LOAD-TRANSFER FOR PIPE PILES IN HIGHLY PRESSURED DENSE SAND

Large-scale loading tests were conducted on closed-toe and open-toe piles driven into dense submerged sand confined in a pressure chamber. Unit load-transfer relations were developed and related to stress conditions in the chamber. Ultimate shaft resistance in compressional loading was found to be approximately equal to the ambient lateral effective stress in the chamber before driving, and was generally not dependent on the geometry of the toe. From this observation it can be inferred that because of installation and loading effects the operative earth-pressure coefficient on the pile shaft approximately doubled from the ambient value that existed before driving. In uplift, ultimate shaft resistance was about 20% lower than in compression, regardless of depth. The open-toe piles consistently remained plugged during static testing but nonetheless exhibited lower bearing capacity than the closed-toe piles. This can be explained by deformation and compression of the soil within the plug as a means of effectively reducing the rigidity index of the soil against which the toe bears.