## 5 Conclusions  
The objective of this study was to introduce and evaluate a new technical method for measuring and monitoring track foundation settlement of the concrete slab track on the transition zone between a tunnel and its embankment, which is composed of a Multi  
Figure 25: Settlement simulation with assumption of a simple supporting slab. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**E (\(\times\)10\({}^{7}\), kPa)** & **I (m\({}^{4}\))** & **B (m)** & **H (m)** & **EI (kNm\({}^{2}\))** & **L (m)** \\ \hline
0.8 & 0.0036864 & 3.2 & 0.24 & 29,491.2 & 2.53 \\ \hline
1.6 & 0.0036864 & 3.2 & 0.24 & 58,982.4 & 3.01 \\ \hline
2.4 & 0.0036864 & 3.2 & 0.24 & 88,473.6 & 3.33 \\ \hline
3.2 & 0.0036864 & 3.2 & 0.24 & 117,964.8 & 3.58 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parametric calculations of void space length. Depth Deflectometer (MDD) combined with a Global Navigation Satellite System (GNSS). The MDD was newly designed with the addition of laser sensor modules for increasing precision and the MDD head was fixed at the top of the track slab. The MDD/GNSS system measures the relative deflection between each track layer as well as the total deflection at the top of the track slab, which may evade the fixed condition problem of the classical MDD. The new MDD/GNSS system was installed at the transition zone between a tunnel entrance and its embankment, which experienced high settlement levels prior to repair. The system was built to monitor whether the repaired concrete track foundation with pressurized cement grouting was stabilized effectively and what track layer position was the most unstable so that it had the most influence. The GNSS system was designed and built for computing the net settlement at each track layer even when the MDD could not be fixed firmly at the end point, which is a major drawback of the classical MDD. The results obtained from the MDD and GNSS measurements indicated significant potential in aiding railway track settlement measurements. The main advantages of the new MDD/GNSS system and observation results are summarized as follows:  
* The monitoring results verified that the combination of MDD with GNSS enhances the capacity to assess effective measurement of the track foundation, providing a more comprehensive perspective on the track monitored system. * Since the MDD head is fixed at the rover position on the track slab, the MDD/GNSS system can measure the relative deflection between each track layer and the slab surface as well as the total deflection at the top of the track slab by a GNSS rover receiver simultaneously, which can evade the fixity condition problem of the classic MDD. * An effective data collection and data transferring system for MDD/GNSS was designed; it works systematically. A real-time monitoring program runs effectively for data storing and for subsequent analysis and processing. By combining the absolute GNSS rover settlement and MDD settlement, an accurate estimation of the total settlement in the concrete slab track layers can be obtained. * Deformation values measured at each MDD position, which are calibrated with GNSS measurement at the top of the track slab, providing meaningful details for analyzing repair performance of track foundation soil under track slabs. This study revealed that there may be a reduced size of the void space remaining below the track slab even after restoration at the site. For example, the 2.0 mm difference in total settlement between Position 1 and other positions (2, 3, 4) in the MDD/GNSS system was due to one main reason: The bearing capacity in the track foundation soil near the slab was still not sufficient to resist the slab weight and the train load fully after restoration. This lack of bearing capacity came from the existing small void space below the slab even though its size was reduced somewhat by grouting restoration.