# Development of Track Support Stiffness Measurement and Evaluation System for Slab Tracks
###### Abstract
(**a**) Pre-work (Dismantling rail fastener and installation Jack-up device); (**b**) Lifting sleeper (RC block); (**c**) Positioning and separating sleeper and rubber boot; (**d**) Replacement and insertion of resilience pad; (**e**) Put the sleeper down; (**f**) Used resilience pad sample. Figures 5 and 6 show the results of the wheel load and vertical rail displacements measured using the wheel load sensors and the displacement meter. Figure 7 shows the track support stiffness calculated by measuring the dynamic wheel load and the displacement of the rail or sleeper through field measurements. Figure 7 shows the load displacement diagram based on Figures 5 and 6. It is difficult to perform field measurements at multiple locations owing to the small time window available (approximately 3.5 h). In addition, technical limitations are encountered when reflecting site conditions as a means for grasping the performance of certain sections using measurement data acquired at specific locations [2]. In the slab-track case, the displacement transducer was mounted on the upper surface of the slab track assuming the slab layer to remain non-deformed when subjected to a moving-train load [1]. By measuring the vertical displacement of tracks subject to moving-train loads, the effect of dynamic loading on track sections can be evaluated  
Figure 4: Photograph of typical field measurement on track. Figure 5: Examples of measured dynamic wheel load. (**a**) Inner rail; (**b**) Outer rail. Figure 6: Examples of measured dynamic rail displacement. (**a**) Inner rail; (**b**) Outer rail. to calculate the track-support stiffness [1]. Although both vertical and lateral displacements were measured during on-field testing, only the vertical displacement was used in track-support-stiffness calculations [1]. Furthermore, using conventional field measurements, the track-support stiffness can be calculated by measuring the dynamic wheel load and displacement of the rail or sleeper. Based on this calculation, the spring stiffness of the resilience pad installed on the lower rail or sleeper can be determined [2; 3; 4; 5; 15]. Therefore, the purpose of evaluating track support stiffness through field measurements and inferring the level of spring stiffness change in the resilience pads in use was to evaluate track support stiffness; however, only the performance at specific positions could be analyzed [5; 15; 17]. In addition, the field measurement or laboratory test and analysis of the adequacy of the track support stiffness had to be differentiated. Thus, a disadvantage in the measurement system was realized in that it was not possible to directly determine the aging level of the elastic material in the field. Therefore, for the economical and efficient maintenance of elastic materials, an integrated maintenance and management system was introduced, such as the measurement system for the elastic material performance test of the slab track, which will be described in this study. This measurement system, i.e., integrated system of measurement and evaluation, can quickly evaluate the performance and condition of elastic materials by simple testing performance changes (degradation) at desired locations during the nightly inspection. In this study, a track support stiffness measurement system for slab tracks was developed by comparing the rate of change of the track support stiffness of elastic materials. This is performed so that the reason for the replacement of elastic materials (necessity of replacement) and the performance improvement effect before and after replacement can be immediately demonstrated based on the experimental data.