Ambarish Ghosh

Compaction Characteristics and Bearing Ratio of Pond Ash Stabilized with Lime and Phosphogypsum

Recycling of waste material is one of the effective solutions of its disposal problem. Fly ash produced by coal-based thermal power plants and phosphogypsum (PG) produced by fertilizer plants producing phosphoric acid as constituent of fertilizers, take huge disposal area and creates environmental problems. Stabilization/solidification of fly ash improves the engineering properties and reduces the environmental problem like leaching and dusting. This paper presents the laboratory test results of a Class F pond ash alone and stabilized with varying percentages of lime (4, 6, and 10%) and PG (0.5, and 1.0), to study the suitability of stabilized pond ash for road base and subbase construction. Standard and modified Proctor compaction tests have been conducted to reveal the compaction characteristics of the stabilized pond ash. Bearing ratio tests have been conducted on specimens, compacted at maximum dry density and optimum moisture content obtained from standard Proctor compaction tests, cured for 7, 28, and 45 days. Both unsoaked and soaked bearing ratio tests have been conducted. This paper highlights the influence of lime content, PG content, and curing period on the bearing ratio of stabilized pond ash. The empirical model has been developed to estimate the bearing ratio for the stabilized mixes through multiple regression analysis. Linear empirical relationship has been presented herein to estimate soaked bearing ratio from unsoaked bearing ratio of stabilized pond ash. The experimental results indicate that pond ash-lime-PG mixes have potential for applications as road base and subbase materials.

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 ...

Finite Difference Method for Computation of 1D Pollutant Migration through Saturated Homogeneous Soil Media

The physical processes such as advection, dispersion, and diffusion and interaction between the solution and the soil solids such as sorption, biodegradation, and retention processes have been considered in the governing equation used in the present study. Finite difference method has been adopted herein to solve the one-dimensional contaminant transport model to predict the pollutant migration through soil in waste landfill. In the finite difference technique, the velocity field is first determined within a hydrologic system, and these velocities are then used to calculate the rate of contaminant migration by solving the governing equation. A total of seven contaminants have been chosen for analysis to represent a wide variety of wastes both organic and inorganic. A computer software CONTAMINATE has been developed for solution of the contaminant transport model. Results of this study have been compared with existing analytical solution for validation of the proposed solution technique. Design charts for ...

Three-Dimensional Analysis of Contaminant Migration through Saturated Homogeneous Soil Media Using FDM

AbstractFinite-difference method (FDM) is applied herein to solve the three-dimensional (3D) contaminant transport model to predict pollutant migration through clay liner or clay deposit in waste landfill. The seven pollutant species typically found in municipal and industrial wastes are considered in this study. Physical processes such as advection, dispersion, diffusion, geochemical reactions, and first-order decay are considered in the governing equation. The computer program CONTAMINATE-3D was developed to solve the 3D analysis of the contaminant migration model. A comparative study between one-dimensional and 3D analysis is presented in this paper based on the proposed methodology considering unidirectional flow and dispersion in three directions. Based on the present 3D analysis, design charts for liners and concentration profiles of contaminant species passing through liner media were developed to facilitate the designers’ work. Contaminant plumes were also developed within the aquifer considering ...

Seismic response of rectangular liquid retaining structures resting on ground considering coupled soil-structure interaction

Seismic response of water tanks resting on ground has been a topic of considerable research in academics as well as energy and infrastructure industry. In many cases, it remains essential that they remain functional even after a major ground shaking. State of the art adapted in different national and international code usually recommends a simplified mathematical model that in many cases digresses from field reality. A three dimensional analysis of the tank plus fluid and foundation soil is surely possible based on finite element analysis. However, in most cases, such exhaustive analysis is done away with, often due to lack of supportive software to tackle such problem, but more out of economic and schedule compulsion, where in many cases engineers do not have the luxury to carry out such expensive analysis, to remain competitive in the market. Thus, a search for a better and more realistic model than what is in vogue is still in quest for this particular problem. Present paper attempts to present a mathematical model based on Lagranges formulation and adapting Galerkins technique that circumvents many of the problems as cited above.

Dynamic response of cylindrical structures considering coupled soil-structure interaction under seismic loading

This paper attempts to develop a mathematical model for estimating the seismic response of a cylindrical shaped nuclear reactor building resting in an elastic halfspace considering foundation compliance. Most of the research carried out on this topic has either been carried out by resorting to finite element method (FEM) which makes the computational cost expensive or based on the simplifying assumption of assuming the cylindrical structure as a multi degree lumped mass stick model with soil coupled as boundary springs. In the present paper an analytical model has been developed in which the deformation of the cylindrical body (including its shear deformation characteristics) has been taken into cognizance and then coupling with foundation stiffness a comprehensive solution has been sought based on Galerkin’s weighted residual technique. The results are finally compared with FEM to check the reliability of the same. The results are found to be in good agreement with the detailed finite element analysis.

Analysis of 1D Contaminant Migration through Saturated Soil Media Underlying Aquifer Using FDM

AbstractFinite-difference method (FDM) has been adapted herein to solve a one-dimensional (1D) contaminant transport model to predict contaminant migration through soil in waste landfill underlying an aquifer. Providing an effective engineered barrier, which will separate the waste from groundwater, can minimize the potential contamination in the groundwater system. In this paper, a solution technique has been developed using FDM for the analysis of 1D contaminant transport in a layer of finite thickness. The present study considers the effects of advection, dispersion/diffusion, geochemical reactions, and decay in a single model with a finite quantity of pollutant in the landfill and transport of contaminants toward groundwater beneath the clay deposit/liner. The computer program CONTAMINATE-1D-FM has been developed using the proposed solution technique to analyze the contaminant migration. The short-term and long-term effects of different factors influencing groundwater contamination have been presented...

An experimental investigation on effect of drawdown rate and drawdown ratios on stability of cohesionless river bank and evaluation of factor of safety by total strength reduction method

ABSTRACT This paper presents an experimental investigation on the stability of a model river bank composed of homogeneous cohesionless soil under rapid drawdown condition. The effects of major influencing parameters controlling Factor of Safety (FoS) of a river bank under depletion of water level have been considered in the present study. A series of laboratory model studies have been carried out to investigate the cases of drawdown rate and drawdown ratios rendering the bank to maximum damage. Moreover, the effect of water level drawdown on the response variables namely pore water pressure, deformation of the bank profile, and shear strength of bank material have been observed and analysed. Stability analysis of the experimental model banks under drawdown conditions was carried out by evaluating FoS using the principle of reduced shear strength methodology. The in-situ total shear strength after each drawdown was measured using a laboratory vane shear apparatus. The minimum shear strength among these values has been identified. Now the FoS against each drawdown ratio has been computed from the ratio of total shear strength obtained after drawdown for that particular drawdown ratio to the minimum shear strength as obtained. This experimental programme examined the optimum combination of drawdown rate and drawdown ratio causing mass failure of the bank. It was revealed from the variation of pore pressure after drawdown that changes of pressures at points close to the toe of the bank slope is strongly controlled by the stress-state induced by drawdown. From the failure observations it was found that the drawdown rate is the dominating cause of maximum deformation of the bank than that of drawdown ratio. The findings of the present research work may help in predicting the actual failure scenario and stability condition of prototype river under similar boundary conditions.

Improvement of Bearing Ratio of Clayey Subgrade Using Compacted Flyash Layer

Abstract This paper presents a laboratory study on California Bearing Ratio (CBR) of flyash overlying a soft clay bed. Flyash sample (Class F) has been collected from Titagarh Thermal Power Plant situated near Kolkata. The type of soil collected locally is silty clay. Different configurations of soil and flyash overlying the soil have been maintained by varying the thickness ratio (ratio of thickness of flyash to that of clay) in the ratios of 1:2, 1:1 and 2:1. Both Standard Proctor and Modified Proctor compaction tests have been carried out to obtain respective maximum dry density and optimum moisture content to be used for CBR tests. The water contents of soil used in this study are 16, 22, 28, 34 and 40% where 16% is the optimum moisture content of the soil as obtained in Standard Proctor compaction test. Similarly water content of the soil has been kept at 12, 18, 24, 30, 36 and 42% for samples prepared using Modified Proctor energy where 12% is the corresponding optimum moisture content of soil. Improvement of CBR values of composite soil-flyash system has been observed when compacted flyash layer is placed above the compacted soil. Out of three thickness ratios tested, CBR value has been found to be the lowest at thickness ratio of 1:2 and the highest at 2:1. The improvement factor is found to be maximum for highest moulding water content irrespective of thickness ratio and compaction energy. It indicates the effective use of flyash soil composite matrix under worse affected condition of high water content. The paper highlights the nature of improvement of clayey soil when compacted flyash layer has been placed on it with different values of thickness ratio and placement moisture content and compaction energy.