## 4 Evaluation of the Coordination of Three Types of Asphalt Pavement Structures
### The Rules Analysis of Sensitivity
#### 4.3.2 The Rules of Stress Sensitivity  
Conducting steps (1) and (2) of the analysis software, the stress sensitivity of the lower surface layer bottom, the lower base layer bottom, and the sub-base layer bottom under three structures within the range of 0-3.6 m under the single and double circular loads was calculated, respectively, as shown in Figures 5-7. Figure 5: Transverse stress sensitivity of the lower surface layer bottom of three structures (unit: %). According to the definition of stress sensitivity and the rules of deflection sensitivity in Section 4.3, the range of stress sensitivity under the uniform load of double circles and single circle was 0.1864-2 m and 0-2 m, respectively. In the selected range, under the double circle and single circle loads, sensitivity of the transverse stress at the lower surface layer was ranked as structure I > structure III > structure II, the longitudinal stress at the base layer was ranked as structure I > structure III > structure II, and the longitudinal stress at the sub-base layer was ranked as structure III > structure I > structure II. Large differences were observed in the ranking results of stress and stress sensitivity of each layer. This was attributed to the fact that the maximum stress of a single point at the bottom of the structural layer represented the most unfavorable mechanical state of the structural layer under the load, and the starting point focused on the structure. On the other hand, the stress sensitivity at the bottom of the layer represented the feedback mechanism of the material of each structural layer after the structure was stressed, and focused on the material. As shown in Figures 5-7, comparing the sensitivity of the three road structures at the same distance as the distance increased, the difference in sensitivity of the three road structures increased first and then decreased. Under the double circle load, the maximum difference in the transverse stress of the lower surface layer, the longitudinal stress of the base layer and the longitudinal stress sensitivity of the sub-base layer was 20.8%, 15.0%, and 3.0%, respectively, and the corresponding distance was 0.3195 m, 0.6 m, and 0.6 m, respectively. Under the single circle load, the maximum difference in the transverse stress of the lower surface layer, the longitudinal stress of the base layer, and the longitudinal stress sensitivity of the sub-base layer was 19.2%, 17.9%, and 3.7%, respectively, and the corresponding distance was 0.213 m, 0.426 m, and 0.6 m, respectively. The difference in stress sensitivity was mainly observed in the surface layer and base layer. This observation is consistent with the understanding that semi-rigid base acts as the main bearing layer. Therefore, the stress sensitivity index was observed as a suitable index for evaluating the mechanical performance of a pavement structure. The stress sensitivity of structure I was greater than that of structure II, which indicated that the utilization efficiency of the asphalt layer and semi-rigid sub-base material of structure I was better  
Figure 6: Longitudinal stress sensitivity of the base layer bottom of three structures (unit: %). Figure 7: Longitudinal stress sensitivity of the sub-base layer bottom of three structures (unit: %). than that of structure II due to the difference in construction method, namely, setting of reinforced semi-rigid base material and roller compacted concrete base material. The semi-rigid sub-base materials of structure I and structure III were approximately identical, with thicknesses of 19 cm and 20 cm, respectively. The stress sensitivity of structure III was greater than that of structure I, which was contrary to the conclusion based on stress sensitivity of the lower layer and the base layer. This contrast might have been related to the thickness.