Bearing capacity evaluation of small-diameter spiral piles in soft ground subjected to combined loads

Abstract

In the current practices, the evaluation method for the bearing capacity of small-diameter spiral piles is a conservative method performed on the safe side, since it does not consider the integration effect with the surrounding ground due to rotational press-fitting. In addition, the evaluation method for the bearing capacity of spiral piles subjected to combined loads has not been established. In this study, a series of push-in, pull-out, and horizontal loading tests on spiral piles constructed on a soft viscous ground is conducted, and a method to easily consider the integration effect of the surrounding ground by rotational press-fitting is proposed. Subsequently, based on the proposed method, small-diameter spiral piles are modelled with a FEM analysis, various test results are reproduced, and coefficients for considering the integration effect of the surrounding ground in a numerical analysis are established. With the same FEM analysis method, using the established coefficients, the bearing capacity characteristics of vertical and batter spiral piles for combined loads are obtained. Finally, based on the results, formulas for the bearing capacity envelopes in the H-V-M space are proposed and the accuracy of the formulas are verified.