## 4 Results and Discussion
### Evaluation of Pavement Foundation Support Conditions  
Subgrade material samples were collected from the core holes at each test site to determine the material index properties of the foundation materials on each site. Laboratory particle size analysis, Liquid Limit (LL) test, and Plastic Limit (PL) test were conducted on the samples collected from core holes to determine the particle size distribu  
Figure 6: Typical pavement conditions of the six test sites. tion and soil index properties according to the Unified Soil Classification System (USCS) and AASHTO classifications. The soil classification test results are summarized in Table 2. The Sites CRCP-23-A, CRCP-4, JPCP-4-A, and JPCP-4-B were classified as Sandy Lean Clay (USCS group symbol: CL). The Sites CRCP-23-B and CRCP-12 were classified as Clayey Sand (USCS group symbol: SC). The plasticity values of the subgrade materials were approximately identical for all the sites. This uniformity in plasticity indicates a certain consistency in the behavior of the materials when subjected to moisture changes. The particle size distribution curves of the foundation materials of the six test sites are shown in Figure 7. The foundation materials at Sites CRCP-23-A, CRCP-4, JPCP-4-A, and JPCP-4-B were similar. The foundation material at Sites CRCP-23-B and CRCP-12 contained more sand and fewer fine materials. Relevant research [49; 50; 51] indicates that a higher content of coarse aggregates can enhance the stability and drainage performance of the subgrade. Following this, DCP and CHP tests will be conducted at all test sites to measure the bearing capacity and drainage performance of the foundation. The DCP tests were conducted to quantitatively analyze the bearing capacity of the pavement foundation. For each test site, two to four core holes were selected to conduct DCP tests after drilling surface cores. The testing blows, DCPI, and CBR versus depth profiles of the six sites are shown in Figure 8. Based on the test results, the pavement foundation-bearing capacity conditions of the six sites can be separated into two groups. The DCP-CBR values of sites CRCP-23-A, JPCP-4-A, and JPCP-4-B were relatively uniform, and no obvious boundary can be observed in their DCP-CBR profiles. However, for sites \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Index** & **Site** & **Site** & **Site** & **Site** & **Site** & **Site** \\
**Properties** & **CRCP-23-A** & **CRCP-23-B** & **CRCP-12** & **CRCP-4** & **JPCP-4-A** & **JPCP-4-B** \\ \hline Liquid Limit, LL (\%) & 31 & 31 & 34 & 30 & 33 & 32 \\ Plastic Limit, PL (\%) & 13 & 12 & 16 & 14 & 14 & 12 \\ Plasticity Index (\%) & 18 & 19 & 18 & 16 & 19 & 20 \\ AASHTO classification & A-6(7) & A-2-6(1) & A-6(5) & A-6(6) & A-6(9) & A-6(9) \\ USCS classification & CL & SC & CL & CL & CL & SC \\ USCS & Sandy & Clayey & Clayey & Sandy & Sandy \\ group name & lean clay & sand & sand & lean clay & lean clay & lean clay \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Soil classification results of the foundation surface materials of the six test sites. Figure 7: Sieve analysis results of the foundation surface materials of the six test sites. CRCP-23-B, CRCP-12, and CRCP-4, the DCP-CBR values of the top 250 mm foundation material are very different from those of the bottom materials. The top layers of sites CRCP-12 and CRCP-4 are much softer than their bottom materials. This led to noticeably premature failures compared to sites JPCP-4-A and JPCP-4-B, despite their shorter service life, as illustrated in Figure 6.  
To evaluate the relative support conditions of the six test sites, the in-situ DCP-CBR values are compared to the Iowa Statewide Urban Design and Specifications (SUDAS) rating [52], which was developed to evaluate the support conditions for subbase and subgrade layers of rigid and flexible pavement systems based on the CBR values. Figure 9 compares the DCP-CBR of the two groups of test sites with the SUDAS rating. Figure 8: DCP test results versus depth profiles of the foundation materials of the test sites.