In recent years, salt cavern failures and sinkholes associated with brine wells in solution mining have created concerns and initiated more restrict regulations and guidelines for solution mining operations. One of the monitoring tools for cavern stability relates to tracking passive microseismic activity during brine well operation. Any gradual or sudden rockmass failure is often associated with pre-failure microfracturing activity in the rockmass which leads to microseismic activity. A suitably designed microseismic system with sufficient sensitivity can capture the pre-failure activity days or months before the failure and along with other instrumentation and geotechnical analysis can provide critical information that can be used to help identify and possibly reduce the risk of catastrophic rockmass failure. This paper presents two cases of induced microseismic monitoring in soft rock media and of salt caverns created by solution mining. An example of a microseismic system installation and calibration in a salt cavern is demonstrated, and the results of advanced analysis from a second salt cavern monitoring are briefly investigated.
Microseismic systems were initially developed for applications in underground hard rock mining due to increased microseismic activity initiated by higher mining depths and therefore higher stress levels. The increased seismic activity and violent rockbursts causing damage and fatalities led to more rapid development of this technology. The main purpose of early microseismic systems was to enhance safety in seismic active areas of the mine. The early systems were only able to provide approximate information on location and magnitude of seismic events.
Today, however, the high-end technology is capable of recording full waveforms on a continuous basis that can further be processed through advanced seismology codes and powerful computers for additional understanding of the rockmass behavior. The systematic mechanism and source parameter analysis of seismic events can now be reliably used as a geotechnical tool to assess strain/stress changes in the monitored volume.