Experimental Research on Acoustic Emission and Natural Frequency Evolution Characteristics During Rock Block Collapse in Tunnel Engineering
Prevention and control technology for tunnel surrounding rock collapse disasters is of great significance to tunnel safety construction,while monitoring and early warning technologies are important for the active prevention and control of tunnel disasters.Because it is difficult to effectively respond to sudden mass disasters in tunnel surrounding rock using traditional monitoring indicators,such as displacement and stress,the evolution rules of acoustic emission and natural vibration frequency during such catastrophic process were examined in this study.Based on a theoretical derivation,the instability process of the block was simplified regarding two-dimensional plane stress,a vibration model of the surrounding rock of a tunnel was established,and the correspondence between the natural frequency of the regular square block and the stress,contact area,friction,and other elements were analyzed under different instability modes.Large-scale physical simulation experiments of indoor block instability were designed and completed.The influences of the stress state,contact area,and other factors on the natural frequency of the block instability process were investigated,and the evolution law of the friction acoustic emission(AE)signal of the sliding surface in the block instability process was further studied.The results show that the natural frequency of the sliding block increases with an increase in the side pressure.When the lateral pressure increases from 0.1 to 0.5 and 1 MPa,the natural frequency increases by 16.18 and 25.79 Hz,respectively.As the contact area decreases,the natural frequency of the block decreases accordingly.The natural frequency of a block effectively reflects the constraint effect of the sliding surface on the key block.Although the main frequency distribution bandwidth of the AE during rock sliding is relatively small,many frequency bands are concentrated.The majority of the AE signals are concentrated near the frequency bands of 0,20,40,50,and 150 kHz,independent of the magnitude of the lateral pressure.The research results can provide theoretical support for the establishment of"AE vibration"joint monitoring and early warning methods for tunnel surrounding rock mass collapse disasters.
tunnel engineeringdisaster evolutionsimulated experimentrock block collapseacoustic emissionnatural frequency
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