Abstract: A series of field tests of high energy dynamic compaction (HEDC) are carried out to investigate the effective depth of improvement (EDI) of foundation backfilled with crushed stone, underlain by thin soft layers and high groundwater level in coastal area. The research work includes the following items: for Test Zone A, single-point dynamic compaction tests under energy levels of 14000, 10000 and 8000 kN·m; comparison tests of single-point dynamic compaction under the same energy level (6000 kN·m) and different bowl pressure (weight) of 34 (180 kN), 50 (250 kN) and 90 kPa (460 kN). For Test Zone B, group-point dynamic compaction tests under energy level of 12000 kN·m. For Test Zone C, group-points dynamic compaction tests under energy level of 15000 kN·m. Cone dynamic penetration tests, standard penetration tests and routine geotechnical experiments are performed, and the monitoring results are analyzed. Through comparative analysis on the bearing capacity of foundation before and after dynamic compaction, the EDI of foundation and the revised coefficient of the Menard formulas are presented under different high energy levels. The results provide the parameters for the design, construction, and detection of high energy dynamic compaction in similar regions.