Development and Evaluation of Expanded Steel Pipe Piles for Enhanced Load-Bearing Capacity and Rapid Installation in Confined Spaces

Recently, advanced types of micropiles have been developed to enhance their load-bearing capacity, responding to increased demands for micropile applications. However, these improved micropiles present challenges for rapid construction within confined spaces due to construction complexities. This study introduces an expanded steel pipe pile, which not only offers improved load-bearing capacity but also facilitates rapid construction in limited spaces. The expanded steel pipe pile is created by expanding a preinstalled small-diameter steel pipe at specific intervals to form shear keys along the length of the pile. In this study, the potential for enhancing the load-bearing capacity of the expanded steel pipe pile was initially verified through preliminary numerical analyses. Subsequently, comprehensive field experiments were carried out comparing two traditional micropiles with two expanded steel pipe piles, each installed using different methods. The results showed that the expanded steel pipe piles installed with grout injection achieved an allowable bearing capacity up to 1.4 times higher than that of conventional micropiles installed using the press-in method. Finally, utilizing the numerical model validated by the field experiment results, the optimal configuration for the expanded steel pipe pile was provided. Considering both load-bearing efficiency and constructability, it was concluded that the expanded steel pipe pile should have a postexpansion diameter of 360 mm (with a deformation ratio of 13%) or less and incorporate at least three shear keys.