## 4 Results and Discussions
### Spatial Distribution of Dynamic Response Indicators by FEM Analysis
#### 4.4.2 Transverse Distribution  
The horizontal plane with a depth of 0.05 m at the bottom of the upper layer was selected to further analyze transverse distributions of stress, strain, and pore water pressure. When the applied vehicle loads of 0.7 MPa and 1.4 MPa reached their maximum values at the speed of 60 km/h, variation trends of dynamic responses with the entire width range of asphalt pavement are discussed and summarized in Figure 15.  
Figure 15: Transverse distributions of dynamic responses at the bottom of the upper layer inside dry and saturated asphalt pavement (h = 0.05 m): (**a**) Vertical stress; (**b**) Vertical strain; (**c**) Transverse strain; (**d**) Pore water pressure.  
As shown in Figure 15a, the regions outside direct contact with vehicle load in the saturated asphalt pavement presented relatively complex distributions of vertical stress compared with those in dry conditions. Compressive stress was observed in the regions in direct contact with the single-axle four-wheel load, while stress in the range of the middle vehicle axle was tensile. Stress in the outer sides of the wheels totally turned into compression from tension after slightly tensile and compressive alternations, while the compressive stress gradually decreased with the increasing distance from the middle vehicle axle. Vehicle load showed a significant effect on the enhancement of compressive stress within the regions in direct contact with the vehicle wheels. In Figure 15b, vertical strain in the regions in direct contact with the vehicle wheels was compressive, but in the outer sides of the vehicle wheels was tensile to a certain extent. The magnitudes of vertical strain in both compressive and tensile regions increased with the increase in vehicle load. In particular, compared with those in dry asphalt pavement, transverse distributions of vertical strain showed obvious tensile properties inside saturated asphalt pavement in the middle region of the vehicle axle. In Figure 15c, transverse strain showed compressive performance in the regions in direct contact with the vehicle wheels but exhibited obvious tensile properties in the outer sides of the vehicle wheels. Water aggravated the tensile degree of transverse strain, while the increase in vehicle load also enhanced the magnitudes of transverse strain in dry and saturated conditions. In particular, transverse strain was observed to be tension in the middle range of the vehicle axle inside dry asphalt pavement, but it turned into compression in saturated conditions.  
Transverse distributions of pore water pressure along the entire width range of saturated asphalt pavement are summarized in Figure 15d, which took two vehicle loads and three vehicle speeds into account. When the applied vehicle loads reached their corresponding maximum values under different vehicle speeds, both the regions in direct contact with the vehicle wheels, the region of the middle vehicle axle, and the middle region between two adjacent wheels exhibited positive pore water pressure, while negative pore water pressure mainly emerged in the regions of the road's edges far away from the outer wheels. In particular, within the direct regions with the vehicle wheels, a parameter combination of \"1.4 MPa-100 km/h\" presented the maximum magnitude of positive pore water pressure. A parameter combination of \"0.7 MPa-100 km/h\" produced relatively larger positive pore water pressure compared with that generated by the parameter combination of \"1.4 MPa-60 km/h\". It indicated that pore water pressure was more sensitive to vehicle speed than vehicle load. Similarly, pore water pressure produced by \"0.7 MPa-60 km/h\" was larger than that generated by \"1.4 MPa-20 km/h\". In this case, a vehicle with light load and fast speed generated a relatively larger magnitude of pore water pressure than that produced by a vehicle with heavy load and slow speed to some extent. It is important to control overspeed and overload for vehicles to alleviate the adverse impact of pore water pressure on asphalt pavement.