Study On Elastic Wave Field Detection Method Used In Under Line Layered Structure Of High-speed Railway

Nowadays, more and more damages of high-speed railway structureappeared, so it is an important and difficult subject to investigate thedamages of railway structure, especially for defect diagnosis in thestructure’s support plate and surface layer of subgrade. However, variousdetection methods at present are limited and without effective solutions. Tosolve this problem, this paper is going to analyze under line layered structureinformation and defect by exploring characteristics of elastic wave when itspreading in the underground medium.According to the survey of structure type and disease, the majority ofhigh-speed railway use ballastless track in our country. The structure ofballastless track is composed by a track plate, a layer of cement asphaltmortar, support plate and bed. There is a thin layer of cement asphalt mortarbetween two plates. The function of this layer is to reduce the vibration ofrailway. Most diseases of structure are concentrated in concrete plate andcement asphalt mortar, such as track plate fracture, cement asphalt mortarwith local loose area, outflow and void.By analysis of structure type and various defects, this paper proposedlayered medium model of railway structure. As a result, the defect amongconcrete plate or cement asphalt mortar could be deduced from thecharacters of amplitude, frequency and time-frequency using the theory ofelastic wave propagation in layered media. It is proved that the amplitude ofelastic wave and spectrum amplitude in defect area will increase in theory.Based on the theory of elastic wave and the characteristics of railway defects, this research establish a three-dimensional model of complexhigh-speed railway structure and make a simulation calculation on theresponse of wave field by the method of dynamic finite element. Based onthe waveform properties, spectrum characteristics and time-frequencycharacteristics of elastic wave, study the dynamic characteristics of elasticwave propagation in high-speed railway structure, analyze the variation ofphysical and mechanical parameters, especially the influence on theresponse waveform from the defect area. As a result, reflection coefficient isan important factor of nondestructive elastic wave detection, thusestablishing a relationship between the reflection coefficient and impactstrength, spectrum amplitude and time frequency, which provide necessarybasis for further developing of the full wave field testing and practicalnondestructive testing.Finally, aiming at the common disease of support plate and subgradelayers in high-speed railway structure, a1:1full scale model of high-speedrailway with defects was realized in the test site. Firstly, according to therequirements of high-speed railway construction process, pouring thesupport plate and the bed layer of mortar, then according to the actualinvestigation of the defects, setting artificial defects in the model, andcomplete supporting lifting installation plate. Finally, carry out a similar testto the actual field on the supporting plate. By analysis of the experimentaldata from waveform properties, spectrum characteristics and time-frequency,validate the correctness of theoretical analysis and numerical simulationresults and the effectiveness of the elastic wave detection method, then putforward the method of data acquisition, data analysis methods andevaluation method.This research supported by Science and Technology DevelopmentProject of Chinese Railway Corporation (2013G004-A-1) and NationalScience Foundation (11372180).