Based on the foundation treatment practice of a large-scale project in the coastal region,we carry out a comparative test of vibroflotation backfill and dynamic compaction to soft foundation treatment.After construction,we take some in-situ test measures including monitoring of pore water pressure,standard penetration test,static cone penetration test and plate loading test to evaluate the pore water pressure changing,the bearing capacity of foundation and liquefaction of sand.Conclusions are drawn as follows:Firstly,the effect of vibroflotation without backfill method is unsatisfactory and unsuitable for the foundation treatment under the geotechnic condition of this project.Secondly,the dynamic compaction method has an obvious compaction effect on improving the geotechnical engineering properties of soil.The foundation bearing capacity is increased,and the possibility of sand liquefaction can be also eliminated.Thirdly,the reinforcement is greatly affected when soft soil interlayer exists below 10 m depth.Under that condition,the soil bearing capacity and compression modulus could not be improved.Finally,the reinforcement depth of 5 000 kN·m energy-level dynamic compaction is about 10 m.