The Response of Pressure-Cast-In-Situ Pile with Spray-Expanded Frustum Using Field Static Load Tests

In this study, the pressure-cast-in-situ pile with spray-expanded frustum (PPSF) was proposed to increase pile bearing capacity, reduce pile settlement, and improve construction speed. The construction process of the PPSF composed of pile body, ribbed plate, and expanded body with double frustum was introduced. To capture the PPSF response, field static load tests on three PPSFs installed with string wire stress gauges were carried out. The ultimate bearing capacity (UBC) of a single PPSF was obtained, and the distribution of axial force, skin friction, and end force were analyzed using the measured results. Following the assumption that the strength of pile–soil interface elements was statistically described by the probability density function of the Rayleigh distribution, the load transfer models of PPSF were established based on the disturbed state concept (DSC) theory. The research results showed that there is a compression effect between the expanded body of the PPSF and the surrounding soil, which can effectively improve the bearing capacity of the PPSF. Considering the concrete consumption per unit volume, the UBC of PPSF is 66% more than that of the cast-in-situ bored pile. According to the results of measured and fitted relationships, the load transfer models of PPSF can be well described using the DSC theory and the Rayleigh distribution.