• 조명전기설비학회논문지
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• 제25권6호
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• pp.108-114
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• 2011

In order to mitigate the possible hazards from electric shock due to the touch and step voltages, the high resistivity material such as gravel is often spread on the earth's surface in substations. When the grounding electrode is installed in two-layer soil structures, the surface layer soil resistivity is different with the resistivity of the soil contacted with the grounding electrodes. The design of large-sized grounding systems is fundamentally based on assuring safety from dangerous voltages within a grounding grid area. The performance of the grounding system is evaluated by tolerable touch and step voltages. Since the floor surface conditions near equipment to be grounded are changed after a grounding system has been constructed, it may be difficult to determine the tolerable touch and step voltage criteria. In this paper, to propose an accurate and convenient method for evaluating the protective performance of grounding systems, the propriety of the method for evaluating the current flowing through the human body around on a counterpoise buried in two-layer soils is presented. As a result, it is reasonable that the grounding system performance would be evaluated by measuring and analyzing the current flowing through the human body based on dangerous voltages such as the touch or step voltages and the contact resistance between the ground surface and feet.

• Geomechanics and Engineering
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• 제23권6호
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• pp.547-560
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• 2020

This paper studies the dynamic foundation-soil-foundation interaction for two square rigid foundations embedded in a viscoelastic soil layer. The vibrations come from only one rigid foundation placed in the soil layer and subjected to harmonic loads of translation, rocking, and torsion. The required dynamic response of rigid surface foundations constitutes the solution of the wave equations obtained by taking account of the conditions of interaction. The solution is formulated using the frequency domain Boundary Element Method (BEM) in conjunction with the Kausel-Peek Green's function for a layered stratum, with the aid of the Thin Layer Method (TLM), to study the dynamic interaction between adjacent foundations. This approach allows the establishment of a mathematical model that enables us to determine the dynamic displacements amplitude of adjacent foundations according to their different separations, the depth of the substratum, foundations masss, foundations embedded, and the frequencies of excitation. This paper attempts to introduce an approach based on a polynomial mathematical tool conducted from several results of numerical methods (BEM-TLM) so that practicing civil engineers can evaluation the dynamic foundations displacements more easy.

• 한국토양비료학회지
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• 제46권6호
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• pp.487-493
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• 2013

The effects of long-term fertilization on soil biological properties and microbial community structure in the plough layer in a rice paddy soil in southern Korea were investigated in relation to the continuous application of chemical fertilizers (NPK), straw based compost (Compost), combination these two (NPK + Compost) for last 40 years. No fertilization plot (Control) was installed for comparison. Though fertilization significantly improved rice productivity over control, the long-term fertilization of NPK and compost combination was more effective on increasing rice productivity and soil nutrient status than single application of compost or chemical fertilizer. All fertilization treatments had shown significant improvement in soil microbial properties, however, continuous compost fertilization markedly increased soil enzyme and microbial activities as compared to sole chemical fertilization. Results of microbial community structure, evaluated by EL-FAME (ester-linked fatty acid methyl esters) method, revealed big difference among Control, NPK, and Compost. However, both Compost and Compost+NPK treatments belonged to the same cluster after statistical analysis. The combined application of chemical fertilizer and organic amendments could be more rational strategy to improve soil nutrient status and promote soil microbial communities than the single chemical fertilizer or compost application.

• 한국환경복원기술학회지
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• 제7권3호
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• pp.35-47
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• 2004

In order to study changes in vegetation pursuant to rooftop revegetation plantation methods, plantation methods for rooftop revegetation were divided into two types through an analysis of recent trends. Then, Planted plants and invasive plants on sites where the planting methods were introduced were monitored. Planting methods were divided into mono-layer meadow cover type and multi-layer planting cover type. They showed some differences in terms of the availability of wetland, the structure of vegetation layers, the planted species, and the material of mulching. According to the results of monitoring the two sample sites for different plantation methods, the number of invasive plants was higher in multi-layer planting cover type and the ratio of naturalized plants was higher by 30% in average in mono-layer meadow cover type. The main reason for such a result is that the natural soil used in the multi-layer planting cover type likely contained some seeds. Moreover, it's harder for invasive plant seeds to germinate in volcanic rocks than in natural soil. Also, it is attributable to wetlands available in multi-layer planting cover type and diverse living environments created by multi-layer planting. The reason of the ratio of naturalized plants being higher by at least 10% in mono-layer meadow cover type is the character of naturalized plants being stronger in unfavorable conditions than nature plants are. Accordingly, the germination rate in the volcanic rock mulching has likely contributed in raising the introduction and germination of naturalized plants. The results showed that multi-layer planting cover type using wetland creation and nature soil can increase the number of invasive plants and lower the ratio of naturalized plants. However, since seeds contained in the natural soil can affect the growth of planted plants, this needs to be clarified, It was judged that mono-layer meadow cover type may affect more greatly on the germination and growth of invasive plants than on those of planted plants, Its potential adoption in highly urbanized areas was examined. By complementing with the mutual benefits of each plantation method, it appeared possible to shift to a rooftop revegetation system suitable to the site.

• 조명전기설비학회논문지
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• 제26권3호
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• pp.53-60
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• 2012

The fall-of-potential method is commonly used in measuring the ground resistance of large-scaled grounding system and the current and potential auxiliary electrodes are horizontally arranged. Because the distances between the ground grid to be tested and auxiliary electrodes are limited in downtown areas, it is very difficult to measure accurately the ground resistance of large-scaled grounding system. In this paper, the fall-of-potential method of measuring the ground resistance with the vertically-placed current and potential auxiliary electrodes was examined and discussed. The validity and good accuracy of the proposed method of measuring the ground resistance were confirmed through various simulations and actual tests carried out in uniform and two-layer soil structures.

• Structural Engineering and Mechanics
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• 제44권5호
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• pp.571-584
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• 2012

Appropriate assessment of lateral capacity of pile foundation is known to be a complex problem involving soil-structure interaction. Having reviewed the available methods in brief, relative paucity of simple and rational technique to evaluate lateral capacity of pile in layered soil is identified. In this context, two efficient approaches for the assessment of lateral capacity of short pile embedded in bi-layer cohesive deposit is developed. It is presumed that the allowable lateral capacity of short pile is generally dictated by the permissible lateral displacement within which pile-soil system may be assumed to be elastic. The applicability of the scheme, depicted through illustration, is believed to be of ample help at least for practical purpose.

• Structural Engineering and Mechanics
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• 제77권1호
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• pp.37-46
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• 2021

In this study, a method for free vibration analysis of wall-frame systems built on weak soil is proposed. In the development of the method, the wall-frame system that constitutes the superstructure was modeled as flexural-shear beam. In the study, it is accepted that the soil layers are isotropic, homogeneous and elastic, and the waves are only vertical propagating shear waves. Based on this assumption, the soil layer below is modeled as an equivalent shear beam. Then the differential equation system that represented the behavior of the whole system was written for both regions in a separate way. Natural periods were obtained by solving the differential equations by employing boundary conditions. At the end of the study, two examples were solved and the suitability of the proposed method to the Finite Element Method was evaluated.

• Geomechanics and Engineering
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• 제34권6호
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• pp.665-681
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• 2023

Liquefaction is one of the most devastating geotechnical phenomena that severely damage vital structures and lifelines. Before constructing structures on problematic ground, it is necessary to improve the site and solve the geotechnical problem. Among ground improvement methods dealing with liquefaction, gravel drain (GD) columns and deep soil mixing (DSM) columns are popular. In this study, the results of a series of seismic experiments in a 1g environment on a structure located over liquefiable ground with different thicknesses reinforced with GD and DSM techniques were presented. The dynamic response of the reinforced ground system was investigated based on the parameters of subsidence rate, excess pore water pressure ratio, and maximum acceleration. The time history of the input acceleration was applied harmonically with an acceleration range of 0.2g and at frequencies of 1, 2, and 3 Hz. The results show that the thickness of the liquefiable layer and the frequency of the input motion have a significant impact on the effectiveness of the improvement method and all responses. Among the two techniques used, DSM in thick liquefied layers was much more efficient than GD in controlling the subsidence and rupture of the soil under the foundation. Maximum settlement values, settlement rate, and foundation rotation in the thicker liquefied layer at the 1-Hz input frequency were higher than at other frequencies. At low thicknesses, the dynamic behavior of the GD was closer to that of the DSM.

• Advances in Computational Design
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• 제3권2호
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• pp.201-212
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• 2018

Decrease in availability of suitable subbase and base course materials for highway construction leads to a search for economic method of converting locally available troublesome soil to suitable one for highway construction. Present study insights on evaluation of benefits of stabilization of subgrade soils in term of extension in service life (TBR) and layer thickness reduction (LTR). Laboratory investigation consisting of Atterberg limit, Compaction, California Bearing Ratio, unconfined compressive strength and triaxial shear strength tests were carried out on two types of soil for varying percentages of stabilizers. Vertical compressive strains at the top of unstabilized and stabilized subgrade soils were found out by elastoplastic finite element analysis using commercial software ANSYS. The values of vertical compressive strains at the top of unstabilized and stabilized subgrade, were further used to estimate layer thickness reduction or extension in service life of the pavement due to stabilization. Finite element modeling of the flexible pavement layered structure provides modern technology and sophisticated characterization of materials that can be accommodated in the analysis and enhances the reliability for the prediction of pavement response for improved design methodology. If the pavement section is kept same for unstabilized and stabilized subgrade soils, pavement resting on lime, fly ash and fiber stabilized subgrade soil B will have service life 2.84, 1.84 and 1.67 times than that of unstabilized pavement respectively. The flexible pavement resting on stabilized subgrade is beneficial in reducing the construction material. Actual savings would depend on the option exercised by the designer for reducing the thickness of an individual layer.

• Proceedings of the National Institute of Ecology of the Republic of Korea
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• 제4권2호
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• pp.86-94
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• 2023

Climate change is more rapid in the Arctic than elsewhere in the world, and increased precipitation and warming are expected cause changes in biogeochemical processes due to altered microbial communities and activities. It is crucial to investigate microbial responses to climate change to understand changes in carbon and nitrogen dynamics. We investigated the effects of increased temperature and precipitation on microbial biomass and community structure in dry tundra using two depths of soil samples (organic and mineral layers) under four treatments (control, warming, increased precipitation, and warming with increased precipitation) during the growing season (June-September) in Cambridge Bay, Canada (69°N, 105°W). A phospholipid fatty acid (PLFA) analysis method was applied to detect active microorganisms and distinguish major functional groups (e.g., fungi and bacteria) with different roles in organic matter decomposition. The soil layers featured different biomass and community structure; ratios of fungal/bacterial and gram-positive/-negative bacteria were higher in the mineral layer, possibly connected to low substrate quality. Increased temperature and precipitation had no effect in either layer, possibly due to the relatively short treatment period (seven years) or the ecosystem type. Mostly, sampling times did not affect PLFAs in the organic layer, but June mineral soil samples showed higher contents of total PLFAs and PLFA biomarkers for bacteria and fungi than those in other months. Despite the lack of response found in this investigation, long-term monitoring of these communities should be maintained because of the slow response times of vegetation and other parameters in high-Arctic ecosystems.