## 3 Simulating HMAC Pavement Deformation in Curved Ramp
### Influential Factor Analysis Using Orthogonal Design Method
The intuitive analysis diagram that indicates the change of pavement deformation with various factors is shown in Figure 9.  
From Figure 9a, it could be seen that the deformation (left \(Y\)-axis) increased linearly with the rise in tire pressure (bottom \(X\)-axis). The deformation under the pressure of 1.6 MPa was approximately  
Figure 9: Change of permanent deformation with factors and levels, (**a**) with tire pressure and ESAL; (**b**) with different layer thickness. five times that under 0.4 MPa. The pavement deformation (right \(Y\)-axis) also increased linearly with the increase in ESAL (top \(X\)-axis). The deformation under ESAL of 2800 (\(10^{4}\) times) is eight times that under ESAL of 200 (\(10^{4}\) times). According to the authors' previous research on HMAC pavement rutting with simple alignment, the deformation correlated well with ESAL in a convex power function whose exponent was 0.303 [32]. In contrast, Figure 9a shows that the pavement deformation in horizontally curved and sloped road increased linearly with ESAL, meaning the deformation susceptibility to traffic load in special road is increased. This result further confirms that heavy duty as well as overloading poses significant negative influence on pavement performance and should be therefore strictly controlled. Also, Figure 9b indicates the deformation in HMAC pavement with sloped and curved alignment changed differently with the change in depth of each structural layer. In detail, the deformation (left \(Y\)-axis) increased by 19.5% when the upper layer depth changed from three to five centimeters (bottom \(X\)-axis), whereas it decreased by 48.3% with the depth increasing to seven centimeters further. This suggests that an upper asphaltic course no less than five centimeters in complicated road is necessary considering the anti-rutting performance of entire pavement. In contrast, the deformation (left \(Y\)-axis) decreased by 43.3% when the middle HMAC course depth (bottom \(X\)-axis) doubled. It could be thereof inferred that increasing thickness of the middle course contributed most to the reduction in pavement permanent deformation since the HMAC was used in this layer. Unlike the upper and middle asphalt courses, increase in the binder course depth (bottom \(X\)-axis) had little effect on the change of permanent deformation (left \(Y\)-axis), according to Figure 9b. It was concluded that the upper and middle asphalt courses were crucial to the rutting resistant performance of HMAC pavement under complicated route conditions. According to the literature, [PERSON] suggested that modified asphalt binder be used in the middle and binder asphaltic layers to relieve pavement rutting in simple alignment [3]. However, this study shows that as far as special road is concerned, the upper and middle courses were more crucial to the pavement anti-rutting performance. This indicates that inclusion of the longitudinal and transverse shear force changed pavement deformation characteristic and the potential rutting area had a tendency to move up in curved ramp. Similarly, Figure 9b shows the pavement deformation (right \(Y\)-axis) changed little with the increase in the depth of semi-rigid base (top \(X\)-axis). Calculation shows that the deformation decreased simply by 12.3% when the base thickness doubled, which suggests that an appropriate thickness that is not too great would be suitable for semi-rigid base.