Uncovering Coal is the Biggest Job

Mining coal is easy. Getting to it is the hard part. At Usibelli Coal Mine, up to 200 feet of unconsolidated sandstone or "dirt" must be moved to uncover the top seam of coal. Another 80 feet must be moved to uncover the second seam.

Dragline does the "dirt" work

The most efficient machines for moving large volumes of dirt are draglines. In 1977, UCM made a major investment by purchasing a 1300W Bucyrus-Erie Walking Dragline. The dragline arrived in parts on 26 railcars and 40 trucks during December 1977. It took 11 months to assemble the 2100 ton machine.

Named "Ace-in-the-Hole" by Healy school children, the dragline is the largest land-based machine in Alaska. The acquisition of "Ace-in-the-Hole" made it possible to double production and initiate UCM's Korean export contract in 1985.

With its 325-foot boom, the dragline has a reach of 270 feet. The bucket weighs 32 tons and will hold 33 cubic yards of material. In one 24-hour period, the dragline can move 35,000 yards of dirt, leaving a 145-foot wide strip of uncovered coal.

Due to the weight of the machine, moving it on tires or tracks is not possible. The dragline moves by "walking." Shoes on either side of the machine lift its base partially off the ground and drag it backward. Each step takes about 40 seconds and moves the dragline approximately 7 feet.

While it takes only one person to run the machine, there are two dragline operators on duty at all times. One operates the dragline from the cab while the other does routine maintenance. For safety reasons, the operators switch positions every hour.

The dragline is powered solely by electricity. A Load Stabilizer System consisting of a 42 ton flywheel and motor/generator serves as a buffer between the dragline and the local electrical grid. The flywheel stores energy to be used whenever the dragline's electrical demand increases too quickly for the local grid. This enables the dragline to operate without causing power fluctuations for other electrical customers.

The dragline has several buckets, which are used on a rotating basis. Each bucket is used on the dragline for about 45 days. After that period, the bucket must be serviced and its ultra-high molecular weight plastic liner must be repaired or replaced.

Shovels, backhoe strip overburden, load coal

While the dragline does the majority of the excavation work at the mine, smaller excavators are needed. Two track mounted O&K RH120C hydraulic shovels help to strip overburden in areas too difficult for the dragline to maneuver and to load trucks with rock and gravel for construction projects. An identical machine, but configured with a backhoe, loads coal trucks. Both the backhoe and the shovels have 16-cubic yard buckets and are powered by twin 567-horsepower diesel engines.

The largest hydraulic shovel in Alaska was added to UCM's fleet in August 1997. The O&K RH-170 shovel has a 26 cubic yard bucket and can load the new 150-ton trucks in four passes.

Trucks, other equipment support operations

A fleet of 15 trucks is used to haul coal and rock. Two WABCO trucks with 75-ton capacities are primarily used as back up for small maintenance projects. Nine 95-ton capacity Dresser HaulPak trucks are used for both hauling coal and stripping dirt.

In 1995, a Caterpillar 785 haul truck was added to the fleet. The new truck has a capacity of 150 tons, over 50% greater than the 95-ton Dresser HaulPaks. By 1997, a total of four 150-ton trucks were in use. A custom modified bed allows coal and dirt to be hauled.

Many other pieces of equipment are needed to support day-to-day activities. UCM has several dozers including a Caterpillar D11N. The D11N is one of the largest tracked dozer manufactured in the world. Two road graders operate during day and night shifts to keep the haul roads smooth for the big trucks. A 75-ton, 14,000 gallon water truck provides road dust control. A high-pressure nozzle mounted on the tank truck is used to clean muddy equipment and fight fires.

Blasting loosens materials, casts overburden

Both overburden and coal are very difficult to excavate. Light blasting is done in order to loosen the overburden and coal before it is handled. A specially designed powder truck transports, mixes and loads explosives into each drill hole.

In some areas of the pit, a technique called "cast blasting" is used to help strip overburden. In cast blasting, the drill holes and explosive charges are designed so that a portion of the overburden is cast laterally by the force of the explosion into the adjacent mined out pit. This technique, when it can be used, reduces the amount of overburden that the dragline handles by up to 50%.