Behavior of Skin Friction of Piles subjected to Top-downward and Base-upward compression Loadings
AbstractIn situ results of Osterberg cell load test and the conventional static compression load test are compared. Finite Element Method (FEM) is used to study the effects of changes in boundary conditions, mechanism of pile-soil interaction and the accompanying change in soil stress, which are responsible for the difference in skin friction under the two loading modes. Pile-soil system is analyzed using Duncan-Chang E-B model while the interface material is modeled using Goodman element. Poisson effect affects the diameter of the loaded end (top or base) of the pile and on the radial stress in the soils around the pile. Changes in radial stress with the direction of loading contribute the major part of the different resistance of the soil-pile system. In-situ and FEM results show lower shaft resistance when the pile is subjected to base-upward compression than when it is compressed from the top. The ratio of skin friction of 0.85 is obtained, the ratio is expected to be different for different soils.
Journal of Civil Engineering, JKUAT (2001) Vol 6, 89-104