A study on a water-inrush incident at Laohutai coalmine

Abstract

An underground water-inrush incident at Laohutai coalmine in China was investigated using an integrated approach based on data from microseismic monitoring, hydrochemistry isotope analysis, meteorology, and mining-induced subsidence. It was found that the incident was closely related to a snow storm and the rapid melting of the snow, and was attributed to the rapid flow of surface water through subsidence-induced fractures into the ground and the capacity of storing a significant amount of water temporarily in the mined-out areas near the active mining stopes. We found that in both a long-range of 60 days and a short-range of 10h before the water-inrush incident, there were a few distinct abnormalities in the seismic data, such as irregularity of P-wave to S-wave velocity ratio VP/VS in the low value range, irregularity of S-wave to P-wave amplitude ratio ASH/APH in the high value range, irregularity of the wave dominant frequency in the low value range, change of waveforms, and reduction of microseismic activities before the fracturing of the walls that bore the inrushed water. It is hence proposed to use the microseismic monitoring technique to monitor and analyze information carried in the seismic waves generated from either mining-induced rock fracturing or active blasting so as to detect unknown water bodies and reduce water-inrush risk in underground mines.