Prediction of the stress state and deformation of soil deposit under vacuum pressure

Stress state and deformation of a clayey deposit under vacuum pressure has been investigated using field data as well as laboratory vacuum consolidation test results. The field vacuum consolidation project was conducted in Saga, Japan for a clayey deposit with prefabricated vertical drain (PVD) installation. Laboratory tests were conducted under triaxial condition using undisturbed soil specimen with a mini-vertical drain inserted in the center to simulate PVD induced consolidation. By comparing the field and laboratory test results, it has been found that the effective confinement from the surrounding soils to the vacuum treated area is close to active earth pressure for a zone about 5 m depth from the ground surface, and below it is between active and at-rest states. A scaling factor has been derived to convert consolidation time in laboratory to the field case. It has been shown that with the scaling factor, the results of laboratory vacuum consolidation test under triaxial condition can be used to predict field settlement curves for vacuum loading.