Mining Topic: Geologic Characterization
What is the health and safety problem?
The U.S. underground mine worker faces a continuing hazard from roof falls and other ground control related hazards. Many injuries and fatalities are related to mine roof that is weakened as a result of geologic factors. The roof may consist of rock that is inherently low in strength such as drawrock, thinly bedded rock, or mudstone. Further, the roof may be weakened or damaged by discontinuities such as clay veins, slickensides, joints, faults, and paloechannels.
What is the extent of the problem?
Research relating to a wide range of geologic factors has contributed to the decline in the number of injuries and fatal accidents resulting from roof falls. However, according to Mine Safety and Health Administration (MSHA) statistics (1999-2008), falls of ground were responsible for the largest portion (26%) of fatal incidents in the coal mining industry and about 40% of fatal incidents in underground coal mining.
How is OMSHR addressing this problem?
The Office of Mine Safety and Health Research (OMSHR) has developed, and is continuing to improve, methods for characterizing ground and its probable response to mining so that potential hazards can be identified and prevented.
What are the significant findings?
A number of tools – in particular classification and test methods – have been and continue to be developed. These include Coal Mine Roof Rating (CMRR) software, ground hazard mapping, ground condition mapping, diagnosis of moisture sensitivity, and gas content testing.
What are the next steps?
Further development of classification and test methods will continue in order to improve the ability of mine workers to anticipate hazards well before they are exposed.
Noteworthy Publications & Products
- A Measurement Method for Determining Absorption Coefficients for Underground Mines (2006-12)
This paper presents a method using a ray-tracing technique to determine absorption coefficients for underground mines. Absorption coefficients are determined and presented for octave bands from 63 Hz to 8 kHz.
- An Approach to Identifying Geological Properties from Roof Bolter Drilling Parameters (2000-08)
Rock drilling parameters including thrust, rotational speed, torque and velocity were examined to determine the ability to identify the strength of the rocks being drilled from the measured parameters.
- Application of the Coal Mine Roof Rating (CMRR) to Extended Cuts (1999-04)
The Coal Mine Roof Rating (CMRR) has been widely accepted as a tool for geologic characterization and mine planning. The application of the CMRR to extended cuts (cuts greater that 6 m (20 ft) in length) is discussed.
- CMRR - Coal Mine Roof Rating (2013-08)
Software for estimating the relative inherent strength of coal mine roof.
- Diagnosing and Controlling Moisture-Sensitive Roof in Coal Mines (2008-01)
Moisture-sensitive roof rocks have contributed to time-dependent roof falls. NIOSH research proves the value of a wet/dry cycling test for rock evaluation.
- Geologic Hazards and Roof Stability in Coal Mines (2003-10)
This report describes the geologic origin, association, and potential danger from the most common hazards. Discussions of weak rock include drawrock, rider coals, head coal, stackrock, and stream valley effects.
- Proceedings of the International Workshop on Rock Mass Classification in Underground Mining (2007-05)
The goal of the workshop was to allow leading practitioners of rock mass classification to share their experiences with the technique. The proceedings contain 16 papers from 9 countries. Applications in both hard-rock and coal mining are represented.
- Stability Mapping to Examine Ground Failure Risk: A Field Study at a Limestone Mine (2009-07)
This paper presents a description of geologic settings, mining conditions, rockmass characterization with geotechnical risk assessment, analysis, mapping, and control techniques used at an underground stone mine in Central Pennsylvania.
- Technology News 478 - Apparatus for Measuring the Gas Content of Coal or Rock Core Samples (1999-08)
An apparatus is described that advances the state of the art in gas content testing of coal or rock core samples. The design goals were to improve sensitivity/accuracy, durability, and ease of operation.
- Technology News 526 - Proceedings of the International Workshop on Rock Mass Classification in Underground Mining (2007-07)
The International Workshop on Rock Mass Classification in Underground Mining provided a forum for leading practitioners of rock mass classification from around the world to come together and share their methods and experiences with the technique.
- Using the Coal Mine Roof Rating (CMRR) to Assess Roof Stability in U.S. Coal Mines (2001-08)
The CMRR quantifies defects in the rock mass and compiles a strength value used for engineering design. The CMRR has been applied to a number of ground stability problems. The CMRR procedure and some of these applications are described in this paper.