NYC Tunnel Boring

Automation Integrator Case Study: Communications network, variable frequency drives, and controllers integrate miles-long underground tunneling and motion control project.

By John F. Wozniak, Chuck Lukasik November 25, 2011

Integration inside: Tunneling, conveying, networking – System integration was vital to the success of this New York City tunnel-boring project. The integrator installed a unique and extensive continuous conveyor system to remove debris from the tunneling operation. Integrating more than eight types of conveyor systems and controls enabled rapid removal of muck from and continuous operation of both tunnel-boring machines (TBMs). The elaborate conveyor system, weighing in at 900 metric tons, was controlled using CC-Link for communications. In one instance, integrating and installing the Overland Conveyor #2 (the conveyor over Northern Boulevard) was initially estimated to take more than 53 hrs—the entire installation was completed in just 29 hrs—nearly 24 hrs fewer than initially estimated. Ease of use and installation of the communication backbone and controls made it feasible to expand the continuous conveyor system by adding additional conveyors and HMIs to the original control setup. That first integration went so smoothly that project planners expanded the system to enhance the emergency evacuation communication system (EECS). 

Moving New Yorkers is no easy task. They expect on-time, consistent, and deterministic results. As everyone knows, New Yorkers do not like to wait. A new Long Island Railroad tunnel project in New York City to connect Long Island, Manhattan, and Queens will dramatically improve traffic flow for these NYC commuters. This urban project is also a case study on how best to work within specific, predefined constraints while maintaining a safe and productive working environment. The project requires using tunnel-boring machines (TBM) to hollow out multiple tunnels 200 ft below the surface. All told, 12.4 km of rock must be bored and all of the associated debris must be removed.

The Robbins Co., Solon, Ohio, builds world-class tunnel-boring machines as well as conveyance and safety systems. Robbins was contracted to provide the tunnel boring, conveyor systems, and associated equipment for this NYC project.

Elaborate conveyor system

The project, located in the heart of downtown New York City, required an elaborate system of continuous conveyors for the removal of debris (called muck) carved out by the boring machine. This muck then had to be moved to a storage area without disrupting neighborhood traffic. The most challenging design element was using two overland conveyors with box trusses for transporting this muck over Northern Boulevard—a major highway.

The system included every type of commonly recognized conveyors—including belt conveyors, TBM conveyors, transfer conveyors, a serpentine conveyor to continuously extend the conveyor to follow the boring machine, an extensible crown-mounted conveyor, a pocket-belt vertical conveyor, two cascading overland conveyors, and one radial stacker.

Conveying problems solved

Removing the muck from inside a tunnel is a common bottleneck in a tunnel-boring operation. In past operations, rail cars transported the material out, but since a tunnel only has one set of tracks, the TBM could only operate when cars were available. That meant when rail cars were full and taking loads out of the tunnel, a TBM could not operate at full capacity. In addition, the further a TBM excavated into the tunnel, the longer it took for rail cars to travel out of the tunnel to dump their load and return. This reduced the efficiency of the TBM as the tunnel became longer.

Conveyor systems were employed to try to improve the muck removal process. When this method was first tried, however, conveyor belts broke, jumped the track, or sometimes flipped, throwing debris to the tunnel floor. These events occurred because of a lack of coordination among many conveyor motors, which must be tightly coordinated to prevent imbalances or overload conditions. If one motor stops, it creates an overload and imbalance on the other motors.

Resolving conveying problems

Variable frequency drives (VFD), manufactured by Mitsubishi Electric, were installed to control the conveyor motors. A Mitsubishi Electric programmable logic controller (PLC) controls the VFDs. The CC-Link communication network connects the PLC and VFDs. Motors controlling the various conveyor systems operate under a load-sharing scheme using CC-Link. In past systems, other communication networks failed regularly due to the required length of the tunnel-boring operation as well as the harsh environmental conditions.

CC-Link communicates over extremely long distances—a necessity in longer tunnels—and withstands harsh conditions and electrically noisy environments. By necessity, the CC-Link communication cable had to be run in the vicinity of the TBM power cables (13.8 kV), and also near motors and other electrically noisy equipment.

Emergency stop monitoring

The CC-Link network monitors the E-Stop functionality within the tunnel system. If an emergency-stop switch is activated in the tunnel, the CC-Link network can pinpoint the activation point and allow controlled shutdown of the conveyor system. Annunciating the location of the emergency-stop activation is critical to dealing with the cause of the problem.

Mitsubishi HMIs are used to display the status and history of the E-Stop system.

Water pump control

In addition to controlling the conveyors that remove muck from the tunnel, the CC-Link communication system also transmits control signals to the pumps that extract water from within the tunnel. Large water pumps are situated throughout the tunnel construction system. Cameras at each pump station allow operators to monitor station water level. When the water level exceeds its setpoint, the water pumps begin working. The water extraction technique consists of four pumping stations, with each pumping station consisting of two 30-hp pumps. These water pumps are controlled via CC-Link, using the same network as the conveyor system.

Tunnel ventilation

As in any operation below ground, airflow is required for equipment operation. The same CC-Link network used for the water pumps and conveyor motors enables fan control for airflow within the tunnel system. Large fans are located just inside the tunnel to force fresh air through flexible ventilation ducts throughout the entire tunnel construction system. Six 150-hp fans circulate fresh outside air into the tunnel on a continuous basis.

Emergency communication

Two years into the project, it was decided to use CC-Link networking to expand the emergency evacuation communication system (EECS) to further enhance equipment operator safety. The contractor is updating the emergency stations throughout the tunnel to incorporate additional features. This enhanced EECS includes an I/O block communicating on CC-Link, using the same network cable as the fans, pumps, and conveyor controls.

In the event of an emergency, a station will sound an alarm and energize an emergency beacon to alert operators throughout the tunnel system. This EECS can be controlled and activated at any station along the tunnel or at any of the HMI control stations located on the TBM, in the engineering offices, or in the tunnel main control station.

Master control panel

Three interconnected CC-Link networks work in conjunction to control more than 70 stations, including the conveyors, pumps, fans, EECS, and HMI inputs and outputs that control other functions within the tunnel construction system. The three CC-Link Master network modules are housed in one rack along with a Mitsubishi Q Series programmable automation controller in the main control center within the tunnel, located underground about 3 miles from the main engineering offices. The main engineering offices, located outside the tunnel in the borough of Queens, house the control panels for the conveyor drives and the HMIs to monitor operations.

“The use of CC-Link in the tunnel-boring operation has proven to be extremely flexible and versatile, with great reliability,” Matthew Gluszak, electrical superintendent, said.

3-network coordination

While the main control center in the tunnel communicates with the engineering offices, it also coordinates communications 3 miles into the tunnel for the two networks that travel to the TBM. These three conveyors, even though controlled via separate CC-Link networks, operate together to remove the tunnel muck. If one conveyor is not operating properly, that’s communicated to the operator and engineering teams to preclude muck from accumulating at any of the conveyor transfer points throughout the tunnel system. These CC-Link networks also work together to communicate system status to the various HMIs located throughout the tunnel system. Status information from all networks, including E-Stop and EECS information, is available to all HMIs regardless of the originating CC-Link network. Each HMI can also make control requests to any point on any of the three CC-Link networks. Using CC-Link networking provides noise immunity over the long distances.

– John F. Wozniak is networking specialist and Chuck Lukasik is director, CLPA-Americas. CC-Link Partner Association (CLPA) manages CC-Link networking technology, with offices in the USA, UK, Germany, Japan, China, Korea, Taiwan, and Singapore.