Study On Load Carrying Mechanism And Design Method Of Large Group Foundations' Thick Pile Caps

As an important load-transferring part of pile foundations, pile cap makes the load transfer efficiently. The thick pile caps of pile group foundations have been applied widely with the development of urban and industry constructions .The model experiments and the engineering practice have shown that:the working properties of pile group and single pile are different due to the pile cap-pile-soil interaction. Therefore, it is necessary to study the load transferring mechanism and the design method of pile group foundations.In this thesis thick pile caps of pile group foundations are studied as follows: Firstly,concept of pile-soil equivalent rigidity is presented ,The concept is to useelastic support to simulate pile-soil interaction, which solved the problem of large number of elements and great amount of computation time with the pile cap-pile-soil model. And the concept's rationality is checked by two- and three-dimensional case study.Secondly, based on ANSYS, computation on thick piles was carried out, and load transferring mechanism of thick pile cap of pile group foundations was explored with many factors considered,such as pile cap's thickness, number of piles, form of pile arrangement, and area of load distribution, etc. According to the results, formula on stress expansion range and beam-strut-tie combinated model are deduced, and the method to determine the dimensions of beams and rods are presented. Formulas to determine the reinforcement and bearing capacity of thick pile cap are selected on the basis of summarizing current design method. Thus, the design method of thick pile caps is put forward.Lastly,a case study based on an actual project is made to check the design method presented in this thesis ,and the result shows that the design method is practical, easy to use and can meet engineering requirement.