## 4 Results and Discussion
### Spring-Thawing Clogging Model of OGFC Based on the Mistcherlich Growth Model
According to the above analysis, it can be seen that the COF-OGFC has an excellent maximum clogging degree and clogging rate value in summer and spring seasons, which indicates that COF-OGFC can effectively resist different modes of clogging behavior and has strong applicability. This is because the oil shale waste has a large specific surface area, dense pore structure and various mesoporous shapes, which means a larger adsorption area and lower probability of redundant asphalt blocking the effective pore. The oil shale waste reshapes the pore structure of permeable asphalt pavement and enhances the permeability properties and resistance to the clogging behavior of permeable asphalt pavement. Effect of Particle Size of Clogging Materials on Clogging of COF-OGFC Base on the Gray Relation Entropy Theory  
Through the above analysis, it is seen that the spring clogging behavior of the permeable pavement in the seasonal frozen region is in a rapid clogging mode, which makes the permeable asphalt pavement quickly lose its permeable function in a short time. Therefore, the effect of particle size of clogging materials on spring clogging behavior of the permeable pavement was discussed in this section, which can provide a reference for the design of the permeable pavement. In this study, the sieved fine sand is synthesized into four clogging materials with different gradation: powdery clogging materials, sandy clogging materials, gravelly clogging materials, and full-scale clogging materials, according to the above statistics on the particle size distribution of spring clogging materials. The gradation of powdery clogging materials, sandy clogging materials, gravelly clogging materials, and full-scale clogging materials is shown in Table 12.  
In this study, the spring physical clogging procedure was applied to evaluate the effect of the particle size of clogging materials on the clogging of COF-OGFC. In order to remain consistent with the above procedure, the simulated vehicle speed is 80 km/h, the water gun pressure is set to 2561.6 kPa, the rotation speed of the cylindrical structure is set to 420 rad/min, and the scouring time of one cycle is 4.8 min. The mass of the clogging materials deposited on the surface of the Marshall specimen before cycles is 43 g, and the dry weight, porosity and permeability coefficient of specimen are measured every 4 cycles for a total of 20 cycles. The permeability coefficient of COF-OGFC with different clogging materials is shown in Figure 13. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Granularity** & **Size Range** & \begin{tabular}{c} **Powdery** \\ **Clogging** \\ **Materials** \\ \end{tabular} & \begin{tabular}{c} **Sandy** \\ **Clogging** \\ **Materials** \\ \end{tabular} & \
\begin{tabular}{c} **Gravelly** \\ **Clogging** \\ **Materials** \\ \end{tabular} &
\begin{tabular}{c} **Full-Scale** \\ **Clogging** \\ **Materials** \\ \end{tabular} \\ \hline Fine gravel & 2360–4750 \(\mu\)m & 0 & 0 & 46.8\% & 19.2\% \\ Very coarse sand & 1180–2360 \(\mu\)m & 0 & 0 & 53.2\% & 21.8\% \\ Coarse sand & 600–1180 \(\mu\)m & 0 & 36\% & 0 & 19.2\% \\ Medium sand & 300–600 \(\mu\)m & 0 & 34.8\% & 0 & 18.6\% \\ Fine sand & 150–300 \(\mu\)m & 0 & 29.2\% & 0 & 15.6\% \\ Very fine sand & 75–150 \(\mu\)m & 62.5\% & 0 & 0 & 3.5\% \\ Silt & \textless{}75 \(\mu\)m & 37.5\% & 0 & 0 & 2.1\% \\ \hline \hline \end{tabular}
\end{table} 
Table 12: The gradation of powdery clogging materials, sandy clogging materials, gravelly clogging materials and full-scale clogging materials. It can be observed in Figure 13 that the permeability coefficients of COF-OGFC with powdery clogging materials, sandy clogging materials, gravelly clogging materials, and full-scale clogging materials were reduced to 71%, 43%, 88%, and 30% of the initial value after 20 cycles.