Thesis (Ph.D.)--Chulalongkorn University, 2012

The research has been carried out by the combination of laboratory experiments and finite element analysis to propose an appropriate method to predict soft soil behavior under vacuum preloading. It can be widely applied at the site to support earth works to avoid any instability of embankment. The prediction behavior of improved soft soil using vacuum preloading method should be concerned significantly not only in the laboratory but also at the field. It aims at avoiding the risks of instability of the embankment surcharging during construction. The simulation vacuum preloading method using tri-axial apparatus is proposed to predict the behavior of soft soil improvement in the laboratory and the increasing of undrained shear strength of soil specimen at any degree of consolidation. This modeling is the effective method to determine the increasing rate of strength of the ground corresponding to loading rate during consolidation process, and to restrict using field test during construction, the cause of damage of airtight sheet membrane, and losing of vacuum pressure. A case study of vacuum consolidation at Nakhorn Sri Thammarat Airport was proposed. During soft soil improvement, the field instrumentations were used to assess the very soft soil behavior and minimize the instability problem in order to enhance effectiveness of this method. The research is proposed to support the engineering task more conveniently. In addition, it is expected to make vacuum preloading method familiarly in the future.