Seismic Helical Pile Response in Nonliquefiable and Liquefiable Soil

Abstract

Three-dimensional finite-element models were developed and validated employing the published results from a comparative shaking table testing program of identical four-pile groups installed in saturated and dry sands. The validated models were used to analyze the seismic lateral and axial responses of helical piles to investigate the soil–helical pile–superstructure interaction. The analysis results demonstrated that the lateral displacements of the helical piles and adjacent soil decreased compared with those of the conventional straight shaft piles. In the saturated soil tests, the maximum bending moments occurred at the interface of the layers, while they occurred at the pile top in the dry tests. The stresses and strains in the helices were higher in the dry tests than in the saturated tests and were less in the double-helical pile helices than in the single-helical pile helix. The end-bearing force increased as the ground motion intensity increased in the dry tests, while it decreased in the saturated tests due to the development of high excess pore pressure in the bearing stratum. As liquefaction occurred, the shaft resistance of the helical piles diminished and the pile settled. However, the higher end-bearing force was mobilized, which compensated for the decrease in the shaft force. This observation demonstrated the excellent performance of helical piles in maintaining their capacity during and after liquefaction and controlling the postliquefaction settlement. The second helix further reduced the helical pile settlement but had a negligible effect on the lateral displacement. Finally, the response of the helical pile groups in the saturated test was dominated by rocking behavior, while flexural behavior dominated the response in the dry tests.