Comparative Study on Ground Improved by Stone Columns and Ground Improved by Hybrid Concrete Columns

Abstract

This paper provides a detailed discussion and comparison of two deep ground improvement techniques, stone columns and hybrid concrete columns (HCC’s), in terms of design, construction procedure and performance, through a case history from a recent petrochemical project in Malaysia. Two full-scale group load tests (GLT’s) were conducted on test columns constructed prior to construction of production columns and used to calibrate the analytical models adopted for the design of stone columns and HCC’s. The ground improved by HCC’s shows a stiffer load-settlement behavior compared to the ground improved by stone columns as predicted by analytical models. In addition, the time-dependent settlement is more obvious in the stone column improved ground than in the HCC improved ground. Stone columns may act as a drainage path helping expulsion of pore water as the applied load increases whereas concrete columns transfer the load to the surrounding soils through the load transfer at the interface between a concrete column and the surrounding soil. The results of all four GLT’s on production columns confirm that the settlement predictions with the calibrated analytical models are satisfactory. This paper also summarizes the key calibration techniques adopted at the project site for quality control during construction. These calibration techniques can be considered as a useful guide for other project sites with similar ground improvement methods proposed in similar ground conditions.