Model test study on the vertical bearing performance of post-grouted piles based on different grouting materials

Post-grouting is an effective engineering technique for enhancing the bearing performance of pile foundations, and the grouting material is a key factor determining the performance of post-grouted piles. In this study, different grouting materials (fly ash-cement, geopolymer, cement, and cement-sodium silicate) were adopted in laboratory tests. Model tests of post-grouted piles were conducted under simulated groundwater flow conditions and long-term loading scenarios to investigate the influence of various grouting materials on pile bearing performance under vertical loading. The research focuses on the characteristics of load- settlement curves, the axial force transfer along the pile, and the mobilization behavior of side resistance and tip resistance, and employs scanning electron microscopy (SEM) tests to reveal the action mechanisms of different grouting materials. The test results indicate that the grouting process significantly enhances the pile-soil interaction. Compared with the ungrouted piles, the bearing capacity of the grouted piles increases markedly. Under flowing-water conditions, the cement-sodium silicate double-liquid grout provides the best reinforcement effect around the pile due to its short gel time, rapid solidification, and dense hydration products, whereas the fly ash-cement and geopolymer grouts mainly improve the soil via permeation grouting, with the hydration reaction of fly ash proceeding relatively slowly.