An underground limestone mine with thin and rigid limestone roof and high horizontal stresses create a burstprone condition and present a major ground control and safety problem at the mine: rock-burst caused severe roof falls. To help the mine address this problem, an Acoustic Emission/Microseismic system was installed at the mine by the National Institute for Occupational Safety and Health (NIOSH). However, the efficiency of this system was severely hampered by high background noise and inaccurate event location. The focus of this research is therefore to resolve these problems. The most beneficial outcome of this research is the demonstration that the source location accuracy at the mine can be significantly improved through a comprehensive and highly efficient source location approach. This includes digital filtering, phase association, sensor array optimization, absolute value based optimization method, advanced Simplex location algorithm, and reliability analysis. The development of this approach provides a unique and reliable solution to the problem.
It is generally accepted that most solids emit lowlevel seismic signals when they are stressed or deformed. In the geotechnical field this phenomenon is generally referred to as Acoustic Emission/Microseismic (AE/MS) activities . When rock fractures, it will produce microseismic signal which will transmit through rock as elastic waves. The application of AE/MS techniques, which monitors self-generated acoustic signals occurring within the ground, has now rapidly increased for stability monitoring of underground structures such as mines, tunnels, natural gas and petroleum storage caverns, as well as surface structures such as foundations, rock and soil sloped.
An AE/MS system was installed by U.S. National Institute for Occupational Safety and Health (NIOSH) at an underground limestone mine in southwestern Pennsylvania, where roof fall was a big problem to the production and safety. The traditional room-and-pillar and a new stress control layout were in use at this mine site. In order to monitor the stability of the roof, minimize the hazardous ground conditions and provide safer working conditions for miners, NIOSH installed a microseismic system, which had 24-channel uniaxial geophones connected with DOS-based data acquisition system. The system started to monitor microseismic activity on Feb 9, 2000 (Figure 1).