pore water pressure and effective depth range of treating soft foundation with vacuum preloading are analyzed. The analytical results show that: the vacuum preloading brings atmosphere about pressure difference between treating groundsill and its entourage; and brings plus pore water pressure; the mechanical relation is accordant with effective stress principle. The test results of pore water pressure are influenced by atmosphere pressure. Vacuum preloading and surcharge have distinct difference in stress action characteristics
stress treating transfer and effective treating range etc.