Influence of Installation Method on the Axial Capacity of Piles in Very Dense Sand.

Three driven precast, four driven cast-in-situ, and four screw injection piles were installed and tested in dense to very dense sand at a site in the Netherlands. Each pile was instrumented with two types of fiber optic sensors and tested under axial compression. Through these tests, a comparison could be made of how different installation methods influence the pile base and shaft response. For example, large residual base stresses were measured in the driven precast piles after installation. Of the three pile types tested, the driven precast piles also reached the highest base stresses, mobilizing their full base resistance at comparatively low displacements. The base response of the driven cast-in-situ piles was also like that of a driven precast pile with residual stresses excluded. In contrast, the screw injection piles mobilized much lower ultimate base resistances and with a much lower stiffness. In terms of shaft resistance, the precast piles showed friction fatigue effects in line with existing models, but this effect was not evident for the driven cast-in-situ or screw injection piles. Finally, shaft and base resistances measured in the dense to very dense sand layers were greater than limiting resistances prescribed in several design standards. By taking this into consideration in design standards, the results would help reduce some of the overconservatism present in design and consequently reduce the financial and environmental cost of pile manufacturing and installation. [ABSTRACT FROM AUTHOR]