Research On Failure Monitoring Of Tunnel Reinforcement Steel Ring Based On Fiber Optic Distributed Acoustic Sensing

The construction of urban underground infrastructure in China is entering the stage of rapid development,especially the number of tunnels is increasing with each passing day.However,the tunnel structure is prone to damage due to external construction events or its own aging,which brings great hidden dangers to the safety of the tunnel and even the underground structure.Steel ring is often used to strengthen the damaged tunnel structure.However,with the secondary damage of the segment or the aging of the steel ring adhesive,a cavity is formed between the segment and the steel ring,which leads to the failure of the reinforced steel ring.The current structure failure detection technology can not realize long-distance,fully continuous online intelligent monitoring,and it is difficult to detect and alert the tunnel steel ring in time when failure occurs.In view of the tunnel reinforcement steel ring monitoring requirements above,this thesis investigated an intelligent recognition technology of the tunnel reinforcement steel ring failure based on fiber optic distributed acoustic sensing technology combined with machine learning intelligent identification.Through the theoretical simulation and experimental analysis,the real-time on-line monitoring and intelligent recognition of steel ring failure in tunnel reinforcement are realized,which has a good application prospect in tunnel structure monitoring.The main research contents of this thesis are as follows:(1)A failure monitoring method of reinforced steel ring based on the principle of nondestructive structure testing is proposed.Based on the acoustic-structure coupling theory and structural vibration response theory,the acoustic detection technology was studied.Combined with the finite element analysis method of COMSOL Multiphysics,the physical model of the tunnel reinforced steel ring under the action of acoustic waves was established,and the feasibility of using acoustic wave characteristics to monitor the failure of the tunnel reinforced steel ring structure was verified by simulation.(2)The failure judgment algorithm of tunnel reinforced steel ring based on fiber optic distributed acoustic sensing technology is designed and developed.The algorithm is based on MATLAB software platform,which is composed of two modules: signal feature extraction and failure grade determination.The signal feature extraction module consists spectrum analysis and wavelet packet decomposition.Based on the machine learning model established by BP neural network,the failure classification module realizes the intelligent failure classification of the reinforced steel ring by recognizing the signal features.(3)An intelligent failure monitoring system for reinforced steel ring based on fiber optic distributed acoustic sensing technology was established,and a cable coupling and packaging scheme suitable for actual tunnel was designed.The system application software of real-time response to vibration signal of reinforced steel ring is developed and tested.Based on LabVIEW software platform,a user-oriented software interface embedded with neural network algorithm is designed and developed.On the basis of this intelligent monitoring system,experimental studies on different failure grades of reinforced steel rings under simulated environment were investigated respectively.The test results show that the average accuracy of 6 failure grades identification is up to 97.8%.