# Displacement Monitoring of Subway Tracks and Tunnels According to Adjacent Construction
## 5 Conclusions  
This study performed safety evaluations using the monitoring data of subway tracks and tunnel structures, considering adjacent excavation work. In subway tunnel structures, vertical and horizontal behaviors were monitored using a tunnel convergence meter sensor. In subway track structures, vertical behaviors were monitored using a track bed settlement sensor. Displacement monitoring data were collected from sites where adjacent excavations were performed for over 18 months. The long-term measurement data collected were quantitatively evaluated using the Gaussian probability density function. The primary research results are summarized as follows:  
(1) Based on the subway tunnel structure safety evaluation, the maximum vertical displacement occurred in the tunnel lining in Section A. However, the adjacent excavation work did not significantly affect the tunnel crown. In Section B, displacement occurred from the left lining to the left ceiling owing to the adjacent excavation work. In addition, the tunnel lining was the most affected in Section A. In Section C, the left and right linings of the tunnel were most affected by the adjacent excavation work. Therefore, the study site was determined to have the most vulnerable tunnel lining owing to the adjacent excavation work. Figure 12: Maximum vertical displacement analysis results (Xc + SD). (2) Based on the subway track structure safety evaluation, the largest vertical displacement was measured at approximately 18 m, where sensor RM-10 was installed at the initial (standard) value of the adjacent excavation work. However, the location of the maximum vertical displacement changed as the adjacent excavation work progressed. The vertical displacement was significantly reduced to approximately 28 m owing to the adjacent excavation work. In addition, the vertical displacement increased significantly at approximately 60 and 80 m from the track bed settlement sensor installation location. Therefore, the track bed settlement sensor was directly affected at the start and end points and the center of the adjacent excavation area. In addition, the track vertical displacement increased and decreased from the center of the adjacent excavation work area to the start and end points, respectively. (3) A comparison of the vertical displacements of the subway track and tunnel structure revealed that the vertical displacement of the track was larger at the start and end points of the excavation work area than at the tunnel. However, at the center of the excavation work area, the vertical displacement of the tunnel was larger than that of the track. This could affect the tunnel structure rather than the track at the center of the excavation work area. In addition, the start and end points of the excavation work area directly affect the track structure rather than the tunnel. Therefore, when performing adjacent excavation work, subway tunnels and track structures must be monitored simultaneously. In addition, periodically evaluating the safety of track and tunnel structures using long-term monitoring results is beneficial. The purpose of this study is to process and analyze massive amounts of data. In addition, tunnel analysis results were used as input data for numerical analysis. A technique for analyzing the continuous behavior of tunnels was presented using numerical analysis. The implications of the study's findings extend beyond the immediate context of subway construction in the Republic of Korea. They offer valuable insights and recommendations for improving safety practices, optimizing monitoring systems, and guiding future urban development initiatives. Conceptualization, J.-Y.C. and D.-H.A. ; methodology, J.-Y.C. ; software, J.-Y.C. and D.-H.A. ; formal analysis, J.-Y.C. and D.-H.A. ; investigation, J.-Y.C. and D.-H.A. ; data curation, J.-Y.C. ; writing--original draft preparation, J.-Y.C. and D.-H.A. ; writing--review and editing. All authors have read and agreed to the published version of the manuscript.