• Korean Journal of Soil Science and Fertilizer
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• v.36 no.6
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• pp.367-375
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• 2003

The aim of this study was to investigate the soil physical properties and the traction characteristics of paddy field before tillage by a computer simulation. Soil physical properties, such as soil moisture content, bulk density, soil hardness, and soil texture were measured in the twelve rice production area. Mathematical model based on dimensional analysis which include soil physical properties and vehicle factors was used for the computer simulation. Most of the soil texture of the investigated area was silty loam, loam and silty clay loam. Soil moisture content ranged between 20 and 40% mostly. Soil bulk density was in the range of 1,500 to $1,700kg\;m^{-3}$. Soil hardness ranged between 2 to $12kg\;cm^{-2}$ mostly. Soil hardness incorporates the effects of many soil physical properties such as moisture content, texture and bulk density, and so the range of soil hardness was greater than that of any other physical properties. The predicted net traction was in the range of 70 to 1,500 kgf depending on the area, but it was above 1,000 kgf for most of the investigated area. Thus it was concluded that 50 HP tractor can pull the four row moldboard plow considering the conventional tillage depth and width. But for the soft soil area such as Andong and Namyang, tractor itself may have mobility problem and show high slip during plowing operation.

• Magazine of the Korean Society of Agricultural Engineers
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• v.22 no.3
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• pp.46-59
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• 1980

This study was conducted to obtain the most effective distribution of grain size and the optimum lime content for lime-soil stabilization. To achieve the aim, the change of consistency, the characteristics of compaction and unconfined compressive strength were tested by adding of 0, 4, 6, 8, 10 and 12 percent lime by weight for all soils adjusted by given ratios of sand to clay. The results obtained were as follows; 1. There was a tendency that the plasticity index of lime-soil mixture was decreased by increasing the amount of lime, whereas the liquid limit was varied irregularly and the plastic limit was increased. 2. With the addition of more lime, the optimum moisture content of lime-soil mixture was increased, and the maximum dry density was decreased. 3. The optimum lime content of lime-soil mixture was varied from soil to soil, and the less amount of small grain size, the less value of optimum lime content. 4. The optimum distribution of grain size for lime-soil mixture was in the soil, having the ratio of about 60 percent of cohesive clay and about 40 percent of sand by weight. 5. In the soil having fine grain size, the effect of curing appeared for long periods of time, whereas the increasing rate of unconfined compressive strength was great on the soil of coarse grain size in the earlier stage of curing period.

• Magazine of the Korean Society of Agricultural Engineers
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• v.15 no.1
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• pp.2904-2912
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• 1973

The density of soil is one of the most important of its engineering properties, and many soil-engineering operations directed toward improving the density characteristics of matecal. This report is a study on relationship between density, permiabilty and other physical properties of compacted soil in various desity grades. The results of the study can be summariged as follow: 1. The optimum moisture content of soil increses with increasing of fine particles and a relationship between both parameter is $w_0=0.1765.n$ Where, n is passing percentage from #200 sieve. 2. The porosity of soil increases with increasing of optimum water content as $e=aw_0+b$ without having relation to compaction ratio. 3. The increment of permeability of soil is high when the compaction ratio is increased and the phenomenon is conspicuous in case of course soil and non-plastic soil. 4. The permeability of soil decreases with increasing of optrimum water content and the phenomenon is conspicuous when compaction ratio decreases. And the permeability is almost constant when optimum water content is more than 25 percent, even though compaction ratio changes. 5. The permeablity of soil increanses when the amount of fine particles is very few, the permeability is almost constant as being impervious condition without having relation to compaction ratio when there in more than 90 percent of fine particles(less than #200 sieve).

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.209-212
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• 2002

Main radionuclides of the soil waste stored in Korea Atomic Energy Research Institute are Co-60 and Cs-137. Moisture content of soil is 12%, pH of soil is 5.8, and content of organic matter is 2.2 %. Radioactive concentrations of the soil particle size of which is less than 0.063mm and soil in the drum surface of which is more than radiation dose rate 0.05mR/hr are higher. Meanwhile, radioactive concentration of soil in the drum surface of which is less than radiation dose rate 0.02 mR/hr are mostly lower. On using the mixing solution of ammonium sulfate and citric acid, 62% Co was removed from soil and 41% Cs was removed. Also, on using the mixing solution of ammonium nitrate and citric acid, 61% Co was removed from soil and 39% Cs was removed, and on using the mixing solution of ammonium potassium oxalate, 36% Co was removed and only 3% Cs was removed. And on using only water, removal efficiency is less than 5%.

• Proceedings of the Korean Society of Crop Science Conference
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• 2017.06a
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• pp.315-315
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• 2017

In Japan, more than 80 % of soybean growing area is converted fields and excess water is one of the major problems in soybean production. For example, recent study (Yoshifuji et al., 2016) suggested that in the fields of shallow groundwater level (GWL) (< 1m depth), rising GWL even in a short period (e.g. 1 day) causes inhibition of soybean growth. Thus it becomes more and more important to predict GWL and soil moisture in detail. In addition to conventional surface drainage and underdrain, FOEAS (Farm Oriented Enhancing Aquatic System), which is expected to control GWL in fields adequately, has been developed recently. In this study we attempted to predict GWL and soil moisture condition at the converted field with FOEAS in Biwa lake reclamation area, Shiga prefecture, near the center of the main island of Japan. Two dimensional HYDRUS model (Simuinek et al., 1999) based on common Richards' equation, was used for the calculation of soil water movement. The calculation domain was considered to be 10 and 5 meter in horizontal and vertical direction, respectively, with two layers, i.e. 20cm-thick of plowed layer and underlying subsoil layer. The center of main underdrain (10 cm in diameter) was assumed to be 5 meter from the both ends of the domain and 10-60cm depth from the surface in accordance with the field experiment. The hydraulic parameters of the soil was estimated with the digital soil map in "Soil information web viewer" and Agricultural soil-profile physical properties database, Japan (SolphyJ) (Kato and Nishimura, 2016). Hourly rainfall depth and daily potential evapo-transpiration rate data were given as the upper boundary condition (B.C.). For the bottom B.C., constant upward flux, which meant the inflow flux to the field from outside, was given. Seepage face condition was employed for the surrounding of the underdrain. Initial condition was employed as GWL=60cm. Then we compared the simulated and observed results of volumetric water content at depth of 15cm and GWL. While the model described the variation of GWL well, it tended to overestimate the soil moisture through the growing period. Judging from the field condition, and observed data of soil moisture and GWL, consideration of soil structure (e.g. cracks and clods) in determination of soil hydraulic parameters at the plowed layer may improve the simulation results of soil moisture.

• Korean Journal of Soil Science and Fertilizer
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• v.46 no.5
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• pp.333-342
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• 2013

Soil compaction is affected by soil texture, organic matter (OM), strength (ST) and soil moisture, which is difficult to understand the degree and effects of related factors. The purpose of the study is to assess the impact of them on the compaction with bulk density (BD). The analysis was conducted with data collected from national-wide monitoring sites including 105 upland soils, 246 orchard soils, and 408 paddy soils between 2009 and 2012. The distributions of soil physical properties were measured. The correlation and multi linear regression analysis were performed between soil physical properties using SAS. The regression equation of BD(y) includes ST, gravitational water contents (GWC), and OM as variables commonly, having additional factors, clay content and sand content in paddy soil and upland soil for only subsoil (p<0.001). Our results show that the BD could be explained about 40~50% by various physical properties. The regression was mainly determined by ST in orchard and upland soil and by the GWC in paddy soil. To mitigate soil compaction, it is important to maintain the proper level of OM in upland soil and to consider the moisture condition with soil texture in paddy soil when making work plan. Furthermore, it would be recommended the management criteria classified by soil texture for the paddy soils.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.2
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• pp.173-180
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• 2014

The development process of a L-Band microwave radiometer for remote sensing of soil-moisture are described in this paper. Achieving the development aim of the measurement accuracy within 2% for soil moisture content of 0~50%, the requirements and specifications of the microwave radiometer and its receiver are drawn. The receiver with high gain, high sensitivity is designed and implemented to satisfy these requirements and specifications. The receiver has the bandwidth of 40 MHz, the system gain of 50 dB and the sensitivity of average value 0.19 K, maximum value 0.313K at 1390 MHz.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1997.05a
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• pp.47-52
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• 1997

The experimental investigations considered in this paper are similar in many respects to those of Lee$^1$, with some key differences. First, there is no layering of the soils in a heterogeneous liner. The only soil investigated is the clay component of the cover liner. This ensures that the clay is exposed to freezing and that frost propagation in the clay can be investigated separate from other processes. Second, a closed system approach to the simulation was adopted. According to Jones$^2$, closed-system freezing occurs when there is no source of water available beyond that originally present in the soil voids. Freezing under such conditions results in very thin or non-existent ice lenses. One of tile objectives of the experiments described in this paper was the moisture migration and the changing of moisture contents of the compacted clay liner in landfill. The closed-system was used to limit tile variables in the experimental simulation to make these calculations more direct, although the final results could be applied to an open system also. As a result, the moisture content decreased about 45%-46% after two freeze/thaw cycles.

• Magazine of the Korean Society of Agricultural Engineers
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• v.20 no.1
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• pp.4575-4591
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• 1978

In order to investigate the effects of grain size distribution, cement content, and molding pressure on the strength and durability of soil-cement mixtures, a laboratory test of soil cement mixtures was performed at four levels of cement content, five levels of molding pressure, and four levels of normal curing periods. The results are summarized as follows: 1. Optimum moisture contents in loam soil and maximum dry density in sand soil increased with the increase of cement content, but in others, both optimum moisture contents and maximum dry density were changed ununiformly. 2. When the specimens were molded with molding pressure, 50kg/$\textrm{cm}^2$, strength of soil cement mixture with cement content, 2 and 4 per cent, was lower than the strength of soil cement mixture without cement content by more than 40 to 50 per cent. 3. The strength of soil-cement molded with molding pressure, 100kg/$\textrm{cm}^2$, was higher than the strength of soil-cement molded with M.D.D. obtained from standard compaction test more than 40 per cent in sand loam cement and 50 per cent in loamy cement. 4. There was highly significant positive correlation among molding pressure, cement content and unconfined compressive strentgh and so the following multiple regression equations were obtained. Loam: fc=1.9693C+0.197P-0.84 Sandy loam: fc=2.9065C+0.235P-0.77 5. When the specimens were molded with molding pressure, 20 to 100kg/$\textrm{cm}^2$, the regression equation between the 28-day and 7-day strenght was obtained as follows. Loam : q28=1.1050q7+7.59(r=0.9147) Sandy loam : q28=1.3905q7+3.17 (r=0.9801) 6. At the cement contents of above 50 per cent, the weight losses by freeeze-thaw test were negligible. At the cement content of below 8 per cent the weight losses were singnificantly high under low molding pressure and remarkably decreased with the increase of molding pressure up to 80kg/$\textrm{cm}^2$. 7. Resistance to damage from water and to absorption of water were not improved by molding pressure alone, but when the soil was mixtured with cement above 6 per cent, damage seldoms occurred and absorbed less than 5 per cent of water. 8. There was highly significant inverse-corelationship between the compressive strength of soil cement mixtures and their freeze-thaw loss as well as water absorption. By the regression equation methods, the relationships between them were expessed as followed fc=-7.3206Wa+115.6(r=0.9871) log fc=-0.0174L+1.59(r=0.7709) where fc=unconfined compressive stregth after 28-days curing. kg/$\textrm{cm}^2$ Wa=water absorption, % L : freeze-thaw loss rate, %

• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.2
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• pp.3778-3783
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• 1975

The objective of this study is to determine an appropriate cement of soil-cement in which silty soil of salty tidal flat with low plasticity was used. Physical, chemical and mechanical tests were conducted to find out the standard properties of the soil to be used. Various cement contents used in this test were 8%, 10%, 12%, and 14%, and the compressive strength was tested after 7 days and 28 days of standard curing in the above each cement content respectively. The results obtaind are summarized as follows. 1. As the cement content was increased from 8% to 14%, Maximum dry density (M.D.D.) and optimum moisture content (O.M.C.) were not changed remarkably. 2. Density of soil-cement was directly proportional to cement content and inversely proportional to water content. 3. OMC was generally decreased in proportion to the increase of cement content. 4. Compressive stranth was directly proportional to centent and inversely proportional to water content. 5. In freezing and thawing test, maximum loss of 10% in the total Weight was found on the 8% cement mixture. and This loss was rapidly decreased to 2% when the Cement content of the mixture was more than 10%.