Axial response and bearing capacity of tapered piles in sandy soil

14 calibration chamber tests were performed to investigate the axial responses of tapered piles in sandy soil. Three instrumented model piles with different taper angles, designed to have the same volume, were used in the tests. Results of the model pile load tests showed that the shaft load of tapered piles continuously increased with pile settlement, whereas that of cylindrical piles reached the ultimate values at a settlement equal to about 2 % of the pile diameter. The ratio of the load capacity of tapered piles to that of cylindrical piles was found to vary with both the taper angle of the piles and the soil condition of the sands. The ultimate unit shaft resistance of tapered piles was always greater than that of cylindrical piles irrespective of soil condition, whereas the ultimate unit base resistance of tapered piles was greater than that of cylindrical piles for dense sand with lateral earth pressure coefficients higher than 0.42. It was also observed that the ultimate unit shaft resistance of piles increases with increasing taper angle regardless of the relative density and stress state of the sand. However, the ultimate unit base resistance of piles increases with increasing taper angle for medium sand, but decreases for dense sand. In addition, based on the results of the model pile tests, taper factors for the ultimate unit base and shaft resistances, which can be used to estimate the base and shaft load capacities of tapered piles, were proposed.