Theoretical Analysis And Experimental Study Of Internal Forces And Deformation Of Single Pile Under H-T Combined Loading

In recent years, with the rapid development of coastal economy, the scale of large offshore infrastructures was expanded unceasingly such as sea bridges, offshore platforms, wind power toweres, etc. Pile foundations are often adopted by these structures to bear lateral loads caused by vehicle braking, wind, wave, earthquake, ships and impact by vessels or flotsam. This kind of horizontal eccentric loads is usually transferred to the pile foundations, which resultz in complex structural response. Disassembling the horizontal eccentric load s on the pile shaft, the loads behave as the combined action of horizontal force H and torque T. If ignored the effect by horizontal eccentric load, unsafe design as well as disastrous consequences may be caused in engineering practice. However, it's hard for the current conventional design methods based on the principle of superposition to consider the coupling effect by H and T, and there are still a lot of problems left to be solved. Therefore, based on available research work and achievements, theoretical analysis and indoor model testing study of lateral loaded pile, torsional pile and H-T combined loading pile were finished in this paper. The main works are as follows:Firstly, distribution characteristics of generalized Gibson foundation soil around the pile shaft were assumed to set up pile-soil system energy equations by using the virtual earth pile theory and minimum potential energy principle. Based on the variational principle, the control equation of pile shaft and subsoil under lateral loading were presented with the pile-soil response obtained through the center differential method. Then, based on the assumption that the plastic zone in the suboil extended down from surface along the pile shaft, the responses of the pile shaft and subsoil were obtained respectively.Secondly, based on the shear displacement method, the balance principle and power function distribution model of the subsoil shear modulus, the load-deformation control equation for the pile shaft and surrounding subsoil under pure torsional load first set up. Then, elastic, elastic-plastic and plastic analytical solutions for the inner forces(torque) and deformation(torsion angle) of the pile shaft under various bearing states were deduced respectively, in which the plastic deformation of subsoil developing from the surface down to the pile tip with the increasing value of torque at the pile top was considered. At the same time, in order to discuss the torsional behavior of single pile in layered subsoil, various bearing states(elastic and plastic) of the subsoil were considered, and the ideal elastoplastic model was used to simulate the load transferring law along the pile shaft under torsional loading. And a recursive algorithm was presented to calculate the torque and twist angle as well.Thirdly, based on the m method and improved finite element method, the relationship between the horizontal load H and torque T was included in the pole element stiffness matrix. Then, the unified pole element stiffness equation was obtained and different boundary conditions were considered to get internal forces and displacement of the pile shaft under H-T combined loading.Finally, the self-made sand box and a pulley block loading device were used to analyze the bearing capacity of single pile in sandy subsoil under pure horizontal force H, torque T and H-T combined loading by indoor model testing, from which the load-deformation curves at the pile top and inner forces-displacement curves along the pile shaft were obtained under various types of loading conditions.