Published in December 2004 American Longwall Magazine

This is the premise behind a research project involving a control system on a roof bolter manufactured by J. H. Fletcher & Co. The research was undertaken by the West Virginia University Department of Mining Engineering by chairman Professor Syd Peng.

Peng presented an overview of the research at the MINExpo conference in September and at the Ground Control in Mining conference in August.

He said the research aimed to predict voids, roof separation and rock strength using collected drilling parameters.

A drill control system was developed for use with a rotary roof bolter. A real time display system was developed along with specially developed software to analyze and interpret drill sensor data.

Algorithms were developed for mapping roof rock strength and geological structures based on the results of numerous underground and laboratory tests.

The Analyzing Software was initially validated in laboratory tests. This was followed up by field trials that have been undertaken at one limestone and six coal mines.

Much of the initial work was undertaken over the last two years at Graymont’s Pleasant Gap limestone mine. The real time display was tested in production at the mine in May this year with excellent results. Importantly the take-up at the mine has been good.

During the first week of production the mine actively changed their bolt lengths a number of times based on void locations indicated by the software.

The use of the real time display in production is generating hundreds of data files on a weekly basis – the first time a machine with the feedback system has actively recorded data from all of the drilled production holes.

To gain an understanding of changing roof conditions, the drill control system monitors 17 parameters, including feed and rotation pressure, penetration and rotation rate, and bit position.

The underground tests found that both penetration and rotation rates affect feed pressure when drilling in hard and soft roof rock.

Feed pressure is the most sensitive parameter when the rock strength changes. In other words, when the drill encounters a void, feed pressure drops, providing a useful indication of the void’s presence. This has lead researchers to conclude that voids can be accurately located by feed pressure.

These tests verified that a void measuring under a sixteenth of an inch thick can be detected by the technology.

With this system the roofbolter operators immediately know relative roof rock strength and location of cracks/fractures as the hole is being drilled.

“The immediate feedback on the local roof condition that the Drilling Display System provides, amounts to a quicker and safer alternative to the scratch hole and the video bore-scope examinations that are performed after the bolting is completed,” Peng said.

He said the system has been shown to be accurate in coal mines roughly 80% of the time.

Definitive recognition of rock types remains elusive due to numerous variables such as bit wear and machine friction. This makes it impossible to calculate the relative hardness of the rock.

Peng believes Relative Material Hardness calculations will ultimately be refined and improved.

“In addition, as this system is utilized by the mine level and its full potential is realized, adding additional, more precise, and more expensive sensors can be justified. With the addition of more precise sensors, this system’s accuracy and potential can only be improved,” he said.