| The concept of negative skin friction of pile was put forward nearly a century ago, and during all these years, scholars have made intensive studies on it. Among different research methods including model test methods, numerical simulation as well as theoretical analysis, the indoor model test has its advantage for being convenient and easy to control, whereupon a researcher could get results spending less time and money. Recently, with the application of the finite element analysis, the numerical simulation analysis becomes a main method for the study of negative skin friction. Researches show that negative skin friction of pile is complex, because it has close relations with different factors including soil compressibility and permeability, the soil stress level and stress history, pile's type, size and stiffness, arrangement of pile, the pile head loading, ground load level and impose order and rate. Therefore, this paper chooses the method of combining the indoor model test with ABAQUS finite element numerical simulation. In this way, influences of compressibility of soil ? methods for constructing pile, the constraint conditions of pile and the pile group effect on the negative skin friction are studied. The main contents are summarized as follows:(1) The concept and the background of the negative skin friction as well as its causes and harms is elaborated. Researches on the negative skin friction from different aspects are summarized, and problems that would be taken into consideration in current studies are given.(2)Through the indoor model tests, the end bearing single pile, the 2×2 group piles with spacing of 3D?4D?5D and 7D and the 3×3 group piles with spacing of 3D?4D are studied. The effects of the soil compressibility and pile spacing on the pile axial force, the negative friction of pile and the development of pile group are studied for both end-bearing and suspended piles.(3) Through the indoor model tests, the changes of the axial force and the negative skin friction for the suspended piles are studied. The parameters of these studies include soil compressibility, pile spacing and the forming of pile. The results are also compared with those for end-bearing piles and the effect of constraint condition is analyzed.(4) On the basis of the actual situation of the indoor model tests and the boundary conditions, a corresponding 3D model with the help of the three dimensional finite element analysis software ABAQUS is built. For the purpose of verifying the rationality of the experimental study, a numerical modeling to some of the indoor experimental study is performed and the simulation results are compared with the test results. |
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