Study On Piled Raft Foundation Of High-rise Building And Variable Rigidity Design Method For Balance Settlement

Piled raft foundation possess good integrity and well performance of reducing settlement and balancing differential settlements, it becomes the most adpted foundation pattern nowdays. Because of the piled raft foundation has wide application prospects, people pay more and more attentions on this research since the 1980's, and a lot of research achievements were acquired. But piled raft foundation and soil have very complex interaction, the bearing meghanism of pillefoundation and load transfer mechanism are not yet completely clear, so people often adopt a conservative approach to ensure the safety factor in the practical engineering design, sometimes it cause unnecessary waste of materials and significantly increase project cost. So, how to optimize the piled raft foundation design and select a reasonable scheme gradually become the research hotspot.The piled raft foundation design key lies in the settlement of the calculation, after reviewing the basis of previous work, This paper summarizes the Settlement calculation methods of single pile or or pile group, and it compares the advantages and disadvantages of each method, proposes the principle of the piled raft foundation desingn and method using finite element analysis.This paper depends on a pile raft foundation model test of one high building, it compares four different schemes of pile raft foundation settlement, differential settlement, soil counterforce, counterforce on the pile head, discusses the working mechanism of the piled raft foundation, then except to seek more common law as a reference for the future design. This paper will use an eliment analysis software ANSYS for numerical simulation of the model test, the pile raft foundation inclues natural groundsill, equably disposed piles, varied distance of piles, varied length of pile. This four schemes will be respectively established model, The calculated results will be compared with the experimental measured data coincident to prove the feasibility of the numerical simulation.According to the theoretical and experimental, numerical results, the piled raft foundation for optimization design have larger space. This paper introduces two kinds of pile raft foundation to improve the efficiency of the main optimization, including adjust the pile arrangement and thickness of raft. Adjust the pile arrangement includes varying distance of piles, length of pile, diameter of piles etc. This paper proposes the choice "outside strong in weak" and "in strong outside weak" main principle. Based on the ANSYS simulation results of the six raft thickness analysis, a raft thickness changes on the piled raft foundation settlement and internal force influence was find, and a raft relative bending-thickness curve was made, then we can easily determine the thickness of selecting a reasonable method of rafts.This paper discusses the pile raft foundation work characteristics, some useful conclusions based on the model test and numerical analysis and variable rigidity design principles and guidelines were summarized. In the end, two main optimization design method were given to provide a reference for the engineering of practical value.