The News in Brief:
- The Grosvenor Decline tunnel marks the first method of a TBM being used in a coal mine in Queensland.
- The unique Crossover Rock/EPB TBM features design aspects from both hard rock Single Shield and soft ground EPB TBMs to bore through a variety of ground.
- The “Crossover” designation is new for Robbins, and will going forward be the designation for all types of Dual Mode TBMs.
- The Crossover TBM for Grosvenor was uniquely designed for excavation in conditions that included the potential for methane gas. It was designed as Class 1, Division 2 Coal Mine Compliant.
- The TBM excavated at rates fourteen times that of a traditional roadheader operation (70 m per week on average vs. 5 m per week).
- The TBM broke through into an active section of the coal mine on February 9, 2015, completing excavation of two mine access tunnels.
Full Press Release:
A ground-breaking TBM brought a mining operation one step closer to first coal on February 9, 2015. The Robbins Dual Mode “Crossover” Rock/EPB TBM completed tunneling at Anglo American’s Grosvenor Project in Queensland, Australia. The “Crossover” designation is new for Robbins Dual Mode TBMs, and will be used for all such projects going forward. The efficient type of TBM used at Grosvenor is now known as an XRE, standing for Crossover between Rock/EPB. Other types of machines are designated the XSE (Crossover between Slurry/EPB) and the XRS (Crossover between Rock/Slurry).
The Grosvenor Mine, a Greenfield coal operation, was the first to utilize TBM technology for mining tunnels in Queensland. Mine owner Anglo American Coal chose the 8.0 m (26.2 ft) machine for two decline access tunnels at grades of 1:6 and 1:8, one for conveyors and another for people and equipment.
The XRE TBM was picked over the traditionally-used roadheader method for several reasons, including excavation speed and tunnel maintenance. The choice proved prescient with the machine excavating at a rate approximately ten to fourteen times faster than a roadheader™bout 70 m per week for the TBM vs. 5 m per week for a roadheader. In addition, the final tunnels have a smooth profile and are segment-lined, requiring minimal upkeep during the planned 40-year life of the mine. “In the coal mining community, and certainly in Queensland, companies are aware of the Grosvenor project and how it has set a benchmark for underground access drift construction,” said Glen Maynard, Robbins Field Service Site Supervisor at Grosvenor.
The machine’s Crossover capabilities enabled it to operate in both hard rock and mixed ground. In addition, the TBM was required to operate during gaseous conditions. The unique TBM design included a cutterhead capable of interchanging hard rock and soft ground cutting tools, a two-stage center-mounted screw conveyor, a “quick removal” shield system, and flame-proof machine components due to the possibility of methane gas in the underground environment.
The TBM was optimized for hard rock and mixed ground excavation in geology ranging from soft clay and soil to sandstone and basalt. The two-stage screw conveyor worked in both ground conditions to draw muck from the tunnel face. Two sets of shields were built for the TBM’s “Quick Removal” system, and were detached from the machine at the end of each blind tunnel to be left in the ground for constant support, a requirement in Australian tunnels. The inner core components of the TBM were then retracted out of the segment-lined tunnels on specially designed transport dollies.
The machine began boring the conveyor tunnel in December 2013, and after completion in May 2014 was successfully retracted and transported to the second tunnel site. The machine was then re-commissioned for the people and equipment tunnel in November 2014 with a new set of shields. Once excavation commenced, boring was completed in 88 days at an average of 10.9 m per day, with a best day of 25.2 m. The bore itself was similar to the first, with few challenges encountered other than elevated methane gas levels that required several temporary stoppages in order to safely remove the gas from the tunnel. “The machine performed very well and had high reliability. The cutting tools, in particular the knife edge bits, were exceptional. The bits were required for most of the drive and one complete set lasted 650 meters,” said Maynard.
The team is now preparing the machine for its final retraction and roll-out, and it will be on the surface in less than two months. The TBM will then be stored onsite for future Anglo American mining projects.
Once the longwall mine is operational in 2016, Grosvenor is expected to produce five million tonnes of coal per year over the next 26 years.
The News In Brief:
- Breaking through on January 28, 2015, the rebuilt EPB at NYC’s Harbor Siphons tunnel overcame obstacles including flooding, extensive rebuild work, and difficult ground.
- The CAT-manufactured machine was fully submerged by Superstorm Sandy in October 2012 and became severely corroded by saltwater.
- Contractor Tully/OHL USA JV hired Robbins to rebuild and refurbish the machine, including all electrical components and an all-new PLC.
- The Robbins rebuild took four months and the machine was re-launched in April 2014.
- Robbins remained onsite to assist in continuing challenges including high water pressure and glacial geology.
- Despite the gamut of obstacles thrown at the machine, crews were able to achieve up to 30.48 m per day and 25 rings in 24 hours.
On January 28, 2015, about 35 m (115 ft) below New York Bay, a celebration was underway. Workers from the local tunnelers union in New York City, USA, known as the Sandhogs, completed the last meters of tunnel alongside workers for subcontractor Tully/OHL and Robbins field service. The team had many reasons to celebrate””not only had their TBM just completed a much-needed undersea tunnel, but it had also done so after a near-catastrophic natural disaster, extensive rebuild and geologic complications.
The New York City Harbor Siphons Project began simply enough””the 2.9 km (1.8 mi) long tunnel between Brooklyn and Staten Island was designed to replace two existing shallow water lines below the bay. The project, managed by the New York City Economic Development Corporation (NYCEDC), replaces the lines with the deeper siphon in order to make way for a larger project””the dredging of the Anchorage Channel. The channel (part of New York Bay) is an important waterway for shipping, and its dredging will allow for mega ships carrying large cargo loads to pass through.
Tully/OHL USA JV procured a 3.8 m (12.5 ft) diameter EPB TBM from Caterpillar in 2012. The TBM, dubbed “Pat”, was designed to drive through highly variable clays, sands, weathered rock and boulders. It was launched from the 35 m (115 ft) deep Staten Island shaft, boring towards the 40 m (131 ft) deep Brooklyn shaft, in August 2012.
In October 2012, the unexpected happened: a massive hurricane, dubbed Superstorm Sandy, barreled down on the U.S. East Coast with winds up to 145 kph (90 mph). Extreme flooding at the waterfront jobsite in Staten Island overtopped protective concrete barriers that had been designed three feet above the 100-year flood level. Seawater rushed into the tunnel and the nearly 113 m (370 ft) long machine was entirely submerged only 460 m (1,500 ft) into its drive. “Obviously this was our biggest challenge,” said Luis Alonso, Tunnel Manager for OHL. “After that, not many people thought we would be able to finish this tunnel.”
After floodwaters began to recede, OHL set about determining the extent of damage on the machine. The TBM was severely corroded by saltwater and sat idle until July 2013. During that time, CAT announced its impending closure of its TBM business, and the contractor looked to other manufacturers. “OHL was always determined to finish this project. After studying other options, we decided to proceed with the full refurbishment of the TBM with the help of The Robbins Company. The whole crew worked together to achieve that goal,” said Alonso.
Robbins coordinated the effort to replace corroded hydraulic components and all new electrical systems in mid-December 2013. Electrical systems had to be reverse-engineered, while the PLC had to be entirely redesigned. The refurbishment also centered on removing the rear eleven gantries and belt conveyor to be cleaned, evaluated and repaired. The rebuild took about four months, much of it done in the tunnel under water pressure, and crews were able to return to mining on April 14, 2014.
To ensure that the project stayed on the incline to success, Robbins Field Service personnel remained onsite to support ongoing maintenance of the TBM. With their help, machine performance steadily increased, eventually reaching rates as high as 30.48 m (100 ft) per day and as much as 25 rings in 24 hours in August 2014.
As excavation picked up, ground conditions changed from marine sediments (clay, silt and sand) to glacial geology with sand, exceptionally hard boulders, and excessive water ingress, resulting in slow propulsion rates. “The TBM needed more thrust and we decided to implement four additional auxiliary cylinders. Robbins field service helped in developing the size, features and location of the cylinders, which were eventually placed in the lower quadrant of the propulsion system,” said Alonso. With the new system crews were able to re-establish forward progress. The constant hurdles continued into early October when a hyperbaric intervention at 4 bar of pressure was required to change the cutting tools in a pocket of glacial soils. Despite the new obstacles, the crew was able to steadily increase the rate of excavation to 5 to 7 rings per day. “This tunnel is an important part of a larger project, and we are proud to be doing what we do every day, dealing with troubles as they come up, until we reach the end of the drive,” said Alonso. Now that tunneling is complete, the stationary and tail shields will be buried at the exit shaft entrance, with the cutterhead and back-up being removed.