## 4 Results and Discussions
### Validation of FEM Model Using Field Measurements  
#### 4.3.1 Comparison of Magnitude of Dynamic Responses Based on Same Settings  
Field measurements were conducted using the full-scale NE-ALT system to validate the FEM models established in this study. The field measuring point was set at the bottom of the upper layer (h = 0.05 m) of asphalt pavement, which was also located in the middle of the outer wheel path nearest to the control building, as shown in Figure 3. The vehicle simulator in the field test was controlled at the parameter combination of 0.7 MPa vehicle wheel grounding pressure and 20 km/h vehicle speed, which was the same as the low-speed group in the numerical simulation. Dynamic responses for asphalt pavement in dry and saturated conditions were monitored during field tests, which were generated by the vehicle's rear axle wheels. The magnitudes of indicators such as stress, strain, and pore water pressure were obtained and then compared with those calculated from the numerical simulation, both of which are summarized in Table 4.  
Values of dynamic response indicators obtained from field measurements and numerical simulation were compared, both of which were found in the same order of magnitude. Values of vertical stress, transverse strain, and pore water pressure calculated by numerical simulation were larger than those measured from the field test, while numerical vertical strain showed a relatively smaller value, which might be induced by the differential compaction degree in the regions where sensors were buried. These differences in indicators' magnitude values were mainly caused by the simplification of both pavement structure, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & & \multicolumn{4}{c}{**Magnitude**} \\ \cline{3-6}
**No.** & **Indicator** & \multicolumn{2}{c}{**Numerical Simulation**} & \multicolumn{2}{c}{**Field Test**} \\ \cline{3-6}  & & **Dry** & **Saturated** & **Dry** & **Saturated** \\ \hline
1 & Vertical stress & 0.650 MPa & 0.675 MPa & 0.491 MPa & 0.530 MPa \\
2 & Vertical strain & 185.6 \(\mu\varepsilon\) & 194.6 \(\mu\varepsilon\) & 353.3 \(\mu\varepsilon\) & 364.7 \(\mu\varepsilon\) \\
3 & Transverse strain & 236.9 \(\mu\varepsilon\) & 197.3 \(\mu\varepsilon\) & 135.1 \(\mu\varepsilon\) & 145.6 \(\mu\varepsilon\) \\
4 & Positive & Pore water & - & 42.5 kPa & - & 252.9 kPa \\
5 & Negative & pressure & - & 45.4 kPa & - & 7.1 kPa \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of responses obtained from numerical simulation and field measurements. materials, and the applied vehicle load in the FEM models, which were undoubtedly different from the actual complicated conditions faced by asphalt pavement in the field test site. In particular, material parameters' values in Table 1 were determined based on empirical assumptions [12; 25; 26], which might be a non-negligible factor to cause differences between indicators' magnitude values of numerical analysis and field measurement. Indicators obtained in saturated conditions showed larger magnitude values than those obtained in dry conditions for both numerical simulation and the field test. This phenomenon indicated the fact that water intensified the degree of dynamic responses inside asphalt pavement, while continuous action by water led to the decline of the overall service life of asphalt pavement. The values of positive pore water pressure obtained from numerical simulation and field test were close and in the same order of magnitude, which verified the effectiveness of the saturated FEM model for the prediction of pore water pressure. However, negative pore water pressure showed a larger magnitude value compared with positive pore water pressure in numerical simulation, which exhibited the reverse order in the field test. This might be induced by the tread pattern on the vehicle wheel, which was not taken into account in the numerical simulation.