Mark also gave input into an Australian Coal Association Research Program (ACARP) project that was evaluating the applicability of the Analysis of Longwall Pillar Stability (ALPS) and the Coal Mine Roof Rating (CMRR) to Australian mines. Both these methodologies, originated by Mark and others, are in current use in many Australian longwalls and have ongoing acceptance.

Subsequent research work undertaken by Mark Colwell resulted in a modification for Australian conditions of the ALPS approach, called Analysis of Longwall Tailgate Serviceability (ALTS). (An update of Colwell's work, which has been developed into software supported by Coffey Geosciences, will be published in late February).

The result of Mark’s visit was a conference paper called “Comparison of Ground Conditions and Ground Control Practices in the United States and Australia”, presented at the 17th conference on ground control in mining in August 1998.

By comparing the CMRR of Australian and US mines, and a range of other conditions, Mark’s major contention is that, contrary to popular belief, there are no unique "Australian" ground conditions, any more than there are unique "US" conditions. ILN will publish Mark’s complete paper in PDF format later in February.

Mark here outlines what is meant by the Coal Mine Roof Rating (CMRR).

To help engineers make better use of geologic information, Molinda and Mark (1994) proposed the Coal Mine Roof Rating (CMRR), which drew from the earlier work by ZT Bieniawski on Rock Mass Rating (RMR). The CMRR combined 20 years of research on geologic hazards in mining with worldwide experience with rock mass classification systems. It was developed in cooperation with several major US coal companies, using field data that was collected from nearly 100 mines across the US.

The CMRR weighs the geotechnical factors that determine roof competence, and combines them into a single rating on a scale from 0 to 100. The underlying philosophy of the CMRR is that it is not the strength of the intact rock that determines the stability of a mine roof, but rather the defects or discontinuities (like bedding planes or slickensides) which weaken or destroy the roof beam.

Originally, the data for the CMRR was collected at underground exposures like roof falls and overcasts. To make it more generally useful, procedures were developed for determining the CMRR from drill core (Mark and Molinda, 1996).

The CMRR has been applied to a variety of mine design problems, including longwall tailgate design, roof support selection, and determining the feasibility of extended cuts. One big advantage of the CMRR is that it can be applied to any coalfield, and allows meaningful comparison even where lithologies are quite different.

The CMRR has been successfully employed in the US, Australia, South Africa, and Canada.

Dr Mark is employed by the National Institute for Occupational Safety and Health (NIOSH) in the USA.