A Study On The Calculation Of Negative Friction On Piles

The negative friction of piles is a hotspot problem in Geotechnical Engineering field. Retrospecting of all kinds of calculative methods, this paper has analyzed the advantage and disadvantage of determining the negative friction and the neutral point. In this paper, either the factors that cause the negative friction are described or the mechanism of negative friction and the methods of decreasing it are also discussed. On the basis of the previous achievements, thus this paper put forward a new calculative method of combining the elastic nonlinear method and the effective stress method.For many layers foundation, the negative friction is calculated, regarding each layers clay as even. However, the clay stress above it and the clay settlement under it are influence on the negative friction of this layer. The relevant program is compiled because of complicated calculation.Traditional elastic method used hypotheses which the gliding between clay and piles is absent. So starting with clay Duncan-Chang model and the elastic theories about piles, the clay and piles settlement is calculated. Thus relative displacement is gotten. Utilizing the relative displacement, the neutral point location is calculated. The measurement of negative friction is figured by the study on clay working to piles. As a result, the maximum of negative friction is calculated. The negative friction is zero in pile tip and augment gradually along with depth. When it arrive at the maximum, the negative friction begin to decrease, till it is zero at neutral point. Accordingly the measurement, the negative friction may be expressed as a interpolation polynomial. Though it suit only from pile tip to neutral point, the effective stress method is applied to boundary condition determining. Moreover the polynomial coefficients are determined by the boundary conditions. So the resolution of the negative friction can be calculated.According to the method and the effective stress method, the negative fiction of an abutment pile is calculated. The solution coincide with observed data and is more precise than the effective stress method, comparing them to the solution of the FEM. ...