# Interlocking Settlement Induced by Widening Subgrade of Railway Line
## 3 Analysis of Results  
Figures 11 and 12 show the results of long-term settlement measurements over time during and after RSR construction on the ground, surface, and rail. The maximum settlements at the ground and surface, which are the positions directly loading the RSR's weight, were 32.50 and 58.50 mm, respectively. The maximum interlocking settlements measured on the outer and inner rails of the existing track were 9.50 and 6.89 mm, respectively, which were relatively larger in the outer rail close to the center of gravity of the RSR. The interlocking settlements tended to appear larger towards the center (at 20 m), which was heavily affected by the RSR loads. Interlocking settlements occurred at 15-28% and 9-16% compared to the ground and surface, respectively. The interlocking settlements occurred within the range of 10 mm, which is the Korean track maintenance standard. Therefore, a widened embankment using RSR can secure the stability of the existing track, even in ground conditions including a shallow soft layer. Regarding the overall tendency of settlements, the closer to the center of gravity of the RSR, the greater the settlement, which is similar to the traditional widening of embankments in previous studies [26; 27]. The large difference in the interlocking settlement with the ground or surface is due to the difference in the distance from the center of gravity of the RSR and the difference in the stiffness of the ground. Because the bottom ground near the embankment toe is less loaded than at the lower part of the existing embankment, where the self-weight of the embankment and the train operation load continued, the difference in stiffness of the bottom ground due to the compression difference [28] may have affected the settlement. Figure 11: Ground and surface settlements. Figure 12: _Cont._The period of increasing settlement can be divided into three parts: backfill stabilization, wall construction, and after wall construction. Figure 13 shows the settlement that occurred according to the measurement period at each measurement point as a percentage of the total settlement. The settlement during the backfill stabilization period compared to the total occurred at 62% and 44% of the ground and surface, respectively, and from 69% to 100% of the interlocking settlement. During the backfill stabilization period, the time-dependent settlement was induced in the soft layer of the bottom ground, owing to the soil weight, and the overall settlement increased with time but showed a tendency to converge at a certain level. The greater the distance from the measurement position to the RSR center of gravity, the greater the rate of settlement during the stabilization period. This can be attributed to the wall load being smaller than the backfill and the wall being installed close to the center of gravity of the RSR. The interlocking settlement during the wall construction period compared to the total occurred at 0-29%. The interlocking settlement due to the wall load was larger in the central part, which was significantly affected by the RSR load, as shown in Figures 12 and 13. However, considering that the interlocking settlement decreased after wall construction at several measurement points and the interlocking settlement only slightly increased (up to 2.02 mm), external factors, such as climate, precipitation, and measurement error, may have affected the results. It can be observed that the effect of the wall load on the interlocking settlement was insignificant. Similarly, in the long-term measurement after RSR wall construction, the closer the wall load applied, the larger the settlement measured. However, the settlement rate was  
Figure 12: Ground and surface settlements: (**a**) Outer rail; (**b**) Inner rail. Figure 13: Settlement rate by period. extremely small (up to 4%), or additional settlement did not occur at several measurement points after wall construction. The interlocking settlements increased for a certain period and then decreased, contrary to those on the ground and the surface.