Characterization Of The Interfaces Of Ballastless Railway Tracks Based On Ultrasonic Echo Principles

Nowadays, a large number of high-speed railway trains have become an inevitable trend and real needs of China’s railway system. Ballastless railway tracks, because of its high orbit smoothness, long maintenance of track geometry and less maintenance work, get the favor of many countries. With the extension of operating time, increase in structural cracking, penetration of environmental pollution and erosion of surrounding environment, the ballastless railway track may be at risk caused by unexpected accidents at any time. The indicators requirement of project quality and safety will be higher, and the line environment of elapsed area will be more complex, therefore the damage of the ballastless tracks must be carefully considered. To keep a high level of structural safety, durability and performance of the infrastructure in each country, an efficient system for early and regular structural assessment is urgently required. Non-destructive testing (NDT) methods have a large potential to be part of such a system. Ultrasonic testing (UT) is a non-destructive testing technique based on the propagation of ultrasonic waves in the object or material tested.The delamination in interface of ballastless tracks is one of the main defects in ballastless tracks. Until now, there is no research concentrating on the Non-destructive testing method in the interface of ballastless tracks. For quality assurance and the detection and localization of possible delamination, ultrasonic echo methods are principally well suited, because the reflection at an air inclusion leads to a total reflection of ultrasonic pulses, which allows a good from a poor bonding to be clearly distinguished.For plate ballastless track systems, the interface of the track plate and the CA mortar layer is an interface of two different materials. The damage in the interface of the track plate and the CA mortar layer belongs to the bonding damage of two materials. And the difference of shear wave velocity between the track plate and the CA mortar layer is similar to the difference of shear wave velocity between concrete and polyamide. In order to simplify the sample, the existence of rebars has been ignored. Thus, a three layer model with two concrete layers and one polyamide layer between them is made to simulate the real ballastless track.In this thesis, both a low-frequency flaw detector A1220 MONOLITH and an ultrasonic tomograph A1040 MIRA have been used for data acquisition. The evaluation software used has been Inter-SAFT, which is a research software from Kassel University. A real Boegl system ballastless track at BAM provided by the German railway company Deutsche Bahn (DB) in the year 2000 has been tested first and used to check the real situation inside the track after 15 years. In experiments of small scale, three small samples being models of a two and a three layer system coupled with a coupling agent transmitting shear waves (glucose) have been made to figure out the characterization of each concrete block, the coupling material, the two layer model and the three layer model. Due to the different velocities in the different layers, a 2D and 3D reconstruction with velocity correction using Inter-SAFT was used to indicate the depth and the size of artificial defects.