• Magazine of the Korean Society of Agricultural Engineers
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• v.35 no.4
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• pp.55-66
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• 1993

Upon freezing a soil swells due to phase change and its compression stress increase a lot. As the soil undergo thawing, however, it becomes a soft soil layer because the 'soil changes from a solid state to a plastic state. These changes are largely dependent on freezing temperature and repeated freezing-thawing cycle as well as the density of the soil and applied loading condition. This study was initiated to describe the effect of the freezing temperature and repeated freezing-thawing cycle on the unconfined compressive strength. Soil samples were collected at about 20 sites where soil structures were installed in Kangwon provincial area and necessary laboratory tests were conducted. The results could be used to help manage effectively the field structures and can be used as a basic data for designing and constructing new projects in the future. The results were as follows ; 1. Unconfined compressive strength decreased as the number of freezing and thawing cycle went up. But the strength increased as compression speed, water content and temperature decreased. The largest effect on the strength was observed at the first freezing and thawing cycle. 2. Compression strain went up with the increase of deformation speed, and was largely influenced by the number of the freezing-thawing cycle. 3. Secant modulus was responded sensitivefy to the material of the loading plates, increased with decrease of temperature down to - -10$^{\circ}$C, but was nearly constant below the temperature. Thixotropic ratio characteristic became large as compression strain got smaller and was significantly larger in the controlled soil than in the soil treated with freezing and thawing processes 4. Vertical compression strength of ice crystal(development direction) was 3 to 4 times larger than that of perpendicular to the crystal. The vertical compression strength was agreed well with Clausius-Clapeyrons equation when temperature were between 0 to 5C$^{\circ}$, but the strength below - 5$^{\circ}$C were different from the equation and showed a strong dependency on temperature and deformation speed. When the skew was less then 20 degrees, the vertical compression strength was gradually decreased but when the skew was higher than that, the strength became nearly constant. Almost all samples showed ductile failure. As considered above, strength reduction of the soil due to cyclic freezing-thawing prosses must be considered when trenching and cutting the soil to construct soil structures if the soil is likely subject to the processes. Especially, if a soil no freezing-thawing history, cares for the strength reduction must be given before any design or construction works begin. It is suggested that special design and construction techniques for the strength reduction be developed.

• Journal of Environmental Science International
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• v.12 no.2
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• pp.111-117
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• 2003

This paper investigates preliminarily spatial distribution soil organic matter (SOM), nitrogen (N) and phosphorus (P) and its environmental influence in wetland soil of different vegetation landscape in the Yellow River Mouth. The result shows the SOM and total nitrogen (TN), efficient N, efficient P in top layer soils of different vegetation district have significantly different content, The SOM is shown as Calamagrostis epigeios wetlands > Phragmites cmmunis wetlands > Tamarix chinensi wetlands above tidal > Suaeda salsa wetlands in high tidal > Tamarix chinensi wetlands in high tidal > tidal flats, the arrange of the TN and efficient N content is the same except that the content in Suaeda salsa wetlands in high tidal is heavier than Tamarix chinensi wetlands in high tidal. In different vegetation landscape wetland types the vertical change of soil nutrients are obvious except for p, gradually decrease from the upper to the lower. This case reflects the function of the vegetation on the wetland development of soil and proves the wetland soil has the characteristic of new born and bad degree of development. SOM, TN, efficient N and efficient P content in wetland soils have significantly positive correlation, but TP have no correlation with them but efficient p. The contents of TN in wetland soils range from 58~1480 mg/kg, total average content 408 mg/kg, average content of above 30 cm is 625 mg/kg. The range of TP content in the soil is 372~1042 mg/kg, total average is 569 mg/kg, average content of above 20 cm is 611 mg/kg. According the P it occurs mainly as calcium phosphates, and the validity is lower, therefore, N and P in the new born wetlands cannot produce serious impact on the environments at present.

• Geomechanics and Engineering
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• v.27 no.5
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• pp.497-509
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• 2021

A large deformation FEM (Finite Element Method) based numerical analysis has been performed to study the behaviour of the bell-shaped anchor embedded in undrained saturated (cohesive) soil with the help of finite element based software ABAQUS. A typical model anchor with bell-diameter of 0.125 m, embedded in undrained saturated soil with varying cohesive strength (from 5 kN/m² to 200 kN/m²) has been chosen for studying the characteristic behaviour of the bell-shaped anchor installed in cohesive soil. Breakout factors have been evaluated for each case and verified with the results of experimental model tests for three different types of soil samples. The maximum value of breakout factor was found as about 8.5 within a range of critical embedment ratio of 2.5 to 3. An explicit model has been developed to estimate the breakout factor (F_c) for uplift capacity of bell-shaped anchor within clay mass in terms of H/D ratio (embedment ratio). It was also found that, the ultimate uplift capacity of the anchor increases with the increase of the value of cohesive strength of the soil and H/D ratio. The empirical equation developed in the present investigation is usable within the range of cohesion value and H/D ratio from 5 kN/m² to 200 kN /m² and 0.5 to 3.0 respectively. The proposed model has been validated against data obtained from a series of model tests carried out in the present investigation. From the stress-profile analysis of the soil mass surrounding the anchor, occurrence of stress concentration is found to be generated at the joint of anchor shaft and bell. It was also found that the vertical and horizontal stresses surrounding the anchor diminish at about a distance of 0.3 m and 0.15 m respectively.

• Journal of the Korean Solar Energy Society
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• v.34 no.2
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• pp.66-72
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• 2014

Ground source heat pump system can achieve high efficiency of performance by utilizing annually constant underground temperature to provide heat source for space heating and cooling. Generally, the depth of constant-temperature zone under the ground depends on surface heat flux and soil properties. The deeper the ground heat exchanger is installed, the higher the heat exchange rate can be acquired. However, in order to optimally design the system, it is necessary to consider both the installation cost and the system performance. In this study, performance analysis of ground source heat pump system according to the depth has been conducted through the case study.

• Journal of the Korean Society of Groundwater Environment
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• v.5 no.2
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• pp.101-109
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• 1998

Hydraulic property of fissured aquifers often depends on geologic structure which acts main channel of groundwater flow. We treated theories of linear flow related to vertical geologic structure. Then, we analyzed the result of two pumping tests conducted in Okmyeong-ri area (Kyeongbook province) using fractal model and found hydraulic characteristic of the fissured aquifer in this area. According to the pump test analyses, groundwater flow around the holes (pumping well D9; observation wells C3 and D7) of test 1 is linear. and is controlled by vertical geologic structure with infinite length and infinitesimally small width. On the other hand, around the hole D10 (pumping well) of test 2, groundwater flow is pseudo-radial (n=1.9) or radial (n=2). Thus, the characteristic of fractured aquifer often shows variable groundwater flow spatially and temporally.

• Journal of the Korean GEO-environmental Society
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• v.10 no.6
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• pp.69-77
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• 2009

The shortage of bearing capacity and settlement, shear deformation may occur when constructing a structure such as harbor, airport and bridge on soft ground such as marine clay, silty clay, sandy soil because it is very soft. The various ground improvement methods were applied to obtain preceding settlement of soft ground and strength increase. The vertical drain method has been used to reduce the required time for consolidation of the soft ground. Especially, the PBD (Plastic Board Drain) has been widely used among in the vertical drain method. In this study, a behavior of characteristic was evaluated by operating a compound drainage capacity test about the PBD (Plastic Board Drain) method applied in soft clay in deep depth. As a result, the settlement gradually occurred with increase of surface load. The consolidation settlement was processed with dissipation of pore pressure after surface load of $500kN/m^2$. Accordingly, it was found that change of settlement through load steps was resulted from dissipation of pore pressure. It was also found that the drainage capacity of vertical drains was considerably reduced with pressure increase and time elapse.

• Journal of the Korean GEO-environmental Society
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• v.5 no.1
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• pp.65-73
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• 2004

The analysis of corrugated steel pipes is depending on a second dimension frame analysis or compressed ring model. This is the analysis not to consider the behavior of soil-structure interaction. The behavior of load resistance system is varied according to the depth of cover and the spacing of corrugated steel pipes structure. Therefore, the behavior characteristic of corrugated steel pipes was confirmed through finite element analysis to consider the activity of soil-structure interaction. If soil cover is filled up to the more of optimal depth, behavior of corrugated steel pipes are similar to those of ductile steel pipes according to the earth pressure distribution and effects of traffic loads are decreased. But, If soil cover is filled up to the less of optimal depth, corrugated steel pipes can't behave completely as ductile steel pipes because the passive earth pressure acting on side of corrugated steel pipes is decreased according to the decrement of vertical earth pressure, and the traffic loads influence on the section forces is increased, so that the traffic loads dominated the behavior of corrugated steel pipes.

• Journal of Korea Water Resources Association
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• v.44 no.5
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• pp.351-362
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• 2011

The soil moisture measurements and correlation analysis are presented to improve understanding the hydrological process at the hillslope scale. The rainfall events is a main driver of soil moisture variation, and its stochastic characteristic need to be properly treated prior to the correlation analysis between soil moisture measurements. Using field measurements for two designated periods during the late summer and autumn seasons in 2007 obtained from the Bumrunsa hillslope located at the Sulmachun watershed, prewhitened correlation analysis were performed for 8, 14, 7 and 7 relationships representing the vertical, lateral, recharge and return flows, for two designated periods, respectively. The analysis indicated both temporal and spatial variation patterns of hydrological processes, which can be explained by the relative contribution of matrix and macropore flows and the impact of transect topography, respectively.

• Journal of agriculture & life science
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• v.45 no.5
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• pp.33-39
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• 2011

This study was conducted to distribution characteristic of root diameter class between natural and planted stands of one-age class in Pinus densiflora for. eracta in Gangwon. Root development presented that 0.5-2.0 mm diameter class was large part in total root number and length but 0.5-2.0 mm diameter class have a low distribution in each stand. Below 5.0 mm diameter class between natural and planted stands observed outstanding natural stand more than planted stand, but reverse over 5.0 mm diameter class. Root development depending on soil level of vertical and horizontal was presented various natural stand more than planted stand because root distribution of planted stand was concentrated low soil level in 10 cm of soil depth and 20 cm of soil horizontal layer. We can understand that the root distribution presented different between natural and planted stand, therefore this result can used as a basic information for correct of outplanting.

• Korean Journal of Soil Science and Fertilizer
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• v.16 no.1
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• pp.1-6
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• 1983

The results of COLE(Coefficient of Linear Extensibility) measurement on various paddy soils in Korea are summarized as follows; 1. The COLE values of paddy soil in Korea varied from 0.024 to 0.094 in the surface soil while in the sub-surface soils those were ranging from 0.022 to 0.115. The poorer the relative drainage and the finer the texture caused, the greater the COLE values. 2. The matured clayey soils on fluvio-marine plains and local alluvium derived from the Tertiary materials have COLE values more than 0.09 which is demonstrated that the necessity of COLE measurement throughout profiles so that could be considered the characteristic in the characteristic of those soils. 3. The clay content has the highest positive correlation (r=0.81~0.76) values. The content of organic matter, water content at 1/3 bar, Atterberg limits, water stable aggregate etc. also have significant positive correlation with COLE values while the context of sand and silt show negative correlation. 4. Although the COLE values measured on horizontal linear bases were slightly greater than those measured on volume bases practicability was for granted. For more accurate measurement of COLE, it is reasonable to have the average values of COLE calculated from the horizontal and vertical bases.