| At present, the pile foundation is the main form of high-rise and super high-rise building foundation, because it has high bearing capacity and strong control settlement deformation ability. In the traditional design of pile-group foundation,only static equilibrium conditions are considered when calculating, the interaction of upper structure, cap and pile-soil tend to be ignored, mostly the way of pile-layout is the same pile length, the same pile diameter, the same pile spacing. In fact, due to pile group effect, the vertical supporting stiffness of each pile is gradually decreased from outside to inside, so the pile-group foundation presents the saucer shaped differential settlement. Especially for the high-rise and ultra high-rise buildings, whose structural style is frame-shear wall structure, frame-tube structure, tube-in-tube structure and so on, because its load is big outside small, the saucer shaped differential settlement will become more obvious. The saucer shaped differential settlement will increase the bending moment of the pile cap, thereby increasing the reinforcement amount of it. Moreover, it will lead the upper structure into generating large secondary stress, thereby greatly reducing the normal service life of the building. In view of the disadvantages above, some experts and scholars creatively put forward the concept of optimization design of pile foundation stiffness to reduce differential settlement, pile-group foundation with variational rigidity came into being, mainly through the change of pile length, pile diameter, pile spacing and so on.For the study of pile-group foundation with variational rigidity, the present research has been carried out deeply. However, the interaction of the upper structure was not considered, and the settlement calculation was mostly based on the pile foundation with equal rigidity. In view of problems above, the finite element method was used in the research of working performance of pile-group foundation with variational rigidity, and the theoretical analysis method was used in the settlement calculation of pile-group foundation with variational rigidity in this paper, the main research contents and results are as follows.Firstly, a model test was selected, and the numerical simulation results which were obtained by ABAQUS were compared with the test results, then the rule of settlement of pile-group foundation with variational rigidity was obtained.Secondly, the model of pile-group foundation combining with an engineering example was established by ABAQUS, and the effects of homogeneous soil and layered soil on the settlement of pile cap, bending moment of pile cap, axial force of piles were researched under vertical loading.Thirdly, an engineering example including upper structure was selected, three-dimensional interaction model of upper structure-piled raft-soil was established with the use of ABAQUS finite element software, change pile length several times until the raft maximum differential settlement was reduced to as small as possible. Meanwhile, the influence of variable length on the upper structure and the foundation of the lower foundation was studied by comparing the four kinds of long working conditions with uniform distribution. On the basis of the above research, through changing the upper structure layer, soil elastic modulus, raft thickness, the effect of them on the upper structure and the lower base in upper structure-piled raft with variational rigidity-soil model was researched. Some reference and guidance for the actual pile foundation engineering was provided after above research.Lastly, the basic principle of the shear displacement method and the principle of load transfer method were mainly adopted in the Theoretical deduction method, considering relative slip between pile and soil, based on the calculation formula of the settlement of the pile-group foundation with variational rigidity in the homogeneous soil, the rationality of the calculation was verified by an example. |
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