Responses Of Pile Foundations With Different Pile-head Restraint And Under Eccentric Lateral Loading

Piles are usually used as preferred foundation for offshore plateforms, bridge bents, transmission tower, tall buildings, and so on. Different connections between piles and superstructures in these structures have different pile-head restraint conditions. Pile-head restraint condition is one of the key factors which influence the deflection of single piles under lateral load. If the pile-head restraint of a pile foundation for a structure is overestimated in design, the deflection of the structure maybe exceeds the design requirements. The structures mentioned above are usually subjected to lateral loading from wind and wave actions, ship impacts, or high-speed vehicles. Because of the positions of lateral loading or some other reasons, the pile foundation beneach the structures may simultaneously subject to significant torsional loads. In view of the real situation, the objectives of this paper are to (1) study the effect of pile-head restraint on laterally loaded single piles and torsionally loaded pile groups,(2) and theoretically analyze the response pile groups subjected to eccentric lateral loading.First of all, based on the assumption of m-method a series of analytical solutions were derived to investigate the effect of pile-head restraint on laterally loaded single piles. The relationships bewteen different parameters which are used to define pile-head restraint were clarified and the features of the parameters were further discussed. The effects of embedded depth and free-standing length of piles on the response of single piles were analyzed. It is found that pile-head percent fixity (λ) can represent the pile-head restraint effectively and the displacement of pile head and the maximum bending moment under ground surface vary linearly with λ. The position of the maximum bending moment on the pile shaft beneath ground surface increases with λ and decreases with free-standing length. It is also found that pile-head restraint has different influence on the responses of rigid piles and elastic piles A simplified method is proposed to calculate the nonlinear response of laterally loaded single pile. As the pile-head rotational rigidty (km) or percent fixity (λ) is known the method can calculate the displacement, bending moment of pile head, the maximum bending moment beneath ground surface and its position. The results from the method have compared with those from p-y method, which proved that the method is accuate and simple enough in engineering design. Pile-head restraint also significantly influences the response of pile groups under torsional loading. The influence was investigated by employing a nonlinear numerical model in sand. The effects of group size and sand density on the response of torsionally loaded pile groups with different pile-head restraint were discussed. The result of a centrifuge test was analyzed using the nonlinear numerical model to backcalculate the pile-head restraint of a2x2pile group employed in the centrifuge test.To investigate the pile-soil-pile interactions in pile groups subjected to eccentric lateral loading, an elastic model was developed. Based on the model, the responses of1x2and2x2pile groups subjected to eccentric lateral loaded with different eccentric diatances were analyzed. It is found the pile-soil-pile interactions in the groups decrease the lateral resistance of pile groups, but increase the torsional resistance. The pile-soil-pile interactions also influence the pile-head shears and deflections of individual piles in each group in two horizontal directions and decrease the torsonal resistances of the individual piles, as well as the assignment of the applied loads in each pile group. In addiont, the pile-soil-pile interactions can induce the pile-head shear resistance and deflection of some group piles in opposite direction.