Research on the Monitoring Law of Acoustic Emission Parameters during TBM Construction of Deep Hard Rock Tunnel

On-site monitoring of deep hard rock tunnels can help understand the rockburst characteristics and provide timely warnings. Based on a deep-buried tunnel excavated by TBM, on-site acoustic emission (AE) monitoring was carried out to explore the AE waveforms and parameter characteristics of different sources (rockburst, TBM vibration, rock breaking of cutterhead, rock drilling of anchor drilling machine, etc.) under different AE sensor installation methods (drilling, tunnel wall, grouting anchors, foot anchors, steel bars). The results show that rockburst AE signals are characterized by short duration, high instantaneous energy (though lower total absolute energy than mechanical noise), and a relatively high peak frequency (several tens of kHz). The TBM vibration and excavation signals and rock drilling signals have extremely long duration, extremely high ringing count and absolute energy greater than that of rockburst signals. The rock-breaking signals from the cutterhead and anchor drilling machine are low-frequency signals with a peak frequency of only a few kHz, while the TBM vibration signals have the highest peak frequency (>120 kHz). The ringing count and energy rate slowly increase 10 minutes before rockburst, and there is a short quiet period when approaching rockburst. At the moment of rockburst, the ringing count and energy rate suddenly increase and reach their peak, and various frequency band signals appear, with a large number of low-frequency signals below 10 kHz. The AE b value significantly decreases to around 1.5. The influencing degree of TBM excavation noise on the AE ringing count and energy under different installation methods is in the order of steel bars>anchor rods>tunnel walls>inside the drilling hole, while the peak frequency characteristics are the opposite. AE technology is mainly suitable for rockburst monitoring during TBM shutdown. If drilling conditions cannot be met or more attention is paid to the temporal characteristics of AE parameters, AE sensors can be installed on anchoring structures such as grouting anchors and foot anchors (waveguide rods) to monitor and amplify AE signals. The research results in this study can provide a reference for AE monitoring methods and result analysis of similar deep-buried tunnels excavated by TBM.