In the Republic of Korea, large-scale deep excavation construction is being conducted adjacent to structures owing to overpopulation in urban areas. Securing the safety of earth-retaining and underground structures is crucial for adjacent excavation work in urban areas. Accordingly, an automated measurement system is used to monitor the behaviors of subway tunnels and track structures; however, the utilization of its results is extremely low. Existing techniques evaluate the safety of track and tunnel structures based on the measured maximum values. This study introduces an evaluation technique for improving behavior monitoring in subway tunnels and track structures. A substantial amount of long-term measurement data on subway tunnels and track deformation was quantitatively evaluated using the Gaussian probability density function. In addition, the results from the same location where the tunnel convergence meter (TL) and track bed settlement (RM) sensors were located were compared. The comparison results revealed a difference in the vertical displacement of the tunnel and track structure owing to adjacent excavation work. A technique to analyze the continuous behavior of the tunnel was presented by numerically analyzing the tunnel measurement results as input data. In addition, they emphasized the need for simultaneous monitoring of tracks and tunnels.

To date, the spring stiffness of resilience pads was mostly evaluated based on conventional (site measurement and laboratory tests) methods. Most studies in the past analyzed the effects of the deterioration of resilience pads on track damage. To examine the deterioration of resilience pads, evaluations were conducted based on laboratory tests using site measurements and samples were collected from the site, or based on loading tests using special equipment. such as TSS. However, no methodology was proposed to prove the theoretical equations of Zimmermann which compute the reaction force at the rail support point. Hence, this study aimed to prove that the reaction force increased if spring stiffness at the rail support point increased; this was achieved by using a pressure sensor according to the theoretical equations of Zimmermann. Furthermore, we aimed to propose a method to evaluate the spring stiffness of resilience pads to predict the extent of deterioration of the pads based on the increase in the pressure measured by a pressure sensor.

The resilience pads of sleeper floating tracks (STEDEF) are key components that absorb shock loads and vibrations induced by train traffic. Currently, under the Korean domestic guidelines for track facility performance evaluation, one sample per 500 m is collected from the field, and the static spring stiffness is assessed through laboratory testing. However, this approach requires nighttime track possession, incurs significant manpower and cost, and provides limited reliability because the condition of an entire section is inferred from a small number of samples. Therefore, this study proposes an impact-hammer–FRF-based method for evaluating the spring stiffness of resilience pads without pad extraction. Field impact-hammer tests were conducted to identify the dominant first-mode natural frequency of the track-support system. Configuration-specific finite element models were then used to derive frequency–stiffness relationships for the investigated STEDEF configurations. The novelty of the proposed method lies in converting the local first-mode frequency measured in situ into a static-equivalent stiffness index that can be directly compared with the maintenance reference value used in the Korean inspection framework. The finite element model reproduced the mean natural frequencies of the reference configurations with differences of 0.08–3.61%. Based on the configuration-specific relationships, estimation equations were developed to support in situ screening of resilience-pad stiffness at the measured locations.

Concrete track systems supported by underground structures may undergo forced deformation due to uplift or subsidence; however, track-type-dependent differences in potential damage locations and influence lengths remain insufficiently quantified. This study compared a sleeper floating track (STEDEF), a precast panel track (B2S), and a direct fixation track (System 336) using three-dimensional finite element analysis. Displacement-controlled uplift and subsidence were imposed on the concrete slab, with selected cases additionally subjected to an 80 kN design wheel load. The three track systems were directly compared under a common imposed displacement of 40 mm for both displacement-only and combined displacement–train-load conditions. Potential regions of tensile- and shear-strength exceedance were identified using code-based concrete strength criteria. Impact-hammer modal tests on a STEDEF specimen were used to examine changes in support conditions associated with resilience-pad pre-compression and near-zero sleeper support. STEDEF exhibited the longest one-sided shear-strength exceedance length, while uplift produced longer tensile-strength exceedance lengths than subsidence in STEDEF and System 336. Modal testing showed a lower natural frequency under simulated support loss and a higher frequency under resilience-pad pre-compression. These findings support track-type-specific damage screening and maintenance prioritization.

Temperature-induced expansion and contraction of the upper highway steel girder can modify the force distribution in the vertical hanger cables and thereby influence the response of the lower railway deck in highway–railway steel composite bridges. This study analyzes three years (2019–2021) of field monitoring data to quantify the relationships among member temperature, highway expansion-joint displacement, and inner/outer cable tensions. Linear temperature-based prediction equations were developed using daily-averaged records and validated against independently estimated cable tensions from vibration-based identification (n = 24 tests; 8 cables × 3 campaigns). The prediction showed mean deviations below 5% and a maximum absolute deviation of 8.4%. A supporting ANSYS model reproduced the first-mode frequencies within 4%. The proposed framework provides practical equations for operational monitoring and maintenance planning within the monitored temperature range.

Resilience pads provide elastic behavior and reduce impact and vibration loads in sleeper floating tracks, but their long-term degradation affects critical track components. Their performance is currently measured using labor-intensive, expensive restricted field sampling and indoor static stiffness testing, which cannot reliably measure entire track sections. The objective of this study was to measure and analyze a rail’s supporting-point reaction force (pressure) using a skin sensor according to the train load (as the force changes with spring stiffness) and the resilience pad spring stiffness of the sleeper floating track. To evaluate the rail-supporting-point reaction force of the sleeper floating track, a skin sensor was installed at the bottom of the concrete sleeper, and the reaction force was measured according to the train load. Laboratory testing demonstrated that resilience pad spring stiffness affects the rail-supporting-point reaction force. Field measurements of the train load were used to examine the sleeper floating track’s supporting-point reaction force and the resilience pad’s spring stiffness, confirming field applicability. Therefore, this innovative skin-sensor-based assessment technique for reaction forces at rail-support points may predict resilience pad replacement and identify anomalies in real time, making it easier to assess performance and diagnose sleeper floating tracks.