## 4 Evaluation of the Coordination of Three Types of Asphalt Pavement Structures
### Analysis of Evaluation Results  
Considering the influence of different sensitivity threshold values on the evaluation results, five different thresholds of 50%, 40%, 30%, 20%, and 10% were selected for the stress sensitivity of the key layers. The coordinates of the bottom of each key layer under different thresholds of three pavement structures were extracted by using the analysis software, as shown in Table 6. The transfer path envelope diagram of each structural layer was obtained and its area was calculated by the analysis software. The envelope diagram is shown in Figure 8 and the envelope area is shown in Table 7.  
Therefore, the envelope area of each layer was divided by the thickness to get the equivalent envelope area. The equivalent envelope area could characterize the ability of the material to bear and transfer stress per unit thickness in the whole pavement structure. The larger the value, the higher the material utilization efficiency, the more uniform the stress distribution, and the more reasonable the pavement structure. The equivalent envelope area is shown in Table 8. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Structural Type** & **Layer** & **50\%** & **40\%** & **30\%** & **20\%** & **10\%** \\ \hline \multirow{3}{*}{Structure I} & Lower surface layer bottom (0.13 m) & 0.331 & 0.367 & 0.420 & 0.532 & 0.935 \\  & Lower base layer bottom (0.51 m) & 0.589 & 0.736 & 0.966 & 1.381 & 2.257 \\  & Sub-base layer bottom (0.89 m) & 1.076 & 1.374 & 1.790 & 2.419 & 3.558 \\ \hline \multirow{3}{*}{Structure II} & Lower surface layer bottom (0.13 m) & 0.283 & 0.303 & 0.328 & 0.370 & 0.529 \\  & Lower base layer bottom (0.37 m) & 0.446 & 0.531 & 0.660 & 0.896 & 1.494 \\  & Sub-base layer bottom (0.75 m) & 1.046 & 1.333 & 1.729 & 2.324 & 3.400 \\ \hline \multirow{3}{*}{Structure III} & Lower surface layer bottom (0.18 m) & 0.329 & 0.364 & 0.410 & 0.487 & 0.710 \\  & Lower base layer bottom (0.58 m) & 0.538 & 0.645 & 0.790 & 1.019 & 1.485 \\ \cline{1-1}  & Sub-base layer bottom (0.98 m) & 1.100 & 1.385 & 1.785 & 2.391 & 3.492 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Threshold distance of each layer (unit: m). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Structural Type** & **Layer** & **50\%** & **40\%** & **30\%** & **20\%** & **10\%** \\ \hline \multirow{3}{*}{Structure I} & Lower surface layer bottom (0.13 m) & 776.4 & 823.2 & 892.1 & 1037.7 & 1561.6 \\  & Lower base layer bottom (0.51 m) & 3494.5 & 4189.5 & 5266.8 & 7269.4 & 12,129.6 \\  & Sub-base layer bottom (0.89 m) & 6324.7 & 8016.1 & 10,472.8 & 14,440.0 & 22,097.0 \\ \hline \multirow{3}{*}{Structure II} & Lower surface layer bottom (0.13 m) & 713.9 & 739.8 & 772.5 & 827.6 & 1033.8 \\  & Lower base layer bottom (0.37 m) & 1748.2 & 2001.1 & 2371.2 & 3039.4 & 4855.2 \\  & Sub-base layer bottom (0.75 m) & 5667.7 & 7083.2 & 9078.2 & 12,236.0 & 18,597.2 \\ \hline \multirow{3}{*}{Structure III} & Lower surface layer bottom (0.18 m) & 1071.5 & 1133.7 & 1216.9 & 1356.6 & 1757.3 \\  & Lower base layer bottom (0.58 m) & 3468.0 & 4034.4 & 4799.2 & 6025.6 & 8780.0 \\ \cline{1-1}  & Sub-base layer bottom (0.98 m) & 6552.0 & 8120.0 & 10,300.0 & 13,640.0 & 19,908.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Envelope area of stress transfer path (unit: cm\({}^{2}\)). As seen in Table 8, the following conclusions were made:  
1. The order of equivalent envelope area of the asphalt layer, base layer, sub-base layer, and pavement structure under the five threshold levels was structure I \(>\) structure III \(>\) structure II, and the order was not affected by the threshold level. 2. The material and thickness of the asphalt layer of structure I and structure II were identical, but the equivalent envelope area for structure I was greater than that for structure II. This indicated that the utilization efficiency of structure I asphalt layer was better when compared to structure II.