Kumar, Ayush and Saride, Sireesh
(2018)
Numerical Studies on Vacuum Consolidation in Soft
Clay Deposits.
Masters thesis, Indian Institute of Technology Hyderabad.
Abstract
Vacuum consolidation is a promising technic to accelerate the consolidation process of soft
soils under favorable conditions over other processes. It is essential to stabilize these soils to
improve load carrying capacity and reduce the consolidation behaviour. Vacuum
consolidation method reduces the pore water pressure inside the soil mass without the
requirement of any additional fill loading, thus eliminating the possibility of shear failure,
allowing faster and safer construction.
In this study, coupled flow deformation analysis is adopted to perform a numerical analysis
of vacuum consolidation in soft clay deposits. A numerical model is formulated using
PLAXIS 2D, a finite element software. Soft soil model is used to model the behaviour of
soft marine clay. PVDs are modelled using linear drain elements under negative vacuum
pressure. The model is simulated in the study of clay deposits at Kakinada port, India. The
geotechnical data was adopted from the case study available in the literature. The numerical
simulations confirmed that there was a vacuum loss in the field. The magnitude of available
vacuum pressure in the field was predicted by several numerical simulations. Mandel-Cryer
effect was observed initially because of application of vacuum pressure between the PVDs.
Influence of staged vacuum application during initial period is also studied. With the
numerical study 85-90% reduction in post-construction settlements were observed.
Equation of radial consolidation is solved using the finite difference method with a wide
range values of coefficient of radial consolidation (Cr) and drain spacing ratio (n). The
solutions obtained are presented in form of a design chart to obtain the desired degree of
consolidation (U) with respect to radial time factor (Tr). The chart is validated with the
available case studies in literature. The results were found to be in good agreement with the
published data for homogenous soil strata.
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