Masters Thesis

Effect of Vertical Stress, Void Ratio and Plasticity on the Coefficient of Consolidation and Permeability of Laboratory Prepared Mineral Mixtures

Soil is unlike other construction materials such as steel and concrete for which humans can control their properties. Therefore, it is important to investigate and test soil in order to predict its response to the construction loading. The coefficient of consolidation (Cv) and coefficient of permeability (k) are two of the dominant and fundamental geotechnical parameters that are used in many applications within the civil engineering discipline. These coefficients are used in dam construction on soft bedrock, erection of retaining walls in weak bearing soil and foundation design on poorly compaction soil. In this study, four types of minerals montmorillonite, kaolinite, illite and quartz were mixed in different proportions, and used to conduct one- dimensional consolidation tests, as summarized in Tiwari and Ajmera (2011). Seven different vertical pressures 3.47 psi, 6.94 psi, 13.89 psi, 27.78 psi, 55.56 psi, 111.11 psi and 222.22 psi were applied. In order to examine the influence of pore fluid chemistry, the soil samples were prepared with distilled water as well as with saline water as the pore fluid. Casagrande’s Logarithm of Time Method were used to estimate the coefficient of consolidation values for forty – two samples with distilled water as the pore fluid and twenty – four samples with saline water as the pore fluid. Also, Terzaghi’s equation was used to determine the coefficient of permeability for the mineral mixtures. The variations of the Cv and k with consolidation pressure and index properties for all mixtures with distilled water and saline water as the pore fluids were examined. It is observed that Cv for kaolinite and illite mixtures with distilled water and saline water as the pore fluids increases with an increase in the consolidation pressure. On the other hand, Cv values for the montmorillonite mixtures with distilled water as the pore fluid decrease with an increase in the consolidation pressure. The Cv values for the montmorillonite mixtures with saline water as the pore fluid increase with an increase in the consolidation pressure. All the soil mixtures with distilled water and saline water as the pore fluids experienced reduction in the values of the coefficient of permeability with the increase in the consolidation pressure. The coefficient of consolidation decreases with an increase in the liquid limit for the kaolinite, illite and montmorillonite mixtures with distilled water and saline water as the pore fluids. The relationship between the coefficient of consolidation and plasticity index for the mineral mixtures with distilled water and saline water as the pore fluids has the same trend as that with the liquid limit. Specifically, the coefficient of permeability decreases with an increase in the liquid limit and plasticity index for the kaolinite mixtures with distilled water and saline water as the pore fluids. Finally, the coefficient of permeability decreases with an increase in the liquid limit and plasticity index for the montmorillonite mixtures with distilled water and saline water as the pore fluids.

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