Deformation Behaviour of Soil Under Vacuum Consolidation

B. R. Deepa1 and R. G. Robinson2

1Formerly graduate student, Department of Civil Engineering, IIT Madras, Chennai, Tamilnadu, India.

2Associate Professor, Department of Civil Engineering, IIT Madras, Chennai, Tamilnadu, India.


Vacuum preloading technique is a viable ground improvement technique for the stabilization of soft grounds. The basic difference between surcharge preloading and vacuum preloading is that surcharge preloading imparts anisotropic stress conditions to the soil whereas the stress induced by vacuum pressure is more close to isotropic as it is applied to the pore phase. Therefore, the soil deform in the outward direction in the former case where as it is inward in the latter case. Though vacuum consolidation technique is extensively used in practice, the mechanism of soil deformation is not properly evaluated in the literature. This paper examines this aspect through an experimental programme on a reconstituted soil using a double wall triaxial cell. Apart from monitoring the vertical deformation, the lateral strain was also computed. It was found that the vertical settlement under vacuum consolidation is less than that obtained from one-dimensional consolidation under the same consolidation pressure. The vertical settlement under vacuum pressure is same as that under equivalent surcharge loading, if 1-D condition prevails.

Keywords: Vacuum consolidation; lateral deformation; experimental study.

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