## 4 Evaluation of the Coordination of Three Types of Asphalt Pavement Structures
### The Rules Analysis of Sensitivity  
#### 4.3.1 The Rules of Deflection Sensitivity  
By conducting the steps (1) and (2) of the analysis software, the deflection sensitivity within the range of 0-3.6m under the single and double circular loads was calculated, respectively, as shown in Figure 4.  
Figure 4: Deflection sensitivity of three structures.  
Comparative analysis of deflection sensitivity of three structures according to Figure 4 revealed the following points: (1) Under the double circle load, the order of deflection sensitivity was structure II \(>\) structure I \(>\) structure III for points 1-26 (i.e., transverse distance 0-2.4 m), and structure II \(>\) structure III for points 27-30 (i.e., transverse distance 2.7-3.6 m). (2) Under the single circle load, the order of deflection sensitivity was structure II \(>\) structure I \(>\) structure III for point 1-28 (i.e., transverse distance 0-3 m), and structure I \(>\) structure II \(>\) structure III for point 29-30 (i.e., transverse distance 3-3.6 m).  
The three structures were also compared for the deflection and deflection sensitivity curves. The comparison revealed the following points: (1) Near the load, the deflection values were quite different, but the deflection sensitivity values were slightly different. (2) With an increase in distance, the deflection curves of different pavement structures came closer and almost overlapped, which indicated that the deflection value at a point far away from the load was less sensitive to the type of pavement structure. Therefore, the deflection and deflection sensitivity far away from the load were not considered in this study, and hence, it was concluded that the order of deflection sensitivity of three pavement structures was structure II \(>\) structure I \(>\) structure III. According to the meaning of deflection sensitivity as in Equation (1), the ranking results of the structural rigidity of the three structures were the same as that of the deflection under the uniform load of double circles, but not the same as that under the uniform load of single circle. (3) With an increase in distance, the sensitivity curves of structure I and structure II were almost identical (Figure 4), but were different from the sensitivity curve of structure III, which showed that the rigidity of structure I and structure II was relatively close and significantly larger than that of structure III. This observation is consistent with the conclusion of the previous analysis of deflection.  
This analysis showed that the deflection value cannot serve as an evaluation index because different conclusions could be drawn with different loading forms. For example, for structure I and structure II in this paper, the order of the maximum deflection value under the uniform load of double circle and single circle was just the opposite. However, the sensitivity of deflection was not affected by the load form, and the conclusion of uniform load form of the single circle and double circle was consistent with that of the uniform load form of the double circle required by the specifications. Furthermore, since the deflection value further from the load was similar for different structures, the deflection value evaluation, which was based on the maximum deflection value of a single point, would present limited information. However, the deflection sensitivity was based on a number of sensitivity values on a line in the Y direction of YZ section, and the curve formed by the sensitivity could distinguish the rigidity of different structural types.