Improved Load Carrying Behavior of Perfobond Rib-Installed Partially Expanded Micropiles

Abstract This study proposed an advanced type of a micropile system. The proposed micropile system consists of perfobond ribs, installed on steel rod to improve shear resistance between the thread and the grout, and partially expanded drill holes to increase shear resistance between the grout and the ground. This study contained experimental evaluations on the proposed micropile system to verify the increase in the shear capacity of perfobond rib installed on the steel rod and the load-carrying capacity of shear key created by the partially expanded drill hole. Push-out tests were conducted on a rolled screw thread and perfobond rib-installed steel rods in order to compare their load-carrying capacities and load carrying behavior. It was confirmed that the proposed micropile system with perfobond-rib installed steel rods show much superior load carrying behavior in terms of initial stiffness, ultimate load, and ductile behavior. Through on-site pull-out tests, it was found that the load carrying capacity of the proposed micropile system increased significantly due to the effect of shear key created by partially expanded drill hole.