Blasting loosens materials, casts overburden

Both overburden and coal can be very difficult to excavate. Therefore, blasting is necessary in order to loosen the overburden and coal before it is moved by the heavy "yellow-iron" equipment. A specially designed powder truck transports, mixes and loads explosives into each drill hole. A technique called "cast blasting" is used to help remove the overburden. During 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 utilized, reduces by up to 25% of the amount of overburden that the dragline must handle. Cast basting is a significant cost savings when compared to utilizing trucks and shovels. There is less wear and tear on equipment, less consumption of diesel fuel, and fewer employees are required.

Dozers move overburden short distances

Many other pieces of support equipment are needed to conduct day-to-day activities. UCM uses dozers including a Komatsu 475A-5 dozer and several Caterpillar dozers including the D11R-CD, Carry Dozer. They are some of the largest tracked dozers manufactured in the world. Two road graders operate during day and night shifts to keep the haul roads smooth for the big trucks. Two water trucks provide dust control on the roads. Additionally, a high-pressure nozzle mounted on the water trucks serves as ready reaction equipment for fighting fires.

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 component parts on 26 railcars and 40 trucks during December 1977. It took 11 months to assemble the 2,100-ton machine. Named "Ace-in-the-Hole" by Healy school children, the dragline is the largest land mobile machine in Alaska. The acquisition of "Ace-in-the-Hole" made it possible to double coal 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 24,000 yards of dirt, leaving a strip of uncovered coal 145-feet (or more) wide. Stability for this heavy machine is achieved by the large steel plate (the tub) which rests on the ground during drag-line operations. Wheels or tracks would be impractical due to its extreme weight. The dragline moves by "walking." Shoes on both sides of the machine lift the base partially off the ground and drag it backward. Each step takes about 40 seconds and moves the dragline a distance of approximately 7 feet. While it takes only one person to operate the controls, there are two 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. Since the dragline was commissioned in 1978, it has operated for more than 100,000 hours of digging. It moves approximately 6 to 7 million cubic yards of overburden every year.     

The dragline is powered solely by electricity. A Load Stabilizer System consisting of a 40-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 process enables the dragline to operate without causing power fluctuations for other electrical customers.

The dragline has several buckets, which are used on a rotational basis. UCM utilizes several different configurations of bucket including 33-, 35-, and a high-production 42 cubic-yard bucket. Each bucket is used on the dragline for approximately 4 to 6 months. After that period, the bucket must be serviced repairing critical surfaces of the bucket vulnerable to the abrasive excavated materials. The bucket is repaired by welding wear plates on critical surfaces vulnerable to the abrasive materials that are excavated.

While the dragline does the majority of the excavation work at the mine, additional excavators are needed. Two track-mounted O&K excavators, RH120C backhoe and an RH170 shovel, are used to load coal and to strip overburden in areas difficult for the dragline to maneuver and trucks with rock and gravel for construction projects. The backhoe has a 16 cubic-yard bucket and is powered by twin 567 horsepower diesel engines. A large hydraulic shovel, the O&K RH-170, was to UCM's fleet in August 1997. Its shovel has a 26 cubic-yard bucket and can load the 150-ton trucks in four passes.