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

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The paper compares stone columns and hybrid concrete columns (HCCs) used to improve weak fill soils at a petrochemical plant in Sarawak, Malaysia. More than 10,000 columns were installed as an alternative to piled foundations. HCCs combine a lower concrete column with an upper stone section that forms a load-transfer platform.<br /><br />Designs used the Priebe method for stone columns and a load-transfer method for HCCs. The models were calibrated against two trial group load tests, then checked with four tests on production columns. Under the same conditions, the calibrated models predicted stiffer load–settlement behavior for HCC-improved ground. At a working pressure of 250 kPa, predicted settlements were 27.6 mm for stone columns and 15.5 mm for HCCs. Trial tests also showed substantially greater time-dependent settlement in stone-column ground, which the authors attribute to drainage and pore-water dissipation through the stone columns.<br /><br />Because soil conditions and competent-layer depths varied across the site, construction quality control included a site-specific correlation between cone penetration resistance and the vibrator’s electrical amperage. This correlation helped verify column termination depth. Recorded amperage was also used to assess stone compaction. Concrete workability and strength were checked through slump, temperature, and cube tests.<br /><br />The analytical predictions were initially adjusted using group-load-test results and site-specific correlations between CPT resistance and constrained soil modulus. Subsequent production-column tests measured settlements below those predicted, meeting project performance requirements.<br /><br />The study concludes that both methods can provide effective ground improvement when properly designed and verified. HCCs were stiffer and showed less time-dependent settlement in this case, while the authors emphasize the importance of site-specific model calibration and construction monitoring.

Keywords

stone columns

hybrid concrete columns

ground improvement

settlement behavior

Priebe method

load-transfer platform

petrochemical plant

cone penetration test

load tests

site-specific calibration