The depth of cover increases rapidly, from zero to more than 2000ft; access to the coal can be difficult due to an extensive burn zone at the outcrop; and five major faults have been encountered at the No. 2 mine alone.

“Igneous sills have penetrated parts of the reserve, coking the coal in place and rendering it difficult to impossible to mine. The immediate roof varies widely, from competent sandstone in some places to very weak mudstone in others. Seam splits and riders also cause local roof problems. Extensive slump faults, caused when the soft sediments slumped shortly after deposition, have been a problem in the Upper B Seam mine in some areas,” said authors** of the Geology, ground control, and mine planning at Bowie Resources paper presented at the 25th International Conference on Ground Control in Mining last year.

So with all this to contend with, what has Bowie done to continue achieving output in excess of 4 million tons per annum? It has implemented one of the nation’s most proactive ground control programs. Some of the unique elements of the Bowie program include:

Roof bolt operators log the stratigraphy of test holes in nearly every cut. These “lith-graphs” are used by section foremen to determine the need for additional roof support, and they are entered into the geologic data base for use in geologic modelling and mapping.

Underground core drilling is conducted to obtain data for Coal Mine Roof Rating (CMRR) and stability maps.

Weekly “Quality Meetings”, involving mine management and technical staff, are held to ensure that ground control information is integrated into production operations.

“What makes the program effective, however, is the day-to-day involvement of the mine’s personnel in ground control, from the mine manager to the production crews,” the paper said.

Another core element of the Bowie program is a comprehensive geologic data collection regime.

“At Bowie, the geologic database is considered a living entity, that grows and changes as new information is collected,” the paper said.

“One important goal is to develop a geologic model that facilitates predictions about conditions in advance of mining. The model provides insight into sandstone channel trends in the roof and floor, seam splits and partings, and fault trends.”

Geologic information is gathered at several scales, beginning with pre-mining surface core drilling and geophysics.

Underground core drilling has been used to fill many of the gaps between surface holes.

Finally, roof lith-graphs and underground mapping provide detailed documentation of the near-seam geology.

With the technical data gathering covered, Bowie perceives it essential that everyone is communicated this information. Two-way communication between the geologic staff and the operations people is essential.

“The geologists know that they must acquire credibility by making predictions that are useful. To do this, they need to understand the needs of the production side,” the paper said.

Bowie conducts weekly “Quality Meetings” attended by the mine manager, technical services manager, development production coordinator, longwall manager, mine engineer, surface operations superintendent, customer relations-shipping manager and the geologists.

Prior to the meeting, a geologist goes underground to map the faces in the development sections and on the longwall and prepares face maps of existing conditions. The attendees discuss the experience of the past week, and the stability map projections and the geologic forecast for the upcoming week regarding conditions, productivity and quality. The stability map and the relevant cross-sections are displayed during the meeting.

“At one recent meeting, one of the development sections was encountering a rider seam, while the longwall was dealing with slump faulting on the face. The geologists were able to predict how much longer these features would be present, and what forms they were likely to take. The discussion focused on control techniques, particularly the proper mining horizon for each face,” the paper said.

Decisions about roof support in the development sections are made daily at the Bowie Mine. While a set of guidelines has emerged over time, the rapidly changing conditions preclude rigid standards. The primary decision maker is the production coordinator, but every member of the ground control team contributes.

Specific lessons learnt at Bowie from its ground control program include:

Bowie conditions are best suited to cross-panel radar imaging which project zones of slumping and weaker roof in the B2 longwall panel.

Roof bolter operators are a key source of data on changing roof conditions. Use of a lith-graph system allows this experience and information to be captured for use in subsequent analyses. The data is particularly important for CMRR analyses and stability analyses.

Weekly quality meetings attended by senior operations, engineering, geology and surface personnel are an important tool in determining developing trends and problems in ground control and as-shipped coal quality.

**Article adapted from a paper by Bowie Resources technical services manager Collin Stewart, Bowie Resources senior geologist Greg Hunt and NIOSH rock mechanics section chief Christopher Mark. “Geology, ground control, and mine planning at Bowie Resources, Paonia, CO” was presented at the 25th International Conference on Ground Control in Mining.