Abstract: Longkou power plant, Shandong province is located in an area of soft sandy clay layer liable to liquification. According to the Design the ground should suppert a load intensity of 245 kPa while the bearing capacity of the soft soil is only 117 kPa. So, it was decided to use stone columns for improTing the poor ground. This paper describes the results of in situ measurement and observed settlements of structures. The in-situ measurement includes:（ 1 ） the ground acceleration due to horizontal vibrating force caused by the vibroflot and its variation with the distance from the vibrating center;（2） large-sized plate loading tests with plate size of 3.2m × 3.2m and small-sized plate loading tests with plate area of 0.25m2 and 0.5m2;（ 3 ） blow count of SPT, penetration resistance of CPT and dynamic paramenters by cross-hole method before and after the installation of stone columns;（4） pore water pressure induced by the installation of stone columns;（ 5 ） heaving of ground surface.Up to now, the maximum settlement of 40 mm of main structure was observed.