The underground coal mines that are currently of concern to subsidence professionals in Colorado were generally mined between 1860 and 1960. This 100-year period saw the coal mining industry advance from the use of picks, hand augers, black powder, and mules to the use of continuous miners and electric motors to mine and haul coal. As technology changed the method by which coal was mined and transported, the design of the typical Colorado room-and-pillar mine also changed. Depending on coal conditions, room size and shape often changed to better accommodate shovel or scraper loaders and shaker or belt loaders. These advances were not, however, adopted simultaneously by all coal mines. Although large corporate mines, like those of CF&I and the Union Pacific, began using such equipment before 1920, some of the smaller Colorado mines were still using hand augers and mules into the 1940’s. Therefore, careful study of dates of mining, production records, mine maps, and interviews with former miners can aid in predicting current mine conditions.
INTRODUCTION
Subsidence has been a problem since underground coal mining began in Colorado in the 1860’s. The camps that were established for the immigrant coal miners and their families at the mines were the only areas affected in those early days. However, some of these early camps have become urban or suburban areas, such as Colorado Springs, Louisville, Lafayette, and southern Jefferson County. Although only skeletons remain of most of the underground mines in Colorado, the problems left by the coal industry remain. Although we cannot go into most of these abandoned mines, we still need answers to our many questions. Questions such as: How were coal mines designed? How was early coal mining carried out? What techniques were used to mine and haul coal?
HOW WERE COAL MINES DESIGNED?
The underground coal mining industry in Colorado utilized the same basic mine design throughout its 100-year history, due to the generally soft, gently dipping subbituminous coal found in the State. This method of mine layout is called the “room and pillar method”, a design brought to the State in the 1860’s by Welsh and English miners. The entrance to a room and pillar mine could be vertical, called a “shaft”, or horizontal or sloping, generally referred to as a “slope” (downward from entrance) or “pitch” (upward from entrance). At the bottom of the entrance shaft or slope would be the main passageway into the coal seam, generally called a main “entry”, “haulageway”, or “motor road” (when electric motors used for haul age of the coal). This entry was nearly always a “double entry”, two parallel tunnels oriented such that fresh air was blown in one tunnel, circulated through the mine for ventilation, and exhausted through the second tunnel. The two halves of this double entry were separated by a chain pillar about 50 feet wide. This pillar was interrupted by “cross-cuts”, or connections between the haulageways about 60′ apart. The sides of haulageway were supported by 50- to 100-foot wide flank pillars. At right angles to the main haulageway were a number of cross entries, called, for example, “3rd & 4th South”, that were separated by 30-foot wide chain pillars. At right angles to the cross entries were the “rooms” or “entries”, which averaged 18- to 20-feet wide and were separated by 20- to 30-foot wide pillars. The length of these rooms varied, depending on the location of the room in the mine and the period during which it was mined. When adjacent rooms were mined to their final length, the pillars between the rooms were mined, or “pulled” as the miners retreated from the room.
Steeply dipping coal seams, as in the Jefferson County Field near Golden and Grand Hogback Field near Newcastle where dips ranged from 30 to 90 degrees, presented special problems for supporting the overhanging roof. In these fields, the rooms were driven above the entries in technique called “battery-breast” mining. A “battery” is a row of timbers that support the loose coal as it is being mined. A “breast” is the equivalent of a room in horizontal mining. In this mining method the miner stands on loose, previously mined coal as he drills and blasts the face above him. “Manways” were cut beside the breast to be used for entrance for the miners and the air. Coal was then loaded from chutes into cars. In this photograph of the Garfield-Vulcan mine near Newcastle, notice the dip of seam and the differences in angles of the timbers.
HOW WAS ROOM AND PILLAR COAL MINED?
The earliest & simplest technique for mining coal in Colorado was 11 pick mining as shown by the late 1800’s miners at Starkville near Trinidad. The open-flame lamps and soft caps used by the miners in the photograph are indicative of the pre-1910 mining era. The demand at this time was for large lump coal with little waste and picking was most efficient way to create large lumps. The daily production rate for a two-man crew of pick miners was generally 8- to 10- 1.5 ton cars, or about 12-15 tons per day. As more uses for coal were found and smaller coal could be used efficiently, undercutting of the face and blasting came into general use. By sitting on the mine floor, or even lying on his side, a miner would undercut the face with his pick. He and his partner would load the valuable pick coal, then drill and blast the face. Undercutting the face was necessary because “Shooting on the solid” weakened the roof rock and produced smaller, less valuable lumps.
About 1880, the first labor-saving coal mining machine was introduced in Colorado coal mines, the Ingersol punching machine. The puncher was a pneumatic (compressed air operated), three-pronged pick which cut an angled trench below the working face. The puncher allowed a 50% increase in production, which was very important at a time when miners were on contract and were paid by the number of tons of coal delivered at the tipple. In 1900, the first “Cutting machine”, a large, electric, horizontal chainsaw, was introduced in Colorado by 2 manufacturers – Sullivan and Jeffrey. These machines were used to cut a 6-inch high kerf 6-feet deep behind the face. The face was then drilled and blasted. These machines revolutionized mining because production nearly doubled, increasing to 20-25 cars/day or as much as 40 tons/day per crew. The machines also created a mechanics job for the man running the machine, who was paid hourly instead of being paid by the ton. Cutting machines were still being used in smaller mines throughout the State until the decline of mining in the 1940s.
HOW WAS COAL DRILLED AND BLASTED?
In the early days of Colorado coal mining, a “breast auger” , a hand-held, hand-operated, 6- to 8-foot 1ong drill, was used to drill shot holes. Black powder cartridges were then rolled by the miner and tamped into the shot holes with a wooden rod. The hole was then plugged with clay and a long, small diameter, copper (to prevent sparks) needle was inserted to open a hole into the cartridge. A “Squib”, a long bottle rocket, was then placed in the hole and lit with the miners open-flame head lamp. Later, mechanical augers were used to drill and Federally-approved explosives, electrically detonated by a professional shot firer, were used for blasting. Roof support in mines often determined mine profitability — too much time and money spent on timbering could drive a mine into the red. Main haulageways were often timbered on 2- to 5-foot centers using “square sets”, two posts supporting a heavy roof beam with a lagging of unpeeled wooden slabs, if more support were needed. Rooms were timbered initially by miners with “props and caps” , a single heavy post with short horizontal cap at the top. These props might be every 5 feet initially, but be moved further apart if the roof were hard sandstone or closer together if the roof were weak shale. These props were generally pulled so that they could be reused, but might be cut or blasted if they were wedged too tightly to be pulled. Pulling timbers allowed for roof collapse when a room was completed, so that the roof strain on adjacent, unmined coal could be relieved. The pulled rooms generally collapsed in a few hours to several days, but some stayed open for months. If floor squeeze (heaving due to overloaded pillars) was a problem, the timbermen often sharpened the bottom of the posts or the timbers not pulled. If the roof was very weak, a cribbing of horizontal timbers filled with rock (Figure 8) was sometimes used, but was nearly impossible to pull.
HOW WAS COAL HAULED FROM ROOM TO SURFACE?
Coal was initially loaded with a #2 shovel. A mine car could hold 2500 to 3000 pounds when the lump coal was stacked around the edges and the center filled with smaller pieces. The primary method of hauling the full and empty cars from the rooms to the bottom of the shaft or slope was by mule. Even into the 1940’s, mules were still in use at some small mines in Colorado. A good mule could haul 6 or 7 loaded cars on level grades. The first electric motors were invented in 1890, but were used only in large mines of the CF&l and Northern Colorado Coal companies until after the 1910-1915 strike. These “motors” were used to haul the loaded cars to the bottom of the shaft, where cars were raised by a hoist, or to the tipple of slope mines as shown near Trinidad. The first mechanical loaders were used in Colorado during World War I due to the shortage of men to work the mines. The Joy loader, first used in 1919, later common throughout the Colorado coal fields, increased production about 50%. This was less than expected because loading was only part of the job of the miner. Loaders loaded coal directly into mine rail cars in some mines, but generally loaded into shuttle cars, “Buggies”, which, in turn, loaded rail cars. Shuttles were generally battery operated, but some were cable-reel operated.
During the mid-1920s, conveyors were first introduced for hauling coal from rooms to rail cars. The first common type was the sectional shaker conveyor, called a “pan line” by miners, which could be moved in 6-foot long sections weighing 125 pounds. A major manufacturer was the Jeffrey Company, which built the pan line in the Monarch #2 near Louisville. Combined with duckbill or Joy loaders, conveyors increased output per crew to 50 to 60 tons per day by the mid-l930s. By the late l930s, continuous mining machines with cutting heads, loaders, & conveyors built into one machine had been invented. Continuous miners were not generally used in Colorado until after World War II due to war production priorities. Because coal was being displaced by natural gas for domestic heating at the same time, only a few, large, generally new mines could afford them. Production rates with the continuous miner increased to 100 to 150 tons per day per crew, but the biggest advantage was the speed of mining. A room that had taken a month for pick miners could be done in one day, so little or no timbering was necessary. As shown in the photo of the Lincoln Mine near Frederick, the shape of the room could also add to roof stability, since an arch roof is stronger than a flat one. Rock bolts were also beginning to be used at this time in main haulageways and cross-entries.
HOW FAST WAS COAL MINED?
Rooms varied in size with the era of the mining. In the days of pick coal and black powder, rooms were 50-feet wide, including pillars, by 100-feet long. At a 4-foot per day rate of advance and retreat, it took 2 men 2 months to 1 ay track, timber, mine, and load one room. Therefore, the roof in one room had to remain stable for at least this period and heavy timbering was required. With the coming of automatic loaders and conveyors, rooms became longer — up to 300 feet long due to the time and effort required to set up and take down the conveyor. Due to mechanization, however, these long rooms could be mined in the same period of time as the older, smaller rooms. Continuous mining machines could create a 50- to 100-foot long room in one day. Therefore, rooms became shorter, but only had to remain open for a few days, not months.
SUMMARY
In conclusion, a knowledge of the period of mining and the techniques used in mining can aide in determining the potential for subsidence over abandoned mines that cannot be re-entered. This knowledge may be gained through the use of mine maps, historical documents, and interviews with miners.
REFERENCES
Margolis, E., 1985, Western coal mining as a way of life: Journal of the West, July.
Rocky Mtn. Coal Mining Institute, 1913, 1918, 1924-26, Proceedings.
Note: This paper was written by Stephen S. Hart of Stratitek Inc., Lakewood, Colorado and published as part of the Colorado Geological Survey’s “Proceedings of the 1985 Conference on Coal Mine Subsidence in the Rocky Mountain Region.”