Abstract: The subsoil （mainly sandy clay and silty sand） at the site of proposed Nantong Power Plant has been improved by use of stone columns. This paper documents the results of field tests and measured settlements of structures. Field tests consisted of （1） seven large scale plate loading tests （plate' s area 3 × 3m）, （2） measurement of vertical stresses on columns and surrounding soil, （ 3 ） determination of the relationship between the peak particle velocity on ground surface caused by the operation of vibrator during installation and the distance from vibrator, and （ 4 ） the change in blow counts of ground soils after installation. At present, the building has settled in the range 3¹0 cm and the degree of consolidation is estimated to be over 80%. The main building and the foundations of all facilities are in good condition and show no signs of foundation difficulties.