Tapered piles responses during large-scale axial static and high-strain dynamic load testing

While significant research has focused on characterizing cylindrical piles with various shapes and material components, as well as their interaction with soil under axial loading, the performance of tapered piles under axial loading has received considerably less attention. Tapered piles provide an attractive alternative to conventional pile types such as driven steel and concrete straight piles, as they have improved the resistance during axial compressive loading. In this study, the performance of tapered piles under axial monotonic and impact loading was examined using laboratory testing. A series of large-scale static compression tests were performed on tapered piles with diameters of 76 and 89 mm under both saturated and unsaturated soil (Baskarp Sand No. 15) conditions. Each test consisted of multiple sub-tests to determine the in situ soil characteristics, and the key findings discussed here are based on results from pile bearing capacities after installation by jacking with an unloading/reloading step. Cone penetration tests were performed to quantify the effect of pile installation on the soil state for different initial relative densities. Dynamic pile testing, which is less costly and time-consuming than the static loading of large-scale piles, was performed with a hammer to assess the piles’ static load bearing capacities. The generalized relationship between static and dynamic bearing capacities was examined according to the Danish pile-driving formulas (DDRs) using the j factor. The results revealed that the DDRs can be used for saturated medium-dense sands with adequate confidence, whereas any application beyond this range may require thorough verification. The piles were then pulled out to enable the decoupling of friction resistance effects from base resistance.