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|Roof falls, even of supported roof, still constitute a major hazard in underground mines. However, associated with any fall or instability is a pattern of roof movement. Therefore, the National Institute for Occupational Safety and Health, Pittsburgh Research Center, has been conducting research into the development of practical extensometer systems that can be used to measure this displacement and to determine if a roof fall may occur, thus increasing miner safety. For extensometers to be used in the detection of potential roof falls in coal mines, an understanding of the movement and displacement rates that will lead to roof failure is required. Because roof falls are unpredictable, it is often very difficult to obtain this information. Therefore, in a coal mine in the lower Kittanning seam in Pennsylvania, a room widening experiment was conducted to intentionally cause a roof fall while roof movement data was collected. In this experiment, two adjacent rooms 5.5 m (18 ft) wide supported with 1.5 m (5 ft) resin-grouted bolts and instrumented with extensometers were widened to 9 m (30 ft). In one of the rooms, 3.6 m (12 ft) cable bolts were installed as supplemental support. In the room with no additional support, a roof fall occurred 72 h after the room was widened. Much of the 3 cm (1.2 in) of movement in this room resulted from the instantaneous and transient response to mining with displacement rates up to 7.6 cm/d (3 in/d) being measured. This was followed by a steady state displacement phase with a rate of 0.43 cm/d (0.17 in/d). Just 12 h before the fall, movement deeper in the roof caused the rate to accelerate to 1.1 cm/d (0.44 in/d). The roof in the room with the supplemental cable support did not fall even though the total roof deformation was over 7.6 cm (3 in). Significant roof movements and strains in the cabled room were detected to a depth of 3 m (10 ft) while maximum cable loads were over 180 kN (40,000 lbf). Essentially, the roof was in postfailure with the cables maintaining the material, while roof stability was indicated by a steady state displacement rate of only 0.025 cm/d (0.01 in/d) at the end of the test.|
Additional chapters/articles from the SME-ICGCM book 16th International Conference on Ground Control in Mining (ICGCM)
|Longwall Mining-Through the Backfilled In-Panel Entries at C||Performance of Various Standing and Cribless Tailgate Suppor||Measurement of Effects of Interaction and Influence on Mine||Effects of Longwall Mining on Streamflow in the Pittsburgh S||Longwall Surface Subsidence Prediction Through Numerical Mod||Long-term Subsidence Over Longwall Chain Pillar Systems and||Subsidence Prediction Influence Assessment and Damage Contro||Formation of Face Headings Using Stress Relief at Asfordby M||Significant Weighting Events on the Longwalls in the Phalen||Full-face Pressure Monitoring in Medium-Weak Roof Condition||Research on the Interaction Between Roof Strata and Shield S||Roof Instability of Longwall Face at Ikeshima Colliery||Gob Canopy Roof Support for Difficult Natural Conditions||Yielding Cement Roof Supports for Longwall Mining||Management of the Dynamic Phenomena of Rock Pressure in Unde||Continuing Development of Innovative Cable Support Systems||Extending the Limits of Strata Bolting by the Use of Flexibl||Implementation and Evaluation of Roof Bolting in MICARE Mine||New Methods and Technologies of Roofbolting in Australia Coa||New Design Criteria for Roof Bolt Systems||Control Mechanism of a Tensioned Bolt System in the Laminate||A Study of the Performance of Glass Fibre Rock Reinforcement||A Method for the Selection of Rock Support Based on Bolt Loa||Strategies for the Application of Rockbolting Technology to||A Troubleshooting Guide for Roof Support Systems||A Statistical Overview of Retreat Mining of Coal Pillars in||Full-Scale Performance Evaluation of Mobile Roof Supports||Effect of the Interchamber Pi Yield on the Surface Strains i||Salt Pillar Design Equation||Case Study of Conditions Observed During the Removal of a Hi||Case Study of the Effect of Stratigraphic Location on Roof S||Ground Control and the Inundation of the Retsof Mine||Weatherability Test of Rocks for Underground Mines||Shear Strength Characteristics of Soft Rock Joints Based on||Comparison of Pillar Strengths Calculated Using Empirical Eq||Effects of In-seam and Near-seam Conditions and Asymmetric P||Ground Control Worker Safety During Extended Cut Mining||Analysis of Extensometer Data from a Room Widening Experimen||Airbag Support for Ground Control in Thin Seam Coal Mining||Development of a Statistical-Analytical Approach for Assessi||Ground Control Criteria for Coal Reserve Optimization in Mul||Calcium Aluminate Kiders in Hard Rock and Coal Mining||Simplified Pre-and Post-Processing Technique for Performing|