Sujit Kumar Pal

Volume Change Behavior of Fly Ash-Montmorillonite Clay Mixtures

AbstractThis paper presents the consolidation and swelling characteristics of fly ash–montmorillonite clay mixes. Nine types of fly ash samples collected from different thermal power plants of the Eastern part of India have been used in this study. The amount of montmorillonite clay added to each fly ash sample is 10, 20, 30, 40, and 50%. The compression index (cc) of the fly ashes indicates that the rate of consolidation is very fast. With an increase in montmorillonite clay content from 0.0 to 50%, the compressibility of the fly ash–montmorillonite clay mix increases, irrespective of the type of fly ash. The value of the compression index (cc) of montmorillonite clay indicates that the embankments and fills made of fly ash–montmorillonite clay mixtures (i.e., 30, 40, and 50% of montmorillonite clay in the mix) and the structures constructed on such fills would suffer large deformation, whereas fly ash and fly ash mixed with 20% montmorillonite clay would not suffer large deformation. Specimens used for ...

Investigation of the Effects of Anisotropic Flow of Pore Water and Multilayered Soils on Three-Dimensional Consolidation Characteristics

Many practical engineering problems are seriously different from the assumptions which are considered for one-dimensional consolidation test and need to concentrate on three-dimensional consolidation of soil under different boundary conditions. In this study three-dimensional consolidation tests are performed with four different anisotropic flow conditions of pore water and fifteen different combinations of horizontal layered soils. Twelve different three-dimensional consolidation tests are also performed with different soils, surrounded by anisotropic vertical soil layers on two opposite sides. From these studies, it is observed that the anisotropic flow of pore water does not have any effect on initial and final surface settlement of soil but has a significant effect during the consolidation process. The anisotropic flow of pore water during the consolidation process has an immense effect on the coefficient of consolidation. Horizontal layered soil has a great effect on both surface settlement and the rate of settlement. Vertical soil layers on two opposite sides of consolidative soil have an immense effect on the horizontal movements of consolidating soil, finally affecting the resultant vertical settlement of soil. Vertical anisotropic surrounding soil layers also have an effect on the rate of consolidation settlement.

Analysis of Slope Stability of Fly Ash Stabilized Soil Slope

Fly ash is a waste product of thermal power plants, can be used as embankment material, stabilization of soft soils, road sub-base constructions, and other geotechnical fields. In this study, fly ash is used as soil stabilizer for an embankment slope. This paper discusses the shear strength parameters of the soil stabilized with fly ash. The soil has been mixed with 10, 20, 30, and 40% fly ash by dry weight for conducting modified Proctor compaction test and direct shear test. The experimental results indicate that the dry density and cohesion value of soil decreases where as the angle of internal friction increases with increase in the percentage of fly ash. The analysis of slope stability of native soil and stabilized soil has been studied by Fast Lagrangian Analysis of Continua (FLAC) slope software. Parametric study has been done to calculate the factor of safety by considering different slope height at constant slope angle under summer and rainy season. The analysis revealed that the slope with native soil was stable up to 12.0 m height under both summer and rainy season. With further increase in height, the slope becomes critically stable and failed under rainy season at 14.0 m height. The addition of fly ash enhances the strength and provides resistance to slope instability under both the conditions up to 14.0 m height. It has been found from the analysis that the factor of safety increases with increase in percentage of fly ash at a particular height. 30% fly ash is obtained as optimum amount as stabilizer for a slope of certain height.

Strength Behaviours of the Clayey-Silt Soil Mixed with Fly Ash and Sand

Fly ash and sand, both the materials have been added in the percentages of 10, 20, 30, 40, 50 and 60% with the clayey-silt soil by dry weight. Modified Proctor compaction was chosen for the California bearing ratio (CBR) tests and applied to soil-fly ash and soil–sand mixes. Un-soaked and soaked CBR of the soil are found as 54.50 and 3.90% respectively under modified Proctor compaction. Both fly ash and sand improved the CBR of the clayey-silt soil but addition of sand show the better result under both un-soaked and soaked conditions. However, the addition of 40% sand to the soil shows the maximum un-soaked CBR value as 70.07%. An addition of fly ash decreases the unconfined compressive strength (UCS) of the clayey-silt soil and increases in UCS observed at 40 and 20% addition of sand to the soil at standard and modified Proctor compaction respectively. The addition of both fly ash and sand to the soil increase the shear strength of the clayey-silt soil at standard Proctor compaction. Depending on availability of the material either fly ash or sand, it can be said that strength of the weaker clayey-silt soil can be improved using any of the additives.

Effect of Vertical Pressure on Horizontal and Vertical Permeability of Soil and Effect of Surcharge Pressure on 3D Consolidation of Soil

Permeability and consolidation of soil are known as the most variable soil properties. The values of permeability and consolidation of soil may vary with depth even in case of homogeneous soil layers, and because of that, the determination of appropriate values of permeability and consolidation is a complex and complicated engineering task. In this study, horizontal and vertical permeability apparatus and a 3D (three-dimensional) consolidation apparatus are developed to determine the effects of vertical pressure on horizontal and vertical permeability and the effects of vertical surcharge pressures on three-dimensional consolidation of soil. A series of horizontal and vertical permeability tests of soil under different vertical pressures and a series of 3D consolidation tests under different surcharge pressures are performed. From the study, it is observed that the horizontal and vertical permeability of soil changes with the changes in vertical pressures, and 3D consolidation of soil also changes with the changes in surcharge pressures. The horizontal and vertical permeability values obtained from the newly developed horizontal and vertical permeability apparatus are used in Terzaghi’s one-dimensional consolidation theory to find out the consolidation characteristics of the soil, and it is compared with the results obtained from the newly developed 3D consolidation apparatus.