| Pile under vertical loading goes through unconsolidated soft soil layer, large area offilled earth around the pile or groundwater recession will cause soil settlement. Negativefriction occurs when the vertical displacement value of soil is higher than that of the pile.During the whole loading process, due to the impact of side negative friction, the axialforce, down drag of single pile and the position of neutral point changes with the verticalload. A large number of tests, theoretical and numerical simulation of negative frictionresistance of pile foundation have been conducted by scholars at home and abroad.However, intensive study is required for some questions, due to the complexity of pile-soilinteraction and various reasons for the negative friction resistance of pile foundation tooccur. In this paper, to the mechanical property of single pile under vertical load, athree-dimensional finite element model which considers about the effect of negativefriction resistance is built to analyze the mechanical property of single pile. A mechanicalmodel is proposed to calculate the negative friction resistance of single pile by the use ofbilinear hardening transfer function model, and the calculation of vertical bearing capacityof single pile under negative friction resistance is discussed. The main contents are asfollows:1. Based on previous research results, the formation mechanism, conditions andadverse impact of negative friction resistance of single pile are discussed in this paper.Common measures to reduce negative friction resistance of pile foundation in engineeringapplication are summarized. A review of the research actuality of characteristics ofnegative friction resistance is given. Some problems existed in real projects are explored inorder to present the objective and significance of this research.2. Regarding negative friction resistance of single pile under surface load and workingload, a single pile3-D finite element numerical analysis model which considers about theeffect of negative friction resistance is built through ANSYS to analyze the mechanicalproperty of single pile. The result of numerical calculation is compared with the test resultto verify the feasibility of numerical calculation model. Based on this numerical model, aparameter analysis of mechanical property under negative friction resistance is performed.Impact from vertical working load, surface load, loading sequence and friction coefficientof pile-soil interface on the on mechanical property of single pile have been researchedrespectively.3. Regarding the single pile under vertical working load and considers about the effect of side negative friction resistance, based on the load transfer method, bilinear hardeningtransfer function model is applied to simulate the relation between side friction andpile-soil relative displacement. A mechanical model of single pile under negative frictionresistance is built to derive the analytical solution of negative friction resistance values ofpile side and pile end soil, position of neutral point, axial force value andloading-settlement relations under different deformation conditions. The change rule ofimpact on load transfer characteristics of negative friction resistance of single pile fromworking load was analyzed in the end.4. The calculation for vertical bearing capacity of single pile under negative frictionresistance is explained, simple methods to identify the negative friction resistance valueand position of neutral point are described. The calculation for vertical bearing capacity ofsingle pile under negative friction resistance in national regulations has also been summedup. |
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