Research On Performances Of Composite Foundation With Rigid-flexible Piles

Research on composite foundation with rigid-flexible piles falls obviously behind the practice application of the foundation at present. In this dissertation, the performances of the composite foundation with rigid-flexible piles are studied by the systematic field tests which include static load tests and in-situ tests, by FEM analysis and theoretical method. The main works include:1. On the basis of systematic tests of rigid pile and flexible pile, failure model, friction force distribution along pile shaft, axial force, load transfer and elastic compression are compared. Furthermore, bearing capacity formula of pile in the code is modified.2.Based on several systematic static load tests, bearing capacity and deformation characteristic of the composite foundation with rigid-flexible piles are studied. Cushion parameters and replacement ratio parameters influence to the performances of the composite foundation are analyzed through comparing with soil stresses, pile-soil stress ratio as well as load sharing ratio. Meanwhile, composite module and the degree of bearing capacity display are also discussed. Comprehensive comparison on load-settlement, soil reaction distribution, pile stress distribution along pile shaft and load transfer mechanism are paid more attention to, test results demonstrate pile-soil interaction of the composite foundation with cushion is better than that without cushion. Besides, load transferring mechanism and deformation characteristics of rigid pile in composite foundation are different from that in free state.3. In-situ tests of the composite foundation with rigid-flexible piles are carried out systematically and comprehensively in Wenzhou. The tests include soil in-depth settlement, building settlement, pile stress and soil stress under foundation, rigid pile stress along pile shaft, flexible pile stress along pile shaft, soil stress along depth, pore-water pressure along depth. Stress field and displacement field as well as load share ratio variation rule are studied. Test results indicate that there are different transferring rule between rigid piles and flexible piles at different area, composite foundation stress and settlement are related with superstructure stiffness.4. The composite foundation with rigid-flexible piles under strip foundation is analyzed by FEM on the basis of field tests. The influence factors including cushion, cap, rigid pile and flexible pile for bearing capacity and deformation characteristics of the composite foundation are studied systematically.5. Load sharing ratio of the composite foundation with rigid-flexible piles by means of theory method on the basis of elastic calculation model. Simple empirical formula is established according to the results of FEM. Compared with theoretical solution and in-situ test results, A pronounced agreement is found. What's more, empirical formula restricted in specific area can satisfy generally engineering request.6.Considerating the influences of rigid pile length, flexible pile length, rigid pile module, flexible pile module and replacement ratio on composite foundation, theoretical solution of composite foundation modulus is deduced by means of shear displacement method. The relationship between parameter variation and composite modulus is analyzed quantitively. Engineering case prove new method is better than traditional one, there is a reasonable agreement...