Standard section of the continuous concrete slab track in high-speed railway system in Korea (Korea Continuous track, KCT, II system), developed based on the German Rheda 2000 system. In addition, the double-layered slab is continuously laid on the subgrade, which imposes a fixed boundary condition at the interface between the bottom of the HSB and the top surface of the subgrade. The two concrete layers (i.e., TCL and HSB) in the concrete railway track are connected by an interface adhesion to resist internal stresses caused by cyclic train dynamic loads and environmental effects. The TCL is supported by a hydraulically stabilized base course (HSB) that is constructed using cast-in-place concrete without steel reinforcements. Steel rails with 60 kg/m are attached to the railway sleeper using a high elastic fastening system.
JBRIDGE 1.74 CRACK PC
Two PC railway sleepers, connected by lattice trusses, are embedded into the cast-in-place concrete slab in TCL.
The track concrete layer (TCL) is a longitudinally continuous reinforced concrete slab without construction joints at the section of earthworks and tunnels but is discontinuous on bridges. The continuous concrete slab tracks in Korea were developed based on the German Rheda 2000 system (see Figure 1). However, it has not been adopted to the field practice yet. The PC tracks have been developed and first constructed in a test section of the Honam line.
The continuous concrete slab tracks have been increasingly used in the Korea high-speed railway (KHSR) system after first being adopted to the second section of the Gyeongbu line (Daegu~Busan) and the Honam line (Osong~Gwangju Songjeong). There are two types of ballastless concrete tracks developed for the high-speed railway system in Korea: (1) continuous concrete slab tracks fabricated using cast-in-place concrete and (2) discrete concrete slab tracks made of precast concrete (PC). The ballastless track is superior to the conventional ballast track due to its higher track stability, more favorable riding comports, longer service life, and especially lower maintenance cost. The results and discussion in this study would improve the understanding of characteristics of multiple IE testing parameters in concrete slab tracks and provide a fundamental basis to develop an effective prediction model of non-destructive evaluation for debonding defects at the interface between TCL and HSB in concrete slab tracks.Ĭoncrete slab tracks (or ballastless tracks) are widely used in the high-speed railway systems in Germany, the Netherlands, China, Japan, and Korea. It was demonstrated that the best evaluation performance was obtained by using average peak frequency or the combination of average peak frequency and average Q factor, obtained by eight accelerometers in the multi-channel IE device.
Bilinear classification models were used to evaluate the individual and a combination of the characteristic parameters. Multi-channel IE signals obtained over solid concrete and debonding defects were reduced to three critical IE testing parameters (the velocity of concrete, peak frequency, and Q factor). The mockup model includes three debonding defects that were fabricated by inserting three 400 mm by 400 mm (length and width) thin plastic foam boards with three different thicknesses of 5 mm, 10 mm, and 15 mm, before casting concrete in TCL. Multi-channel Impact-echo (IE) testing was used to evaluate debonding defects at the interface between track concrete layer, TCL, and hydraulically stabilized base course, HSB, in a real scale mockup model of concrete slab tracks for Korea high-speed railway (KHSR) system.