Study on Non-Excavation Subgrade Reinforcement Technique and Scheme for Expressways

Some expressway emergency lanes adopt simplified pavement structures that fail to meet load-bearing requirements after reconstruction. To address the issue of subgrade reinforcement without excavation, a finite element method was employed to analyze the effects of enlarged-borehole grouting (EBG), considering variations in grouting depth and inter-pile subgrade modulus, on pavement load-bearing capacity. Furthermore, field experiments were conducted to evaluate grouting techniques, including enlarged-borehole micro-expansive cement casting (EB-MECC) and enlarged-borehole steel flower pipe split grouting (EB-SFPSG), and three composite grouting schemes. Results indicated that EBG effectively improved the fatigue cracking life of the semi-rigid base layer. Reinforcement effectiveness was positively correlated with grouting depth and subgrade modulus, with the latter exhibiting a more significant influence. Therefore, a 1.5 m grouting depth combined with splitting or compaction is recommended to enhance subgrade stiffness. Field experiments showed that EB-SFPSG effectively enhanced pile–subgrade interaction and mitigated stress concentration around the pile–pavement interface. Comparison of the three composite grouting schemes revealed that both the scheme employing only EB-SFPSG and the hybrid scheme using EB-SFPSG in the middle row with EB-MECC in the side rows exhibited favorable mechanical performance. The latter, however, was achieved at a lower construction cost. Another hybrid scheme that further replaced the middle row with enlarged-borehole conventional pressure grouting (EB-CPG) provided limited reinforcement and poorer uniformity.