Detection Of Invisible Damage In Ballastless Track Based On Wave Method

In recent years,with the rapid economic development,China has vigorously promoted the development of railways.With the completion of the "four vertical and four horizontal" fast passenger transport corridors,as of today,our country has the world’s largest high-speed network.There are two main types of railway track structure in China: ballasted track and ballastless track.Ballastless tracks are gradually replacing ballasted tracks with their characteristics of stability,smoothness,and low maintenance.The ballastless track structure is composed of foundation,base plate,CA mortar(emulsified asphalt mortar),track slab and rails from bottom to top.However,during the actual operation of the ballastless track,due to the influence of load,environment and construction technology,the CA mortar layer,which is responsible for connecting the track slab and the base slab,is prone to cracking defects.The separation of CA mortar will reduce the safety of track operation and affect driving safety.Therefore,the completion of the safety monitoring and safety evaluation of CA mortar defects is very important to the development of ballastless track structures.The specific work of this paper is summarized as follows:(1)Through the analysis of the propagation path of the stress wave in the layered medium,it is proposed that the void in the CA mortar can be detected according to the amplitude,frequency and wave arrival time of the stress wave.According to the wave propagation theory,it is proposed to use the impact-echo method and piezoelectric smart aggregate to detect the voids of the mortar of the built ballastless track and the newly-built ballastless track respectively.(2)The finite element simulation and experimental analysis of ballastless track specimens containing 5 different degrees of CA mortar voids were carried out,and the propagation characteristics of the stress wave in the ballastless track structure were studied.When the void size in the CA mortar layer is different,the reflection duration of the stress wave is different.When the void size increases,the propagation path of the stress wave increases,which prolongs the propagation time of the stress wave in the structure.According to the time domain and frequency domain signal characteristics of the response waveform,the feasibility of detecting mortar void by impact-echo method is discussed.The experimental results prove that the impact echo method can well detect the size of CA mortar defects.(3)The piezoelectric smart aggregate fixed on the track plate and the piezoelectric smart aggregate fixed on the base plate are used as signal exciter and signal receiver respectively to study the feasibility of the embedded piezoelectric sensor to detect the void of CA mortar.The wave analysis method was used to identify the void damage of CA mortars of different sizes.The time difference analysis and time-domain analysis of the output signal show that the adopted method can effectively identify the damage,which proves that the piezoelectric ceramic-based wave analysis method is feasible and effective for the CA mortar void damage identification method of ballastless track.