Abstract: When using the vacuum preloading with surcharge method to improve the saturated peaty soils, the degree of vacuum underneath the membrane and its vertical delivering into the deeper layer are critical to the duration of the preloading and the result of the soil improvement. This paper presents a case history of using this method from the microscopic point of view. The degree of vacuum change with soil depth and factors that affecting the degree of vacuum in the soil are analyzed. It is concluded that the degree of vacuum change in the soil is a process of air particles moving from high density areas to low density areas. The peaty soil media has a strong damping effect to the air particles and the energy dissipation in this soil is strong. Under 20 meters below the ground, the degree of vacuum cannot be detected. The vacuum formed below the ground water line is formed by lowering the ground water table.

Key words: Vacuum-Preloading with Surcharge, Degree of Vacuum, Vacuum Transfer, Influence Factors