Fractal and seismic b-value study during dynamic roof displacements (roof fall and surface blasting) for enhancing safety in the longwall coal mines

Abstract

Mining of coal has always been a very risky task from older times and, is often associated with various fatal accidents in form of rock bursts, gas outbursts, slope/bench failure. Studies carried out by various safety agencies around the world such as MSHA (USA), DGMS (India), State Administration (China), have reported higher fatality rates in underground mines, and are mostly resulting from the sudden roof falls. Most of the roof falls occur suddenly in the running mine due to support failure or adverse strata conditions. The present study focuses on the monitoring of the roof falls in the longwall mine of Central India, as the presence of stable roof has resulted in several roof fall related accidents in various Indian longwall panels including Churcha mine, Kothadi mine and GDK-11A incline. The aforesaid accidents was also responsible for the poor performance of longwall mines in India, which is considered to be one of the best mining practices in majority of the coal producing countries of the world. The paper incorporates the spatial distribution and magnitude of microseismic events released before/during the roof falls and surface blasting in terms of Fractal Dimension as well as b-value. These two parameters helped in getting precursory signatures for spatio-temporal forecasting of minor and major roof falls, as well as helped in monitoring strata behavior during surface blasting. A total of sixty-four minor falls (LF1-LF64), seventy-six major falls (RF1-RF76) and fifteen surface blasting (SB1-SB15). The results showed decreasing trend in the both Fractal Dimension (D) and b-value before roof fall, as microseismic events emitted were highly clustered and had higher magnitude. Whereas, higher Fractal Dimension (D) and lower b-value was seen during surface blasting, when the emitted microseismic events had higher magnitude but were found to be dispersive in nature.