of a unique tunnel boring machine that will be used to repair the longest continuous tunnel in the world. The TBM will be used to overhaul a section of New York City’s Delaware Aqueduct, a 137 km (85 mi) long tunnel that delivers about 50 percent of the City’s drinking water each day. Over the span of two days in February, representatives from the owner New York Department of Environmental Protection (NYDEP), consultant McMillen Jacobs (MJ), and JV contractor Kiewit-Shea Constructors (KSC) traveled to the Robbins facility in Solon, Ohio to witness the Factory Acceptance Testing of the custom tunnel boring machine.
The Robbins Single Shield TBM will bore a tunnel to replace a 3.8 km (2.4 mi) stretch of the Delaware Aqueduct. The Delaware Aqueduct currently leaks about 75 million liters (20 million gallons) of water per day into the Hudson River. Investigations of the Delaware Aqueduct dating back more than a decade revealed cracks in the tunnel lining. While several inspections with an automated underwater vehicle showed that these cracks were stable, it was determined they could not be fixed from within the existing tunnel. New York City then decided that a new tunnel would be built under the river to bypass the leakage.
To build a bypass tunnel around the aqueduct’s leaking section, Robbins manufactured the 6.8 m (21.6 ft) diameter Single Shield TBM to safely seal against pressures up to 30 bar, and to operate in variable hard rock conditions. The Delaware Aqueduct was completed in 1944. During its original construction, work crews documented groundwater inflows of 7.5 to 15 million liters (2 to 4 million gallons) per day. Because this particular section of the tunnel lies 183 m (600 ft) below the Hudson River, the inflows are under immense head pressure and thus require the unique tunneling technology.
Due to the challenges presented by the Aqueduct Repair, such as difficult geology and considerable water inflows, the TBM had to be designed accordingly. Difficult Ground Solutions (DGS) features, including powerful drilling, grouting, and water inflow control systems have been incorporated into the machine’s design to overcome the expected challenges. “One unique feature of this TBM is the closeable bulkhead, which allows the excavation chamber to be sealed off,” said KSC Tunnel Manager Niels Kofoed. “We expect this to be a key feature in the event that groundwater flows (shunt flows) from the excavated portion of the tunnel cause washout of the annulus grout. Once the bulkhead is closed the groundwater flows are stopped and secondary grouting of the precast liner can be performed, effectively cutting off the flow path of the shunt flows.”
Robbins Project Manager Martino Scialpi further noted that, “the TBM was designed with a 9,500 liter/min (2,500 gallon/min) dewatering capacity. The machine is equipped with two drills in the shields for drilling through the head in 16 different positions and a third drill on the erector to drill through the shields in an additional 14 positions. Drilling and pre-excavation grouting will be a routine job to control and minimize water inflows.” In addition, water-powered, high pressure down-the-hole-hammers will allow for drilling 60 to 100 m (200 to 330 ft) ahead of the machine at pressures up to 20 bar if necessary.
In order to provide access to launch and retrieve tunneling equipment, two deep shafts were constructed in the towns of Newburgh and Wappinger, New York, where the bypass will begin and end. The
project site itself poses challenges to the assembly and launch of the TBM because of the limited space available.
Robbins worked closely with KSC to ensure that TBM components were designed and sized so all could be lifted with the contractor’s hoist system and fit down the narrow, 270 m (885 ft) deep shaft. Once assembled, the machine is expected to begin boring in autumn 2017.
Chile’s Los Condores HEPP is a high cover, hard rock challenge, with 500 m (1,640 ft) of rock above the tunnel and a high-altitude jobsite 2,500 m (8,200 ft) above sea level. As of January 2017, a 4.56 m (15.0 ft) Robbins Double Shield TBM had completed boring its 900 m (2,950 ft) long access tunnel and was well on the way to boring the first section of headrace tunnel. The machine embarked on its journey on May 27, 2016, and has since excavated over 1,300 m (4,270 ft) of tunnel in total.
The journey to machine launch was an arduous one, requiring shipment of TBM components and vehicle transport on unpaved, mountainous roads. Contractor Ferrovial Agroman is responsible for the intake tunnel at the Los Condores Hydroelectric Project, and was well aware of the challenges associated with machine launch: “The location of the work is a big constraint due to its rugged terrain and geographical location in the Andes. With all this, we are anxious to perform work in an efficient manner,” said Pello Idigoras, Tunnel Production Manager for Ferrovial Agroman.
The jobsite, located 360 km (224 mi) south of Santiago, Chile, is part of a new 150 MW power plant and intake tunnel. The Robbins Double Shield TBM is boring two sections of the intake tunnel, the first measuring 6 km (3.7 mi) and the second measuring 4.4 km (2.7 mi). A section between the two tunnels will be excavated by drill and blast to connect them, making the intake tunnel about 12 km (7.5 mi) in length. “This project brings an increase in energy production in the country, thus contributing to the overall improvement in the welfare of its citizens,” said Idigoras of the effect the completed hydropower project will have on surrounding areas.
The tunnel, located in the mountainous Maule Region of Chile, is being bored in two types of rock: sedimentary and volcanic. The rock has been tested at strengths up to 100 MPa (14,500 psi) UCS, with at least two fault zones””the first of which has already been traversed in rhyolite, andesite, tuff, and breccia. For Idigoras, the conditions are well-suited to Double Shield tunneling: “We have good quality medium to hard rock for Double Shield excavation overall,” he said. Despite that, some areas of challenging ground persist. To cope with the conditions, including steadily increasing water inflows at rates of up to 3,500 l/min (925 gal/min), the contractor is utilizing cementitious grouting and chemical grouting with polyurethane and foam. Such ground conditioning techniques were anticipated and the Robbins Double shield was designed to effectively apply these techniques.
As the TBM excavates, it is lining the tunnel with 250 mm (10 in) thick, 1.2 m (3.9 ft) long concrete segments in a 4+1 arrangement. The machine is currently progressing at a rate of up to 25 rings per 20 hours of boring. Crews are operating in two 10-hour shifts with one 4-hour shift dedicated to maintenance. Idigoras sees the TBM performance and completion of the access tunnel as huge project milestones, though much work remains to be done. “After many months working in engineering, manufacturing, installation, and commissioning, we are proud to see this result. It would be impossible to name all the people who participated in this project thus far but they, as a whole, have managed to get the TBM started digging and boring well.”
After an Onsite First Time Assembly (OFTA) lasting just 2.5 months, Atlanta Georgia, USA’s newest TBM, dubbed “Driller Mike”, made its initial startup on October 13, 2016 and ramped up to full production two weeks later. Atlanta’s Mayor Kasim Reed and city officials gathered with local and national media to celebrate the occasion. The 3.8 m (12.5 ft) diameter Robbins Main Beam TBM is now boring the 8.0 km (5.0 mi) Bellwood Tunnel after being walked forward 100 ft into a starter tunnel. The Bellwood Tunnel path will travel from an inactive quarry and run below a water treatment plant and reservoir before ending next to the Chattahoochee River.
The project was green-lighted by the City of Atlanta’s Department of Watershed Management due to the city’s current emergency water supply shortage. The PC/Russell JV, the project’s construction manager at risk, sub-contracted with the Atkinson/Technique JV to operate the TBM and will oversee construction of various intake and pumping shafts as well as final lining operations. The project is of utmost importance for the City of Atlanta, explained Bob Huie, Sr. Project Manager for the PC/Russell JV. “Right now, the downtown area’s emergency water supply is approximately three days. With the tunnel the supply will increase to between 30 and 90 days. To be a part of the city’s emergency water supply solution is huge. This tunnel will protect the city for a very long time.”
With the tunnel on the fast track, swift TBM assembly was key. The OFTA process involved coordination by multiple crews at the large quarry site. “The OFTA went very well. The overall assembly process was well organized and supervised by the Atkinson/Technique JV and Robbins. We had a good team of folks to put it all together,” said Huie. He continued: “This is a unique job where there’s a lot of people with a variety of backgrounds, but everyone came together to make the OFTA happen.”
The Robbins TBM is now excavating in granite, with at least 300 m (1,000 ft) of zones in three separate areas that will require continuous probing. In a section directly below an existing reservoir, monitoring will be particularly crucial to ensure no water inflows occur. The Robbins machine will also be required to negotiate several curves: “We have one curve in the first 300 m (1,000 ft) and the main 370 m (1,200 ft) radius curve is 1,800 m (6,000 ft) in. We plan to do short TBM strokes in this section™bout 20 cm (8 inches) to 30 cm (1 ft) shorter than normal to get through the curves,” said Larry Weslowski, Tunneling Superintendent for the PC/Russell JV.
Excavation is scheduled to be completed in the first quarter of 2018. After final lining, the tunnel will be filled with water and the quarry site will become Atlanta’s largest reservoir and park, totaling hundreds of acres. While the park site is a bonus for residents, the water storage capacity it will provide is critical. Nearly 1.2 million customers, including 200,000 passengers who pass through the world’s busiest airport every day, count on the water supply each time they turn on the tap. “If the city were to lose water supply for a day, the estimated economic impact would be at least USD $100 million per day. If you consider that this is a USD $300 million project, that seems a pretty good investment in comparison to what could happen,” said Huie.
On September 23, 2016, Bangalore’s last TBM for the city’s metro rail project broke through, marking the end of TBM tunneling on the Namma Metro phase 1. The Robbins-operated machine, known as “Krishna”, bored a 750 m (2,460 ft) drive through challenging conditions between Chickpet and Majestic stations. Cleanup and final commissioning of the tunnel will be completed in 2017, and is the last obstacle before owner Bangalore Metro Rail Corporation Ltd. (BMRCL) can open the Malleswaram-Majestic link. The TBM’s sister machine, “Kaveri”, completed a parallel tunnel in June 2016.
The success follows a gauntlet of challenges on the two tunnel sites. Due to severe delays on the original tunnel drives, Robbins was approached and asked to take over the operations of the remaining two competitor-manufactured TBMs in February 2015. After obtaining agreement from the project owner and the contractor, Robbins took over the responsibility for all aspects of the underground operations. “We provided a team of over 60 staff including TBM operators, TBM technicians, ring builders, a grouting team, and more. We were also responsible for running surface installations and equipment such as the grout batching plant, gantry cranes and power supply. Contractor Coastal Projects Ltd. (CPL) provided a team of people including surveyors, QC engineers, and loco operators who reported directly to our site management team,” explained Jim Clark, Projects Manager for Robbins India.
The Robbins crew carried out tunneling operations while the Chickpet station was being constructed around them to mitigate delays incurred before they took over project operations. The project’s most difficult challenges included a low overburden and unconsolidated ground along the alignment, and the discovery of several uncharted wells directly on the alignment. Difficult ground frequently prevented proper pressurization during cutting tool replacement, requiring a grout solution to be pumped in to fill voids and left to cure. Initially the curing process took up to 36 hours, but with improved application methods this was reduced to a 12-hour curing time.
Another challenge involved the sensitive building structures along the tunnel path. Issues with surface vibration, explained Clark, required that cutterhead speed be limited to 1.8 RPM during the day shift and 1.2 RPM during the night shift. Despite the obstacles, the TBMs advanced at rates of up to 50mm (2 in)/min in highly weathered rock.
“This is an industry first, wherein a TBM manufacturer has utilized their in-house expertise and knowledge to take on this level of responsibility for a project,” said Clark, addressing the magnitude of the successful breakthroughs. “The fact that it was “˜a first’ and we were successful in bringing this high-profile project back on track is a great achievement for The Robbins Company.”
Now that tunneling is complete, the North and South runs of the Namma metro will be connected–a line that, once in service, will carry an estimated 40,000 passengers daily. It is anticipated that Phase One of the metro will be opened in its entirety in 2017.
On Tuesday, September 6, 2016, one of the longest-running Robbins TBMs embarked on its most extensive project yet. The 6.2 m (20.2 ft) Main Beam machine, owned by the Shea-Kiewit (S-K) JV, is boring the 8.5 km (5.3 mi) long White River Tunnel as the first in the next phase of the DigIndy wastewater tunnels below Indianapolis, Indiana, USA. In addition to that work, the machine will bore the Lower Pogues Run, Fall Creek, and Pleasant Run Tunnels™ scope of work totaling about 28 km (17 mi) through limestone and dolomite rock.
The rebuilt Robbins hard rock TBM was first used in Indianapolis on the 12.5 km (7.8 mi) long main tunnel, called the Deep Rock Tunnel Connector (DRTC). On that tunnel, the speedy machine achieved world records in its size class of 6 to 7 m (20 to 23 ft), including “Most Feet Mined in One Day” (124.9 m/409.8 ft); “Most Feet Mined in One Week” (515.1 m/1,690 ft); and “Most Feet Mined in One Month” (1,754 m/5,755 ft). “It’s nice to start the job with a machine that has already been proven and successful,” said Stuart Lipofsky, Project Manager for S-K JV.
However the DRTC was far from the TBM’s first job. The machine, originally built in 1980, has been used on New York City’s Second Avenue Subway, as well as projects in Massachusetts and Canada. Once the machine has completed the DigIndy network of tunnels, it will have bored more than 51 km (32 mi) of tunnel™n achievement making it one of the hardest working Robbins TBMs ever put into service. “The age of the machine wasn’t a concern for us, it was a positive. We knew it could perform in harder, abrasive rock,” said Lipofsky.
The machine was launched from the 67 m (220 ft) deep White River shaft following a refurbishment that included new motors, gearboxes, electronics, and other elements. As of the last week of September, the TBM has bored over 300 m (1,000 ft) of the White River Tunnel. About one mile into the White River Tunnel, the drive will bifurcate eastwards to bore the 2.7 km Lower Pogues Run Tunnel in front of Lucas Oil Stadium in downtown Indianapolis. The machine will then be backed up to the bifurcation point before continuing north for completion of the White River Tunnel.
As the machine bores, Robbins continuous conveyors remove muck in an extensive system that was highly successful at the DRTC. Much of the conveyor structure remains the same for the new tunnels, with new horizontal and conveyor belting provided. The conveyors will wind through curves as sharp as 300 m (1,000 ft) in radius, as the tunnels follow the path of the White River overhead.
The S-K JV has until 2021 to complete the White River and Lower Pogues Run tunnels for local owner Citizens Energy Group, and until 2024 to complete all the tunnels. The use of one TBM was seen as a positive: “The use of one machine was more efficient for our crews. The schedule allowed us to run with one TBM and we feel we can do it with one machine. It also was a less costly option than running two machines in terms of the owner funding the project,” said Dan Martz, vice president for J.F. Shea. Once complete, the EPA-mandated deep tunnel project will reduce the amount of raw sewage overflows and clean up tributaries along the White River.
The Robbins Company announced the appointment of Joe Lechner to the role of Small Boring Unit (SBU) Sales Manager. With over 18 years of industry experience, the role is a natural career progression for Lechner. It brings him back to his early roots of working with SBUs, while more recently he worked with TBMs. Lechner can continue his success with the company in this new capacity with the trenchless division.
In his new position, Lechner will handle SBU sales and rentals for Robbins, assist customers in equipment specifications for projects, and provide full-spectrum customer support. In addition, Lechner will be responsible for many other tasks such as generating quotes for cutters and spare parts, shop scheduling, forecasting, internal operations for Robbins, and field service support, as needed.
“I want customers to know they can come to me with any issues. I have a good understanding of the industry and our business,” said Lechner. “I want to provide an all-around good experience. Robbins wants your project to be successful, with our equipment and support.”
Lechner began working with SBUs in 1998, starting in field service. When he wasn’t out in the field, he was building SBUs and cutters. He started up and commissioned SBU-As in the field, and transitioned over to working with TBMs worldwide in the mid 2000’s. With his diverse worldwide field experience, Lechner’s knowledge will continue to benefit Robbins and its customers.
Lechner said his goals as Sales Manager for the SBU product line for the next two years include increasing stocking levels and providing fast deliveries to customers. He noted the division is streamlining inspection quoting and repair processes to ultimately provide the most efficient services possible. With a few hundred machines in service, some of which are working around the clock, he anticipates product sales, rentals and repairs all will remain consistent moving forward.
“We’re lucky to have Joe working with Robbins,” said Tom Fuerst, Utility Tunneling Sales Manager. “With his background and extensive knowledge, he’ll easily implement the best solutions for our customers.”
In February 2015, Robbins, with its operating company Robbins India, was asked by Bangalore Metro Rail Corporation Limited to take over the operation and maintenance of two competitor-owned EPBMs. The machines were stalled due to low performance and financial issues from the Operating Contractor and lack of support by the original machine supplier. As the North-South Bangalore Phase 1 Metro tunnels were on the critical path, the BMRC looked to Robbins to step in and take over the troubled project. A Robbins/Robbins India team of 70 field service personnel refurbished and modified the existing equipment, both while in the tunnel and before relaunching the machines in Chickpet station. In addition, the on-site Robbins/Robbins India Team supervised all aspects of TBM excavation, segmental lining, mucking and grout plant operations since the relaunch of the machines for both drives.
“I am particularly proud of being involved in this project, and to support BMRC with the completion of this tunnel drive and bringing the project back on schedule. This is also the first time The Robbins Company has been responsible for the complete scope of operations on a project,” noted Jim Clark, Projects Manager with Robbins India. “One of the biggest challenges we faced was carrying out cutterhead interventions under compressed air in mixed ground conditions that consisted of varying grades of granite in the lower half of the face, and loose, unconsolidated material in the upper section of the face.”
Clark said that on numerous occasions, compressed air would percolate through to the surface, forcing crews to abort cutterhead interventions. They eventually found a solution by pumping a weak mix grout though the mixing chamber, and into the geology surrounding the tunnel face. The weak mix grout stabilized the ground sufficiently so the cutterhead interventions could be completed.
The Robbins crew carried out tunneling operations while the station was being constructed around them to mitigate delays incurred before they took over project operations. The project’s most difficult challenges included a low overburden and consolidated ground along the alignment, and the discovery of several uncharted wells directly on the alignment. In addition, the majority of the tunnel was bored directly beneath buildings constructed upon what is today considered substandard foundations.
This portion of the Phase One Metro tunnels runs from Chickpet to Majestic at Namma Metro. Once Krishna breaks through, the North and South runs of Bengaluru will be connected, allowing service to an average of 40,000 passengers daily. It is being completed under a tripartite agreement between Robbins India, Coastal Projects Limited, the lead contractor, and project owner, Bangalore Metro Rail Corporation Limited. It is anticipated Phase One will be open in its entirety by November, 2016.
On March 29, 2016, North America’s first Crossover TBM broke new ground in Mexico City. The 8.7 m (28.5 ft) diameter Robbins XRE™ –a cross between a rock TBM and an EPB–emerged into an intermediate shaft at Emisor Poniente (TEP) II.
The machine is undergoing some maintenance before continuing on to bore the final 3.2 km (2.0 mi) of tunnel. The customized TBM, for a consortium of Aldesem, Proacon, and Recsa, was chosen based on a number of parameters that included challenging ground conditions below an area to the west of downtown Mexico City.
The tunnel path travels through a mountain with cover as high as 170 m (560 ft), through fault zones and in a section with cover as low as 8.0 m (26.2 ft) above the tunnel crown. Much of the tunnel consists of andesite rock with bands of tuff, and softer material in fault zones as well as an 874 m (2,870 ft) long section in soft ground at the end of the tunnel.
“The geological profile of the project comprises six different lithologies, among them hard rock such as dacite. To get the best operation in both areas required use of dual mode technology such as the Crossover TBM,” said Enrique del Castillo of contractor Aldesem. The 8.7 m (28.5 ft) diameter Robbins XRE (Cross between Rock/EPB) is a design that allows for the TBM to effectively bore in both hard rock and mixed ground.
The machine setup includes a canopy drill and positioner for enhanced ground consolidation, as well as gear reducers to adjust torque and RPM based on ground conditions. The TBM, initially launched in hard rock mode, can be operated in EPB mode later on by switching out the belt conveyor with a screw and converting the cutterhead.
The Robbins Crossover machine began its journey in August 2015, and advance rates picked up quickly. Project records were set in January 2016 after the machine achieved a best day of 42.8 m (140 ft) and a best week of 185.1 m (607 ft). By mid-March the machine had bored through the first of the contact zones, a 30 m wide section of fractured and blocky rock. While the excavation through the contact zone was slow going, progress picked up again in the more competent rock. Final breakthrough is expected in autumn 2016.
Once complete, the 5.8 km (3.6 mi) tunnel will supplement an existing and overtaxed wastewater line built in the 1970s. The deep drainage tunnel will serve to prevent recurrent flooding in Valle Dorado, and will benefit the cities of Cuautital Izcalli, Tlalnepantla, and Atizapan de Zaragoza, an area with a total population of 2.1 million inhabitants.
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