Author: Robbins

Cutting Edge 2018

Event Name: Cutting Edge 2018
Dates: October 29-31, 2018
Location: Atlanta, Georgia
Venue: Lowes Atlanta Hotel

The Robbins Company is heading south for Cutting Edge, which is being held this year in Atlanta, Georgia from October 29 through 31. Visit table 7 between presentations, including a panel discussion with Robbins President Lok Home and a presentation by Robbins Director of Engineering Brad Grothen, to discuss current projects and tunneling techniques.

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Difficult Ground Brochure

Even in the most well-planned projects, tough conditions can come up. Everything from squeezing ground to fault zones to sudden inflows of water and mud can delay your project significantly. Find out how our field service teams have dealt with the most challenging
conditions worldwide.

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Nepal’s First TBM bores 1,000 Meters in One Month

Nepal’s first tunnel boring machine, a 5.06 m (16.6 ft) diameter Robbins Double Shield, is living up to the nation’s high expectations. The TBM, supplied in summer 2017 for the Bheri Babai Diversion Multipurpose Project (BBDMP), recently bored over 1,000 m (3,280 ft) in one month and has been averaging an impressive 800 m (2,630 ft) per month. The project is owned by the Government of Nepal’s Department of Irrigation (DOI) and operated by contractor China Overseas Engineering Group Co. Ltd. Nepal Branch (COVEC Nepal).

The decision to use a TBM for the BBDMP project—designated by the government as one of Nepal’s 11 National Pride Projects—was a departure for a nation where drill & blast has long been the preferred tunneling method. Early studies done on the tunnel path predicted that drill & blast excavation of the 12.2 km (7.5 mi) tunnel would take close to 12 years to complete.  The tunnel is located in the Siwalik Range, part of the Southern Himalayan Mountains, where geology consists of mainly sandstone, mudstone, and conglomerate.

Mr. Wang Wu Shui, General Manager for COVEC Nepal, cited several factors that have contributed to the good advance rates so far, “In China, there is a proverb about TBM construction: ‘geology is the premise, equipment is the foundation, and talents are the key’. The great advance rates achieved at present mainly lie in preliminary planning, process control, and professional construction personnel.” Shui added that technical training and guidance are provided for each position so that all personnel can fully understand their job and team responsibilities. If unforeseen circumstances arise and there is no operator for a certain position, others have enough training to fill the role.

To ensure the best TBM performance and to prevent downtime, machine maintenance occurs daily at a fixed time. Geological engineers are sent to analyze the ground conditions twice daily so that construction personnel can adjust the tunneling parameters and prepare for auxiliary measures if geological changes are predicted.

The ground conditions during the record-setting month consisted mainly of sandstone and mudstone, but that is set to change.   At about the 5.8 km mark, the machine will encounter a major fault zone known as the Bheri Thrust. Clay and water ingress are expected throughout the fault, which is about 400 to 600 m wide.

COVEC Nepal are prepared for the conditions and have worked out efficient tunneling logistics to decrease downtime. “The two working procedures of tunneling and segment erection are carried out simultaneously under the double shield tunneling mode, and the time to erect a ring of segments is 15 minutes in general,” said Shui. “Under the single shield tunneling mode, segment erection comes after tunneling in a sequential process, but the segment erection time is still about 15 minutes.” To further reduce time, consolidation grouting is carried out in advance during daily maintenance to avoid the impact of downtime for grouting on the overall construction progress.

Once complete, the BBDMP will irrigate 60,000 hectares of land in the southern region of Nepal, and benefit an estimated 30,000 households. It will divert 40 cubic meters (1,400 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 water will also be used for hydroelectricity, with a generating capacity of 48 MW benefiting the country with NPR 2 billion (20 million USD) annually. The initial success of the TBM operation has already inspired developers and contractors to opt for TBMs over conventional excavation methods on upcoming Nepalese tunnels.

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Twin Robbins Crossover TBMs to bore on Mumbai Metro Line 3

On June 11, 2018, a Robbins Crossover XRE destined for Line 3 of India’s Mumbai Metro arrived in Mumbai port following a successful factory acceptance test in April. The machine, combining features of a hard rock Single Shield TBM and an Earth Pressure Balance Machine, is one of two 6.65 m (21.8 ft) Crossover machines that will bore under contract UGC-01. Operation of these two machines will be carried out by Larsen & Toubro, part of the Larsen & Toubro -Shanghai Tunnel Engineering Co Joint Venture (L&T-STEC JV). The Robbins Company will provide key personnel for the initial boring phase. “During the factory acceptance testing, we observed that the machine and back-up system are robust enough for hard rock tunneling,” stated Palwinder Singh, Head of Tunnel Operations for L&T-STEC JV.

During the bores, consisting of parallel 2.8 km (1.7 mi long) tunnels, geologic conditions will include mixed ground and possible water pressures up to 2 bar. According to Singh, “A Crossover XRE was chosen because of the expected geology,” which includes basalt rock and transition zones consisting of black carbonaceous shale, tuff, and breccia. Rock strengths are anticipated to range between 15 MPa and 125 MPa (2,200 and 18,100 psi) UCS. The machines will bore with only 15 to 20 m (50 to 70 ft) of cover above the tunnel and the structure will be lined with reinforced concrete segments in a 5+1 arrangement.

The metro tunnels will run between the Cuffe Parade Station and Hutatma Chowk station, passing through the Vidhan Bhavan and Church Stations. Both Crossover machines will be launched from the same 25 m (82 ft) deep by 22 m (72 ft) long shaft at the Cuffe Parade Station. “The limited length of the shaft requires running the TBMs for the first 100 m (328 ft) with some or all the back-up decks at the surface,” said JP Bayart, Robbins Project Engineer. “The TBMs and back-up systems are connected with umbilical cables and hoses.”

The TBMs will begin their excavation in hard rock mode. “Each cutterhead is optimized for operation in rock, as this is what is expected. The machines can also operate in soft ground thanks to the screw conveyor with bulkhead gate and discharge gate,” said Bayart. “The Robbins Torque-Shift System, consisting of two-speed shifting gearboxes coupled to the main drive motors, allows for the high cutterhead torque required for soft ground operation.” The face of each machine is equipped with six muck buckets and six large internal muck loading plates. This design, in combination with the screw conveyor located at the centerline of each machine, will allow for the option of fully emptying the cutterhead chamber, resulting in minimal wear when EPB mode is not required. Muck will be removed from the tunnels via muck cars.

Assembly and launch preparations for the first XRE TBM began on 20 June and are estimated to take about six weeks. The second Robbins XRE TBM underwent factory acceptance testing at the end of May and will arrive at the jobsite at the end of July for its assembly. “Our target is to achieve an average of 250 m (820 ft) of boring per month,” said Jim Clark, Robbins Projects Manager India. “The target to complete the boring operations is 20 months, which includes the additional time required for the short start-up using umbilicals on the initial drives, dragging the machines and re-launching through three stations.” Contractor L&T plans to work crews on double shifts to cover a full day of operations in order to keep to this timeline. The machines will join two Robbins Slurry machines boring a separate contract of the Mumbai Metro Line 3. The first of those machines will be launching in August 2018. The Metro Line 3 project as a whole is estimated to be completed by 2021.

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The Risks Associated with TBM Procurement and the Next Steps Towards Industry Change

Risk management in the world of TBM tunneling is, in itself, a risky business. The underground often presents obstacles and complex projects spanning miles of tunnel multiply those risks. However, there are ways to manage and reduce risk in our industry; i.e., by ensuring that thorough geotechnical studies are done and that contingency plans are in place. The TBM itself can be designed with risk reduction in mind, using tools that expand visualization of the ground around the machine and arm the contractor with ways to get through challenging ground conditions with minimal delays. This paper explores risk in TBM tunneling from the viewpoints of the consultant, the contractor, and the equipment manufacturer. It also seeks to make recommendations as to how risk can be better managed in today’s tunneling industry.

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Boring Hard, Abrasive Gneiss with a Main Beam TBM at the Atlanta Water Supply Program

Atlanta, Georgia’s water supply program is a priority project involving a 5.0-mile long tunnel connecting up with the Chattahoochee River, which will establish an emergency water supply for the city. A 12.5 ft diameter Main Beam TBM is boring the area’s deepest tunnel through hard, abrasive Gneiss rock at rates of up to 100 ft per day. This paper examines the project specifics and design, as well as the performance of the TBM. It also draws conclusions as to the optimal TBM design for excavation in the area’s exceedingly hard geology based on this project and past projects in the area.

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TBM Tool Wear Analysis for Cutterhead Configuration and Resource Planning in Glacial Geology

The abrasive nature of glacial geology generally results in Tunnel Boring Machine (TBM) cutting tool inspection and replacement needs that may require hyperbaric interventions and are a cost and risk factor. Correlation analysis of geotechnical conditions, TBM operational parameters, and tool wear measurements is a proven way to gain insight into the wear system behavior. This paper presents findings from various TBM drives in the Seattle and Vancouver, B.C. metropolitan areas on the performance of disc cutters and ripper-type tools in glacial and inter-glacial deposits. The authors provide recommendations for cutterhead configurations, tool management strategies, and the use of monitoring technology.

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Logistics and Performance of a Large-Diameter Crossover TBM for the Akron Ohio Canal Interceptor Tunnel

The Ohio Canal Interceptor Tunnel (OCIT) below the city of Akron is utilizing the first large diameter Dual Mode, “Crossover” type TBM in the United States. The 30.4 ft diameter machine is excavating in variable conditions including soft ground and shale rock. Due to the unique conditions, the TBM has been designed with features including a flexible cutterhead design and abrasion-resistant plating on the cutterhead and screw conveyor. As part of a predictive maintenance plan, measurements for the screw conveyor’s exposed features will be taken along the drive to report on the wear rate of these components in shale. This paper concentrates on the logistics and process of the TBM launch, and component wear and performance at the jobsite in variable ground conditions.

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Europe’s First Crossover TBM breaks through at Moglicë Headrace Tunnel

On May 3, 2018 a 6.2 m (20.3 ft) diameter Robbins Crossover (XRE) TBM broke through into an underground chamber, marking the completion of the first TBM-driven tunnel in Albania. The TBM, operated by contractor Limak, was also the first Crossover machine to operate in Europe, and bored through geology including ophiolite, sandstone, breccia and siltstone flysch.

“The cutterhead and cutters have achieved outstanding performance,” said Engin Gur, TBM Manager for Limak. The TBM achieved rates as high as 648 m (2,126 ft) per month in April 2018, and as much as 37.4 m (122.7 ft) in one day. The Crossover TBM did not encounter high-pressure water and was thus used in hard rock Double Shield mode throughout tunneling.

“The TBM performed very well, as did a Robbins-supplied adit conveyor that operated in a 180-degree continuous curve. It was impressive,” said Max Walker, Robbins Field Service Superintendent. Several field service personnel remained onsite throughout operation of the TBM to provide guidance and trouble-shooting.

The machine was launched in November 2016 following Onsite First Time Assembly (OFTA), which enabled the machine to be initially assembled at the jobsite. The crew ramped up production slowly over the next 230 m (755 ft). “Ground conditions were good and we did very few cutter changes—only 20 cutters were used during the bore,” said Walker. Two-stage grouting was carried out as the TBM bored and lined the tunnel in three 8-hour shifts. “The personnel on this project have created a friendly work environment; they’ve made it enjoyable coming to work each day. They’re good guys to work with,” he added.

While the TBM did not need to be sealed, the unique machine design took into account a predicted high risk of water inflows. The Crossover XRE machine used a belt conveyor and not a screw conveyor for muck removal, so the muck chute needed to be able to be sealed off in the case of an inrush of water. The bulkhead was thus designed with a large sealing gate just above the belt conveyor. These pressure-relieving gates could also be used in a semi-EPB mode: As the pressure built in the cutting chamber, the gate would then be opened by the pressure, and material would spill onto the belt. As the pressure lowered, the gates would then automatically close, again sealing off the chamber. In extreme cases, the gates could be sealed and the probe/grout drills could be used to drill, grout, and seal off water. Additionally, the gripper shoes and inner telescopic shield were designed with inflatable seals to further protect against inrushes of water.

With the breakthrough now complete, grouting will continue behind the TBM segments. No additional lining will be added, and the tunnel is expected to become operational by May 2019.

The 6.7 km (4.2 mi) long Moglicë headrace tunnel is part of the Devoll Hydropower Project, a Build-Own-Operate-Transfer (BOOT) scheme to construct two hydropower plants along the Devoll River, named Moglicë and Banja. The project is owned by the Norwegian power company Statkraft AS. The completed Devoll Hydropower Project will increase Albania’s electricity production by 17% and will have an installed capacity of 242 MW.

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Excavating Turkey’s Most Challenging Project: The Gerede Water Transmission Tunnel

At the Gerede Water Transmission Tunnel in Central Turkey, a 31.6 km long water supply line has been designated a national priority due to severe and chronic droughts in the capital city Ankara. Drawing water from the Gerede River (and conveying to Çamlıdere Dam), it will be the longest water tunnel in Turkey once complete.

But completing the tunnel has been an obstacle in itself. The project has been called the most challenging tunnel currently under construction in Turkey, and with good reason. Out of three standard Double Shield TBMs originally supplied to bore the tunnel, two became irretrievably stuck following massive inflows of mud and debris. In 2016, a hybrid type “Crossover” machine was launched to excavate the final 9 km of tunnel, but to do so it would need to cross dozens of fault zones and withstand intense water pressures up to 20 bars.

To accomplish this, the machine was designed with a number of unique features including the ability to be sealed up to 20 bar pressure. In the event of a large water inflow, the stopped TBM would hold back the water/muck and allow time for pre-consolidation grouting. The machine is also equipped with a bottom screw conveyor and a unique cutterhead design that facilitates effective muck transportation in both hard rock and mixed ground, among other features. This paper discusses the performance of the machine in exceedingly difficult conditions, and outlines the challenges yet to be overcome and how they may be surmounted. The paper also covers the unique aspects of this urgent Turkish projects and the unique logistical requirements of assembling and launching a machine deep within an existing tunnel.

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