## 4 Engineering Application  
To illustrate the application of the proposed model to pavement maintenance, a typical highway section was adopted for a case study. The highway section was asphalt concrete pavement with a design life of 15 years. The pavement structures from top to bottom included 4 cm medium-grain asphalt concrete, 5 cm coarse-grain asphalt concrete, 7 cm hot mix asphalt crushed stone, 20 cm cement-stabilized crushed stone base and 35 cm line-stabilized soil. Since the completion of the pavement, the traffic volume has been heavy, and the proportion of overloaded and heavy vehicles has been relatively high. Therefore, under long-term traffic load, serious network cracks appeared on the road surface (Figure 7). After water flowed through the cracks to the base, the hydrodynamic pressure soon softened the fine soil and undermined its strength under traffic load. Thus, this could result in mud pumping from the fine soil. With the gradual deepening of pavement damage, the highway exhibited more serious mud pumping and insufficient bearing capacity. Therefore, it was necessary to use cement grouting technology to repair the damage. The specific process is as follows:  
1. FWD was used to test the pavement bearing capacity before grouting, so as to evaluate the degree of pavement damage.
2. The pore structure parameters of this highway section should be quantitatively analyzed by drilling and coring, and corresponding to the parameters in the model.
3. According to the model deduced in this paper, the optimum spacing of grouting holes was designed according to the characteristics of the pavement pore structure and cement grout on site.
4. An appropriate cement slurry ratio was selected to implement grouting on the pavement.
5. After grouting was completed, the grouting holes were filled with road sealant to prevent water from penetrating the road surface.
6. Fourteen days after grouting, FWD was used to test the pavement bearing capacity after grouting, so as to evaluate the pavement repair effect under the grouting parameters [5; 5].  
Through an analysis of borehole data, the characteristic structural parameters of the injected medium were determined (\(\varphi\) = 0.52, \(\lambda_{\text{min}}/\lambda_{\text{max}}\) = 0.0492, \(D_{T}\) = 1.12, \(D_{f}\) = 1.69 and \(D_{m}\) = 1.5). The water-cement ratio of the cement grouting material was 1.0. Substituting these parameters into the model, according to the law of Figures 1 and 2, the grouting spacing was set at 1.5 and 1.25 mm in the longitudinal and transverse directions, respectively (Figure 8). The drilling process is shown in Figure 9. The cement grouting process is shown in Figure 10.  
Figure 6: Proportion of pores and cracks in SEM morphology.  
Figure 8: Schematic diagram of grouting design.  
Figure 7: Cracked state of the pavement.  
Figure 9: Drilling process.  
Figure 11 shows the deflection changes before and after grouting. The deflection of the pavement was effectively reduced after grouting. This was because the cement material could fill the pores inside the base, reduce the porosity, increase the degree of compaction, produce cementation to strengthen the base and raise the pavement's bearing capacity.