Research On Theory And Method Of Directional Seismic Wave Based On Tunnel Environment

With the rapid development of China's economy,a large number of tunnels need to be built in railway and highway transportation,water conservancy and hydropower,energy mines,municipal engineering and other fields.Tunnel construction often encountered a variety of complex geological conditions and unfavorable geological sections,water gushing,rock burst,gas outburst,collapse and other serious geological disasters occur from time to time,which can affect the construction progress and cause major engineering accidents,and even cause huge economic losses and casualties.Therefore,advanced geological prediction is an essential link in tunnel construction.It is very important to use advanced geological prediction technology to find out the unfavorable geological body structure and location in front of tunnel face in advance to ensure construction safety,disaster prevention and control.Tunnel advanced Prediction technology mainly from the 1970 s began to rise,ahead of Tunnel Seismic Prediction(TSP)can use the Seismic reflection wave exploration method to obtain the lithology,location,scale and other information of bad geological body in front,and has the advantages of high detection accuracy and relatively long detection distance,so it is favored by the engineering community.However,due to the complex geological conditions of surrounding rock in tunnels,the seismic wave field is extremely complex.At present,there are still some problems to be solved urgently in the application of the advanced detection technology of seismic waves in tunnels:(1)Currently,the detection distance of TSP technology is 100~200 m,and the specific situation is related to geological conditions and environmental noise interference,etc.At present,a kind of advanced detection method with longer detection distance is required to improve work efficiency;(2)In TSP detection,the acquisition system not only receives the reflectionsignal in front of the palm,but also receives the reflection signal from the side,which is difficult to distinguish and easy to misjudge,resulting in unreliable detection results;(3)The detection of adverse geological bodies in the tunnel side is extremely important for the reinforcement of surrounding rock and safe construction of the tunnel.However,there are few detection technologies for tunnel side targets at present;(4)The distance of TSP detection is closely related to noise.Typical noise interference includes industrial electricity,pump vibration and a large amount of random noise,which seriously affects the estimation of surrounding rock velocity of the tunnel,and further affects the lithology analysis of geological body structure,leading to unreliable detection results.Directional seismic wave technology can form directional seismic beam by receiving array data array mode,which can not only enhance coherent signal to suppress random interference,but also realize directional filtering function.Therefore,it can be considered to apply directional seismic wave technology to tunnel environment to solve problems such as short detection distance,unreliable detection results and detection of side targets.Paper is structured according to this idea as follows: Firstly,directional seismic wave technology can form directional seismic wave field by array and enhance the intensity of seismic wave field in this direction.Similarly,when applied to the tunnel,the intensity of the seismic wave field in front of the palm surface can be enhanced,so as to increase the detection distance and improve the detection accuracy.Secondly,the directional filtering feature of directional seismic wave technology can be adopted to filter out the interference waves in other directions and only keep the front effective waves,so as to distinguish the front signal from the side interference and improve the reliability of detection results.Then,when detecting the tunnel side target,the tunnel side can be used as the target direction for seismic processing,and then the effective signal of the tunnel side target can be obtained.Finally,as the effective signals collected bythe system are often accompanied by periodic and random interference,it is necessary to suppress periodic interference first,and then use directional seismic wave technology to suppress random interference,so as to improve the detection results.In this paper,the research on the theory and method of the formation of directional seismic waves in the tunnel environment is carried out from four aspects,including the theory,the demand for long-distance detection,the identification and extraction of side target signals and the method of directional seismic waves in strong periodic interference.The main contents are as follows:In terms of theory,firstly,the theory of directional seismic waves under complex geological conditions is derived and the characteristics of directional seismic waves under complex geological conditions are analyzed.Secondly,the ability of directional seismic waves with variable frequency to improve target signals under complex geological conditions is analyzed by numerical simulation.Finally,the field experiment results show that the detection depth increases from 60 m to 240 m with the 9-element array directional seismic wave technology,which further reveals the effectiveness of directional seismic waves from the experimental perspective.The directional seismic wave method based on tunnel environment is studied for remote detection in front of tunnel face.Because the number of data channels collected by the TSP system is relatively small,direct treatment with directional seismic wave technology will introduce false multiple wave interferences(FMWI),showing multiple in-phase axes on the seismic record,which will lead to misjudgment of geological structure interpretation by the staff.The study shows that the essential reason for the appearance of FMWI is that the correlation of adjacent records is increased when multiple noises are added.In order to reduce or destroy the data correlation influence because of the small amount of data,the random dislocation directional deismic wave(RDDSW)theory and method was proposed for the first time delay in this paper.Numerical simulation results show that this method can suppress FMWI effectively,improve data quality and increase detectiondistance.In the detection of tunnel lateral targets,due to the wide range of the incident Angle of seismic waves,there will often be converted waves,resulting in extremely complex wave field,and it is difficult to distinguish the front and side target signals;Aiming at the problems existing in seismic wave detection of tunnel side target,we propose a KL-beamforming method based on tunnel side target recognition and extraction.When using this method to extract the side target signal in different noise environment,we put forward delay parameter estimation methods such as direct estimation method,local correlation method and directional scanning method,which can effectively extract the side target signal and lay a theoretical foundation for the subsequent determination of the spatial location,shape and size of adverse geological bodies.In the practical application of advanced tunnel seismic detection,strong periodic disturbances such as industrial electricity and water pump are often accompanied.In view of the shortcomings of directional seismic waves in dealing with periodic interference,it is proposed to firstly use Hankel-SVD-ICA method to suppress periodic interference in records,and then use directional seismic wave method to further suppress random interference in records.Numerical simulation and field experiment data analysis results show that the Hankel-SVD-ICA method can effectively suppress periodic interference without damaging effective signals.RDDSW method can effectively suppress random interference,further improve data quality,and improve detection distance and accuracy.To sum up,this paper puts forward the theory of directional seismic wave based on tunnel environment for the first time,and studies the method of directional seismic wave for advanced geological detection of tunnels.Firstly,the technology of directional seismic waves with variable frequency is used to study the typical complex media,and its feasibility and effectiveness are verified.Secondly,for the detection of the front and side sides of the tunnel,the validity of RDDSW and KL-beamforming methods for increasing detection distance and extracting sidesignals is studied.And corresponding delay parameter estimation methods are proposed for different noise levels.Finally,the Hankel-SVD-ICA method presented in this paper is for the strong periodic interference in the tunnel environment,which can effectively suppress power frequency and pump interference and improve the accuracy of the tunnel detection.The main innovations of this paper include:directional seismic waves with variable frequency under complex geological conditions,RDDSW and KL-beamforming for tunnel environment,and Hankel-SVD-ICA for periodic interference suppression.