Seismoacoustic Monitoring of a Longwall Face Using Distributed Acoustic Sensing

Violent, dynamic failures of rockmasses in underground mines pose significant hazards to workers and operations. Over the past several decades, hardrock mines have widely adopted seismic monitoring to help address such risks. However, coal mines, particularly those employing the longwall mining method, have struggled to implement similar monitoring strategies. This is because typical longwall mines are much larger and mine more rapidly than hardrock mines. Moreover, regulations place significant restrictions on the subsurface use of electronics in coal mines due to potentially explosive atmospheres. We present a new monitoring concept that uses distributed acoustic sensing (DAS) to turn an entire longwall face into a seismoacoustic array. After exploring the acoustic response of our sensors in the laboratory, we deployed the array at an active underground longwall mine for several days. We examine 33 events recorded by both the in-mine DAS array and a surface seismic network. We observed that the array records both seismic vibrations traveling through rock and mining equipment as well as sound waves propagating in the workings. We show that waveform moveouts are clearly visible, and that the standard deviation of the audio recordings is a straightforward yet promising metric that could help quantify burst damage. Although improvements are needed before mines can routinely use this monitoring strategy, DAS-based seismoacoustic arrays may assist in understanding coal-burst mechanisms and managing associated risks in underground longwall mines as well as enable better understanding of damage associated with dynamic failures in other underground environments.