Journal Articles
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Item A Critical Review of Construction, Analysis and Behaviour of Stone Columns(Kluwer Academic Publishers, 2013) Dheerendra Babu, M.R.; Nayak, S.; Shivashankar, R.Stone columns have been used as an effective technique for improving the engineering behaviour of soft clayey grounds and loose silt deposits. The soil improvement via stone columns are achieved from accelerating the consolidation of weak soil due to shortened drainage path, increasing the load carrying capacity and/or settlement reduction due to inclusion of stronger granular material. This paper discusses the techniques, methods of construction of stone columns, mechanisms of stone column behaviour under load and associated design philosophies along with some practical findings from recent research programs. © 2012 Springer Science+Business Media B.V.Item Modeling and experimental validation of valve and pumping actuator of a piezo-hydraulic pump(Zibeline International Publishing Sdn. Bhd., 2019) Nayak, S.; Rao, M.; Rao, R.This paper presents experimental investigations on valve actuator and pumping actuator of a piezo-hydraulic pump with active valves. Quadratic arm flexurally amplified piezoelectric actuators (QAFAPA) are designed for the pumping actuator and the valve actuator. Simulations are carried out to determine the voltage-displacement characteristics of the QAFAPA using MATLAB/Simulink software. To perform the pumping action, slotted pumping diaphragm is designed considering acrylic as the material and is analyzed for its stiffness using ANSYS analysis software. The slotted pumping diaphragm is fabricated, and the stiffness is experimentally determined which matched well with the analysis result. One pumping actuator and one actuator similar for inlet and outlet valve is developed. Voltage-displacement experiments are carried out on the valve actuator and the pumping actuator. Further, the displacement of the slotted pumping diaphragm when assembled with pumping actuator is experimentally determined. Simulation and experimental results were compared, and the results obtained were in good agreement with each other. © 2019 Zibeline International Publishing Sdn. Bhd. All rights reserved.Item A Review on the Design, Applications and Numerical Modeling of Geocell Reinforced Soil(Springer Science and Business Media Deutschland GmbH, 2021) Vibhoosha, M.P.; Bhasi, A.; Nayak, S.For improving the stability and load carrying capacity of weak subgrade, strengthening methods are to be followed in the field. Among the various approaches, geocells have been identified as an effective soil reinforcement technique for improving soft subgrade behaviour. The three-dimensional honeycomb structure of geocell offers more lateral confinement to the infill soil resulting in improved load carrying capacity. This led to the widespread use of geocells for different geotechnical applications like pavements, foundations, embankments, slope protection, erosion control etc. Many researchers in the past have confirmed the suitability of geocell reinforcement through their experimental, numerical and field studies. In this paper, a comprehensive review of the reinforcement mechanisms, design aspect and numerical modelling techniques of geocell reinforced soil is provided. In addition, this paper highlights the various field application scenarios where different types of geocells have been used and explores the research challenges and scope for further research in this field. © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Item Effect of pH on the geotechnical properties of laterite(2006) Sunil, B.M.; Nayak, S.; Shrihari, S.Environmental Geotechnology has emerged as an interdisciplinary science, aiming and forecasting, analyzing and solving the geotechnical problems involving the influence of environmental factors. Lateritic soil of west coast region of India was studied to investigate the effect of soaking on the engineering properties and chemical characteristics of soil, soaked in different pH solutions (pH = 5.0, pH = 7.0, pH = 8.0). 12 N hydrochloric acid and 15 M ammonia solution were used to monitor the pH of the solution for about ninety days. Results showed that the pH of the solution has strong influence on the chemical characteristics of lateritic soil. The engineering properties of soil are altered when compared with the initial characteristics of the soil. The reason for this observed behavior of the soil is addressed in this paper. © 2006 Elsevier B.V. All rights reserved.Item Hydraulic and compaction characteristics of leachate-contaminated lateritic soil(2007) Nayak, S.; Sunil, B.M.; Shrihari, S.Large quantities of leachate-contaminated lateritic soil results from dump yards in the southwest coast of India. These dump yards receive large quantities of municipal solid waste which includes chemical, industrial and biomedical wastes. Large areas of land are currently being used for this purpose. An extensive laboratory testing program was carried out to determine the compaction characteristics and hydraulic conductivity of clean and contaminated lateritic soil. Batch tests were used to study the immediate effect of leachate contamination on the properties of lateritic soil. Contaminated specimens were prepared by mixing the lateritic soil with leachate in the amount of 5%, 10% and 20% by weight to vary the degree of contamination. The results indicated a small reduction in maximum dry density and an increase in hydraulic conductivity due to leachate-contamination. The change induced by chemical reaction in the microstructure of the soil was studied by scanning electron microscope before and after contamination of soil with leachate. The structure of the leachate contaminated soil sample appeared to be aggregated in scanning electron microscope analysis. The aggregated structure increases the effective pore space and thus increases the hydraulic conductivity. Fifty percent increase in hydraulic conductivity was observed for specimens prepared at standard Proctor density and mixed with 20% leachate. Compaction characteristics did not change much with the presence of leachate up to 10%. With 20% leachate the maximum dry density decreased slightly indicating excess leachate in the soil. However the changes are not significant. © 2007 Elsevier B.V. All rights reserved.Item Anti-diarrheal potential of Aegle Marmelos Corr. root bark extract in rats(2007) Vrushabendra Swamy, S.B.M.; Nataraj, K.S.; Jayaveera, K.N.; Gopkumar, P.; Nayak, S.; Kumar, G.S.; Umachigi, S.P.A study was undertaken to evaluate the effect of methanolic extract of the rootbark of Aegle marmelos Corr. (MAMC) against several experimental models of diarrhoea in rats. MAMC treated animal's showed significant inhibitory effect against castor-oil induced diarrhea and PGE2 induced enteropooling in rats. The extract also showed a significant reduction in gastrointestinal motility in the charcoal meal test in rats. The results obtained to establish the efficacy and substantiate the folkare claim as an anti-diarrhoeal agent.Item Shear strength characteristics and chemical characteristics of leachate-contaminated lateritic soil(2009) Sunil, B.M.; Shrihari, S.; Nayak, S.Leachate is a hazardous liquid and is a major cause of concern in landfills. Numerous environmental problems such as soil and groundwater contamination occur in unlined landfills due to free flow of leachate. Large quantities of leachate-contaminated soils result from open dumping in the study area. These dump yards receive large quantities of municipal solid waste which includes chemical and industrial wastes. Large areas of land are currently being used for this purpose. An extensive laboratory testing program was carried out to determine the properties of clean and contaminated lateritic soils. Laboratory prepared municipal solid waste leachate was used in this study. Contaminated specimens were prepared by mixing the soils with MSW leachate in the increments of 0%, 5%, 10% and 20% by weight to vary the degree of contamination. The results showed that the MSW leachate affects the Atterberg limits, shear strength and chemical characteristics of the lateritic soils. The liquid limit and the plasticity index of the lateritic soils increases with MSW leachate concentration. For specimens tested at the Proctor density, effective cohesion increases and effective friction angle decreases due to increase in leachate concentration. This is attributed due to the increase in clay content of lateritic soil after interaction with the leachate. This led to increase in cohesion parameter and the friction angle decreases. The pH measurements of lateritic soil contaminated with MSW leachate indicated an increase in pH values. This is also accompanied by slight increase in the cation exchange capacity of the soil. The change in chemical characteristics of lateritic soil contributed due to addition of leachate may be detrimental to foundation concrete in real field conditions. The present work deals with an attempt to study the effect of leachate on the Atterberg limits, shear strength properties and chemical characteristics of lateritic soil. © 2009 Elsevier B.V. All rights reserved.Item Characterization of small-scale groundwater irrigation schemes in a humid coastal region of southern India(2009) Nayak, S.; Nandagiri, L.Small-scale groundwater irrigation schemes involving large diameter wells are prevalent in the coastal district of Uttara Kannada, Karnataka State, India. A study was conducted to assess the characteristics of these large diameter open wells and the hydraulic properties of shallow aquifers. Field tests were conducted in 19 wells to assess their potential to supply irrigation water requirements of the region. Constant discharge pump tests indicated significant spatial variations in aquifer transmissivity (5.60 to 64.55 m2·day-1) and specific yield (0.063 to 0.95). Low transmissivity values signify poor potential of the aquifer to supply irrigation water needs. Exponential prediction models linking transmissivity and well specific capacity gave a good fit. Implications of spatial variability in aquifer parameters on irrigation development in the region are highlighted.Item Stone Columns with Vertical Circumferential Nails: Laboratory Model Study(2010) Shivashankar, R.; Dheerendra Babu, M.R.D.; Nayak, S.; Manjunath, R.This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the improvement in stiffness, load carrying capacity and resistance to bulging of stone columns installed in soft soils. A new method of reinforcing the stone columns with vertical nails installed along the circumference of the stone column is suggested for improving the performance of these columns. Tests were carried out with two types of loading (1) the entire area in the unit cell tank loaded, to estimate the stiffness of improved ground and (2) only the stone column loaded, to estimate the limiting axial capacity. It is found that stone columns reinforced with vertical nails along the circumference have much higher load carrying capacity and undergo lesser compression and lesser lateral bulging as compared to conventional stone columns. The benefit of vertical circumferential nails increases with increase in the diameter, number and depth of embedment of the nails. The improvement in the performance of stone column was found to be more significant, even with lower area ratio. It is found that reinforcing stone column with vertical circumferential nails at the top portion to a depth equal to three times the diameter of stone columns, will be adequate to prevent the column from excessive bulging and to improve its load carrying capacity substantially. © 2010 Springer Science+Business Media B.V.