Mining Topic: Slope Stability

What is the health and safety problem?

Slope Stability

Whether underground or on the surface, unexpected rock movement can cause injuries and can potentially result in a mine catastrophe. Even relatively shallow strip mines and quarries can experience devastating consequences from slope failure. Open-pit mines are deeper than ever before, and because rock mass strength at these large scales is difficult to evaluate, massive slope failure can occur with little warning.

What is the extent of the problem?

The injury and fatality rates from surface mining rock fall accidents are significantly less than from underground rock falls. Over the last 5 years there were only 7 fatalities caused by highwall or slope failure. However, these infrequent events have the potential for catastrophic failure that could affect many mine workers.

How is OMSHR addressing this problem?

The Office of Mine Safety and Health Research (OMSHR) has examined (1) design of augering patterns for safe mining of coal from highwalls has also been examined through numerical modeling, analytical and empirical techniques; and (2) technologies to identify zones of weakness in a mine slope and determine the likelihood of slope failure.

What are the significant findings?

OMSHR developed and released a software package, called ARMPS-HWM, for design of extraction patterns in highwall mining. A software package for assessing bench stability in highly fractured rock slopes was also developed, examining plane wedge, step path and wedge failure modes (Bplane, Bstepp and Bwedge – respectively). A number of developing technologies with potential for revealing zones of weakness in a mine slopes have also been examined. These experimental methods may one day contribute to remote sensing of potential areas of weakness in mine slopes.

What are the next steps?

OMSHR is monitoring the industry to determine if there is an upswing in associated hazards.

Noteworthy Publications & Products

• A Portable Spectro-Polarimetric Imager: Potential Mine Safety and Geologic Applications (2012-08)
  High-resolution hyperspectral imagery operating in the visible to shortwave infrared can help identify and map argillic zones in host rocks; these zones add a significant risk in assessing and modeling catastrophic slope movement in open-pit mines.
• A User's Guide for the Bplane, Bstepp, and Bwedge Computer Programs (2012-08)
  This guide covers the theoretical basis, application, and operation of three computer programs: Bplane, Bstepp, and Bwedge. These programs can be used to evaluate potential plane shear, step-path, and wedge failures along the crest of a slope bench.
• Analysis of Bench Crest Performance at the Yellowstone Mine: A Case Study (2008-07)
  A case study is presented that relates statistical descriptions of joint sets to the distribution of local wedge failures along the crest of a catch bench at the Yellowstone Talc Mine.
• Analysis of Practical Ground Control Issues in Highwall Mining (2012-08)
  This article discusses highwall stability, reasons for early pull out of highwall miner holes, and geotechnical engineering and planning factors, as well as operating practices to improve highwall stability and minimize the risk of a trapped miner.
• Analysis of Safety Aspects and Mining Practices for Effective Ground Control in Surface Mining (2012-08)
  To determine causes of slope failure and highwall/spoilbank failure, this study reviews accident statistics, surface mining laws, the relevant literature, and observations from mine visits. The study emphasizes surface mines in WV, OH, and PA.
• Applications of the Point Estimation Method for Stochastic Rock Slope Engineering (2012-09)
  The point estimation method for the probability of sliding is efficient and expedites slope stability simulation routines in NIOSH software to stochastically describe rock slope behavior and assist engineers in catch bench design for large slopes.
• Assessing and Monitoring Open Pit Mine Highwalls (2012-08)
  This paper introduces warning signs of slope instability so operators are better able to recognize hazards. The most common slope monitoring equipment and practical methods of installation are discussed as well as the limitations of these systems.
• Economics of Safety at Surface Mine Spoil Piles (2012-08)
  Short-dumping rather than edge-dumping might reduce dumping-related accidents, but many operators believe it is less cost effective. To evaluate this perception, NIOSH reviewed the costs of various dumping methods at waste and spoil piles.
• Ground Control Design for Highwall Mining (2012-08)
  Highwall stability remains a major concern during highwall mining. Geologic structure (hillseams) and pillar stability are the two major factors affecting highwall stability.
• Simplified Hyperspectral Imaging for Improved Geologic Mapping of Mine Slopes (2010-06)
  A prototype portable hyperspectral imager was field tested at an open-pit mine as part of an investigation of remote sensing technologies for use in detecting and monitoring conditions in surface mines that could lead to catastrophic slope failure.