Nondestructive Detection Of Tunnel Lining Void Based On Acoustic Spectrum Analysis

Lining is a concrete structure built on the surface of tunnel body,which is the main bearing structure of tunnel structure.The strength and stability of lining structure affect the safety and durability of tunnel.The common cast-in-place lining is completed by the lining trolley in the field.Because of the invisibility and complexity of the lining pouring process,there may be areas of uncompacted grouting after the completion of lining pouring,which may lead to the internal cavity of the lining structure and other diseases,affecting the safe use of the tunnel structure.Therefore,the quality inspection of lining structure is of great significance.The quality inspection of tunnel lining structure is mainly divided into two parts:the defect inspection for the completed tunnel and the grouting process monitoring for the tunnel under construction.Acoustic nondestructive testing is a widely used testing method.Through the comparative analysis and extraction of spectrum features of the time-domain and frequency-domain signal spectrum of the test signal,the extracted feature parameters to describe the internal situation of the structure can improve the detection efficiency and accuracy.The main research contents and conclusions are as follows:(1)The acoustic detection of the internal void defects of concrete lining structure was simulated.The finite element models with different void height were established by the way of finite element simulation.The time-domain spectrum and frequency-domain spectrum of the simulation signals received by different models were compared and analyzed.The influence of void height on the characteristics of the spectrum is observed.The characteristic parameters are extracted from the spectrum signals and defined as the signal density ratio to describe the void height of the lining structure.The results show that the signal density ratio is very sensitive to the void height,and increases linearly with the increase of the void height,and the signal density ratio can identify the void degree of different test positions in the void area.(2)The acoustic monitoring of grouting density in the process of grouting of steel formwork lining structure was simulated.Through the way of finite element simulation,the finite element model of steel formwork lining structure injected with concrete slurry of different height was established.The time-domain spectrum and frequency-domain spectrum of the simulation signals obtained from different models were compared and analyzed,and the centroid frequency in the spectrum signal was extracted as the characteristic parameter to establish the relationship between the centroid frequency and grouting height.The results show that with the increase of grouting height,the centroid frequency tends to decreaseparabola.In addition,the change of excitation frequency will change the falling rate of centroid frequency.(3)The local models of concrete lining structure and steel mold lining structure were made respectively.The test results of concrete lining model show that the signal density ratio can effectively describe the void degree of different test points on the test surface,and can be used to quantitatively describe the void size of concrete lining.The test results of steel formwork lining model show that the centroid frequency decreases parabola with the increase of grouting height,which can help to identify the grouting state in the lining steel formwork.In this paper,the characteristic parameters of the test signal were extracted through the spectrum analysis,and the relationship between the characteristic parameters of the signal and the main characteristics of the defect was established,which provides a theoretical basis for the realization of rapid detection and quantitative detection.