In this paper, vacuum consolidation accompanied by the substitution of pore water with air is called "the air inflow vacuum consolidation". In this vacuum consolidation, inflow of air into the soil mass is permitted during consolidation. Due to this inflow of air, pore water in the soil mass is replaced by the air and drying shrinkage of the soil mass occurs, resulting in the considerably large acceleration of settlement. This phenomenon was accidentally found in the laboratory vacuum consolidation tests which were conducted for examining the effects of vacuum consolidation on peats. In this paper, presented are the characteristics of the air inflow vacuum consolidation.
Vacuum preloading is considered as the more effective and economical method for improving soft grounds. The improving area is sealed with an airtight membrane and a vacuum is created underneath it by using vacuum pump. In this method, it is very important for the best vacuum performance to prevent inflow of air into the improving area through the defects in the membrane or the seal between the membrane and the ground (Matsumoto et al, 2000; Cognon et al, 1994; Jacob et al, 1994). However, it was found that due to the inflow of air into the soil mass, settlement rate became larger than that of no inflow of air. That is, due to the inflow of air into soil mass, pore water is replaced by the air and drying shrinkage of soil mass occurs, resulting in the considerably large acceleration of settlement. This phenomenon was accidentally found in a series of laboratory tests on peats in which the effects of vacuum consolidation for improving peat soils were investigated. In these tests, owing to the mistake of sealing the specimen, inflow of air into the specimen had occurred in some tests.