Mining Topic: Rock Falls

Rock fall

What is the health and safety problem?

Falls of rock from the roof are one of the leading causes of injuries and fatalities for mine workers.

What is the extent of the problem?

Underground mining still has one of the highest fatal injury rates of any U.S. industry—more than five times the national average compared to other industries. Between 1999 and 2008, nearly 40% of all underground fatalities were attributed to roof, rib, and face falls. Small pieces of rock falling between bolts injure 400–500 coal mine workers each year.

How is OMSHR addressing this problem?

The Office of Mine Safety and Health Research (OMSHR) is working to combine empirical, laboratory, and numerical studies to advance the state-of-the-art methods for protecting mine workers from all forms of rock fall. Major roof falls and rib falls are the focus of our current work, including studies to improve the support design methodologies and to provide "best practices" through training and health communications. OMSHR is also funding and collaborating on external research projects. This work focuses on early fall warning devices and improved bolting equipment, which primarily involves smart bolters that evaluate the roof composition and conditions in real time while bolting.

What are the significant findings?

OMSHR has made significant findings in the areas of "best practices" related training and improved fall warning devices. Improvements in technology, such as the use of personal bolter screens to prevent small falls and reduce injuries, have been found to provide significant protection to mine workers in many instances.

What are the next steps?

OMSHR is actively investigating how to protect mine workers from rock falls in ribs of coal mines and apply numerical modeling tools to design support that will reduce large falls of roof. OMSHR’s comprehensive approach to ground control looks at global stability which can be maintained with good pillar design, local stability which can be maintained with good roof controls, and surface or skin control with screening.

Noteworthy Publications & Products

• Comparative Analysis of Moisture Sensitivity Index Tests for Coal Mine Roof (2012-08)
  This paper describes the work NIOSH has completed in evaluating three moisture-sensitivity index tests on roof rocks from 23 U.S. coal mines.
• Early Strength Performance of Modern Weak Rock Mass Shotcrete Mixes (2012-08)
  A field-expedient test method and portable on site test equipment have been developed to measure shotcrete strength in the first six hours after application.
• Numerical Model Calibration for Simulating Coal Pillars, Gob and Overburden Response (2012-08)
  The paper provides a basic set of input data and a modeling approach that can be used for numerical modeling investigations of various coal mine designs using the FLAC3D software package.
• Pillar Strength in Underground Stone Mines in the United States (2012-08)
  Stone mines in the eastern and midwestern United States use the room-and-pillar method of mining to extract relatively flat-laying sedimentary formations. A survey of pillar performance was carried out to identify potential modes of instability.
• Potential of Roof Screening to Reduce Workers’ Compensation Cost (2012-09)
  Many rock fall injuries can be prevented with roof screen, but many coal mines are reluctant to use it due to added cost. This study looked at potential savings in workers’ compensation premiums due reduced rock fall injuries after roof screening.
• Reduced Workers’ Compensation Costs With Roof Screening (2012-08)
  This paper quantifies potential savings in WC premiums due to a reduction in rock fall injuries after roof screening in Pennsylvania’s underground coal mines. Two hypothetical mines with realistic injury and WC premium estimates were used.
• Stability Mapping to Examine Ground Failure Risk: A Field Study at a Limestone Mine (2012-08)
  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 455 - Roof Hazard Alert Modules (2005-04)
  The new permissible-type, intrinsically safe design modules described here represent an engineering intervention strategy toward improving miners' ability to recognize and avoid the hazardous zone of unsupported mine roof.
• Time Dependent Roof Deterioration at a Central Ohio Coal Mine (2012-08)
  This paper describes a NIOSH field study to evaluate mine entries with highly moisture-sensitive roof rock for long-term stability and seasonal effects. It presents the results from the field study and the key issues determined from the study.