Going the Distance
The scope of the Niagara Tunnel Project is only eclipsed by the wonder of the famous falls of the same name. A new massive diversion tunnel will add additional hydroelectric power to an existing generating station with enough electricity for 160,000 more homes. The project will divert 35% of the Niagara River at night so that the famous Falls tourist destination will continue to awe future generations. An entire fleet of Schwing concrete and shotcrete pumps, under the guidance of Pumpcrete, conveniently located in Niagara Falls, are working around the clock on the project. The company is no stranger to tunnel lining and is supplying more than 11 Schwing stationary pumps in various configurations along with their extensive fleet of Schwing boom pumps to assist on the project.
Besides their advantageous location to the project, Pumpcrete has an extensive tunnel lining resume, including the 9.5 mile Chattahoochee Tunnel in Cobb County, Georgia and the 4 mile River Mountain tunnel near Lake Mead in Nevada. “The difference with this tunnel is its immense diameter,” explains Dave Moriarity, Pumpcrete manager, “Those other two were 15 to 20-feet in diameter. This one you could erect a five story building inside the tunnel.”
Creating a 14.4-meter bore hole required the largest Hard Rock Tunnel Boring Machine (TBM) in the world. The process began at the outlet end and proceeded on an incredible five year, 10.2 km journey towards the intake side. The TBM was designed and manufactured by The Robbins Company in Solon, Ohio. The tunnel design and construction is in the hands of Austria based Strabag AG, the general contractor for the Niagara Tunnel Project.
Inevitably issues arose during the tunneling process, which was routed under the city of Niagara Falls. “The TBM is a hardrock boring machine but unfortunately not all of the rock was hard,” according to Bernhard Mitis, Strabag’s manager for the concrete portion of the project. More than 30 cubic meters of material had to be removed for every meter of forward progress under ideal conditions. Additional overbreak hindered the progress when material fell onto the TBM which added haul time for overbreak material and required repair to the equipment. In all 1.6 million cubic meters of rock was removed during the tunneling process which ended on May of 2011 when the cutter head broke through, an event that was celebrated by the entire crew.
Shotcreting was part of the excavation contract to stabilize the bore hole perimeter but additional shotcrete was required to fill voids in loose soil conditions. The company utilized three Schwing SP 500 split units to apply the shotcrete to a thickness of 13 cm through hand-held hoses and shotcrete robots attached to the TBM. The wet shotcrete was applied over reinforcing mats anchored into the tunnel walls. A shotcrete arm provided extra reach to fill voids that occurred when soil conditions were not ideal. A Schwing SP 1000 was used to feed the arm and to provide additional velocity to the shotcrete. Strabag subcontracted batch plant operations and trucks supplied the pre-mixed shotcrete to the electrically powered pumps. More than 120,000 cubic meters of shotcrete was applied over the five years of tunneling.
Following behind the shotcreting operation is the form and pour for the tunnel invert – the bottom one-third of the tunnel lining. Pumpcrete utilized two Schwing SP 2000 Schwing stationary pumps that are fed by agitator trailers hauled in by trucks. The tunnel lining concrete is a “pumpable mix” according to Moriarity, explaining that the mix designs are proprietary. Output to the two form systems that leapfrogged their way through the bore hole was between 40 and 50 cubic meters per hour. The form systems travel about 50 meters in front of the electric-powered trailer pumps. Each pour advances the invert 12.5 meters and consumes 120 cubic meters of concrete. Water is used to clean out the pipeline systems with a diversion valve on the pump’s discharge that sends wash water and residual concrete into trailers to be disposed of outside the tunnel.
A circular cross-section is an indispensable prerequisite for a
pressure tunnel, as the loads must be spread evenly throughout the tunnel’s circumference. Therefore, all voids need to be grouted in order to keep the thickness of the inner lining within specified tolerances of 30 centimeters. Because of the internal water pressure of up to 15 bar (2,175 psi), the lining must be fitted accurately into the surrounding rock.
Prior to the form being moved into place, a membrane is installed to maintain a waterproof environment for the tunnel. Waterproofing Manager Stefan Mackinger explains why elaborate waterproofing is mandatory for the success of this tunnel, “ The tunnel designer specified a single-layer waterproofing membrane
for non-swelling rock and a double-layer membrane for the Queenston
Formation, an area that contains argillite, which swells in contact with
water and would ruin the concrete lining.”
Once the invert operation reached approximately 2,000 meters into the bore, pumping began on the arch forms to complete the remaining two-thirds of the concrete tunnel. Pumpcrete chose a Schwing electric SP 5000 split unit that was positioned under an 8 cubic meter Maxon Maxcrete agitating surge hopper to travel into the bore hole. A Schwing SP 8000 outside the tunnel fed the surge hopper.
Pumping the arch forms required a more complicated distribution system to reach the eight openings that fill the form with 260 cubic meters of concrete. A subsidiary of Strabag designed the arch form system and included a rotator that allows the discharge pipeline to be moved on a turntable and hooked into individual pipeline sections with hoses that extend to the form shutters for even filling. The rotator is mounted centrally inside the form liner and an operator uses a hand lever to lift the discharge pipe, rotate it and reconnect to one of eight different output lines. This method was used to evenly fill the forms while radio communications with the pump operator relieved pressure when rotating the discharge line. The lines running to the shutters were cleaned out using compressed air at the end of each pour.
Because of traffic through the tunnel, the SP 8000 pumped through a five-inch line for as long as possible, “We were amazed that the Schwing was able to push the mix as far as 1.7 kilometers, “ explained Pumpcrete owner, Ken Williams, Jr.,“That’s more than a mile and probably some sort of record.” The crews eventually resorted to feeding the pump with trucks and trailers.
By the end of the project more than 300,000 cubic meters will be pumped with the Schwing units. Pumpcrete’s contribution to the project is immeasurable. “A partner in concrete placement means good equipment, experience, reliable operators and parts support especially in tunneling. Pumpcrete has supplied all of these components.“ according to Mitis.
The rigors of pumping underground around the clock, challenge the men and machines on this monumental project. The continuous overbreaking during tunneling tested the limits of technical and economic reasonableness and the feasibility of the project was questioned. While being two years late and more expensive due to delays in boring, the clean energy potential will have long term benefits over its expected 100-year life, according to Dalton McGuinty, Premier of the Canadian province of Ontario, “Yes, some of it has come at a price that hasn’t been easy, but neither was it easy for our parents and grandparents to build our original electricity system, to build our schools, to build our roads. But they did it anyway, because they were builders. And so are we.”
Scheduled to flow water in 2013, the Niagara Tunnel Project invert was at 7,786 meters and the arch form was at 5,330 meters in mid-February 2012. The overall length of the tunnel is 10,150 meters.
Owner: Ontario Power Generation
General and Concrete Contractor: Strabag AG, Vienna, Austria
Pumping Contractor: Pumpcrete, Niagara Falls, Ontario
Equipment: 3 – Schwing SP 500 electric powered split unit stationary pumps; 2 – Schwing SP 5000 electric powered split units stationary pumps; 2 – Schwing SP 8000 trailer-mounted pumps; 1 – Schwing SP 8800 electric powered split unit stationary pump; 2 – Schwing SP 2000 Electric powered trailer-mounted pumps; 1 – Schwing SP 1000 trailer-mounted pump; 1 – SP 750 trailer-mounted pump.