Seismicity pattern during violent roof movements in longwall mines

Abstract

The accidents occurring in the underground mines are mostly related to roof/side fall, winding, inundation and other miscellaneous reasons. Out of the aforesaid mentioned reasons, roof fall has been mainly responsible for maximum mine-related causalities. Therefore, the real-time monitoring of the roof strata movement and temporal forecasting of untimely roof falls is very necessary towards ensuring safety in the coal mines. The present study also uses this robust technique in a longwall panel of Central India (overlain by thick hard sandstone bed) for studying the behaviour of distressed zone during coal excavation. The present study includes the estimation of fractal and b-value (from passive mine microseismicity), which has been earlier used in several studies related to earthquakes, fracture monitoring, identification of stressed zones, magnitude study, and so on. The fractal dimension and b-value have been used in the present study for locating the stressed zones in the overlying strata of an active longwall panel and spatio-temporal forecasting of roof fall in real time for enhancing safety in the working area. The change in the fractal dimension has been shown in terms of fractal gradient, which helped in monitoring the abrupt stress in roof strata during mining. The estimated fractal values were carefully studied for identifying the pattern of graph before major roof falls. It was seen that the aforesaid critical values of fractal dimension (d ≤ 0.4) were mostly obtained within 24 hours prior to major roof falls, thus making it a very significant result towards monitoring roof displacements and enhancing safety. Thus, the present study very much helped in mitigating several issues related to the safety of underground mines. Most important, the aforesaid study can be carried out in any form of underground mines (coal as well non-coal), which will be very helpful in enhancing its safety and smooth operation.