IN OCTOBER 2012, New York’s Harbour Siphons Project and its 3.8m (12.5ft) CAT EPB ground to a halt when hit by Superstorm Sandy. Despite contractor Tully/OHL JV’s best efforts to mitigate anticipated flood risks, the launch shaft was inundated with seawater, flooding the tunnel and TBM just 460m (1,500ft) into the 2.9km (1.8mi) long drive. A team of Robbins and OHL personnel were able to document, reverse engineer, and refurbish severely corroded components of the TBM while in the tunnel, resulting in a successful re-launch in April 2014. The Herculean efforts required by all of those involved are documented herein.
Redesigning the Channel
Construction of the siphon tunnel is part of a much larger project. The Anchorage Channel, an integral part of the shipping trade with access to New York Harbour and the rest of the Port of New York and New Jersey, is one of the more heavily used water transportation arteries in the world. Future cargo volumes are expected to double over the next decade and possibly quadruple in 40 years. The channel must be deepened in order to accommodate the new generation of cargo mega-ships, which have drafts that exceed 14m/46ft (the present depth of Anchorage Channel), and ensure the City’s ability to benefit from the anticipated increase in this sector of the economy.
Using funding authorised by the Federal government, the Port Authority of New York New Jersey (PANYNJ) and the United States Army Corps of Engineers (USACOE) proceeded with dredging operations to deepen the Anchorage Channel to 15m (49ft) below mean low water over a length of 5,800m (19,000ft), from the Verrazano-Narrows Bridge to the channel’s confluence with the Port Jersey Channel.
In order to complete their project, however, the two existing siphons owned by NYCEDC had to be removed, ultimately requiring replacement by a larger tunnel. The new siphon required a 3.6m (11.8ft) diameter, 2,883m (9,458ft) long tunnel. NYCEDC was responsible for the construction of the USD 300M project on behalf of the New York City Department of Environmental Protection.
The new siphon will be finished with a backfilled 1.2m welded-steel water pipe. Full backfill around the riser pipes in the shafts will also be installed. Water transmission mains connecting the tunnel to the existing system will be constructed in open cut. Microtunneling machines will drive two additional crossings, about 99m and 37m long, under the Staten Island Railroad. Once the new tunnel is complete, the existing siphons will be decommissioned and abandoned. The new tunnel will serve as a backup to the 900ft deep Richmond main water tunnel that was built under the harbour between Brooklyn to Staten Island in the 1960s through hard rock.
Startup and Flood
Tully/OHL USA JV procured a 3.8m (12.5ft) diameter EPB TBM from Caterpillar in 2012 to bore the new siphon tunnel. The TBM, dubbed "Pat", was designed to drive through highly variable clays, sands, weathered rock and boulders. "The contract allowed for both EPB and Slurry. The geology of the project, with around 75 per cent excavation in clay, was more favorable for an EPB machine," said Luis Alonso, Tunnel Manager for OHL. It was launched from the 35m (115ft) deep Staten Island shaft, boring towards the 40m (131ft) deep Brooklyn shaft, in August 2012. An onsite crew from the local tunneling union, known as the Sandhogs, assisted OHL in the tunnel construction.
The project started off well, but 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 1m (3ft) above the 100-year flood level. Seawater rushed into the tunnel and the nearly 113m (370ft) long machine was entirely submerged after boring only a few hundred meters. "Obviously this was our biggest challenge," said Alonso. "After that, not many people thought we would be able to finish this tunnel." The damage extended beyond just the jobsite — much of Staten Island is a designated flood zone and many businesses, homes, and major pieces of infrastructure had been substantially compromised.
"It was a shock for us," continued Alonso. "No one could imagine something like that happening." After floodwaters began to recede and some additional water had been pumped from the tunnel, OHL set about determining the extent of damage on the machine. There had been one cutterhead intervention just two weeks prior to the flood, so there was some confidence that even though the machine had been stalled in the tunnel at earth pressure, the cutterhead would be in good shape. Crews entered the tunnel to do analyses of the bearing cavity and rotary union.
The TBM was determined to be severely corroded by saltwater, and extensive rebuild would be needed. The machine 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. The whole crew worked together to achieve that goal," said Alonso.
Extensive Rebuild
Robbins arrived onsite in July 2013 to begin the assessment. The general plan for the refurbishment centered on removing the rear eleven gantries and belt conveyor from the tunnel and shipping them by truck to an offsite facility where the backup gear could be completely cleaned, evaluated and repaired. The remaining two gantries, screw conveyor, segment erector, stationary shield and forward shield would have to be refurbished onsite in the tunnel. The segmented concrete lining would not permit the removal of these items. Per the scope of work, the cutterhead and main bearing of the TBM were excluded from the refurbishment, as they were under earth pressure and not accessible. The Robbin team would need to complete the refurbishment taking into account unknowns, such as the condition of the cutterhead, and the thrust cylinders, as the machine had stalled at pressure with the thrust cylinders retracted.
The parties involved set about immediately on a twopronged approach of shipping the removed equipment to the manufacturer’s facility in Solon, Ohio and organising a plan for the onsite refurbishment of the remaining items. By early August, the gantries were back in Solon and production was proceeding to inspect and disassemble equipment in order to evaluate and order items where necessary. Onsite, local 15 mechanics and local 147 sandhogs worked diligently identifying, disassembling and evaluating system components.
"We had to be absolutely vigilant about the earth pressure of 3 bar, as we were doing much of the rework inside the tunnel. There were some components we were simply not able to reach, such as the screw conveyor doors and guillotine door, as these were under pressure," said Roger Cope, Robbins Field Service Technician, who was at the site throughout the refurbishment until breakthrough. Major failed components, such as grout pumps, drive motors and propulsion hydraulic blocks were shipped by truck back to Solon for repair, while less complicated items were ordered for shipment directly to site. Additionally, a local hydraulic supply house was selected to provide onsite hose making capabilities up through 50mm (2 inches) diameter. In this way, replacement of worn hoses could be produced as needed, saving precious time. By September, 2013, the gantries in Solon were being refitted, while onsite the bulk of the evaluations were complete and workers turned to cleaning and re-hosing the forward shields and first two gantries. Steel components of the machine were stripped with abrasives, then sanded and repainted. However, the challenges were just beginning.
Reverse Engineering
The Robbins crew was additionally contracted to guide onsite personnel in replacing corroded hydraulic components and all new electrical — from Variable Frequency Drives to PLCs and wiring — inside the small tunnel.
"We had some manuals, but no autoCAD drawings and no supporting materials from the manufacturer. We had to identify each component and reorder it. The PLC took the longest by far," said Bogdan Tudor, Robbins Field Service Technician. Essentially the crew had to observe how the TBM worked and create a detailed report to redesign the system from the ground up — from the segment operation to steering control and more.
One major difference was the steering between Robbins EPBs and CATdesigned EPBs. "Robbins EPBMs use quadrant steering. The CAT machine, however, had 16 cylinders, each independently operating with its own controller." That required researching and designing a system the team was initially unfamiliar with, in addition to other challenges. "There were other things like the flowmeters, which monitor critical flows in the lube system, that weren’t responding. The physical components of the meters interact with a card, and we determined that since we had gotten a new PLC from another manufacturer, the original cards didn’t interact with it. We needed to determine which cards would interact with the PLC and replace them," said Tudor. The entire conversion and rebuild of the electrical system required a team of six electricians and took about four months.
The Restart
In the final phase of the refurbishment, a Robbins PLC technician was able to complete the commissioning of the TBM and on April 14, 2014 the machine officially returned to mining. To ensure continued success, the team remained on site to support ongoing maintenance of the TBM. In the coming months, the machine performance steadily increased, eventually reaching as high as 100ft (30.48 m) per day in August 2014. This result — the equivalent of 25 rings in 24 hours — significantly outperformed the machine as designed before the flood, which had a maximum of 16 rings per day (segment rings are 5+1 precast concrete, 1.2m in length).
By August, the project appeared to be on target for a mid-September completion. However, in early September, 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.
After installing the 50-ton auxiliary cylinders in the lower propulsion system, crews were able to re-establish forward progress but at a reduced rate. The TBM pushed on, but in early October the project was faced with another hurdle. The machine encountered a pocket of glacial soils comprised of larger, hard stones. The hardened material led to tool failure and the TBM was stalled for the majority of November while a hyperbaric intervention at 4 bar was performed to install new tooling. With the intervention complete and a new dressing of rippers installed, the TBM began mining again in late November. Despite the obstacles, the crew was able to steadily increase the rate of excavation to 5 to 7 rings per day.
Once mining was reestablished, the TBM faced a final critical crossing beneath Belt Parkway, a busy thoroughfare built on sensitive harbour-side soils. Monitors were installed in the roadway and around critical utilities including a highpressure gas line to make sure settlement remained within the set parameters as the machine passed 34 m (112ft) below. As crews mined, they injected polymer to maintain a smooth flow of muck and consistent earth pressure, while pre-mixed single component grout was used for backfill of the annular gap. The grout was delivered via grout pumps to ports behind the segments at the edge of the tail shield. Ultimately, the crossing was successful and monitored settlement was well within specified limits.
Break Through
By 24 January 2015 the machine had mined through the first 1m thick slurry wall of the exit shaft. Its completion point was just beyond the sand-filled exit shaft, past a second slurry wall where the TBM would be buried. The final metres were completed days later on 28 January. The completion of the project marks the first successful excavation by an EPB in the NYC area.
"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.
"With tunneling complete, the stationary and tail shields were buried at the exit shaft entrance, with the cutterhead and back-up removed.
