Study on Uplift Bearing Characteristics of Micropile Group in Gravel-Containing Silty Clay Regions

Considering the diverse mountainous environments, the uplift resistance of conventional micropiles is constrained when configured with small diameters.The integration of belled micropiles may serve as a viable alternative to enhance the micropiles' pull-out performance, with the aim of improving pullout performance while achieving both economic benefits and outstanding performance.This study establishes a belled micropile model through mutual validation between prototype tests of uniform section micropile configurations and numerical inversion models.It compares the load-bearing performance of single micropiles and micropile groups between uniform section and belled micropile designs.Additionally, it proposes a simplified calculation method for the ultimate pull-out capacity of belled micropiles and elucidates the load-bearing mechanisms of belled micropiles.The results highlight that uniform section micropile groups have limited pull-out capacity due to steep load-displacement curves, risking sudden failure.In contrast, belled micropiles exhibit asynchronous load distribution during uplift, with bells contributing over 50% of total capacity.The bearing capacity of bell-shaped micropiles is roughly double that of uniform section micropiles.This integration resolves uplift issues, offering cost-effectiveness and safety.Based on the results obtained, the bell-shaped micropile is expected to outperform traditional micropiles in terms of load-bearing capacity enhancement.