## 5 Analysis of the Numerical Results
### Comparative Analysis of the In Situ Monitoring Results  
To verify the correctness of the simulations while ensuring the engineering safety, long-term, real-time monitoring was implemented over the deformation of slope, overlying road and surrounding rocks, and Figure 23 displays the specific locations of the monitoring points. At an excavation distance of 30 m, a horizontal settlement monitoring line was arranged on the ground surface, which included  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Model**} & \multirow{2}{*}{**C/H**} & \multirow{2}{*}{**D/W**} & \multirow{2}{*}{**Surcharge** (**kPa**)} & \multirow{2}{*}{**Existing** **Tunnel**} & **Surface** & **Maximum** & **Slope** & **Maximum** \\  & & & & **Settlement** & **Computed** & **Deformation** & **Computed** \\  & & & **Condition** & **Upper Limit** & **Settlement** & **Upper Limit** & **Settlement** \\ \hline \multirow{4}{*}{A-A} & \multirow{4}{*}{0.378} & \multirow{4}{*}{20} & htn & 6.1 & 3.2 \\  & & & hty & 3.5 & 3.0 \\  & & & htn & 9.4 & 4.1 \\  & & &  
10 monitoring points (completely corresponding to the line 1 of the numerical model). The monitoring point P1 was put on the outer slope surface of the tunnel sidewall directly below line 1 for monitoring the horizontal deformation of the slope. Points P2 and P4 were put on the left and right sidewalls of the tunnel, respectively, for monitoring the horizontal displacement of the sidewalls. Point P3 was put on the roof of tunnel. In the same way, a monitoring line (comprising 10 points in total) was arranged on line 2 in the numerical model, which corresponded to monitoring points P5-P8 at the slope and tunnel interior. Based on the simulation results, the critical area with the largest deformation was chosen as the monitoring point arrangement area such that the monitoring results were highly representative. The monitoring points for the deformation monitoring of the slope and surface settlements were already set up prior to the tunnel construction, while those for the deformation monitoring of the rocks surround the tunnel could only be set up as soon as possible after excavation of the tunnel. As the deformation curve of the whole process of the surrounding rock could not be obtained in the field, the displacement that was not monitored was also approximately reflected in the monitoring curve according to the excavation contour of surrounding rock. Thus, Figure 24a shows rather complete monitoring data, whereas Figure 24b-d only shows the relative displacements of the surrounding rocks following excavation. It is clear from Figure 24 that the critical stage affecting the deformation of slope and surrounding rocks was the approaching phase of the tunnel face [21]. All the monitored values were lower than the corresponding simulations, of which the slope stability deformation monitoring value was about 20% lower than the simulated value, and the final stability deformation monitoring values of the tunnel surrounding rocks were all lower than the upper limits (15 mm and 20 mm) for tunnel deformation stipulated by the Land Transport Authority (2000) and Building Department (2009) [9]. This indicates that the actual average mechanical parameters of the surrounding rocks were higher than those used in the simulation. Thus, the monitoring results not only proved the correctness of the simulation results, but also implied extra redundancy regarding the degree of engineering safety. Figure 23: Schematic of in situ monitoring point locations. Figure 24: Deformation monitoring comparisons of the slope and the rocks surrounding the tunnel: (**a**) comparison of the time-history curves for the slope horizontal displacement, (**b**) comparison of the time-history curves for the tunnel vault vertical displacement, (**c**) comparison of the time-history curves for the tunnel left sidewall horizontal displacement, and (**d**) comparison of the time-history curves for the tunnel right sidewall horizontal displacement.