Effects of installation disturbance on behavior of multi-helix piles in structured clays

Helical piles and anchors are installed by applying torque to the pile head. Their application as a foundation option has gained popularity in recent years because of their intrinsic advantages of rapid installation with minimal vibration and noise, and the development of powerful hydraulic driving heads. In spite of extensive research that investigated the behavior of helical piles and anchors, discrepancies between predictions and actual observations of axial behavior of helical piles installed in clay still exist. This is, in large part, because much of previous research involved installation of helical pile models in remolded (reconstituted) cohesive materials rather than natural soil deposits. Since the strength of the remolded materials does not change significantly, the effects of installation cannot be distinguished in remolded materials. In this study, full scale uplift and compression load tests data are analyzed and different failure patterns have been investigated for helical piles and anchors installed in structured clays. The research findings indicate that the behavior of the helical piles and anchors is significantly affected by the degree of soil disturbance induced by penetration of pile shaft and helices. In addition, back-calculated undrained shear strength mobilized by different sections of pile revealed that, for helical piles and anchors installed in structured clay, the undrained shear strength should be reduced to account for installation disturbance.