Full-scale field investigations and numerical analyses of grouting effect for large-diameter steel-concrete composite piles in offshore wind turbines

The bearing behaviors of post-grouted piles for offshore wind turbines are significantly affected by the grouting effect, especially in heavily weathered granite, which has attracted considerable attention in the academic community. This paper presents field static load tests on a large-diameter steel-concrete composite pile for offshore wind turbine foundations in deeply weathered granite formations. The influence of combined end-and-side grouting on the bearing behaviors of large-diameter steel-concrete composite piles in heavily weathered granite was thoroughly investigated through core drilling and CT scanning. Furthermore, numerical simulations were employed to conduct a parametric analysis of the combined post-grouting of large-diameter steel-concrete composite piles in heavily weathered granite formations, systematically studying the influence of grouting pressure and grouting volume on the bearing properties of post-grouted piles. The results indicated that compared to that before combined grouting, the bearing capacity of large-diameter steel-concrete piles is effectively enhanced after combined grouting. Core drilling clearly revealed the distribution of cement grout around and below the pile, indicating that the influence range of cement grout in heavily weathered granite formations extends from 0.5D below the pile tip to 5.3D above the pile tip. CT scanning results confirmed that cement grout could form cementation in heavily weathered granite, validating the effectiveness of combined post-grouting in such formations. The findings can serve as a reference for evaluating the grouting effect of post-grouted piles and contribute to advancing the application of post-grouted piles in heavily weathered rock formations.