Comprehensive Utilization of Borehole AFET and Logging Method Detecting Goaf Area in Coal Mines

Abstract

China, as the world's largest coal producer and consumer, faces increasingly severe challenges from coal mine goaf areas formed through decades of intensive mining. These underground voids, resulting from exhausted resources or technical limitations, not only cause environmental issues like land subsidence and groundwater contamination but also pose critical safety risks for ongoing mining operations, including water inrushes, gas outbursts, and roof collapses. Conventional geophysical methods such as seismic surveys and electromagnetic detection demonstrate limited effectiveness in complex geological conditions due to susceptibility to electrical heterogeneity, electromagnetic interference, and interpretation ambiguities.This study presents an innovative integrated approach combining the Audio-Frequency Electrical Transillumination (AFET) method with multi-parameter borehole logging to establish a three-dimensional detection system. The AFET technique employs 0.1-10 kHz electromagnetic waves to identify electrical anomalies associated with goafs, enabling extensive horizontal scanning. This is complemented by vertical high-resolution profiling through borehole measurements of resistivity, spontaneous potential, and acoustic velocity. Field applications in Shanxi Province's typical coal mines achieved breakthrough results: Using a grid-drilling pattern (15m spacing, 300m depth), the method successfully detected three concealed goafs missed by conventional approaches, with spatial positioning errors under 0.5m. Notably, it accurately identified two un-collapsed water-filled cavities. This surface-borehole synergistic approach overcomes single-method limitations, enhancing goaf detection accuracy to over 92%. The technique provides reliable technical support for safe mining practices and represents significant progress in precise detection of hidden geological hazards in Chinese coal mines, offering valuable insights for global mining geophysics.