Abstract: This paper presents a ground improvement case study of a pump station project with the alternating of cohesive and liquefiable sandy soils near the Central Business District. Based on the engineering and hydrological geologic conditions, the effect of the installation preparation, installation sequence and method on the rammed gravel column with expanded base is evaluated in detail through various trial tests. The installing the gravel column can be divided into five steps. The quantity of the gravel backfill at each time should be controlled with 0.3 cubic meters. Larger ramming energy should be used to compact the gravel and the energy should be reduced when the depth is less than two meters from the ground surface in order to minimize the ground heave. The rammed gravel column installation quality control criteria, testing items and design parameters in the alternating of cohesive and liquefiable sandy soils are discussed in this paper.

Key words: Liquefaction of Sandy Soils, Rammed Gravel Columns with Expanded Base, Ground Improvement