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Author: Robbins
Tunneling in Mixed Face Conditions: An Enduring Challenge for EPB TBM Excavation
EPB TBM tunneling in mixed face conditions—partially in both rock and soil—is inherently problematic for even the most experienced crews. Over-excavation, excessive damage to cutter tools and regular cutterhead interventions are major challenges when negotiating mixed face geology. This paper draws from real field experiences, including successful bores in abrasive rock and soil at India’s Chennai and Bangalore metro projects, to determine the optimal operational parameters for TBMs in such conditions. It also addresses reduction of air losses to facilitate cutterhead interventions under hyperbaric conditions when installation of safe-haven grout blocks is not an option due to surface structures.
7.93 m Open TBM Shotcrete System Improvement and Innovation - Jilin Project, China
In May 2018, a 7.93 m diameter open gripper (Main Beam) TBM completed the 24.3 km long Jilin Lot 3 tunnel under a maximum overburden of 272.9 m. The tunneling operation for the water transfer project, located in northeastern China, achieved a national record of 1,423.5 m in one month despite challenging conditions. This paper presents an improved, innovative shotcrete system for TBM preliminary lining, developed through experience on previous projects. The shotcrete system, along with other structural design elements and a properly developed ground support program, allowed the TBM to bore successfully in variable hard rock and fault zones. The paper discusses how the shotcrete system and structural design increased safety and improved performance in a cost-effective manner. It defines the variables that allowed the TBM to advance at rapid rates and makes recommendations for future types of projects that could benefit from the shotcrete system.
Overcoming Extreme Tunneling Conditions in Vietnam's Longest Tunnel
Vietnam’s Thuong Kon Tum Hydroelectric project is a 17.4 km headrace tunnel that will be the country’s longest once complete. A section of the tunnel was excavated by a 4.5 m diameter Main Beam TBM in granitic rock up to 250 MPa UCS. Started in 2012, the project’s original contractor left due to non-satisfactory performance. In 2016, the contract to refurbish the TBM and excavate the remaining 10.45 km of tunnel was awarded to a joint venture of Robbins and a local contractor. Robbins was fully responsible for the TBM operation, including supplying operational crews. The crew overcame massive granitic rock, fault zones gushing water at 600 l/s, and difficult conditions. In under two years, the TBM advanced from a standstill at 15 percent project completion to 85 percent complete. This paper addresses the refurbishment of the TBM in the tunnel, the work to streamline operation, and challenges faced.
Rescuing and Rebuilding TBMs in Adverse Ground Conditions
Modern TBMs deliver high performance with availability rates that are beyond 90%. The TBM design concepts make the machines highly versatile for employment in varying soil and ground conditions. Machines can now withstand extreme loads and impacts in rough underground environments because of the components made for longtime use. Regular maintenance and planned service is the vital element in prolonging a machine’s life and for high performance and availability. A well-serviced machine provides excellent performance as well as active project safety. Proper operation in variable conditions is also key. For instance, a hard rock TBM may run into zones of swelling rock. The most appropriate method to overcoming the swelling rock is to keep going, avoiding any unnecessary stops. Worn disc cutters that have not been maintained in due course are a prominent example of such avoidable stops, which may result in long downtimes and severe damage to the machine. However with modern and advanced techniques to underground tunneling, rescuing and rebuilding TBMs is possible to save the project. This paper discusses methods and tools for modern TBM service and maintenance using present case studies about TBM rebuilds in extreme project conditions.
Extreme Ingress: Managing High Water Inflows in Hard Rock TBM Tunneling
Managing water inflows is not new to TBM tunneling, but today there are an increasing number of methods and best practices to handle potentially high water inflows efficiently and safely. High volumes of water can be safely contained or managed in hard rock TBM tunneling, but this requires the proper foreknowledge and planning. This paper outlines how machines can be designed ahead of time for expected high water, and how risk can be mitigated during tunneling. It also covers the importance of pre-planning and includes a look into the future of water control methods. Case studies of hard rock tunneling with heavy water inflows are examined, with a focus on New York, USA’s Delaware Aqueduct Repair, the 3.8 km long bypass tunnel below the Hudson River requires excavation through limestone rock at water pressures of up to 20 bar. A unique 6.5 m diameter Single Shield TBM, sealable for high pressure excavation, is boring and lining the tunnel.
Challenging Mixed Face Tunneling at India's Sleemanabad Carrier Canal
India’s Sleemanabad Carrier Canal is a prime example of just how challenging mixed face conditions can be, although other examples exist. The water transfer tunnel is being bored using a 10 m diameter hybrid-type rock/EPB TBM. However, in 6.5 years of tunneling the machine had only advanced 1,600 m. Commercial issues for the original contractor stalled the project frequently, while ground conditions turned out to be even more difficult than predicted. Low overburden of between 10 and 14 m, combined with mixed face conditions, transition zones and a high water table restricted advance rates. The TBM manufacturer mobilized a team to refurbish the TBM and within a period of 6 weeks a team of 180 people had been deployed to take over all aspects of tunneling and support activities. Production rates improved dramatically as the TBM advanced more than 400 m in four months. This paper discusses the problems faced and the methodology that enabled good advance rates in highly variable mixed face conditions.
TBM DiGs 2019
Event Name: Tunnel Boring Machines in Difficult Grounds (TBM DiGs)
Dates: November 14-15, 2019
Location: Golden, Colorado
Venue: Sheraton Denver West Hotel
Booth No: 12
The 2019 Tunnel Boring Machines in Difficult Grounds (TBM DiGs) 4th International Conference will be held in Golden, Colorado, USA from November 14-15. Stop by our booth to speak with our international experts or learn more at our two technical presentations:
Thursday November 14, 3:00 PM
Technical Session IV: New Technology and Extreme Tunneling
Effective design and assembly of a large diameter slurry TBM in hard rock
conditions presented by Matt Greger
Friday November 15, 10:50 AM
Technical Session VI: Hard Rock Tunneling Challenges
TBM tunneling in extremely hard rock presented by Sindre Log
Robbins EPB caps 62 km of Tunneling with Final Breakthrough at Emisor Oriente
On May 23, 2019, a celebration was in order: The last of six 8.93 m (29.3 ft) diameter EPBs had completed excavation at Lot 4 of Mexico City’s Túnel Emisor Oriente (TEO), a feat marking the completion of ten years and 62.1 km (38.6 mi) of tunneling. “We are proud of having successfully finished the excavation, despite all the adversities we faced, such as large inflows of water, hydraulic loads and constant changes in geology. We solved these by adapting the excavation mode according to each type of geology found,” said Hector Arturo Carrillo, Machinery Manager for Lot 4 contractor Carso Infraestructura y Construcción (CARSO).
Despite multiple challenges, the operation achieved a project record of 30 m (98 ft) in one day, and a high of 528 m (1,732 ft) in one month. It’s a result that, Carillo says, has much to do with the continuous conveyor system being used for muck removal: “It should be noted that our advance rates were achieved thanks to the great Robbins conveyor design. The tunnel conveyor was composed with elements such as the booster, vertical belt, curve idlers, and advancing tail piece, as well as elements on the surface. Personally, I think it is a great, admirable system that has helped us achieve the TBM’s performance.”
The breakthrough was the latest and greatest milestone for an urgently needed wastewater project that spanned some of the most difficult geology ever encountered by EPBs. The 10.2 km (6.3 mi) long Lot 4, running from Shaft 17 to Shaft 13 at depths of up to 85 m (280 ft), included sections of basalt rock interspersed with permeable sands with high water pressure. “Our machines had to go through the worst geology, but they were designed for it,” said Roberto Gonzalez Ramirez, General Manager for Robbins Mexico, of the three Robbins EPBs and continuous conveyor systems used on Lots 3, 4, and 5 of the project.
All of the machines were designed for water pressures from 4 to 6 bars, with mixed ground, back-loading cutterheads to tackle variable ground conditions. High pressure, tungsten carbide knife bits could be interchanged with 17-inch diameter carbide disc cutters depending on the geology. Other features included man locks and material locks designed to withstand pressures up to 7 bar, a redesigned bulkhead, and Hardox plates to reinforce the screw conveyors as well as removable wear plates to further strengthen each screw conveyor flight. The rotary union joint was redesigned to improve cutter change times during cutterhead interventions, while a new scraper design offered more impact resistance in mixed ground conditions with rock.
The Lot 4 TBM was assembled in the launch shaft no. 17 and commissioned in August 2012, with the bridge and all the back-up gantries at the surface. Two months later in October 2012, after advancing 150 m (490 ft), the machine and its back-up were completely assembled in the tunnel. One month later, the continuous conveyor system was installed and running.
After 405 m (1,328 ft) of excavation, the presence of rocks, scrapers, parts of the mixing bars and other wear materials in the excavated muck prompted a cutterhead inspection. With high pressure up to 3.5 bars, it was determined that a hyperbaric intervention was necessary, and on June 2nd, 2013 the first hyperbaric intervention through an EPB in a tunnel was performed in Mexico. However, these interventions were done at great cost and proved to be time-consuming. After about 50 hyperbaric interventions the remainder of the project’s interventions were done in open air. “The interventions carried out in atmospheric mode were the biggest challenge. The great influx of water tested the limits, because we were excavating on a decline. In all of these interventions we had to implement a double pumping system, at both the TBM and the shaft,” said Carrillo. Despite the challenges of pumping water at volumes up to 180 l (48 gal) per second and cleaning fines from the tunnel each time the operation was performed, atmospheric interventions were still lower in cost and quicker than those done at hyperbaric pressure.
Even when conditions were tough, Carrillo felt his operation was well-supported by Robbins Field Service: “Robbins were always present giving ideas and contributing all their experience to solve the problems. One of the most recent examples, almost at the end of this project, was where the machine encountered a blockage to the shield and could not move forward. It became necessary to implement the exceptional pressure hydraulic system, reaching a pressure range of 596 bar on 28 thrust cylinders. Robbins personnel helped us during all that time and we were able to get through it.”
When the Going Gets Tough: Thuong Kon Tum Hydroelectric Project
Take a trip with Robbins to the scenic Thuong Kon Tum project in Vietnam where a 4.5 m Main Beam TBM has completed boring. After being left in high humidity and groundwater for 14 months, it was up to Robbins and contractor CC47 to step in and turn this project around. Watch the video for an inside look at how Robbins crews tackled multiple fault zones and major water influxes, all while maintaining the required advance rates.
Robbins TBM breaks through nearly One Year Early in Nepal
In April 2019, a Robbins Double Shield TBM defied the notoriously difficult geology of the Himalayas to break through about one year ahead of the overall project schedule, and seven months ahead of the TBM tunneling schedule. Nepal’s first tunnel boring machine, at 5.06 m (16.6 ft) diameter, achieved over 1,000 m (3,300 ft) monthly advance on two separate occasions and averaged over 700 m (2,300 ft) per month over the course of tunneling. The machine completed the 12.2 km (7.5 mi) Bheri Babai Diversion Multipurpose Project (BBDMP) for the Government of Nepal’s Department of Irrigation (DOI) and contractor China Overseas Engineering Group Co. Ltd. Nepal Branch (COVEC Nepal).
The large and well-attended ceremony featured a speech by the Prime Minister of Nepal KP Sharma Oli, where he praised the project and its success for the future of TBM projects in the country. “It is not just that new technology has entered Nepal; it is a matter of great gain. The government has plans to execute various other multipurpose projects such as the Sunkoshi-Marin Diversion Project.”
The machine’s completion of the tunnel in just 17 months came nearly a year ahead of the DOI’s deadline for completing the tunnel of March 28, 2020, with the contractor’s schedule being more aggressive. “The breakthrough ceremony was great. We’re proud that we finally did it and were ahead of the overall schedule by almost one year,” said Mr. Hu Tianran, Project Manager for COVEC.
When the BBDMP was fast-tracked as one of the country’s “National Pride Projects” feasibility studies showed that Drill & Blast excavation of the tunnel could take as long as 12 years. The DOI needed a faster option, and they found it in TBMs. They began working with local Robbins representatives MOSH Tunnelling to bring what would be the first Nepalese TBM ever into the country. The process for the DOI to acquire funding for the project and select a contractor through international competitive bidding took seven years, spanning from 2007 to 2015, when project commencement officially began. “We are proud to have introduced TBM technology successfully,” said Prajwal Man Shrestha, Robbins Representative in Nepal with MOSH Tunnelling. “Despite roadblocks and resistance along the way, we eventually introduced this technology, which broke all tunneling records in Nepal. The country has received international attention and contractors and developers from around the world are now considering Nepal for future TBM projects.”
The tunnel is located in the Siwalik Range, part of the Southern Himalayan Mountains, where geology consists of mainly sandstone, mudstone, and conglomerate. “Using the TBM method instead of the conventional drill and blast method was the key factor for the success of this project. It has set a good example for the implementation of a large number of similar tunnels in Nepal’s water/energy/transportation projects in the future. There are promising prospects in the application of TBM technology in Nepal in my point of view,” said Mr. Hu.
To ensure the best TBM performance and to prevent downtime, machine maintenance occurred daily at a fixed time. Geological engineers analyzed the ground conditions twice daily to adjust the tunneling parameters if needed. The careful plan of excavation worked: The knowledgeable COVEC team traversed a risky fault zone, the Bheri Thrust at the 5.8 km (3.6 mi) mark, with no problems, and overcame a stuck TBM shield at another point with a bypass tunnel constructed in just five days. To cope with the conditions, the Robbins machine was designed with Difficult Ground Solutions (DGS), a suite of features including enhanced probe drilling and forepoling capabilities, as well as a stepped machine shield and smooth cutterhead design to avoid becoming stuck in collapsing ground.
The secret to the machine’s rapid excavation is good planning, says Mr. Hu: “As the contractor and the equipment supplier jointly carried out in-depth research and detailed design in the preliminary stage, the TBM was matched to the various conditions of the project. Together with the advantages in hard rock construction that The Robbins Company has, we made an excellent performance of the TBM on this project.”
Once the BBDMP is operational, it will irrigate 51,000 hectares of land in the southern region of Nepal, and provide 48 MW annual generating capacity. It will divert 42 cubic meters (1,500 cubic feet) of water per second from Bheri River to Babai River under a head of 150 m (490 ft) using a 15 m (49 ft) tall dam, providing year-round irrigation in the surrounding Banke and Bardia districts. The estimated annual benefit in Nepalese Rupees is $2.9 billion for irrigation, and $4.3 billion for hydropower, making a total of NPR $7.2 billion (approx. USD $64 million) in benefits once the project becomes active.