Hidden structural weaknesses in metro corridors can be detected easily with new framework

Researchers have developed a new monitoring framework for detecting ground settlement over wide urban areas. The team has developed a forensic multi-scale remote sensing (MSRS) framework integrating InSAR, laser scanning (L/S), and ground penetrating radar (GPR).Researchers also revealed that conventional techniques, however, relying only on a single mode of monitoring, are limited in providing reliable monitoring over large areas. Combining complementary monitoring techniques can therefore provide a more comprehensive assessment of ground settlement. Staged framework linking wide-area monitoring “Our approach allows problems associated with excavation, inadequate compaction, and other construction defects to be characterized in greater detail than would be possible by using any single technology,” explains master’s student Tae-Yong Park from the Department of Civil Engineering at Seoul National University of Science and Technology.Published in Volume 174 of Tunnelling and Underground Space Technology, the study advances efforts to integrate satellite InSAR, laser scanning (L/S), and GPR into a staged framework linking wide-area monitoring, site-specific validation, and near-surface condition assessment along an urban subway corridor. Results demonstrated a settlement pattern First, long-term settlement is measured along the entire corridor using satellite InSAR time-series analysis. InSAR estimates surface displacement by comparing radar signals acquired repeatedly over the same area. In the study, the team also applied a technique called “seasonal-trend decomposition using LOESS” to exclude the seasonal fluctuations in settlement. InSAR analysis of the subway corridor revealed a ventilation shaft with a distinct settlement signal, which was then selected for subsequent detailed analysis. Further analysis showed a progressive long-term settlement, according to a press release.Next, field L/S was conducted at the selected shaft. Since visual inspection revealed multiple cracks and signs of repair on the ceiling, L/S was used to analyze the settlement tendency of the ceiling. The results demonstrated a settlement pattern that became more pronounced towards the part of the ceiling directly beneath the roadside above the shaft, as per the release.Researchers also revealed that later GPR was carried out along the road section above the shaft. GPR is a non-destructive technique that uses high-frequency electromagnetic pulses to investigate subsurface features. The GPR survey showed signals representing void-like structures near the shaft and reduced continuity of layer boundaries, indicating non-uniform subsurface conditions.The three results enabled showed that the detected settlement anomaly was not an artifact from any one technique but a reliable result obtained from a multi-scale analysis, thus reducing interpretational uncertainty.“Our research could help shift the paradigm of urban disaster management from reactive response to proactive prevention,” concludes Mr. Park. “In the long term, the MSRS system will support timely maintenance and targeted investigations of high-risk areas, thereby reducing the risk of sudden sinkholes, structural damage, and infrastructure failure.”