• Geomechanics and Engineering
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• v.14 no.3
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• pp.283-291
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• 2018

Cracks in soil provide significant preferential pathways for contaminant transport and rainfall infiltration. Water exchange between the soil matrix and crack is crucial to characterize the preferential flow, which is often quantitatively described by a water exchange ratio. The water exchange ratio is defined as the amount of water flowing from the crack into the clay matrix per unit time. Most of the previous studies on the water exchange ratio mainly focused on cracked sandy soils. The water exchange between cracks and clay matrix were rarely studied mainly due to two reasons: (1) Cracks open upon drying and close upon wetting. The deformable cracks lead to a dynamic change in the water exchange ratio. (2) The aperture of desiccation crack in clay is narrow (generally 0.5 mm to 5 mm) which is difficult to model in experiments. This study will investigate the water exchange between a deformable crack and the clay matrix using a newly developed experimental apparatus. An artificial crack with small aperture was first fabricated in clay without disturbing the clay matrix. Water content sensors and suction sensors were instrumented at different places of the cracked clay to monitor the water content and suction changes. Results showed that the water exchange ratio was relatively large at the initial stage and decreased with the increasing water content in clay matrix. The water exchange ratio increased with increasing crack apertures and approached the largest value when the clay was compacted at the water content to the optimal water content. The effective hydraulic conductivity of the crack-clay matrix interface was about one order of magnitude larger than that of saturated soil matrix.

• Journal of the Korean Geotechnical Society
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• v.25 no.1
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• pp.65-76
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• 2009

The unsaturated characteristics of Korean weathered granite soils have been studied to investigate the influence of saturated permeability, rainfall intensity and soil-water characteristic curve (SWCC) on the slope stability. The upper, average and lower SWCCs were estimated from the publication and experimental results using the statistical concept. The roughly estimated SWCC can be used for the soils without experimental results by relating SWCC with the particle size distribution curve. An appropriate ratio between the saturated permeability and the rainfall intensity ($k_s$/i) was also suggested for practical use in designing the slopes by investigating the time-dependent variation of slope instability during the rainfall. The slope stability was deteriorated from the initiation of rainfall and recovered again after the factor of safety reached the critical value. The FS of the slope decreased at first and then increased after reaching the critical value during the rainfall. As a result, the slope instability was not related with an absolute rainfall intensity but with the ratio between the saturated permeability and the rainfall intensity. In case of the upper SWCC, the critical condition occurred when the ratio between the saturated permeability and the rainfall intensity was in the range of $1.0{\sim}2.0$.

• Journal of the Korean Society of Groundwater Environment
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• v.5 no.2
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• pp.57-65
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• 1998

Recently, many researchers have studied on the estimation of groundwater storage and its usable amount in Korea. Those studies were, however, mostly on the groundwater recharge amount over the nation or for the large extent of areas. On the other hand, it has been also needed to study on the regional recharge rate for the planning of groundwater management or for the assessment of groundwater development impacts. In this paper, two practical methods for the estimation of regional groundwater recharge have been studied and proposed, which are $\circled1$ the estimation of the groundwater recharge due to the SCS-CN infiltration method, and $\circled2$ the estimation of groundwater recharge ratio by analyzing groundwater level hydrographs.

• Journal of The Korean Society of Agricultural Engineers
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• v.50 no.1
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• pp.13-21
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• 2008

Water losses in irrigation canals are mainly estimated as the sum of conveyance and delivery water loss. The losses occur via the evaporation, infiltration, gate operation and water distribution processing. Recently, the study regarding these water losses are not satisfactory enough, also delivery water loss has not been mainly considered on field design. The objective of this study is to investigate and analyze the volume of water loss in irrigation canals considering condition of actual farm land. A field measurement was performed at four research sites, which are managed by Korea Rural Community & Agriculture Corporation, to evaluate conveyance and delivery water loss for 2 years. The measurement was performed by canal type, size and designed flow using the inflow-outflow method at a major points such as start and end of each canal, derivation point of canal and inlet of paddy fields. Results of this study showed that water loss ratio in lateral canals was bigger than that of main canal unlike current design standard and the loss decrease as flow increase. The total of water loss ratio including conveyance and delivery water loss in several irrigation canals ranged between 33.25 and 45.0%.

• Journal of the korean academy of Pediatric Dentistry
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• v.31 no.1
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• pp.26-33
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• 2004

Self-etching priming bonding system was recently developed in order to simplify the clinical skills & save chair time after continuous improvements on dentin bonding agents. To test the magnitude of microleakage of a new "self-etching priming bonding agent" using sound premolar 4th, 5th, 6th generation dentin bonding agent was applied. Measure the magnitude of infiltration to the gap of enamel-restoration interface and dentin-restoration interface. After bonding of composite resin to sample surfaces according to the manufactures direction and 500 times thermocycling on dwell time 30 second, and microleakage was measured by the ratio of the depth to the axial wall and the magnitude of infiltration. Afterward analyzed by ANOVA test. The result were as follows ; 1. Enamel groups showed lesser microleakage (Group I, II, III, IV) than dentin groups(Group V, VI, VII, VIII). (p<0.05) 2. There are no statical differences among the dentin groups, in enamel groups, group IV showed more microleakage than group I, II, III. (p<0.05). For a clinical acceptance, better enamel marginal adaptation is required.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.260-260
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• 2017

This study aims to compare the performance of TRIGRS (Transient Rainfall Infiltration and Grid-based Regional Slope-stability model) and TiVaSS (Time-variant Slope Stability model) in the prediction of rainfall-induced shallow landslides. TRIGRS employs one-dimensional (1-D) subsurface flow to simulate the infiltration rate, whereas a three-dimensional (3-D) model is utilized in TiVaSS. The former has been widely used in landslide modeling, while the latter was developed only recently. Both programs are used for the spatiotemporal prediction of shallow landslides caused by rainfall. The present study uses the July 2011 landslide event that occurred in Mt. Umyeon, Seoul, Korea, for validation. The performance of the two programs is evaluated by comparison with data of the actual landslides in both location and timing by using a landslide ratio for each factor of safety class ( index), which was developed for addressing point-like landslide locations. In addition, the influence of surface flow on landslide initiation is assessed. The results show that the shallow landslides predicted by the two models have characteristics that are highly consistent with those of the observed sliding sites, although the performance of TiVaSS is slightly better. Overland flow affects the buildup of the pressure head and reduces the slope stability, although this influence was not significant in this case. A slight increase in the predicted unstable area from 19.30% to 19.93% was recorded when the overland flow was considered. It is concluded that both models are suitable for application in the study area. However, although it is a well-established model requiring less input data and shorter run times, TRIGRS produces less accurate results.

• Journal of Korean Society on Water Environment
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• v.34 no.6
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• pp.569-578
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• 2018

To minimize the negative alterations in hydrologic and water quality environment in urban areas due to urbanization, Low Impact Development (LID) techniques are actively applied. In Korea, LID facilities are classified as Non-point Pollution Reduction Facilities (NPRFs), and therefore they are evaluated using the performance evaluation method for NPRFs. However, while LID facilities are generally installed in small, distributed configuration and mainly work with the infiltration process, the existing NPRFs are installed on a large scale and mainly work with the reservoir process. Therefore, some limitations are expected in assessing both facilities using the same method as they differ in properties. To solve these problems, in this study, a new method for performance evaluation was proposed with focus on bio-retention LID facilities. EPA SWMM was used to reproduce the hydrologic and water quality phenomena in study area, and SWMM-LID module used to simulate TP interception performance by installing a bio-retention cell under various conditions through long-term simulations. Finally, an empirical formula for Load Capture Ratio (LCR) was derived based on storm water interception ratio in the same form as the existing method. Using the existing formula in estimating the LCR is likely to overestimate the performance of interception for non-point pollutants in the extremely low design capacity, and also underestimate it in the moderate and high design capacity.

• Journal of the Korean Ceramic Society
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• v.31 no.8
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• pp.849-860
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• 1994

The microstructural evolution and crystalline phases of this infiltration of Ti+Al liquids in TiC, SiC, TiC+C, and SiC+C preforms have been investigated. As the Ti and Al mixing ratio in Ti+Al infiltrated liquid changes, the newly formed reaction products, which were reacted from the Ti+Al liquid with preforms, consisted of three major phases as Ti3AlC, Al2Ti4C2 or Al4C3. The TiC grain shape was changed to spheroid, when Ti3AlC was formed. In case of Al2Ti4C2 formation, the platelet grain was formed from the original TiC grain. When Al4C3 was formed, nodular or intergranular fine-grained Al4C3 was formed around the TiC grain, while the original TiC grain shape was not changed.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 1998.10a
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• pp.1-7
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• 1998

To investigate the water balance in a paddy rice field with the pumping station for irrigation water supply, flow measurements and analysis on various components of water balance were carried out. The investigated area is 103.7 ha, and the irrigation water was supplied for 102 days during the total irrigation period starting from June 1. It was found that the consumption rate was increased as the growing stage was progressed. The variation of evapotranspiration rate was shown same tendency as the consumption rate, while no apparent tendency was found in infiltration rate upon different growing stages. And the ground water input to the area was predominant during the early stage of growing period, while ground water output from the study area was predominant at the end of the growing stage. The range of return flow rate, the ratio of total outflow to total inflow in every decad, was 57.6 to 85.7%. These values are slightly higher than reported values from the other investigation projects.

• Journal of The Korean Society of Agricultural Engineers
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• v.46 no.5
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• pp.3-11
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• 2004

The objective of this study is to develop water saving irrigation method using water balance model in order to save rural water. Daily water balance components such as irrigation water, drainage water, effective rainfall, ET, and infiltration were measured in paddy fields. Model simulations were performed for different outlet heights and ponding depths. The outlet heights and the ponding depths are 2 cm, 4 cm, 6 cm, 8 cm, and 10 cm, respectively. Based on the simulation very shallow ponding depth of 2 cm with 10 cm outlet height showed the largest effective rainfall ratio and the smallest irrigation amount. Until the introduction of laser leveling dozer and automatic inlet control devices, it would be desirable to adopt 4cm ponding depth because of difficulty of land leveling and frequency of farmer's field visit. The results of this study will be applied in the paddy farming and can improve water use efficiency.