Abstract: To examine the influence of strengthening effect of skin resistance on the bearing mechanism of laterally loaded pile, this study firstly established τ-s curve models with consideration of strengthening effect under horizontal loading. Then its numerical solution for resisting moment per unit length caused by vertical shaft resistance was obtained. This work performed the analysis on normalized curves with form of Ms,ini /Msu,ini-θ/θref,ini under the influence factors including pile diameter, critical displacement and limit shaft resistance. Accordingly, based on the theory of strengthening effect of skin resistance, this paper deduced simplified theoretical solutions of resisting moment for τ-s curves with linear elastoplastic type, hyperbolic type, clay and sand type of API Code, respectively. Moreover, combined with the principle of transfer matrix method, this work obtained the semi-analytical solutions for laterally loaded pile considering resisting moment effect. The results from proposed calculation models compare well with validation cases, which verify the reliability of simplified solution of side friction caused resisting moment and of proposed pile responses considering resisting moment effect. The comparisons also indicate that the influence of strengthening effect of skin resistance on bearing capacity of laterally loaded pile is non-negligible. Finally, the results reveal that in case of no test data for reference, the recommend values of rigidity indexes for interfaces of sand-pile and clay-pile could be 0.725 and 0.600, respectively. This resisting moment effect will increase as pile diameter, ultimate shaft resistance increases or increase as critical displacement decreases, while pile diameter has more notable influence.

Key words: pile foundation, lateral loading, resisting moment, strengthen effect of shaft resistance, transfer matrix method