Three 30,000m3 storage tanks are located at a hydraulic-filled reclamation site and close to an earthquake active area in Taiwan. In order to reduce the risk of liquefaction in loose silty sand of foundations, the soil improvement methods of both dynamic compaction and vibro-replacement stone column are applied. One storage tank foundation was improved using vibro-replacement stone column approach only, and the treatment pattern consisted of stone columns on a triangular grid arrangement with three spacing patterns. A combination of the dynamic compaction and vibro-replacemenr stone column technique was utilized on foundations of the others. The dynamic compaction was performed at two different storage tank foundations with two types of impact energy first, then vibro-replacement stone column technique was carried out. To understand the effect of time on soil strength after soil improvement, CPT soundings were frequently performed at short interval time. It was found from results of CPT that soil strength increased with decreasing spacing of stone columns and increasing dynamic compaction impact energy. But during the short period of time after improvement, soil strength has no obvious change with time
