Full-scale laboratory investigation of installation effects and advancement rate for tapered continuous helical and helical piles in saturated sand

Screw and helical piles are classified as displacement piles. A displacement pile will always cause soil disturbance during installation. Full-scale laboratory tests were conducted to examine the effects of advancement rates (ARs) on installation torque and compressive bearing capacity in saturated sand with different relative densities using three different pile geometries. The influence of a constant AR = 0.5 showed varying results for each of the pile geometries, indicating that the impact of AR is highly dependent on the pile geometry. In the same relative density with AR values of 0.5, 0.8, 1, and 1.2, the compressive bearing capacity decreased by 67% for AR = 0.5 and increased by 1% for AR = 1.2 compared to the recommended AR of 1, which minimizes the disturbance. The friction correlation factor K c , between installation torque and bearing capacity, reflected the effects of both varying AR and relative density. It is advised to monitor the AR during installation in commercial projects. To ensure reliable bearing capacity of screw and helical piles, they should be installed with an AR between 0.8 and 1.2.