Measurements of Acoustic Emission During Backfilling of Large Excavations

Review on In Situ Acoustic Emission Monitoring in the Context of Structural Health Monitoring in Mines

“…The third and biggest group shows applications in salt mines in Germany. These in situ measurements in rock salt often focused on monitoring AE activity caused by work like backfilling [39,40], excavation [41] or gas and fluid injection [42]. Early projects in in situ AE monitoring were limited to small rock volumes.…”

“…In the central section of the underground repository, the borehole sensors are distributed at three excavation levels and installed in 3 to 20 m deep boreholes. Originally, a network of 24 AE sensors monitored this section and covered an area of 150 m × 100 m × 120 m. This network was enlarged to 48 channels and covers a rock volume of about 250 m × 200 m × 120 m [37,39,69]. The average depth of the monitored volume is 400 m. This in situ AE monitoring provides a dataset of currently approximately 15 million located events per year [92].…”

“…The actual geological situation and the arrangement of cavities is more complicated and strongly varying along the strike. Stress redistribution causes high AE activity at the walls of the cavities (in the EDZ) particularly, where cavities are close to one another and at the boundary between rock salt and anhydrite [39]. provides a dataset of currently approximately 15 million located events per year [91].…”

“…For most events no waveforms are stored, but only the results of real-time processing. The aim of in situ AE monitoring is to investigate micro-and macrocracking, which are important for the evaluation of the stability of cavities and the hydraulic integrity of the rock, which is of special interest in the case of an underground disposal of hazardous waste in salt rock [39]. Figure 8 shows a cross section (sketch) through the central part perpendicular to the average direction of strike, where cavities in rock salt were mined beneath thick anhydrite blocks.…”

“…Sketch of geology and geometry of rooms in the central mine segment, where the AE network was installed (levels L1 to L3)[39]. Reproduced with permission.…”