Mining Project: Support Design Procedures for Difficult Ground Conditions

Research Summary

Ground falls remain the highest single cause of fatalities and injuries in underground coal mines. Over the 5-year period 2003 to 2007, falls of ground were responsible for 40% of all fatalities in underground coal mines. Overall, failure of the support system contributed to 38% of all the fatalities that occurred in room-and-pillar excavations. In pillar recovery operations failure of the support system accounted for 23 of the 24 reported fatalities. In addition, more than 2,000 unplanned roof falls are reported annually in underground coal mines. Each of these roof falls represents a failure of the installed roof support systems. 

This project developed improved support design guidelines for coal mines based on an engineering assessment of the ground conditions, support capacity, and rock loading of the support systems. The guidelines were developed from a combined effort of field studies, laboratory testing, and advanced numerical model applications. The field and laboratory studies provided essential data for numerical model development and verification. This project contributed to the strategic goal of reducing ground fall fatalities and injuries in underground mines through improved support design. The project outcome is a reduction in rock fall injuries and fatalities caused by a failure of the ground support system.

The project tasks included:

• Task 1: Ground Characterization (1/2010 – 9/2011): Review of published data and laboratory testing to determine rock and bedding plane properties and likely variation of properties. Identify the in-situ field stresses, loading conditions, failure mechanisms and characteristics of the different mining districts. Develop numerical modeling procedures to realistically simulate ground response around coal mine entries.
• Task 2: Support Characterization (1/2010 – 9/2011): Review USBM, NIOSH, and other published laboratory and field tests of support systems to obtain data on load transfer from supports to the rock mass, impact of grout, anchorage issues, grout annulus, rock integrity, and installation difficulties such as incomplete resin mixing. Obtain published properties of bolts, cables, trusses, and associated installation hardware such as bearing plates. Calibrate numerical models against rock bolt performance in laboratory tests.
• Task 3: Field Studies (1/2010 – 6/2012): Provide technical support and oversight during NIOSH-funded field study site in collaboration with Southern Illinois University. Review and collate the field data into suitable format for analysis and calibration of numerical models. Conduct an additional field study if collaborative opportunity arises.
• Task 4: Support System Analysis (9/2010 – 6/2012): Develop analysis techniques for numerical models of rock-support interaction around coal mine entries including the identification of roof collapse and the quantification of roof stability. Model verification through back analysis of field studies and published case studies.
• Task 5: Design Guidelines (1/2012 – 6/2014): Apply verified numerical models to analyze support systems under various geologic and loading conditions to investigate specific design questions. Evaluation of results of field studies, current support practices and numerical analyses to develop support design guidelines. Compilation of guidelines into a product suitable for dissemination to stakeholders.
• Task 6: Dissemination (6/2013-9/2014): Preparation and distribution of NIOSH Information Circular and Tech News publications. Presentations at industry seminars and open industry briefings.