Project Categories: Main Beam TBM
The Manapouri Hydropower Station is the largest hydropower station in the country and supplies 5100 GWh of electricity annually. In 1997, the project owners, Electricity Corporation of New Zealand (ECNZ), proposed an expansion of the hydropower station from its then output of 585 MW. The plan included a second 9.6 km (6.0 mi) long tailrace tunnel connecting the underground power station at Lake Manapouri to its discharge point in Doubtful Sound.
In 1997 ECNZ awarded the construction contract, worth US $85 million, to a Joint Venture of Fletcher Construction (New Zealand), Dillingham Construction (U.S.), and Ilbau (Austria). The joint venture awarded the contract to Robbins for one 10.05 m (33.0 ft) diameter Main Beam TBM to excavate the tunnel.
The tunnel passed through Paleozoic metamorphic and igneous rocks. The metamorphic rocks included gneiss, calcsilicate, quartzite, and intrusions of gabbro and diorite. The tunnel geology also included five sub-vertical fault zones with high potential for water inflows.
Robbins designed the 10.05 m (33.0 ft) diameter TBM for the mixed face hard rock conditions in the tunnel. The Robbins design was then built by Kvaerner-Markham (U.K.) and shipped to the job site. The cutterhead featured sixty-eight 17 inch (432 mm) cutters with loading from either the front or back. Eleven two-speed electric motors powered the cutterhead with 3,463 kW (4,642 hp), generating a torque of 9,859,400 N-m (7,271,919 lb-ft). The 470 m (1,542 ft) long back-up system, built by Rowa Engineering, included a secondary rock-bolting station and a robotic shotcrete station.
The Robbins TBM began boring in June 1998 and finished in 33 months. The tunnel progress was divided into four sections, or reaches. During Reach 1, about 1.8 km (1.1 mi) into the bore, the machine experienced few problems. During Reach 2 (spanning 2.4 km (1.5 mi)), the machine encountered heavy water inflows through the fault lines. These inflows reached proportions of 1,300 liters (343 gallons) per second and pressures up to 7.2 MPa (1.0 ksi). These high volumes of inflow necessarily slowed progress throughout Reach 2. Geological conditions improved in Reach 3 (spanning 2 km (1.2 mi)), and by Reach 4 (spanning the final 3.2 km (2.0 mi)) the machine was progressing at a substantial rate.
Despite setbacks due to water, the Robbins TBM suffered no major breakdowns and availability remained high throughout the dig. In addition, total TBM spare parts usage was far below the industry average for this type of job.
The Kárahnjúkar Hydropower Project created the Kárahnjúkar Power Plant to provide 4600 GWh of electricity annually to a nearby aluminum smelting plant. Three dams feed the main Hálslón reservoir and several other dams join the outflow in a combined headrace tunnel to an intake. The intake water travels to the powerhouse through two steel-line vertical shafts and exits from a tailrace tunnel that empties into the Jökulsá i Fljótsdal River.
Project owner Landsvirkjun awarded the construction contract for the hydroelectric project to the Iceland branch of Impregilo S.p.A. The contractor awarded the contract to Robbins for three Robbins Main Beam High Performance TBMs for three lengths of tunnel.
The machines began boring between April and September 2004 in basalt, moberg, and pillow lava geology up to 300 Mpa (44,000 psi) UCS. A number of fault lines and water inflows were encountered during boring, though the machines made good progress.
All three TBMs were the first ever machines designed with back-loading cutterheadsfor 19” cutters. The successful design increased cutter life and reduced the time needed for cutter changes. All of the TBMs were equipped with probe and roof drilling capabilities and were specially designed for the ground conditions. The cutterhead designs featured rock deflectors to protect the cutterhead from fractured and blocky ground, as well as abrasion-resistant wear plates and carbide buttons to bore in abrasive rock.
Main Headrace Tunnel
By June 2006 the machines had made good progress despite difficult geologic conditions in the tunnels. TBM 1 finished its drive on September 9, 2006 after achieving impressive advance rates with a best month of 864.6 m (2,755 ft) in March 2006. On the same day, TBM 2 tied a world record in its size class after excavating 92 m (302 ft) in 24 hours. The TBM tied the record with another TBM that bored on the Epping to Chatswood Rail Link. TBM 2 finished its initial drive in Fall 2006 and was then disassembled and transported to bore an additional 8.7 km (5.4 mi) long section of the Jökulsá Diversion Tunnel in 2007. The third TBM finished its main tunnel drive on December 5, 2006. All of the TBMs achieved impressive monthly advance rates despite troublesome rock conditions.
Jökulsá Diversion Tunnel
The Jökulsá Diversion Tunnel adds to the water supply capacity of the powerhouse by connecting the Ufsarlón Reservoir to the main headrace tunnel. Work began in April 2007 and finished in April 2008. During the 8.7 km (5.4 mi) drive, TBM 2 continuously turned in record-breaking performances, beating its own record in June 2007 by excavating 106.1 m (348.2 ft) in 24 hours.
In August 2007, the machine achieved the feat again by excavating 115.7 m (380 ft) in 24 hours and 428.8 m (1,400 ft) in one week. The machine excavated at consistently high rates and finished its bore on schedule.
The Sydney Urban Train System was extended with the addition of The Epping to Chatswood Rail Link. The extension consists of two twin parallel tunnels 12.5 km (7.7 mi) in length. The New South Wales Government awarded the contract for the project to the Theiss Hochtief Joint Venture (THJV), a collaboration of Australian and German construction firms.
In 2002, THJV awarded the contract to Robbins to build two 7.2 m (23.6 ft) diameter Main Beam TBMs. The TBMs excavated the two tunnels in two sets of drives beginning at Delhi Road Station (about the center of the tunnels), and advanced at impressive rates throughout the project.
Both tunnels pass through Hawkesbury sandstone and deposits of Ashfield shale. One fault line exists along the route, near Macquarie Park Station, about 2 km (1.2 mi) into the first drive.
TBMs and Conveyors
The two Main Beam TBMs had a cutterhead power of 2300 kW (2957 hp) and a maximum thrust force of 1400 metric tons (1500 US tons). Robbins designed both machines with innovative features for the project. A unique rolling back-up system allowed concrete roadbed to be poured while the machines excavated the tunnels. This construction method enabled the use of rubber-tired vehicles during excavation and the rapid installation of train tracks.
Robbins also designed custom conveyors consisting of five integrated systems: two horizontal conveyors, two vertical conveyors, and one stacker conveyor. The crown-mounted horizontal conveyors ran for 6 km (3.7 mi) with more than 80 percent in curves.
The TBMs began boring the tunnels in August and September 2003. Both machines broke through the tunnel at Epping in July 2004. Boring began a second time in November 2004 and the machines broke through at Chatswood in June and July 2005. During the excavation, one machine set an advance rate world record for its size class by boring 92 m (302 ft) in one day. Their best week was 368 m (1,207 ft) and the average advance rate for the project was 200 m (656 ft) per week. The TBMs ran into few problems and were available for 80% of the total project time.
The New Wuchieh Diversion Tunnel is part of a water transfer system that feeds into the Sun-Moon Lake Hydraulic Power Plant, one of the largest single power sources in Taiwan. Project owners Taipower commissioned the new 6.3 km (3.9 mi) long tunnel after the original Wuchieh Diversion Tunnel was found cracked and degraded after 70 years of service.
The tunnel stretches from its source at Sun-Moon Lake to the intake structure at the hydraulic power station. The new tunnel, along with another water transfer tunnel feeding into Sun-Moon Lake, will increase the output of the power plant to 7,600,000 KWh annually.
Taipower awarded the construction contract for the new diversion tunnel to Kumagai Gumi Co. Ltd. The contractor chose a 6.2 m (20.3 ft) diameter Robbins Main Beam TBM for the project.
The tunnel passes through quartzite, sandstone, and slate. There are also some areas containing broken rock.
Robbins rebuilt a used 6.2 m (20.3 ft) diameter Main Beam TBM for the New Wuchieh Tunnel. The refurbished TBM featured 17 inch (432mm) wedge-lock cutters and 1,890 kW (2,534 hp) of cutterhead power. The 380 tonne (420 ton) machine also generated a maximum torque of 1,774,415 N-m (1,307,550 lb-ft) at the cutterhead.
The TBM began boring in July 2000 and finished in 24 months on June 7, 2002. The TBM’s average monthly advance was over 400 m (1,312 ft) and it acheived a best month of 650 m (2,133 ft). After half of the tunnel had been excavated some broken ground was encountered and tunnel linings such as ring beams, mesh, and shotcrete were applied. Some portions of the tunnel were also lined with cast iron segments for additional support.
In September 2001, Typhoon Toraji hit the area and flooded the site with mud, water, and rocks. Some of the shipping containers containing spare parts, cutters, and workshops were completely submerged. Fortunately, the flood level stayed below the working tunnel level and operations were merely delayed. The remainder of the excavation went smoothly and the finished tunnel was celebrated as the first tunnel ever completed solely by TBM in Taiwan.
The Little Calumet Leg Tunnel is the final element in Phase 1 of Chicago’s long-running Tunnel and Reservoir Project (TARP). The project involves storm water storage, reservoirs, and feeder tunnels that have greatly improved water quality in Chicago-area Rivers. The Little Calumet Leg is part of a longer TARP tunnel system that prevents combined sewer overflows from spilling into the Little Calumet River.
In 2002, the project owner, Metropolitan Water Reclamation District of Greater Chicago (MWRDGC), awarded the construction contract to the Jay Dee/Affholder Joint Venture. The two contractors split the work, with Jay Dee responsible for surface works, shallow tunnels, and shafts. Affholder was responsible for deep tunnels and TBM boring. The joint venture chose a 5.56 m (18.2 ft) diameter Robbins Main Beam TBM to bore a 12.8 km (8.0 mi) section of tunnel.
The rock consisted of Silurian age dolomitic limestone with an Unconfined Compressive Strength (UCS) of 97 – 241 MPa (14 – 35 ksi). The limestone had few faults and was considered good tunneling ground.
Robbins refurbished the Main Beam TBM specifically for the project. The machine featured 39 wedge lock 19 inch (483 mm) cutters and a cutterhead thrust of 9,101 kN (2,044,050 lb). The cutterhead was driven by seven 335.6 kW (450 hp) AC electric motors that supplied 2,350 kW (2,975 hp) of power to the cutterhead. The machine also generated 1,882,877 N-m (1,389,705 lb-ft) of cutterhead torque.
Muck was transported by a Robbins conveyor system, including an an advancing horizontal conveyor, S-type vertical conveyor, surface conveyor, and stacker conveyor.The muck was transported from the bridge conveyor on the back-up to the main horizontal conveyor. A conveyor with self-adjusting curve idlers was necessary for most of the tunnel in order to negotiate tight curves.
Excavation of the tunnel began on February 13, 2003. The tunnel was driven in two sections from a central launch shaft with an initial bore of 6.1 km (3.8 mi). After the initial drive, the head cutterhead support were hoisted out of the reception shaft. The rest of the machine was then reunited with the head and cutterhead support and taken back through the tunnel for the second 6.7 km (4.1 mi) drive.
The machine executed both drives flawlessly. The TBM broke the world record for best advance in a single eight-hour shift at 45.75 m (150.1 ft), best advance in a day at 116.7 m (382.9 ft), and best advance in a week at 474.7 m (1,557 ft). It also broke the record for most rock excavated in 24 hours at 2,836.55 cu m (3,710 cu yd). The TBM holed through in February 2004.
The Lesotho Highlands Water Project, a cooperative effort between Lesotho and South Africa, seeks to rejuvenate South Africa’s heavily populated and arid Gaucheng Province. It’s first phase began in 1992 and involved construction of the 180 m (590.5 ft) high Katse Dam, part of the Orange (Sequ) River system in Lesotho. The dam, finished in 1998, supplies water to South Africa’s Vaal river system via a water transfer tunnel and two delivery tunnels.
The two countries awarded the construction contract to the Lesotho Highlands Project Contractors (LHPC), a joint venture of Spie Batignolles (France), LTA Ltd. (South Africa), Ed Zublin AG (Germany), Balfour Beatty Ltd. (U.K.) and Campenon Bernard (France).
In 1991, LHPC contracted The Robbins Company to supply three new tunnel boring machines (TBMs) for the longer water transfer tunnel and one rebuilt TBM for the delivery tunnel. Two other TBMs from Atlas Copco and Wirth also participated in the dig.
The route of the water transfer tunnel passes through basaltic flows of volcanic rock. The area also includes some blocky conditions along faults and within doleritic dykes.
The south delivery tunnel passes through sedimentary rock, including the Clarens formation. This formation consists of horizontally layered siltstone and sandstone with occasional doleritic dykes and layers of claystone.
TBMs and Conveyors
Robbins supplied two new 5.03 m (16.5 ft) diameter Main Beam TBMs to excavate the 45.6 km (28.3 mi) water transfer tunnel. These machines were equipped with 35 disc cutters, all 17 inches (432 mm) in diameter. Both machines were designed with back-loading cutterheads which allowed for later installation of 19 inch (483mm) diameter cutters. The TBMs featured five 315 kW (422 hp) water-cooled motors that supplied 1,575 kW (2,111 hp) to the cutterhead.
An additional 5.18 m (17.0 ft) diameter TBM was deployed on the south delivery tunnel after being refurbished by Harrison Western Corp. The refitted Main Beam TBM featured 37 cutters all 17 inches (432mm) in diameter. The machine was powered by six 185 kW (248 hp) motors that provided 1,110 kW (1,489 hp) to the cutterhead.
Robbins built the 5.0 m (16.4 ft) diameter Mark-15, an open hard rock TBM, with 4 center cutters, 22 face cutters, and 8 gauge cutters, all 17 inches (432 mm) in diameter. Three 560 kW (751 hp) motors supplied 1,680 kW (2,253 hp) to the cutterhead and produced a torque of 1,588 kNm (1,171,523 lb-ft).
All four of the TBMs supplied were equipped with rock drill and trailing back-up systems.
The first Main Beam TBM began boring the 17.4 km (10.8 mi) transfer tunnel section in June 1992 and set world tunneling records for its diameter class. It achieved a best day of 86.3 m (283.1 ft), a best week of 399.8 m (1,311.7 ft), and a best month of 1,344.3 m (4,410.4 ft). The TBM set these records despite challenging geology along the tunnel route. Rock jointing necessitated rock support measures, especially at the beginning of the drive. This support took up 24 percent of the total job time. The machine’s average rate of penetration was 4.59 m (15.1 ft) per hour and its average advance rate was 33.4 m (109.6 ft) per day. It broke through in September 1994.
The second Main Beam TBM began its 17.3 km (10.7 mi) drive in July 1992. It achieved an average rate of penetration of 4.1 m (13.5 ft) per hour while maintaining average advance rates of 27.6 m (90.6 ft) per day and 620 m (2,034 ft) per month. The TBM turned in a superior performance with a best day advance of 66.8m (219.2 ft), a best week of 325 m (1,066 ft) and a best month of 1,221 m (4,006 ft).
The Mark 15 also began boring the water transfer tunnel in May 1992 and achieved breakthrough in September 1994. Difficult rock conditions slowed the boring and decreased the machine’s advance rate. Its best day was 62.9 m (206.4 ft), its average rate of penetration was 3.9 m (12.8 ft) per hour, its best week was 289 m (948 ft), and its best month was 987 m (3,238 ft). Rock support (i.e., bolting, rock straps, mesh, and concrete) took up about 15 percent of the total job time.
On October 13, 1994, the final Robbins TBM broke through ventilation shaft #3, completing excavation of the water transfer tunnel.
The refurbished Main beam TBM for the south delivery tunnel began boring in February 1992 and broke through 20 months ahead of schedule in August 1993. The TBM attained this feat in three drives of 2.1 km (1.3 mi), 5.2 km (3.2 mi), and 5.7 km (3.5 mi). Its average rate of penetration was 3.86 m (12.7 ft) per hour or 39.9 m (130.9 ft) per day (in three eight-hour shifts). The best day for the machine was 82 m (269 ft), the best week was 384 m (1,259.8 ft), and the best month was 1,324.4 m (4,345.1 ft).
The Chattahoochee Sewer Tunnel is part of a project that meets increasing wastewater capacity needs in East Cobb County. The tunnel provides flow equalization to the RL Sutton Water Reclamation Facility and curbs potential wastewater overflows due to the growing population in Cobb County.
In 2000, project owner Cobb County Water Systems awarded the construction contract to the Gilbert-Healy Joint Venture. The contractors selected two 5.58 m (18.3 ft) diameter Robbins TBMs to bore a 14.6 km (9.1 mi) long section of the 15.3 km (9.5 mi) tunnel.
The geology of the Atlanta area consists of medium grade metamorphic rocks with some granitic rocks. Much of the rock includes gneiss, mica, and schist with an Unconfined Compressive Strength (UCS) of 150 – 230 MPa (22 – 33 ksi). These rocks have undergone intense weathering and erosion with some regional uplifting.
A key characteristic of the region is a thick layer of residual soil with a transition zone of soil and fractured rock underneath it. This geology posed groundwater problems for the tunnel because the soil zone is porous and water leaks into the fractured transition zone below. Faults in the bedrock can thus have very large water inflows.
Tunnel designers grappled with the difficult geology by pre-testing the rock along the tunnel area using packer tests. A section of rock was bored out and water was injected into the bore hole under pressure. In this way, bedrock permeability could be tested.
Robbins provided one new and one rebuilt TBM for the tunnels.
The new TBM for the South tunnel featured 19 inch (483 mm) cutters and generated up to 12,144 kN (2,730,000 lb) of cutterhead thrust. The machine was also capable of creating a cutterhead torque up to 2,082,885 N-m (1,536,257 lb-ft).
The rebuilt TBM for the North tunnel was completely redesigned for the project. The machine included 19 inch (483 mm) cutters and the same thrust and torque capacities of the South tunnel TBM.
Each machine was fitted with three rock drills — two behind the cutterhead to install rock bolts as well as one for drilling probe holes and pre-grouting holes to seal off any water inflows.
The conveyors, provided by Robbins, were continuous conveyors that ran along the tunnel as well as in the access shaft.
The TBM in the South tunnel began boring at the Elizabeth Lane shaft near the south end of the tunnel in August 2001 and finished in October 2002. The TBM experienced few problems and advanced 650 m (2,133 ft) in its first month of boring.
The TBM in the North tunnel began boring in November 2001 and finished in December 2002. It also experienced few problems and completed its task on time and within budget.
Pumping facilities in both the North and South Tunnels were capable of removing up to 18,000 liters (4,750 gallons) per minute, although the expected water inflows were much smaller — up to 1,800 liters ( 475 gallons) per minute. The pumping systems were precautionary and sufficient to control the water inflows encountered.
The San Manuel Mine tunnel was developed to extend the life of the mine in Arizona. It is one of the largest underground mines in the world, but projections before the tunnel was built estimated its reserves would be depleted by 1998. The tunnel allowed the development of the Lower Kalamazoo orebody, in the vicinity of dwindling orebodies that had already been tapped.
The project owner, Magma Copper Company, awarded the construction contract to a joint venture of Frontier-Kemper Constructors Inc. and Deilmann-Haniel GmbH. The joint venture chose a 4.6 m (15.1 ft) Main Beam Robbins TBM to bore the mining tunnel.
The Lower Kalamazoo geology is quite complex, consisting of orebodies, porphyry, and granodiorite. The tunnel route includes numerous faults and dikes — it passed through the San Manuel fault six times and the Virgin Fault five times. Much of the rock had been weakened by hydrothermal metamorphosis.
Robbins designed the new hard rock Main Beam TBM specifically for the geological conditions. The 4.6 m (15.1 ft) diameter cutterhead could reverse rotational direction to prevent jamming when it encountered fractured rock. The machine also featured thirty-three 17 inch (432 mm) backloading disc cutters for greater safety.
The TBM had an installed power of 1,260 kW (1,690 hp) and could generate a cutterhead thrust of 8,558 kN (1,924,000 lb). A torque of 2,969,911 N-m (2,190,494 lb-ft) could also be reached.
Additions to the TBM included roof drill fixtures, and a ring beam erector.
The back-up system extended 120 m (394 ft) on 16 rail-mounted desks behind the TBM. The unit housed electrical supply and control systems, the hydraulic power pack, and auxiliary equipment.
Muck was loaded onto a back-up conveyor and then transported by three trains of muck cars. The track also included a California switch.
Boring began on November 11, 1993 in a specially prepared concrete chamber. There were no major problems crossing the San Manuel Fault, but wet clay at the Virgin Fault resulted in slow boring. The TBM continued to encounter soft clay and crumbling ground.
Robbins and the contractors added several features to the machine to optimize performance. They increased muck flow through the cutterhead, increased cutterhead torque, and added additional rock support to the tunnel. After the initial modifications, TBM performance greatly improved. Daily advances tripled to 22.94 m (75.3 ft) per day for the first 15 months of boring and the machine averaged more than 30 m (98.5 ft) per day for the rest of the project.
The TBM stayed on schedule and holed through on December 4, 1995.
The 275 KV Cable Tunnel on Hong Kong Island provides a transmission line from a power station at nearby Lamma Island. Electricity travels through the 5.4 km (3.3 mi) long tunnel via six 275 KV cables to increase power supply to residents on the eastern side of Hong Kong Island.
The Hong Kong Electric Co., owner of the project, contracted Nishimatsu Construction Co. to build the tunnel. Nishimatsu chose a 4.8 m (15.8 ft) diameter Main Beam Tunnel Boring Machine (TBM) for the project, the first ever TBM to bore in Hong Kong.
The cable tunnel passes through three mountains and beneath catch-water facilities of the Tai Tam Reservoir five times along the tunnel route. The geology consists of a granite and quartz mixture with some volcanic rocks holding hard tuffs and lavas. Hong Kong granites are considered among the world’s hardest.
Robbins equipped the high-performance TBM with thirty-two 19 inch (483 mm) disc cutters, a cutterhead thrust capacity of 10,291 kN (2,313,531 lb), and a cutterhead drive of 2,275 kW (3,050 hp). The machine’s design included adjustable side supports and hydraulic roof shields to stabilize the cutterhead and aid cutter tracking. A long boring stroke maximized boring time and kept regrips to a minimum.
Boring on the 5.4 km (3.3 mi) long tunnel began in March 1991. The TBM advanced at a grade through granite. Initial water inflows required concrete invert section and fissure grouting to be applied along tunnel walls.
A section of the tunnel on the Wong Nei Chung fault line caused some difficulties. Shattered and weathered granites required rock support and advance probe drilling which slowed the boring process. Regardless, TBM performance remained high throughout the drive with only 55 shift hours lost to delays.
The machine broke through the tunnel in October 1991, only 53 working weeks after tunneling began. The TBM’s average advance rate was 100 m (328 ft) per week and its average rate of penetration was 2.8 m (9.1 ft) per hour.
The Seymour-Capilano Water Filtration Project seeks to improve the filtration of drinking water in Vancouver, British Columbia. The completed filtration system will clean 1.8 billion liters (475.5 million gallons) of water a day and will lower the water turbidity (cloudiness) and micro-organism levels to meet federal standards for drinking water.
The project calls for twin tunnels, each 7.2 km (4.5 mi) long. The tunnels will transport untreated water from the Capilano reservoir to a filtration plant in the Lower Seymour Conservation Reserve and will return treated water to the Capilano reservoir for public consumption.
In 2004, the project owner, Greater Vancouver Regional District, awarded the construction contract to Germany-based Bilfinger Berger. The contractor chose two 3.8 m (12.5 ft) diameter Main Beam Robbins TBMs to bore the tunnels in intrusive granitic rock with strengths of 200 – 265 MPa (29 – 38 ksi).
Each TBM is outfitted with probe drills, to be used for the entire length of the tunnels. The probe drills probe ahead 40 m to check for pockets of underground water and verify the geology. The tunnel is unlined during excavation, but each machine is equipped with a ring beam erector to install full or partial beams depending on the geology.
The first of the two TBMs was delivered on May 18, 2006 and began boring on July 1, 2006. The second Robbins TBM was launched from the same shaft. Both machines were assembled in very short (60.5m/200ft and 70.5 m/230 ft) starter tunnels at the bottom of the 180 m (591 ft) shaft. Because of the short tunnel lengths, both TBMs excavated with their back-up systems partially constructed until they bored ahead 200 m (650 ft). The TBMs were assembled with only 11 decks of their respective 35 deck back-up systems.
After difficult ground conditions halted both TBMs for more than a year, excavation restarted in April 2009. New contractor, Frontier-Kemper/J.F. Shea/Aecon, restarted the machines and achieved advance rates of up to 29 m (95 ft) per day.
On November 4, 2010, the final breakthrough for the second of two Robbins TBMs capped more than two years of hard rock tunneling over a four year period. Frontier-Kemper successfully dealt with rocky conditions and some faulting using a program of rock bolts, wire mesh, and steel sets. Rock support varies from bare rock in good ground (Class I), to steel sets every 760 mm (30 in) in Class V poor rock.
The second Robbins TBM holed through at an angle into the other tunnel, where a chamber will now be built to conduct raise drilling of the 270 m (885 ft) deep Capilano shaft.
- Use of a Tunnel Boring Machine on Nepal’s First and Second TBM-Driven Tunnels
- Robbins Double Shield Sets Record in Nepal
- Final Breakthrough at Bahçe-Nurdaği Railway
- Record-Setting Large Diameter Mixed Ground Tunneling in Turkey: The Eşme-Salihli Railway Tunnel
- Lessons Learned During Excavation of the Incredibly Challenging Yin Han Ji Wei Water Diversion Tunnel