Numerical Studies on Vacuum Consolidation in Soft Clay Deposits

Kumar, Ayush and Saride, Sireesh (2018) Numerical Studies on Vacuum Consolidation in Soft Clay Deposits. Masters thesis, Indian Institute of Technology Hyderabad.

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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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