Abstract: In current ground improvement practice, a certain period of time is required after ground improvement by compacted sand\|gravel columns before the in\|situ quality assurance testing can be performed. However, the quantitative influence of time on the QA test results within the columns has not been reported. The influence of time on the QA results is evaluated through a case study of soft ground improved by compacted sand\|gravel columns for man\|made hills of a theme park. Dynamic Penetration Tests (DPT) were performed on two sand\|gravel columns with lengths of 8 m and 22 m. The tests were performed at different times after construction of the sand gravel columns ranging between 0 and 39 days. The testing results indicate that the DPT test is a simple and effective testing method for quality control of the density and the length of compacted sand\|gravel columns. The blow counts in the columns are consistent at least 8 days after the completion of sand\|gravel columns. It is recommended that the DPT should be performed 8 days after the column completion.