Cylindrical shear resistance of helical piles subjected to seismic loads

ABSTRACT: The design of helical piles in seismic regions should consider the detrimental effects produced by dilatational and shear waves travelling through soils. The dilatational wave produces an increase in pore pressure, which leads to a decrease in the effective stress and consequently a decrease in the soil shear strength. Furthermore, dynamic shear stresses are produced due to the propagation of shear waves and due to the increase in pile loads caused by the overturning moment acting on the superstructure. Helical piles manufactured with multiple helices derive their compressive resistance from shaft friction, cylindrical shear resistance (CSR) and end bearing. Given that the displacement to fully mobilize end bearing is relatively large, helical piles subjected to seismic loading must rely on cylindrical shear to resist the increment in compressive load if large settlements are to be avoided. A methodology based on Zeevaert’s theory is presented in the present paper that allows designing CSR for seismic loads.