Laboratory tests on the frictional capacity of core pile–cemented soil interface

Pre-bored grouted planted (PGP) piles are a new type of composite pile in which a core pre-stressed high-strength concrete (PHC) pile is surrounded by a cemented soil (CS) layer. The frictional capacity of the core PHC pile–CS interface has a significant effect on the bearing capacity of a PGP pile. In this work, a series of shear tests was carried out to determine the frictional capacity of pile–CS interfaces for both smooth square piles (SPs) and smooth pipe piles (PPs). The shear test results revealed the following. The peak skin friction (PSF) of the SP–CS and PP–CS interfaces both increased with the CS strength. The PSF of the SP–CS interface was smaller than the PSF of the PP–CS interface of identical pile (equivalent) diameter due to the occurrence of a stress concentration at the corners of the SP. The PSF of the SP–CS and PP–CS interfaces both decreased with the pile (equivalent) diameter. The occurrence of cracks in the CS caused brittle failure of both the SP–CS and PP–CS interfaces.