## 5 Dynamic Mechanical Response Analysis of Asphalt Pavement under the Influence of Groundwater
### Impact of Groundwater on the Variation Patterns of Road Surface Deflection  
During the service life of road structures, the roadbed is significantly influenced by groundwater factors, resulting in fluctuations in internal moisture within a certain range. The mechanical properties of the roadbed, such as the resilient modulus, also undergo substantial changes with variations in the moisture field, thereby affecting the overall stiffness of the road. Roadbed materials, as a typical porous medium, are typically studied based on the relationship between porous media and moisture characteristic curves to understand their hydraulic characteristics. Currently, the Van Genuchten model provides a  
Figure 8: Theoretical deflection comparison chart between this study and Abaqus method. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Measurement Point Locations**} & **D1** & **D2** & **D3** & **D4** & **D5** & **D6** & **D7** & **D8** & **D9** \\ \hline \multirow{3}{*}{20} & ABAQUS (\(\mu\)m) & 169.27 & 138.97 & 124.11 & 96.41 & 90.55 & 75.19 & 61.62 & 48.50 & 40.17 \\ \cline{2-10}  & Proposed Algorithm (\(\mu\)m) & 168.22 & 138.47 & 122.57 & 97.12 & 90.14 & 73.83 & 61.22 & 49.24 & 40.65 \\ \cline{2-10}  & Error (\%) & 0.62 & 0.36 & \(-\)1.24 & 0.74 & 0.45 & 1.81 & \(-\)0.65 & 1.52 & 1.19 \\ \hline \multirow{3}{*}{45} & ABAQUS (\(\mu\)m) & 322.58 & 240.42 & 218.14 & 193.54 & 176.83 & 143.03 & 115.42 & 90.66 & 74.44 \\ \cline{2-10}  & Proposed Algorithm (\(\mu\)m) & 320.82 & 239.70 & 216.92 & 195.13 & 175.90 & 141.68 & 113.32 & 91.19 & 74.58 \\ \cline{2-10}  & Error (\%) & \(-\)0.55 & \(-\)0.30 & \(-\)0.56 & 0.81 & \(-\)0.53 & \(-\)0.95 & \(-\)1.85 & 0.58 & 0.19 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of maximum deflection values at various sensor locations between the two methods. reasonable description of the relationship between soil moisture content and potential and has been widely applied. It is represented by Equation (26). \[\theta=\theta_{\text{r}}+\frac{\theta_{s}-\theta_{r}}{\left(1+\left(\alpha h \right)^{n}\right)^{m}} \tag{26}\]  
where \(\theta\) is volumetric water content; \(\theta_{s}\) is saturation water content; \(\theta_{r}\) is residual water content; \(\alpha,m,n\) are the fitting parameters; and \(h\) is soil water potential. By altering the groundwater table's elevation, the matric suction at a specific point within the roadbed was calculated. The moisture content at different distances from the groundwater table in the roadbed was determined using the soil moisture characteristic curve. The results are depicted in Figure 9.  
The migration of moisture within the roadbed follows [PERSON]'s law, where the velocity of groundwater through the roadbed medium is directly proportional to the magnitude of the hydraulic gradient and the permeability of the fill material. This relationship can be expressed as Equation (27):  
\[Q=K\bullet A\bullet\frac{\Delta h}{L} \tag{27}\]  
in which \(Q\) is the seepage flow rate, \(K\) is the permeability coefficient, \(A\) is the cross-sectional area for water flow, \(\Delta h\) is the head loss, and \(L\) is the path length. This paper comprehensively analyzes the variations in the mechanical response of road structures under different humidity conditions, considering the water-soil characteristics of roadbed fill material and the migration patterns of groundwater within the roadbed based on control equations. In this research, medium plasticity silt was selected as the roadbed fill material, and the impact of varying groundwater levels on road surface deflection was thoroughly examined. The roadbed was divided into layers, with each layer representing a 1% change in moisture content. Assuming the groundwater level was at distances of 1 m, 2 m, 4 m, 6 m, and 7 m from the top of the roadbed, we calculated the corresponding pavement deflection values. The relevant results are shown in Figure 10.  
Figure 9: Predicted equilibrium moisture content in the roadbed.