Acoustic Emission Source Location Method’s Optimization And Experimental Verification In Complex Environment

With the mining of deep mineral resources and the development and utilization of underground space,mining engineering continues to move towards deep.The deep space environment is complex and changeable.The engineering disturbance caused by underground excavation make a large amount of energy accumulated in deep rock mass released instantaneously,and rock burst accidents increase sharply.Acoustic emission technology can effectively monitor the location of rock micro fracture.However,acoustic emission source location is usually affected by complex factors such as temperature,stress and hole structure.Using acoustic emission technology,this paper studies the acoustic emission source location under three complex environmental conditions:temperature change,stress change and structure with unknown empty area.The main research contents and conclusions are as follows:(1)In this paper,an acoustic emission source localization experiment was designed using a point heat source to heat the hollow hemispherical specimen to change the temperature to study the effect of temperature on the location accuracy of acoustic emission source.The results show that the average location error of the acoustic emission source is maintained at1.6 cm-2.0 cm at the beginning and middle of the heating period(room temperature～82°C),and increases sharply to 8.9 cm at the end of the heating period(82°C-94°C)due to the appearance of cracks.This suggests that the thermal expansion inside the structure caused by temperature changes and thus the cracking of the structure largely reduces the location accuracy of the acoustic emission source.This is due to the fact that the elastic wave cannot pass directly through the crack and the actual wave path is no longer equal to the pre-calculated path.At the same time,recommendations are given to reduce the acoustic emission source localization error under temperature variations: real-time adjustment and actual propagation paths are needed for acoustic emission source location in structures with significant temperature variations.It is of great safety importance to accurately determine the time and location of structural cracking and to select more appropriate position’s sensors for localization in order to optimize the location method.(2)In order to study the influence of stress on the location accuracy of acoustic emission source,this paper designs an acoustic emission source location experiment of granite biaxial compression,and explores the acoustic emission source location under different stress states.The results show that the average location error and the standard deviation of the error both show a trend of decreasing and then increasing with the increase of stress.Different stress stages of the rock correspond to different wave velocity changes,and the internal wave velocity is gradually increasing when the rock is loaded from 0 to 50 MPa;when 50 MPa to 94 MPa,the internal wave velocity decreases rapidly.This is related to the compacting of the original cracks and the continuous expansion of new cracks inside the rock.The adopted location method can reduce the location error of the acoustic emission source caused by the change of wave velocity to a certain extent,but the structural cracking is still the cause of the significant decrease of the location accuracy.By dynamically adjusting the wave speed and reducing the difference between the localized wave speed and the measured wave speed,the location accuracy of the acoustic emission source can be improved;meanwhile,a wave speed measurement device can be used to monitor the change of wave speed of the loaded structure to determine the stress state and internal damage of the structure to be located,so as to determine the damage location and optimize the acoustic emission location method.(3)In order to study the influence of the structure with unknown empty area on the location of acoustic emission source,five empty area samples with different shapes,sizes and positions were selected,and the acoustic emission pulse and lead breaking experiments were designed.TD and the newly proposed SUEA are used for location respectively.The results show that structures containing unknown empty areas have a greater impact on the conventional location method TD.SUEA can identify the shape,size and location of the empty areas in the unknown region by exciting the active acoustic emission source and using the collected acoustic emission signals.Then,on the basis of the identified empty areas,precise localization of the unknown acoustic emission source is performed.It improves the average localization accuracy by 78% compared to TD.This shows that the newly proposed localization method can achieve more effective and accurate acoustic emission source localization in the region containing unknown null areas.It not only provides a theoretical basis and technical support for the detection of anomalous regions in complex structures and the localization of acoustic emission sources,but also facilitates the prediction and control of engineering disasters.