Analysis Method Of Elevated-cap Pile Group Foundations Subjected To Multidirectional Loads And Its Applications

Major offshore infrastructures, such as oversea bridges, offshore oil platforms, oversea transmission tower and wind turbines, are affected by multidirectional loading from gravity, ship impact, wind and waves, as a result of the complex environment. These multidirectional loading can easily cause the collapse of elevated-cap pile group foundations. Frequent reports of the pile foundations’failure caused by multidirectional loading have been heard. At present, just a few analysis methods of pile group foundations, subjected to multidirectional loading, have been conducted all around the world. In order to solve this problem, appropriate research should be undertaken.A hybrid model of pile groups was presented in this paper, which included a rigid cap, elastic beams and nonlinear springs of soil, to analyse elevated-cap pile group foundations subjected to multidirectional loading. The nonlinear stiffness of each pile was computed by p-y curve method in horizontal direction, load transfer method and τ-θ curve method in vertical direction, respectively. Pile group effect and load coupling effect of single pile in lateral and torsional degree have been taken into consideration. The lateral loaded pile group effect has been achieved by setting p multipliers while the load coupling effect has been completed by fixed-solo-pile analysis model subjected to lateral and torsional load. Newton’s iterative method has been used to solve the model of elevated-cap pile groups.The analysis method of elevated-cap pile groups subjected to multidirectional loading has been used in this paper to analyze3×3pile groups under lateral and torsional load. Analysis results were consistent with the large scale physical model tests, which meaned this calculation method was reliable. Through the comparative analysis by setting multiple p multipliers, it was found that the lateral pile group effect with small eccentricity was close to the one under lateral load alone while the lateral pile group effect with big eccentricity was close to the one under torsional load alone. Additionally, parametric analysis was carried out. It was found that the distribution of shear force in each pile head was observably nonuniform. The variation of axial force of individual pile in the group with different free length was presented as well.Combining with engineering data and test results of piles under vertical load, this paper has accomplished the analysis of oversea iron tower foundation with batter piles, gained the distribution of internal forces together with deformation of pile group. It showed us the guidance to fulfill this engineering design.