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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.

When it comes to the general design of laterally loaded piles in offshore environments, bedding resistance is usually modelled by the p‐y method recommended in the offshore guidelines (OGL). Several investigations presented in the literature indicate that the head displacements of large‐diameter monopiles are underestimated for extreme loads but overestimated for small operational loads. An extensive evaluation of the OGL method is presented here using three‐dimensional numerical simulations. The evaluation has shown that the OGL method is not applicable for the design of large‐diameter piles. Moreover, modified p‐y formulations presented in the literature accounting for the effect of the pile diameter are also not generally suitable for piles with arbitrary dimensions and load levels. Therefore, the derivation of a new p‐y approach is presented in detail. The new approach consists of “basic p‐y curves” that are valid for a pile of infinite length exhibiting a constant horizontal deflection. In an iterative scheme, these basic curves are adapted depending on the pile deflection line and the pile length to account for a more realistic bedding resistance along the pile shaft. A comprehensive parametric study with 250 pile‐soil systems reveals that the new p‐y approach is able to predict the horizontal loadbearing behaviour as well as the local pile‐soil interaction quite realistically.Ein neuer statischer p‐y‐Ansatz für Pfähle beliebiger Abmessungen in Sand. Für die Bemessung horizontal belasteter Offshore‐Pfähle wird der Bettungswiderstand üblicherweise durch die in den Offshore‐Richtlinien (OGL) empfohlene p‐y‐Methode ermittelt. Verschiedene Untersuchungen aus der Literatur zeigen, dass die Verformungen von Monopiles mit großen Durchmessern für Extremlasten durch die OGL‐Methode unterschätzt, für geringe Betriebslasten dagegen überschätzt werden. Der vorliegende Artikel beinhaltet eine umfassende Bewertung der p‐y‐Methode basierend auf dreidimensionalen numerischen Simulationen. Als Ergebnis ist festzustellen, dass die OGL‐Methode zur Bemessung von Pfählen großer Durchmesser nicht geeignet erscheint. Auch modifizierte p‐y‐Ansätze zur Berücksichtigung des Einflusses des Pfahldurchmessers sind nicht generell anwendbar für Pfähle beliebiger Abmessungen und Belastungen. Diesbezüglich soll die Ermittlung eines neuen p‐y‐Ansatzes dargestellt werden. Der neue Ansatz basiert auf sogenannten “p‐y‐Basiskurven”, welche Gültigkeit für einen unendlich langen Pfahl mit einer über die Länge konstanten horizontalen Verschiebung aufweisen. In einem iterativen Vorgehen werden diese Basiskurven zur Erreichung eines realistischen Verlaufs der Bettungswiderstände in Abhängigkeit der Pfahlbiegelinie und ‐länge angepasst. Eine umfassende Parameterstudie mit 250 Pfahl‐Bodensystemen zeigt, dass der neue p‐y‐Ansatz geeignet ist, sowohl das globale Tragverhalten als auch die lokalen Pfahl‐Boden‐Interaktionen realistisch zu prognostizieren.

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