Denver, CO: U.S. Department of the Interior, Bureau of Mines, TN 381, 1991 May; :1-3
Objective: Apply state-of-the-art monitoring and computer systems technology to remotely monitor geostructural data and evaluate ground conditions in near real-time. Background: Recently, the coal mining industry has progressed dramatically from a labor-intensive industry to highly mechanized and automated systems achieving significantly higher production rates. In underground longwall coal mines, production and face advance rates have increased by almost tenfold in the last 15 to 20 years. With increasingly high advance rates, geologic anomalies which affect rock mass quality are encountered more frequently, far exceeding the current rate at which ground control information can be processed and analyzed. As a result, mine operators find themselves with insufficient time or resources to cope with the rapidly changing ground conditions. To keep up with the technological advancement in mining and the associated ground control problems, the Bureau of Mines is conducting a multi-phase research program to implement a computer-assisted Ground Control Management System (GCMS). Research is ongoing at present, but when completed the system will be designed to 1) monitor and evaluate data on rock properties, geologic conditions, and rock mechanics data from underground sensors in near real-time; 2) interpret the analyses to evaluate the interaction between various critical ground control parameters; 3) assess the structural integrity of the mine; and 4) determine failure modes and provide recommendations for control measures, design modifications, and alternative support procedures. The system will be expanded into its full capability during various phases of this research program. Approach: The GCMS combines existing mine monitoring and sensor technology with automated computer analysis techniques specifically for ground control applications. The Bureau, in cooperation with the mining industry, has installed and is operating the GCMS in an underground western U.S. coal mine. A comprehensive instrumentation program using a fully automated, mine monitoring system and the remote processing techniques of the GCMS network was implemented to evaluate rock mass behavior during mining of longwall panels. Six sites were instrumented to monitor stress changes and strata movement information in and around two longwall panels. Pressure transducers were installed on both legs of nine shields, evenly spaced along the face, to evaluate shield. loading behavior during mining. Pressure sensors were also connected to hydraulic borehole pressure cells in. stalled in the panels, the roof, and pillars of the gateroads to provide near real-time ground pressure prof1les as the longwall face advances. Additional instruments, including sonic distance meters, roof extensometers, and room cl0sure meters, were installed to monitor strata movement. The field data are transmitted over a dedicated telephone line at 6-sec intervals and are available underground, at the mine surface, and at the Bureau's Denver Research Center, 150 miles from the mine. Test Results: Data collection and processing capabilities of the GCMS have demonstrated its potential to become an effective planning and evaluation tool used by the mine engineer in anticipation of ground hazards that occur as mining progresses. To date, this research program has identified the fol. lowing major ground control applications of the system: 1. Continuous monitoring of ground pressure and strata movement during longwa1l mining has improved the understanding of the abutment load transfer phenomena, pillar loading-yielding behavior, and roof caving meclw1iams. This information can be used to optimize the design of gateroads and future panel layouts. 2. Continuous monitoring of shield-leg pressures has proven to be an indicator of the development of high. stress zones along the face, and may indicate impending gateroad ground hazards such as roof falls and floor heave in advance of mining. This information can be used to plan and implement appropriate ground control measures, and to assess the need for supplemental supports to control gateroad ground conditions. 3. The difference between the time weighted-average shield leg pressure and the shield setting pressure (TWAP. SP) appears to be an indicator of periodic loading of the shields that possibly relates to the roof overhang behind the shields and the structure of the mine roof. This information may be used to warn of impending high stress abutment zones along the face and to assess the need for induced caving or other control measures.