Abstract:  The cement-soil mixed column with tapered rigid inclusion is a new type of composite column applied in the soil improvement projects. To study the axial behaviors of this type of composite column, axial pile loading tests on four composite columns with different tapering angles, inclusion length ratios and average area core ratios were performed. The load-displacement curve, axial force distribution along the rigid inclusions, end resistance and shaft resistance of the piles were studied and evaluated. The test results show that the ultimate axial capacity of the cement-soil mixed column with a tapered rigid inclusion is about 1.2 to 1.4 times of that of the cement-soil mixed column with a uniform section rigid inclusion; The axial force within the cement-soil mixed column changes abruptly at the bottom section of the rigid inclusion, so the strength at the bottom of the rigid inclusion should be checked in the design; In the process of load transfer, only 5.3% to 21.4% of the interface resistance between rigid inclusion and the cement-soil mixed column is mobilized; The rigid inclusion shares more than 90% of the applied axial load, and increasing the taper angle will increase the load sharing ratio of the rigid inclusion, but the average area core ratio and rigid inclusion length ratio have limited effect on the load sharing.

Key words: cement-soil mixed column and tapered rigid core inclusions, vertical load, ultimate axial capacity, load transfer, load sharing ratio