B. Hanumantha Rao

Determination of distribution coefficient of geomaterials and immobilizing agents

The fate and transport of reactive contaminant(s) in geomaterials (i.e., soils and rocks) and efficacy of the immobilization–remediation methodology of the contaminated geomaterials is governed mainly by the sorption and desorption characteristics of these geomaterials and immobilizing agents. As such, establishment of these characteristics becomes mandatory. To achieve this, batch tests are usually conducted and a distribution coefficient is obtained from Freundlich, linear, and Langmuir isotherms. However, the relative efficiency of these isotherms needs to be ascertained for selection of the appropriate distribution coefficient for a contaminant geomaterial – immobilizing agent system. With this in mind, conventional batch tests were conducted on various geomaterials and immobilizing agents, to establish their sorption and desorption characteristics. However, it should be noted that batch tests do not represent the real-life contaminant geomaterial – immobilizing agent interaction, and are quite cumber...

A Critical Review of the Methodologies Employed for Determination of Tensile Strength of Fine-Grained Soils

Tensile strength of fine-grained soils plays a significant role in assessing their cracking characteristics, which govern their suitabil- ity as a construction material for landfill liners and covers, earthen dams, embankments, and pavements. As such, determination of this property of these soils becomes essential. In this context, various experimental techniques that have been developed by earlier researchers to determine tensile strength of fine-grained soils are worth appreciating. Based on the experimental results obtained from these studies, several empirical relationships have been proposed. However, these relationships relate tensile strength of the soil with a single parameter (i.e., suction, plasticity index, liquid limit, CEC, clay content, or water content).This necessitates: (a) critical evaluation of such relationships, and (b) development of a generalized relationship that employs multiple soil properties. With this in view, investigations were carried out on some fine-grained soils and their tensile strength was determined by conducting undrained triaxial tests and suction measurements. Details of the methodologies adopted are presented in this paper and efforts have been made to achieve the two objectives mentioned above.

Establishing Soil-Water Characteristic Curve of a Fine-Grained Soil from Electrical Measurements

Application of a pressure membrane extractor PME to establish soil-water characteristic curve SWCC of fine-grained soils, in 0-1,500 kPa range, is well established. However, this technique requires testing of several identical specimens, corresponding to same or different pressures, and their subsequent removal from the PME chamber for moisture content determination. This turns out to be a cumbersome process and even the results are considered less accurate, by the research fraternity. This is mainly due to the fact that removal of the specimen before equilibration time may not incorporate the influence of the applied pressure, precisely. This calls for the development of an alternate technique that can be employed for measuring the instantaneous moisture content of the specimen when it is pressurized, sequentially, without removing it from the PME chamber. In this context, the utility of electrical measurements i.e., the voltage across two points in the specimen for determining moisture content was investigated and its details are presented in this paper. This technique has been found to be quite promising and hence can be employed for acquisition of the data which would yield the moisture content of the specimen, without removing it from the PME chamber, easily and quickly. Validity of the methodology has been demonstrated by comparing the obtained SWCC vis-a-vis those obtained by conducting studies using a dewpoint potentiameter, WP4, and by employing the fitting function and a pedo-transfer function available in the SoilVision database. DOI: 10.1061/ASCEGT.1943-5606.0000267 CE Database subject headings: Membranes; Measurement; Soil suction; Fine-grained soils; Soil water. Author keywords: Pressure membrane extractor; Electrical measurements; Soil suction; SWCC; Fine-grained soils.

A Generalized Relationship for Estimating Dielectric Constant of Soils

ABSTRACT: Efforts were made in this study to develop a methodology for estimating the dielectric con-stant of the fine- and coarse-grained soils, based on their dielectric dispersion. A generalized relationshipthat can be employed for estimating the dielectric constant of any type of soil, corresponding to a given acfrequency and any compaction state, has been developed. The utility and efficiency of this relationship hasbeen demonstrated based on the results reported in the literature for different types of soils and glass-beads. KEYWORDS: impedance spectroscopy, dielectric dispersion, fine-grained soils, coarse-grainedsoils, glass-beads Nomenclature porosity volumetric moisture content in % bulk density in g/cc d dry density in g/cc dmax maximum dry density in g/cc C percentage of clay fraction in % C c coefficient of curvature C u coefficient of uniformity D 50 particle diameter corresponding to 50 % finer in mm e voids ratio f frequency of ac in Hz G specific gravity k M dielectric constant of the mineral

Application of thermal flux for establishing soil–water characteristic curve of kaolin

Application of field and laboratory insertion tensiometers, pressure membrane extractor, PME, a dew point potentiameter, WP4, and a geotechnical centrifuge for establishing soil–water characteristic curve (SWCC) of fine-grained soils is well established. However, these techniques are quite elaborate, cumbersome to follow and resort to invasive and destructive techniques for moisture content determination. This calls for development of an alternate technique that can be employed for (a) creating unsaturated state of the soil mass, and (b) measurement of moisture content and soil suction in a non-destructive and non-invasive way. Needless to say, such a technique would be quite helpful for establishing the SWCC, quite easily and rapidly. In this context, possibility of creating unsaturated state of the kaolin soil mass by imposing thermal flux was investigated and its details are presented in this paper. This technique in conjunction with electrical measurements (i.e. voltage in the soil mass) has been found to be quite promising for establishing the SWCC. Validity of the proposed technique has been demonstrated by comparing the resultant SWCC vis-à-vis the SWCCs reported in the literature for this soil and Fredlund et al. (1997; 3rd Brazilian Symposium on Unsaturated Soils, Rio de Janeiro, Brazil, 1997, April 22–25, pp. 13–23) pedo-transfer function (PTF) available in the SoilVision database.

Lysimetric studies for modelling radioactive contaminant transport in soils

To assess the movement of contaminants in the soil mass surrounded by near/subsurface waste repository, researchers have developed several mathematical and numerical modelling techniques. However, most of these techniques consider remolded state of soil mass, which fail to reproduce exact in situ conditions and also have used inactive salts as model contaminants. Hence, in order to model transport of radioactive contaminants, in situ lysimetric studies were conducted at a waste disposal site and efforts were made to predict long-term transportation of these contaminants by employing VS2DT software. Results obtained have been critically examined vis-a-vis those obtained from soil coring experiments.

Accelerated Diffusion Test on the Intact Rock Mass

Contaminant transport through intact rock mass is predominantly diffusive and its modeling using the conventional laboratory tests is extremely time consuming. In addition, maintaining constant ambient conditions over a long duration is difficult and practically impossible. This necessitates modification of the conventional laboratory diffusion experiments so that the diffusion of ions through the intact rock mass is accelerated. To achieve this, researchers have employed an electric field across the samples of concrete and clays. However, the influence of the applied electric field on diffusion characteristics of the intact rock mass has not been studied in detail. With this in view, diffusion tests were conducted on the samples of chalk and sandstone by applying electric fields of different strength. Details of the testing methodology are presented in this paper. Efforts were also made to study the influence of the applied electric field on diffusion characteristics of these rocks.

Determination of Diffusion Characteristics of Intact Rock Mass : A Critical Evaluation

Intact rock mass is the most suitable geological formation for disposing of hazardous wastes. Hence, for safety assessment, establishment of contaminant transport mechanism(s) in/through the rock mass becomes essential. Conventional diffusion cells have been employed by earlier researchers for establishing diffusion characteristics of the intact rock mass. However, due to extremely low porosity of the intact rock mass, the time required for obtaining the “break-through curve” runs into a few months, during which maintaining the ambient conditions becomes extremely difficult. To overcome these limitations, researchers have resorted to accelerated diffusion tests, in the recent past. Several analytical models have been developed by the earlier researchers, which can be employed for determining diffusion characteristics of the intact rock mass. This calls for a comparative study of the diffusion characteristics obtained from these models so as to establish their suitability. With this in view, diffusion characteristics of the intact rock mass of different types were established by conducting accelerated diffusion tests and employing these models. In addition, diffusion characteristics of the intact rock mass were determined based on the concept of cumulative concentration accumulation of ionic species (CCAIS) in the measuring reservoir. It has been found that the models reported in the literature over-predict the diffusion coefficients for the intact rock mass. The superiority of CCAIS model, has been demonstrated by computing the hydraulic conductivity of the intact rock mass and comparing it with the centrifuge modeling results.