Abstract: To investigate the impact of distributed post-grouting technology on pile foundation-bearing capacity, the grout diffusion mechanism and soil reinforcement effects of this technology were intuitively analyzed through model pile excavation tests. Furthermore, based on the self-balancing load test results of three large-diameter bored piles from the Yuanyang to Zhengzhou section of the Anyang to Luoshan Expressway project, the differences in bearing behavior of large-diameter post-grouted piles before and after distributed grouting were analyzed. The influences of the length-to-diameter ratio and the holding layer on pile foundation bearing capacity and grouting effectiveness were thoroughly explored. The results of the study show that: The distributed post-grouting process can realize small spacing, high density and multi-section grouting, which is more capable of improving the pile-side mud skin and soil disturbance problems of the bored pile construction compared with the combined post-grouting, and there is a significant difference in the mechanism of grout diffusion and reinforcement effect in different soil layers. Both distributed post-grouting and combined post-grouting can significantly improve the bearing performance of pile foundation, and the ultimate bearing capacity is increased by 116%−121% and 118%, respectively, while distributed post-grouting shows better improvement in the late loading stage, and at the same time, the length-to-diameter ratio as well as the holding layer both have significant influence on the bearing capacity of the test piles before and after grouting, as well as the effect of grouting. Compared with the combined post-grouted piles, the distributed post-grouted piles are more efficient in grout utilization and their axial force is slightly larger; while in the distributed post-grouted piles, the grouting effect of the test piles in the fine sand holding layer is better than that of the test piles in the pulverized clay holding layer. Distributed and combined post-grouting have significant reinforcement effects on the soil at the pile side, but the small spacing and high density of the distributed post-grouting process results in a more centralized distribution of friction enhancement coefficients at the pile side. The pile tip resistance of test piles with different holding layers is significantly increased after grouting, and the distributed post-grouted piles with fine sand holding layer have greater pile tip resistance enhancement coefficient due to grout infiltration and cementation.

Key words: bored pile, distributed post-grouting, self-balancing static load test, bearing performance, holding layer, grout diffusion