Abstract: Soft clay deposits with confined underground water were strengthened by vacuum-surcharge.Technology of the tearing membrane combined with the non-tearing membrane was introduced.The details of settlements,multi-point settlements and deep horizontal displacements were presented and analyzed for the field tests on Gangwan substation.It was shown that the main settlements could be eliminated effectively by vacuum-surcharge preloading at soft foundation with confined underground water,the average degree of consolidation of soft soil was 83% which would last for more than 100 years.The shear strength and bearing capacity of silt would increase obviously after preloading as indicated by indoor and outdoor comparison tests.Viewed from the flow of single pump and the compression of stratum with confined underground water,the lower confined underground water was not influenced by vacuum loading.The success of this technology would promote greatly the application of vacuum-surcharge preloading.