Void ratio is one of the most important evaluation indicator of the silt compactness; the study shows that there are certain corresponding relations between liquefaction indexes and void ratio of saturated silt subgrade treated with vibroflotation; when the post-treated void ratio drops to bellow 0.75

the liquefaction of saturated silt subgrade could be eliminated. Based on the testing result and three-phase composition analysis of soil before and after the vibroflotation

the vibration effectiveness and compaction effectiveness of vibro replacement stone column are quantified; and the estimate method of post-treated void ratio is also derived. Compared with measured values

the estimate values calculated through the estimate method have errors within ± 1.5%. Meanwhile

the estimate method of post-treated void ratio are used to rapidly approach the optimal combination of pile spacing and pile diameter

so as to provide a reliable basis for saving the cost and speeding up the progress of pile testing.