Abstract: The rigidflexible composite column is a soft soil improvement method by inserting a rigid column into the center of the flexible column. The rigidflexible composite columns could be the same length or different lengths for different subsurface soil conditions. For two or more layers of subsurface soil strata, the flexible columns could be placed at shallow layer and the rigid columns could be installed in the deeper layer. Different column lengths could be used for different subsurface soil conditions for the total and differential settlement control and axial capacity improvement. This composite column could effective minimize the “bump” at the bridge approaches. Based on load transfer mechanism study, an improved Berezantzev Method for axial capacity estimation method is proposed. Using the pile foundation code for buildings, this new method considers the roadway surcharge load and effective stress induced by the side frictions for the prediction of the tip resistance and side frictions.

Key words: rigid columns, flexible columns, rigidflexible column composites, berezantzev method；pile ultimate axial capacity