The Relationship Between Settlement Property And Bearing Capacity Of Single Pile Under Axial-loads

In the pile foundation calculation theory and designing, the settlement and bearing capacity of single pile under axial loads is very important. Domestic and overseas scholars have achieved a series of valuable conclusions in this field through long-term exploration. Subsequent research has been done on the bearing mechanism and settlement analysis of piles under axial loads. But the pile-soil system is a very complex mechanical system and its engineering design is still in a semi-theory and semi-experience state till now. Lots of researches are still needed due to the complicated inter-action between piles and the surrounding soil. There are five main theory methods used in analyzing pile settlement: LTA-load transfer approach, ETM-elastic theory method, SDTA-shearing deformation transfer approach, NCM-numerical computation method(including the FEM-finite element method, BEM-boundary element method etc.), and other predigest or experiential methods. Using normative information in certain regions and ready-made, appropriative computer programs, the LTA is very simple and effective. Once the load transfer function is confirmed, the load-settlement curve can be obtained by simple data calculation .The LTA is effective in analyzing the mechanic character of single pile and pile groups and in solving the vertical stratification and nonlinear response. The test in-situ is simple and accurate, but the theory analysis method can predict and contrast quickly and accurately, and is economical to use.There are 9 load-transferring functions put forward by scholars at the present. A detailed analysis of the load transfer procedure, the load changing regularity and the load-settlement mechanism of vertically loaded plies have been tested in east of Xi'an city. In this paper I will firstly analyze how the friction resistance force work between the pile shaft and the loess. As we know, the upper layers of loess are unsaturated and lower layers are saturated. According to the different relationships between stress and strain of different soil layers ,then propose an improved load transfer model :the trilinear model for lateral friction resistance and the bilinear model for end resistance. The detailed formulas are followed as:Three conditions are discussed. Firstly the rigidity coefficient-kS2i is equal to zero, then ks2i is bigger than zero, at last ks2i is smaller than zero. When the rigidity coefficient kS2i is equal to zero the formula is same as the elastic-plastic function, when kS2i is bigger than zero the formula is same as the hardening function, when ks2i is smaller than zero the formula is same as the softening function. Then I will unite the elastic-plastic function, hardening function and softening function into a singleformula. There is a need to calculate the depth effect when designing the driven pile and the pressed pile. When fixed lateral friction resistance is taken there is a big error between the computation and practical measurement for driven pile and pressed pile. The depth effect is taken into account by means of the depth effect coefficient i of the lateral friction resistance. The trilinear model changes according to the soil deformation. The improved load transferring function can comprehensively simulate the actuality of the pile-soil interaction.For the superstructure which is sensitive to settlement or whose Q-s curve is gentle without obvious failure point, the top settlement of pile is the dominating parameter in design and calculation. Based on the improved trilinear model and Eitiking Iterated Algorithm, mainly considering the important factor of the top settlement in elastic, elastic-plastic or plastic status, a series of formulas are deduced for controlling the vertical bearing capacity of pile by means of the top settlement values. The formulas can simulate the pile-soil interaction accurately and simply as well as considering the sandwich construction of soil, nonlinear prosperity and so on. Compared with the finite element method, these formulas are suitable for field practice becau...