• Geomechanics and Engineering
• /
• v.16 no.5
• /
• pp.559-567
• /
• 2018

Technological innovations in sustainable materials for soil improvement have attracted considerable interest due to energy crisis and environmental concerns in recent years. This study presents results of a comprehensive investigation on utilization of nanocarbons in reinforcement of a residual soil mixed with 0, 10 and 20% bentonite. Effects of adding proportionate quantities (0, 0.05, 0.075, 0.1 and 0.2%) of carbon nanotubes and carbon nanofibers to soil samples of different plasticities were evaluated. The investigation revealed that the inclusion of nanocarbons into the soil samples significantly improved unconfined compressive strength, Young's modulus and indirect tensile strength. It was observed that carbon nanofibers showed better performance as compared to carbon nanotubes. The nanosized diameter and high aspect ratio of nanocarbons make it possible to distribute the reinforcing materials on a much smaller scale and bridge the inter-particles voids. As a result, a better 'soil-reinforcing material' interaction is achieved and desired properties of the soil are improved at nanolevel.

• Geomechanics and Engineering
• /
• v.28 no.3
• /
• pp.239-253
• /
• 2022

Suitable techniques to stabilize organic soil and improve its engineering behaviour are in demand. Despite various alternatives, nano-additives proved to be an effective stabilizer owing to their strength enhancing properties. The study focuses on using nano-silica as a potential stabilizer to improve organic silt. Soil was treated with four dosages of nano-silica namely 0.2%, 0.4%, 0.6% and 0.8% of dry weight of the soil. Nano-silica treated soil showed a strength increase of nearly 25% at a dosage of 0.4% after curing for two hours. Strength of the treated soil improved with age. Strength improved by nearly 62.9% after 28 days of curing and 221.4% after 180 days of curing due to formation of Calcium - Silicate - Hydrate (CSH) gel in the soil matrix. Dosage of 0.6% nano-silica is observed to be the optimum dosage. Coefficient of permeability and compression index showed an increase by 13.32 and 5.5 times respectively owing to aggregation of particles and creation of void spaces as visualized from the scanning electron micrographs. Further model foundation study and numerical parametric studies using PLAXIS 2D indicate that optimized and economic results can be obtained by varying the additive dosage with depth.

• Geomechanics and Engineering
• /
• v.28 no.4
• /
• pp.385-396
• /
• 2022

The accurate determination of the subgrade reaction modulus (K_s) of soil is an important factor for geotechnical engineers. This study estimated the K_s of soft soil improved with floating deep cement mixing (DCM) columns. A novel prediction model was developed that emphasizes the accuracy of identifying the most significant parameters of K_s. Several multi-layer perceptron (MLP) models that were trained using the Levenberg Marquardt (LM) backpropagation method were developed to estimate K_s. The models were trained using a reliable database containing the results of 36 physical modelling tests. The input parameters were the undrained shear strength of the DCM columns, undrained shear strength of soft soil, area improvement ratio and length-to-diameter ratio of the DCM columns. Grey wolf optimization (GWO) was coupled with the MLPs to improve the performance indices of the MLPs. Sensitivity tests were carried out to determine the importance of the input parameters for prediction of K_s. The results showed that both the MLP-LM and MLP-GWO methods showed high ability to predict K_s. However, it was shown that MLP-GWO (R = 0.9917, MSE = 0.28 (MN/m²/m)) performed better than MLP-LM (R =0.9126, MSE =6.1916 (MN/m²/m)). This proves the greater reliability of the proposed hybrid model of MLP-GWO in approximating the subgrade reaction modulus of soft soil improved with floating DCM columns. The results revealed that the undrained shear strength of the soil was the most effective factor for estimation of K_s.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.7
• /
• pp.99-104
• /
• 2007

The deep soil mixing, on ground modification technique, has been used for many diverse applications including building and bridge foundations, port and harbor foundations, retaining structures, liquefaction mitigation, temporary support of excavation and water control. This method has the basic objective of finding the most efficient and economical method for mixing cement with soil to secure settlements through improvement of stability on soft ground. In this research, the experiments were conducted on a laboratory scale with the various test conditions of mixing method; the angle of mixing wing, mixing speed. Strength and shapes of improved soil of these test conditions of deep mixing method were analysed. From the study, it was found that the mixing conditions affect remarkably to the strength and shapes of improved soils.

• Korean Journal of Organic Agriculture
• /
• v.25 no.1
• /
• pp.125-134
• /
• 2017

This study was carried out to examine the effects of soil sulfur mixture on the control apple valsa canker in apple orchard for two years. In organic apple orchard, The recovery percentages of apple valsa canker were compared among control (no treatment), lime sulfur, and soil sulfur in organic orchards. In conventional apple orchards, those of recovery percentages were compared among control, neoasozin, lime sulfur, and soil sulfur. Compared with control, soil sulfur treatments significantly improved the recovery percentages of apple valsa canker infected trees in organic orchard. However, there were no differences between lime sulfur and soil sulfur treatment in organic apple orchard, except BongHyun orchard experiment in 2013. Compared with control fruit qualities, fruit skin red color and fruit firmness were improved in lime sulfur and soil sulfur treatment, respectively. In conventional orchard, apple trees treated with lime sulfur, soil sulfur or neoasozin improved recovery percentages, compared with those of control trees. Soil sulfur treatments recovered 87.5~97.5% of infected 'Fuji'/MM106 apple trees in organic and conventional apple orchards. The trees applied with neoasozin showed significant lower shoot growth than those of soil sulfur treatment in conventional orchard. Soli sulfur treatment improved fruit red color, but did not affected fruit weight, fruit firmness, soluble solids concentrations, and titratable acidity.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2005.03a
• /
• pp.998-1004
• /
• 2005

U.J.S.(Ultra Jetting System) is a new ground improvement method registered as a Utility Model No.0205798, which has fundamentally improved the existing jetting method of J.S.P.(Jumbo Special Pattern System). In this study, the uniaxial compressive strengths of improved soil-grout structures by U.J.S. and J.S.P. which have been conducted on the construction site are compared. Also, the differences between the U.J.S. and J.S.P. are analyzed by considering the role of the auger bit, the injection distance measured from the axis of boring tubes, and angle of injection measured from the horizontal. The specimens of soil-grout structures are taken from the improved soils by using the U.J.S. and J.S.P. The uniaxial tests for the samples are conducted after the curing period of 28 days. The uniaxial compressive strengths and the coefficients of elasticity of surface and distance from the axis of boring. This study shows that the mean strength of the improved structure by J.S.P. is 1.9 times greater than by J.S.P.

• Geomechanics and Engineering
• /
• v.19 no.2
• /
• pp.179-191
• /
• 2019

Based on the effective stress principle, a new formula for shear strength of unsaturated soil is derived under the general nonlinear Mohr-Coulomb (M-C) strength criterion to improve the classical strength criterion of unsaturated soil. Meanwhile, the simple irrigation model under steady seepage is adopted to obtain the distribution of the matrix suction or the degree of saturation (DOS) above the groundwater table in the slope. Then, combined with the improved strength criterion of unsaturated soil and the simple irrigation model under steady seepage, the limit equilibrium (LE) solutions for the unsaturated slope stability are established according to the global LE conditions of the entire sliding body with assumption of the stresses on the slip surface. Compared to the classical strength criterion of unsaturated soil, not only the cohesion soil but also the internal friction angle is affected by the matric suction or the DOS in the improved strength criterion. Moreover, the internal friction angle related to the matric suction has the nonlinear characteristics, particularly for a small of the matric suction. Thereafter, the feasibility of the present method is verified by comparison and analysis on some slope examples. Furthermore, stability charts are also drawn to quickly analyze the unsaturated slope stability.

• Agricultural and Biosystems Engineering
• /
• v.4 no.1
• /
• pp.28-33
• /
• 2003

Achievements in the real-time soil spectro-photometer are: an improved soil penetrator to ensure a uniform soil surface under high speed conditions, real-time collecting of underground soil reflectance, getting underground soil color images, use of a RTK-GPS, and all units are arranged for compactness. With the soil spectrophotometer, field experiments were conducted in a 0.5 ha paddy field. With the original reflectance, averaging and multiple scatter correction, Kubelka-Munk (KM) transformation as soil absorption, its 1st and 2nd derivatives were calculated. When the spectra was highly correlated with the soil parameters, stepwise regression analysis was conducted. Results include the best prediction models for moisture, soil organic matter (SOM), nitrate nitrogen (NO$_3$-N), pH and electric conductivity (EC), and soil maps obtained by block kriging analysis.

• Journal of Soil and Groundwater Environment
• /
• v.23 no.3
• /
• pp.10-26
• /
• 2018

This paper reviews the soil conservation policies (SCP) in the global community and suggests the improved options in SCP in Korea. Soil Environment Conservation Act in Korea states soil is a valuable natural resource and it's value should be enhanced to provide the benefits that soil ecosystem can offer to people. However, SCP in Korea limits its application to not only the scope of soil environment but also the issues on soil pollution. The SCPs in the advanced countries have shifted their scopes from soil environment to soil ecosystem, put emphasis on the conservation of soil health rather than soil quality, and set the goals to optimize the soil ecosystem services to people while minimizing the soil threats. In this context, the soil security initiative was recently proposed to accomplish this goal while employing the nexus concept to bridge the soil ecosystem services with water, atmosphere, climate and biodiversity. Therefore, the key policies in soil conservation in Korea should expand the scope from soil environment to soil ecosystem, focus on soil health management, and develop the holistic governance among diverse stakeholder to maximize the soil ecosystem services. Soil ecosystem should be secured by national soil policies for human health.

• Agricultural and Biosystems Engineering
• /
• v.4 no.2
• /
• pp.45-49
• /
• 2003

Achievements in the real-time soil spectro-photometer are: an improved soil penetrator to ensure a uniform soil surface under high speed conditions, real-time collecting of underground soil reflectance, getting underground soil color images, use of a RTK-GPS, and all units are arranged for compactness. With the soil spectrophotometer, field experiments were conducted in a 0.5 ha paddy field. With the original reflectance, averaging and multiple scatter correction, Kubelka-Munk (KM) transformation as soil absorption, its 1st and 2nd derivatives were calculated. When the spectra was highly correlated with the soil parameters, stepwise regression analysis was conducted. Results include the best prediction models for moisture, soil organic matter (SOM), nitrate nitrogen ($NO_3-N$), pH and electric conductivity (EC), and soil maps obtained by block kriging analysis.