Incorporated in 1974, The Falkirk Mining Company is a wholly owned subsidiary of The North American Coal Corporation. Falkirk supplies about seven million tons of lignite annually to a 1,100 megawatt electric generating station owned and operated by the Great River Energy Cooperative of Minnesota, from two pits near Underwood in central North Dakota, about 100 kilometers north of Bismarck. They are currently working two coal seams, one of them about 1 meter in thickness and the other about 3-4 meters, at depths of 8-40 meters, separated by about 6 meters of clay and sandstone interburden. Overburden consists mostly of sandy shale and glacial material. The pits are about 3 km long and 60 meters wide, and are worked by a pair of Marion 8750 electric-powered walking draglines.
As required by the Surface Mining Control and Reclamation Act, the land is being restored to its pre-mining condition. Land reclamation is being accomplished contemporaneous with the mining operations in strict compliance with state and federal regulatory requirements. As the dragline works its way down the pit, a dozer fleet levels and grades the spoil piles of overburden to the approximate desired contour. A truck shovel fleet then brings in subsoil from newly uncovered land, followed by tractor-scrapers with topsoil. The land is graded to the approximate original contours, referring to topographic maps created prior to the excavations. In the case of Falkirk, the terrain is mostly flat or gently rolling prairie, used primarily for agriculture or grazing.
Pioneer in Satellite-Based Machine Guidance
Falkirk was one of the first mines in the United States to adopt GPS machine guidance technology. The company started investigating the use of GPS for machine guidance in 1997. After evaluating several potential vendors, they began a demonstration project in April 1998 using the new Dozer 2000 GPS system from Leica Geosystems, integrated with specialized software developed by Carlson Software. The demo system was installed on one of the Caterpillar D11 bulldozers working primarily in overburden grading. In June, a second system was installed on a supervisor’s pickup truck for further evaluation.
The Dozer 2000 machine guidance system includes a ruggedized high-precision GPS receiver, radio data receiver and touchscreen computer. The GPS antenna is mounted on the top of the cab, where it has a clear view of the orbiting satellites. The GPS receiver calculates its position in three dimensions 10 times per second. The position data is corrected for local-area errors using data transmitted from a fixed differential GPS reference station. The touchscreen computer is mounted in the cab. The computer compares the actual GPS position to the desired finished terrain, using grid files created from topographic maps. The large, bright display provides visual guidance to the operator for maneuvering the vehicle and positioning the blade to achieve the cut and fill values needed to match the computer model.
According to Gerry Lannoye, software engineer/analyst, who has been deeply involved in Falkirk’s GPS program from the beginning, the system was an immediate hit with machine operators. "We took daily feedback reports from the machine operators during the trial period," he said. "Then we worked closely with Leica and Carlson to fine tune the system and iron out glitches."
Based on the success of the initial trials, additional Dozer 2000 systems were purchased over the next two years. Today, Falkirk has a total of 12 systems installed on a variety of vehicles, including eight bulldozers (four Caterpillar D11s, one Caterpillar D8, one Caterpillar D10 and two Komatsu D375A’s, one motor grader, one tractor scraper and two pickup trucks. The D11s are mostly used for spoil pile leveling, while the D8 and D10 are used in subsoil respread. The Komatsu dozers work on the dragline bench.
A fixed differential GPS (DGPS) reference station, consisting of a Leica MC1000 GPS receiver, GPS antenna and one-watt radio transmitter has been established on top of Falkirk’s coal silo to provide local-area error corrections for the satellite signals. The DGPS data is transmitted via 900 MHz radio frequencies through repeaters to the GPS "rovers" working in both pits. The mobile Dozer 2000 systems use the error correction data to fine-tune the position accuracy to 2-5 centimeters.
Lannoye reports that Falkirk has achieved important cost savings and productivity gains by reducing rehandling of overburden and subsoil. "Our goal is to put the right amount of dirt in the right place the first time. This means handling the material once. Rehandling is very expensive, in terms of labor, machinery maintenance and life-cycle costs for the equipment."
Using the Dozer 2000, the operators can typically bring the surface within 9-12 cm of the design grade without the use of survey stakes, even at night. There is less downtime, since the dozer operators no longer have to wait for surveyors to come to the site and replace stakes that have been knocked down or covered over.
While it is harder to measure, there has been a tremendous upsurge in morale among the machine operators. "The operators love the system," said Lannoye. "It empowers them to do a great job independent of surveyors and stakes. They get a better ‘feel’ for the terrain model and can better visualize the contours. The topographic files displayed in the cab clearly show drainage, hilltops, valleys, wetlands and other terrain features. We already had the best operators in the industry and this tool enhances their performance."
The machine operators like the touch-screen display with its large graphics and intuitive operating procedures. At a glance, the operator can see the cut and fill values needed to match the topographic design model.
There is a lot less friction between shifts, especially in the morning. The morning shift no longer has to worry about undoing work that had been done during the night. When the new operator climbs into the cab, he simply touches an icon on the screen. When he sees the "target" symbol in the upper right corner, he knows that the surface is within design tolerances.
Lannoye also pointed out that the system has made it easier to measure productivity. "In the past, we were unable to quantify the amount of spoil being handled by each machine. Now we can track productivity on each machine," he said.
The Dozer 2000 technology has encouraged more innovation by machine operators, who are constantly seeking out new applications.
For instance, last winter, when freezing temperatures made it impossible to handle topsoil, the truck shovel and tractor scraper fleet was redeployed for final highwall reclamation at another site that was being closed. Because some of these vehicles were not equipped with Dozer 2000 systems, the reclamation supervisor was able to drive his GPS-equipped pickup truck to the site and stake it out quickly for the shovel and tractor scrapers. This resulted in considerable savings, according to Lannoye.
In another case, one of the bench dozer operators used the Dozer 2000 to map breaks in the dewatering pipes that had been ruptured by bench building for the draglines. This made it easy to guide the pump crews back to the exact location of the buried pipes, to make repairs. And in another, a dozer operator used the slope function in the Dozer 2000 to engineer a runoff slope and drain a large water puddle in the spoil area, permitting work to resume without waiting for pumpout.
Falkirk innovated and served as a testbed for GPS machine guidance technology in The North American Coal Corporation. Following the field trials at Falkirk in 1998, a number of other North American Coal subsidiaries also purchased and installed Dozer 2000 systems. Today, North American Coal has 37 Dozer 2000 systems operational at the San Miguel lignite mine in South Texas, the Sabine mine in Texas the Coteau mine in North Dakota and Mississippi Lignite Mining Company, which was recently acquired by North American Coal.