Micro-Tunneling: The New Rescue Challange

Micro-Tunneling: The New Rescue Challange

BY RONALD E. KANTERMAN

Getting from “here to there” has gotten a lot easier for the tunneling industry over the past 25 years or so. This method of running utilities has gotten more popular and more affordable. It enables companies specializing in water mains, sewers, and other underground utilities to do their work with little or no disturbance to the streets and thoroughfares of towns and cities and industrial facilities across the country. But, it also presents increased challenges for rescuers.

WHAT IS MICROTUNNELING?

The term microtunneling refers to methods of horizontal earth boring that employ remote-controlled, laser-guided boring machines that are extremely accurate. These unmanned “gophers” can run through all classes of dirt, including solid rock, up to 150 feet underground. They range in diameter from very small (water service) to extra large such as those used in the Chunnel between England and France.

The two main methods of microtunneling are slurry and auger. The slurry method requires that a jacking pit be constructed whereby the boring unit and the lengths of pipe that follow are hydraulically jacked through the earth, sometimes at pressures of up to 1,600 tons of force. Jacking pits are as deep and as wide as necessary to lower the size of pipe being installed. As the cutting head churns the earth, water is pumped to the front to create a slurry that is then pumped topside and separated. In essence, the spoil pile is removed hydraulically. The conveying fluids are also used to counteract hydrostatic forces created by ground water pressures at the head of the unit. This force and other forces must be considered to create a balance underground and to avoid settlement at the surface. All of the pressure data are transmitted to a remote-control operating station at the surface, where the operator can make proper adjustments as necessary.

Most slurry operations are automatic balancing systems that adjust for types of soils and underground terrain and are safe and efficient. As important as the cutting head itself is the rear of the machine, which has all of the controls and a closed-circuit TV camera that transmits a picture of the controls to the topside operator. The operator can then make any necessary adjustments such as equalizing pressures, redirecting steering, and shutting down if necessary.

The auger method also involves jacking the pipe and the cutter through the earth, but a continuous flight auger removes the soil. Steering is accomplished by an articulated steering head in the tunneling machine that can be positioned using steering cylinders. This method also employs soil-storage chambers for later manual removal.

The slurry method is desirable in most cases. However, each method has its applications.

GENERAL INFORMATION

Any pipe that can withstand the hydraulic jacking and compressive forces can be used for microtunneling–e.g., steel, ductile, fiberglass, vitrified clay, PVC, reinforced concrete, and so on. The auger method will work for pipe diameters from 10 to 40 inches and the slurry method for diameters up to 120 inches. The system can install piping up to 750 feet long. If longer lengths of lines are needed, intermediate jacking may be necessary. The only real disturbances to the ground surfaces are the jacking pits and receiving pits (from which the machine is retrieved) and the general work area–lay down, soil-water separator, control room trailer, for example. The great advantage of microtunneling is the accuracy with which the piping can be placed, especially sewers and the like, for which the correct pitch of the piping is essential for computerized installation and steering through laser technology.

SO, WHAT`S THE PROBLEM?

If everything is done by remote and from the surface, what`s the problem? The problem can start in the jacking pit. Workers (usually three or four) are positioned at the bottom of the pit to help guide the sections of pipe as they are lowered into the jacking machines. Although personnel are limited in this area, there is the potential for accident or injury. General confined space and shoring rescue practices would apply here–e.g. lowering and hauling systems, patient packaging, and so on. The contractor should be using a permit system (OSHA 1910.146) that entails atmospheric monitoring, the listing of the names of those who have entered, the presence of an attendant or standby person, and all other requirements outlined in the standard.

The bottom of the pit usually can be accessed with portable or fixed ladders. The real challenge, however, is when there is a breakdown in the boring equipment that may be 300, 400, or 700 feet in length. The cutting machine cannot be backed out once the pipe is jacked behind it. It must be repaired in place, or a receiving pit must be dug so the machine can be retrieved. A broken electrical line and a broken TV cable are the problems most likely to be encountered. You must think about how a worker or two can be taken out before they go in. A good preplan is needed. Fire and rescue departments should meet with contractors prior to the start of the project and then tour the site as the job commences.

SOLUTIONS

Picture yourself carrying a patient in a stokes basket or a stretcher 600 feet through a 48- or 54-inch tube wearing SCBA and in a bent-over or hunched position. I would venture to guess that even our fittest members who have placed well in the “Combat Challenge” would have difficulty here.

Think about having enough air, too. An industrial fire and rescue department recently discovered as 19,000 feet of microtunneling commenced on its facility that one-hour SCBA bottles did not provide enough air for the longest tunnel proposed and that carrying a patient while bent over was not an option. Through a cooperative effort with the project managers and the contractor, some solutions were born:

In addition to all of the electric lines (two 440-volt that power the main unit), a TV cable, and slurry piping, the contractor installed a 2- 2 12-inch piece of lumber to create a runway on the bottom of the tube. Rescue personnel then modified a fiberglass stokes with two sets of three four-inch wheels so that it would run along the runway. The contractor then set up a mock of the tunnel near the fire station with all of this equipment in it so the members could test this theory. With a little adjustment, the system worked.

Air supply. OSHA will allow only 300 feet of airline hose, so the use of supplied air respirators was out of the question. After some research, four-hour rebreathers were purchased.

Other safety issues arose out of the constant meetings between the players.

–The contractor purchased additional baskets and attached wheels to them for use as equipment carts or caddies to get heavy items down the tunnel.

–A 30-minute SCBA was placed every 15th length of tunnel pipe (10-foot lengths) jacked, to have additional air in the tube for workers who might have to wait for the rescue team or escape from the tunnel.

–An entry-rescue board was installed topside at each jacking pit (in addition to issuing a confined space entry permit). The board contains photos–with names–of personnel working in the pit, serving as the tunnel entry team or attendants or as personnel and equipment monitors. This tag even lists the workers` levels of training, e.g., SCBA, so that rescue personnel would know how capable they are of helping themselves and following instructions throughout the emergency. This board gives the responding unit a quick picture of “how many and who” for size-up purposes.

Microtunneling is the state-of-the-art method of getting from “here to there” underground. Get as much information as you can on this technology. It has eliminated the trench rescue but has created a new rescue challenge at the same time. n

Special thanks to the E. E. Cruz Company for supplying the technical data on microtunneling used in this article and for allowing its equipment to be photographed.

(Top left) Boring machine with the cutting head exposed. This unit will bore a 54-inch hole, followed by the depositing of a composite tube made of concrete and fiberglass. (Photos by author.) (Top right) The rear of the boring machine. Note the gauges, wires, and other components. The small TV camera hanging about dead center transmits information back to the control room. (Bottom) The boring machine being lowered into the jacking pit onto the hydraulic jacking machine. The floor of this pit is three feet thick; the walls are about two-foot-thick concrete. All are reinforced with steel rebar. This operation is 30 feet below the surface.

(Top left) As the boring machine churns the earth, the jacking unit pushes to help it along. The four shiny chrome-looking units are the hydraulic pistons that exert forces up to 1,600 tons. (Top right) Inside the control room. The entire operation of the boring unit–from adjusting pressures to steering–takes place in this room and is accomplished by one person. (Bottom left) The control room is merely a steel shipping container, making the operation as portable as it can be. (Bottom right) Receiving pit where the boring unit will be retrieved from underground. The rounded flat area in the foreground is a manhole, which the tunnel tube will meet as it makes entry into the pit–from the rear of the photo to the front of the photo.

(Top left) The liquids-solids separator topside used for the slurry system. (Top right) A modified stokes basket with two sets of three four-inch wheels is a back saver. (Bottom right) This piece of tubing will be lowered into the pit with all of the slurry piping, wiring, and so on, already in it. The utilities are then connected just prior to the jack`s starting to make “the push.” Note the 2- 2 12-inch piece of lumber installed on the floor of the tube. It will act as a “runner” for the wheeled stokes basket.

This status board, which has on it the pictures, duties, and training levels of workers in and around the pit and tunnel, is used to closely track personnel.

RONALD E. KANTERMAN is the chief of emergency services for Merck & Co. in Rahway, New Jersey. He has a B.A. in fire administration and an M.S. in fire protection management from John Jay College of Criminal Justice in New York City. Kanterman also is an adjunct professor of fire protection at Middlesex County College in Edison, New Jersey. He is a member of the New Jersey State Fire Safety Commission Codes Advisory Council, the IAFC Haz Mat Committee, the National Fire Academy Alumni Association board of directors, the FDIC Educational Advisory Committee, and the Fire Engineering editorial advisory board.