U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health TRAPED

MENT OF HEALTH & HUMAN SERVICES . USA

Figure 1.—A strata control engineer collects data for the CMRR.

NIOSH Releases New Coal Mine Roof Rating Software

 

Introduction

The Coal Mine Roof Rating (CMRR) is a roof classification

system. It was first introduced to the mining community in 1994.

The CMRR filled a longstanding need to quantify geologic

description of coal measure rocks into an engineering value that

could be used for mine design. It has now been written to a userfriendly visual basic code that can be run on any PC with a Windows

operating system.

Background

Rocks that form the roof of coal mines can vary widely and

quickly in composition, extent, and defects. This results in an equally

broad range of rock properties that can substantially affect the ability

of the rock mass to form a stable mine roof. The CMRR was

designed to evaluate the properties of the coal mine roof rock mass

that contribute to its weakness and convert them into a relative

strength rating from 0 to 100. These properties include the cohesion

and frequency of discontinuities like bedding, slips, shears, and

joints; uniaxial compressive strength (UCS); and moisture sensitivity.

With simple lab and field tests and observation, the CMRR can be

calculated by technical and operating personnel with a minimum of

training.

The CMRR has been widely accepted in both U.S. and

international coalfields. As a result, a number of roof control

applications have been found for the CMRR. It is currently used as

an input component in the Analysis of Longwall Pillar Stability

(ALPS) program, which is used to design longwall chain pillars. It

can be used as a criterion for determining the appropriate width of

mine entries. It has also been used to indicate the appropriate length

of cut in weak ground. The CMRR can be used as a strength

parameter to characterize interburden between mined seams in the

numerical modeling of subsidence effects. In any area where an

estimation of coal measure rock mass strength is required, the CMRR

can be adapted to fill this need.

How It Works

Originally designed to be used with underground exposures, the

CMRR can also be calculated from core. The chisel test for bedding

cohesion and the ballpeen hammer test for UCS are inappropriate for

core. These tests have been replaced by point load testing both

axially and diametrally. Two other measures that are common to

standard core logging—Rock Quality Designation (RQD) and

fracture spacing—are also used to estimate rock weakness. With

these easily obtained parameters, the CMRR can be calculated from

core and used in the mine planning and exploration phase.

The input screens allow calculation of the CMRR for both

underground exposure and core. The CMRR is reported both as a

"dry" value and as a groundwater-adjusted value for moisturesensitive rocks. There is a graphical output report featuring a

lithologic column with annotated unit ratings and a roof bolt symbol

representing the height of the bolted horizon. Another important

feature is an AutoCAD interface. This feature allows the export of

located CMRR data directly to an AutoCAD layer in XYZ form. In

this way, drill hole data can be inserted directly to a base map.

Technology News

Milestones in Mining Safety and Health Technology

SAFER HEALTHIER PEOPLE

No. 505 April 2003
Figure 2.—Data screen with calculated CMRR values

For More Information

To order a free disk containing the CMRR software, along with

all of the other NIOSH ground control software (ALPS, ARMPS,

STOP, SHIELD, TGRSS, ARBS, AHSEM, DUCS, and

LAMODEL), contact Donna Opfer at (412) 386-6564, e-mail:

dopfer@cdc.gov. Or you may complete the order form below,

detach, and mail to: Donna Opfer, NIOSH Pittsburgh Research

Laboratory, Cochrans Mill Rd., P.O. Box 18070, Pittsburgh, PA

15236-0070, or fax to (412) 386-6891.

To receive more information about occupational safety and health

problems, call 1-800-35-NIOSH (1-800-356-4674), or visit the

NIOSH Web site at www.cdc.gov/niosh

Mention of any company name or product does not constitute

endorsement by the National Institute for Occupational Safety and

Health.

G Please send me a free disk that contains the Coal Mine Roof Rating software, along with the other NIOSH

ground control software (ALPS, ARMPS, STOP, SHIELD, TGRSS, ARBS, AHSEM, DUCS, LAMODEL).

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