Abstract
The modified Cam clay (MCC) model is used to study the response of virgin compressed clay in undrained compression. The MCC deviatoric stress-strain relationship is obtained in closed form. Elastic and plastic deviatoric strains are taken into account in the analysis. For the determination of the elastic strain components, both a variable shear modulus and constant shear modulus are considered. Constitutive relationships are applied to the well-known London and Weald clays sheared in undrained
compression.
Key Words
modified Cam clay model; constitutive relations; elastic and plastic deviatoric strains; virgin compressed clay; undrained compression; comparisons.
Address
Vincenzo Silvestri: Department of Civil, Geological, and Mining Engineering, Ecole Polytechnique, P.O. Box 6079, Station Centre-Ville, Montreal, Quebec H3C 3A7, Canada
Ghassan Abou-Samra: Department of Civil, Geological, and Mining Engineering, Ecole Polytechnique, P.O. Box 6079, Station Centre-Ville, Montreal, Quebec H3C 3A7, Canada
Abstract
Electroosmosis (EO) is the movement of water in a porous medium under the influence of a direct current (dc). In past decades, electro-osmosis has been successfully employed in many soil improvement and other geotechnical engineering projects. Metal electrodes, such as steel, copper and aluminum have been used traditionally to conduct current. The shortcoming of these electrodes is that
they corrode easily during an EO treatment, which results in reduced effectiveness and environmental concerns. More recently, conductive polymers are developed to replace metal electrodes in EO treatment. Electrical vertical drainages (EVDs) are one of these products under trial. The goal of this study is to assess the performance of EVDs for soil improvement and to further understand the scientific principle of the EO process, including the voltage drop at the soil-EVD interface, electrical current density, polarity
reversal, and changes in soil physico-chemical properties generated by electroosmosis. It is found from the study that after 19 days of EO treatment with a constant applied dc electric field intensity of 133 V/m, the soil\'s moisture content decreased by 28%, the shear strength and pre-consolidation pressure increased more than 400%. It is also found that the current density required triggering the water flow in the soil tested, the Korean Yulchon marine clay, is 0.7 A/m2. The project demonstrates that EVDs can serve as both electrodes and drains for soil improvement in short term. However, the EVDs, as tested, are not suitable for polarity reversal in EO treatment and their service life is limited to only 15 days.
Key Words
Soil improvement; land reclamation; electroosmotic consolidation; electrical vertical drains.
Address
J.Q. Shang: Department of Civil and Environmental Engineering, The University of Western Ontario, London, ON N6G 1G9, Canada
Q.H. Tang: Department of Civil and Environmental Engineering, The University of Western Ontario, London, ON N6G 1G9, Canada
Y.Q. Xu: Department of Civil and Environmental Engineering, The University of Western Ontario, London, ON N6G 1G9, Canada
Abstract
One-dimensional soil-column studies were carried out to understand the interaction of three industrial effluents namely amino acid (\'highly acidic\'), surfactant (\'highly organic\') and pharmaceutical (\'organic and toxic\') on the physicochemical behavior, index properties and shear strength of bentonite due to artificial contamination extending to nearly 300 days. Changes in inorganic and organic pollutants present in the effluents due to the interaction of the above effluents and soil were assessed to understand the physico-chemical behaviour. Batch and continuous modes of operation, 8 hrs and 16 hrs Hydraulic Retention Time [HRT] and 25%, 50% concentrations of effluents, were the parameters considered. Amino acid, surfactant and pharmaceutical effluents have shown a high variation in pH (7 to 8) after artificial contamination on bentonite that is their original characteristics of the above effluents have been completely reversed. Further, it is found that the shear strength of bentonite has reduced by about 20%, and with respect to liquid limit and plastic limit shows an increasing trend with time within the period of contamination.
Key Words
industrial effluents; amino acid; surfactant; pharmaceutical; bentonite; physico-chemical behavior;
index properties and strength strength of soils.
Address
V. Murugaiyan: Department of Civil Engineering, Pondicherry Engineering College, Puducherry-605014, India
R. Saravanane: Department of Civil Engineering, Pondicherry Engineering College, Puducherry-605014, India
T. Sundararajan: Department of Civil Engineering, Pondicherry Engineering College, Puducherry-605014, India
Abstract
The paper employs a feed forward neural network with back-propagation algorithm for modeling time dependent swell in clays containing carbonate in the presence of sulfuric acid. The oedometer swell percent is estimated at a nominal surcharge pressure of 6.25 kPa to develop 612 data sets
for modeling. The input parameters used in the network include time, sulfuric acid concentration, carbonate percentage, and liquid limit. Among the total data sets, 280 (46%) were assigned to training, 175 (29%) for testing and the remaining 157 data sets (25%) were relegated to cross validation. The network was programmed to process this information and predict the percent swell at any time, knowing the variable involved. The study demonstrates that it is possible to develop a general BPNN model that
can predict time dependent swell with relatively high accuracy with observed data (R2=0.9986). The obtained results are also compared with generated non-linear regression model.
Address
P.V. Sivapullaiah: Department of Civil Engineering, Indian Institute of Science, Bangalore - 560 012, India
B. Guru Prasad: Department of Civil Engineering, University of Wollongong, Wollongong-2500, NSW, Australia
M.M. Allam: Department of Civil Engineering, Indian Institute of Science, Bangalore - 560 012, India
Abstract
Gravels forming part of the base of flexible pavements experience abrasion and crushing as a result of static and dynamic loads. Abrasion takes place when the sharp corners of the particles of gravel are removed as a result of compressive and shear loads. As a result of abrasion, the particles change in shape. Crushing is caused by the fragmentation of the particles into a mixture of many small particles of varying sizes. In this study, the abrasion and crushing of gravels are evaluated experimentally and
analytically. The laboratory component of this study involves gravels that were subjected to abrasion and
dynamic compression tests. The evaluation of the abrasion and crushing experienced by the gravel was carried out using fractals. In this study, the fractal dimension concept from fractal theory is used to evaluate: (a) the changes in shape, and (b) the crushing (fragmentation) of the original particles of gravel. It was determined that the fractal dimension of the profile of the particles decreased as a result of abrasion. With respect to crushing, the fragmentation fractal dimension was found to increase with the degree of breakage of the gravel. To understand the influence of crushing on the permeability of the gravels, the hydraulic conductivity of the gravels was measured before and after crushing. The hydraulic
conductivity of the gravels was found to decrease with an increase in their level of crushing. Also, changes in the angle of friction of the granular materials as a result of abrasion was calculated using the Krumbein
Key Words
crushing; abrasion; granular materials; laboratory analysis; fractals.
Address
Luis E. Vallejo: Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA
Zamri Chik: Department of Civil and Environmental Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA
