Mining Topic: Roof Support
What is the health and safety problem?
All underground mines can be subjected to ground falls. As a result, over 90 % of the more than 700 underground mines use some form of roof or rib support. Therefore, ground falls represent a significant hazard to undergrounds mine workers. Appropriate support selection and adequate support system design is critical to the prevention of the ground falls and ground fall accidents.
What is the extent of the problem?
Ground fall accidents in underground mines cause 8 to 10 fatalities and over 800 injuries every year. This represents about 30% of the fatal accidents and 15% of the injuries that occur each year in underground mines. In addition, there are nearly 2,000 reportable non-injury ground falls.
How is OMSHR addressing the problem?
The Office of Mine Safety and Health Research (OMSHR) has conducted research on a number of issues pertaining to ground support. Research areas include the design and performance of intrinsic support systems, the performance of standing support systems, surface control systems, and the effects and mitigation of horizontal stress.
What are the significant findings?
OMSHR research has developed information and software on the design and performance of various ground support systems including:
Standing Support Systems – The Support Technology Optimization Program (STOP) is a software package that provides load-displacement performance curves, design guidelines, and recommendations for the installation and use over 100 different types of standing supports. The load-displacement characteristics of the standing support systems are determined in the OMSHR Mine Roof Simulator (MRS).
Intrinsic Roof Support – An empirically based software package, Analysis of Roof Bolt Systems (ARBS), has been developed to assist in design of roof bolt systems in coal mines.
Surface Control – OMSHR publications have documented the advantages of using roof screen or mesh to prevent ground fall injuries. The performance characteristics of the roof screen have also been developed. For shotcrete, tools have been developed to measure the early strength, toughness, and in situ adhesion and installation quality.
Coal Mine Roof Rating (CMRR) – The Coal Mine Roof Rating is a roof classification system that was first introduced to the mining community in 1994. The CMRR is a rock mass classification system that calculates the inherent strength of coal mine roof, primarily within the bolted horizon. It can be used in the design of gateroads, roof bolt selection, extended-cut decisions, and numerical modeling.
Stone Mine Roof Span Design – A survey on roof span issues and design practices discusses the observed factors contributing to roof instability.
What are the Next Steps?
OMSHR is researching the design of roof support systems in coal mines by developing an improved understanding of how intrinsic support systems function in supporting coal mine roofs. Testing of new standing support systems is ongoing in the Mine Roof Simulator.
Noteworthy Publications & Products
- Analysis of Roof Bolt Systems (2001-08)
A statistical study of roof bolt performance was conducted in 37 U.S. mines. Analysis of the results led to guidelines for making preliminary estimates for bolt length, capacity, and pattern to improve roof stability in difficult conditions.
- Computer Simulation of Ground Behaviour and Rock Bolt Interaction at Emerald Mine (2004-08)
This paper focuses on a computer simulation used to model roof behavior and rock bolt interaction in a collaborative study of ground behavior, reinforcement performance, and stress redistribution in a coal mine entry under severe horizontal stress.
- Development and Application of the Coal Mine Roof Rating (CMRR) (2007-05)
This paper discusses the sources used in developing the CMRR, describes the CMRR data collection and calculation procedures, and briefly presents a number of practical mining applications in which the CMRR has played a prominent role.
- Mistakes, Misconceptions, and Key Points Regarding Secondary Roof Support Systems (2001-08)
This paper discusses misconceptions about how roof supports perform and factors that impact their performance. The paper is limited to a discussion of secondary roof support systems and powered roof supports such as longwall shields.
- Optimizing Secondary Roof Support with the NIOSH Support Technology Optimization Program (STOP) (2000-08)
The 1990s saw an unprecedented increase in technologies for more effective, easier to install roof support in underground mines. To facilitate application and improve mine safety, NIOSH developed the Support Technology Optimization Program (STOP).
- Performance Characteristics for Welded Wire Screen Used for Surface Control in Underground Coal Mines (2009-02)
The load-deformation characteristics and the load capacity of welded wire screen (roof screen) used to control ground fall were evaluated in the laboratory in a specially built test frame.
- Proceedings: New Technology for Coal Mine Roof Support (2000-10)
The proceedings provide information on several new technologies including guidelines for roof bolt length, pattern, and capacity; a new design method for longwall tailgate supports; and a technique for measuring loads developed within cable bolts.
- Proceedings: New Technology for Ground Control in Retreat Mining (1997-03)
This proceedings volume contains papers presented at technology transfer seminars sponsored by the National Institute for Occupational Safety and Health (NIOSH) on New Technology for Ground Control in Retreat Mining.
- Pumpable Roof Supports: An Evolution in Longwall Roof Support Technology (2008-12)
This report examines the development of modern pumpable roof support technology and provides a full description of the performance capabilities of each of the support products now on the market.
- Roof Span Design for Underground Stone Mines (2010-07)
In this paper, the findings of a survey of roof span stability issues and design practices are presented, and the observed factors contributing to roof instability are discussed.