On the behavior of piles in non-cohesive soil under combined horizontal and vertical loading

In many fields of application, piles are used for the transfer of both axial and lateral loads into the ground. This combined loading leads to interaction of the horizontal and vertical load-bearing behavior. However, in current engineering practice these effects are usually neglected, since a clear description of the interactions and of their quantitative importance dependent on system parameters is lacking. A numerical simulation model was therefore established to identify and quantify the effects of combined loading of piles in sand soil. The model is validated by comparison with the results of published model tests. The model results are of good quality. Moreover, deficiencies of the model tests and their assessment with respect to interaction approaches were identified. The results of the numerical study show that with combined compression loading mostly favorable effects arise, with combined tension loading mostly unfavorable ones. However, the interaction behavior is very complex, and, depending on loading conditions, opposite effects on system stiffness and ultimate load can occur. An interaction diagram is presented, which gives a good impression of the importance of interaction effects. A parametric study shows that compact piles with a small length-to-diameter ratio and piles with almost rigid behavior show particularly strong interaction effects.