# Development of Track Support Stiffness Measurement and Evaluation System for Slab Tracks
###### Abstract  
The track support stiffness measurement and evaluation system for slab tracks proposed in this study enables the calculation of the load-displacement diagram at the various measurement positions. Therefore, it is possible to evaluate the track support stiffness directly on-site without evaluating the spring stiffness of the elastic material through sampling or in situ testing, also enabling the evaluation of the deterioration of the elastic material. In addition, the performance evaluation data for elastic materials obtained through field tests using measurement equipment and software to track support stiffness are integrated and managed on the administrator's computer. Therefore, the replacement plan is established, and the maintenance history is managed by identifying the replacement time and location of elastic materials. It is possible to evaluate the performance and condition of the elastic material at various points during track inspection and the track support stiffness and durability of the elastic material (spring stiffness variation rate, replacement periods, among others) at the current operating condition. slab track; track support stiffness; measurement system; elastic material; durability +
Footnote †: journal: MedicalPresently, the maintenance of elastic slab-track materials is performed by collecting resilience pads from various sites through an overnight rack work, and subsequently, an accredited laboratory, such as the Seoul Metro, is requested to perform a spring-stiffness test on the collected resilience pad. The performance of the elastic material is then estimated, based on the load-displacement test result, and is used to determine the elastic material should be employed or discarded [11; 12; 13; 14]. However, this requires an expensive, dangerous, and complicated process of dismantling the rail, rail fastening, and lifting the sleepers to remove the resilience pads, as shown in Figure 2. As depicted Figure 2a,b, rail fasteners are first dismantled to remove the elastic pad, followed by lifting of sleepers. The elastic pad can be removed (Figure 2c), replaced with a new elastic pad (Figure 2d), and reassembled (Figure 2e) prior to sleepers being put down, Figure 2f depicts a used resilience-pad sample. Figure 1: Slab-track system. The location of sensor installation is shown in Figure 3. As a method for evaluating the current track support stiffness, a field measurement is performed, as shown in Figure 4[2]. In this study, a straight track section was selected for performing track-support stiffness measurements. The speed and axial load of the train equaled 100 km/h and 160 kN, respectively. As the field measurement is a field test of the railway track in a serviced line, it should be performed in the field during the nightly train cut-off time to install a wheel load sensor and a displacement meter and measure track behavior under the operating train load during the daytime train hours [3; 4; 5; 15; 16]. In this study, vertical rail displacements were measured using displacement transducers, such as linear variable differential transformers (LVDTs), mounted on a jig anchored to the concrete layer of the subway structure, as illustrated in Figure 4[1]. LVDTs (CDP-25M) used in this study demonstrated a sensitivity of \(500\times 10^{-6}\)/mm along with 6.25-mV/V \(\pm\) 0.3% rate power and 7-Hz frequency response. All displacements were measured and automatically recorded using a computer-controlled data-acquisition system. Figure 4 depicts the attachment of the wheel-load sensor to the sleeper for the evaluation of the rail deflection. Additionally, a newly developed track support stiffness (TSS) tester can be attached to the middle of the sleeper. However, field measurements in this study were performed on the sleeper to calculate the direct displacement of the elastic spring at the rail-support point. Figure 3: Location of sensor installation. Figure 2: Photograph of collecting for used resilience pad samples.