• Water for future
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• v.28 no.4
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• pp.215-222
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• 1995

The water retention function which has the hysteresis phenomena is required to analyze the Richards equation which is a governing equation of the unsaturated flow, and its hysteresis phenomena has influence upon the characteristics of the unsaturated flow. The accuracy of the published hysteresis models is compared by using experimental data of the water retention function. The apparatus to experiment the hysteresis phenomena on the soil is developed, and experimental data for the main wetting process and the main drying process of the water retention function are obtained. The parameters of the van Genuchten equation are calibrated by using experimentally obtained data. As a result of the comparison of the selected hysteresis models which simulate the main drying curve from the main wetting curve, the Model I-1(Mualem) overestimates and the Model II-1(Mualem) underestimates but the Model III-2(Park and Sonu) similarly estimates the experimental data of the main drying curve.

• Textile Coloration and Finishing
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• v.10 no.1
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• pp.33-37
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• 1998

It is rather important in the water and oil repellent finishing for wool fabric what kind of water-repellent agents will be used. In many cases, Fluorocarbon-based water-repellent agents(eg.Oleophobol-S), the surface tensions of which very low, were recom-mended on account of good water and oil repellencies. In repellent finishing, fabrics were padded in a bath which contained aqueous solution of water-repellent agents, and wetting agents, followed by drying and curing. The most suitable treating condition for excellent repellency was as follows Fabrics were padded at liquor pick-up ratio of 50%, with aqueous solution which contained $30g/\ell$ of water-repellent agents, and $40g/\ell$ of wetting agents. And the padded fabrics were dried at $110^\circ{C}$ for 1 minute, and cured at $160^\circ{C}$ for 2 minutes. For the fabrics, water and oil repellencies and durability to repeated dry-cleanings are observed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.1
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• pp.88-96
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• 2020

In this study, the effect of cyclic wetting-drying on the self-healing of cementitious materials containing superabsorbent polymers (SAPs) were experimentally evaluated. In each cycle, cracked cement paste specimens containing various SAP dosages were exposed to wet conditions for 1 h, during which the capillary water absorption tests and water flow tests were conducted, and then exposed to dry conditions for 47 h. The capillary water absorption test results showed that the sorptivity values of the specimen without SAPs, SAP 0.5%, SAP 1.0%, and SAP 1.5% specimens were decreased by approximately 22.9%, 36.8%, 42.8%, and 46.3%, respectively, after 8 cycles. In addition, the water flow test results showed that the amount of water runoff through the cracks of all cracked specimens gradually decreased over wet/dry cycles, especially the reduction ratio of the amount of water runoff increased with increasing SAP dosage. Furthermore, the swelling behavior of SAPs in cracks by in gress water was con firmed via X-ray computed tomography (CT) analysis. These results indicate that the effective crack width can be reduced as SAPs absorb water and swell, while the water absorbed in SAPs can be released to crack surfaces under dry conditions, further promoting healing product formation. This study demon strates that the in corporation of SAPs can in crease the water tightness of cracks, thereby improving the self-healing efficiency of cementitious materials.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.4C
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• pp.169-175
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• 2012

Soil water retention characteristics are influenced by factors of the confining stress and hysteresis in the variably saturated soil. In the description of effective stress based on hydraulic characteristics, the contribution of a matric suction to effective stress then varies with depth or is different between the processes of infiltration and evaporation. Unsaturated effective stress can be described based on suction stress characteristic curve, in which a representative soil water retention curve is required to evaluate. Pressure palate extractor tests under various confining stresses were performed and the hysteresis of drying and wetting process was also acquired. In the process of drying or wetting, a unique relationship has been estimated on the effective volumetric water content and the matric suction, which defines suction stress characteristic curve. In the unsaturated shear strength from triaxial tests, the suction stress and the effective stress were evaluated by matric suctions. The failure envelop by effective stress based on soil water retention characteristics was unique and the same as the saturated one. The measured suction stress from triaxial tests was similar to that from the soil water retention curve. Therefore it is verified that a representative soil water retention curve can be defined which is independent of the confining effect under wetting or drying process of the hysteresis.

• Journal of the Korean Geotechnical Society
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• v.30 no.3
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• pp.47-58
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• 2014

To investigate the unsaturated characteristics of the tailings obtained from the waste dump at Imgi mine, matric suction and volumetric water content were measured in both drying and wetting processes using Automated Soil-Water Characteristics Curve Apparatus. Based on the measured result, Soil Water Characteristic Curves (SWCC) were estimated by van Genuchten model. According to the unsaturated soil classification method, the tailings of the waste dump correspond to clayey sand. As a result of Suction Stress Characteristic Curve (SSCC) by Lu and Likos model, SSCC has a shape of S which is similar to SWCC. The hysteresis phenomenon occurred in SSCCs, which means the suction stress of drying path is larger than that of wetting path in the same effective degree of saturation. The effective stress of unsaturated soil is equal to that of saturated soil when matric suction is less than Air Entry Value (AEV). However, the effective stress of unsaturated soil is larger than that of saturated soil when matic suction is more than AEV. Meanwhile, unsaturated hydraulic conductivity by van Genuchten model decreased with increasing matric suction, and the hydraulic conductivity of drying path is larger than that of wetting path.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.2
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• pp.70-80
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• 2000

Princeton Ocean Model (POM) is modified to construct a three-dimensional, semi-implicit hydro¬dynamic model with a wetting-and-drying scheme. The model employs semi-implicit treatment of the barotropic pressure gradient terms and the vertical mixing terms in the momentum equations, and the velocity divergence term in the vertically-integrated continuity equation. Such treatment removes the external mode and thus the mode splitting scheme in POM, allowing the semi-implicit model to use a larger time step. Applied to hypothetical systems, both the semi-implicit model and POM give nearly the same results. The semi-implicit model, however, runs approximately 4.4 times faster than POM showing its improved computational efficiency. Applied to a hypothetical system with intertidal flats, POM employing the mode splitting scheme produces noises at the intertidal flats, that propagate into the main channel resulting in unstable current velocities. Despite its larger time step, the semi-implicit model gives stable current velocities both at the intertidal flats and main channel. The semi-implicit model when applied to Kyeonggi Bay gives a good reproduction of the observed tides and tidal currents throughout the modeling domain, demonstrating its prototype applicability.

• Journal of Wetlands Research
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• v.21 no.1
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• pp.43-56
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• 2019

Irrigated and flooded rice paddy contributes to the greenhouse gas emissions (GHG) that affect climate. This in turn affects the supply and reliability of the water needed for rice production. This dynamic makes current rice production methods foreseeably less sustainable over time while having other undesirable effects. Intermittent irrigation by a means of the system of rice intensification (SRI) and alternate wetting and drying (AWD) methods was reviewed to reduce global warming potential (GWP) from 29% to 90% depending on site-specific characteristics from flooded rice paddy and analyzed to be a promising option for enhancing the productivity of water as well, an increasingly constraining resource. Additional benefits associated with the SRI/AWD can be less arsenic in the grain and less degradation of water quality in the run-off from rice paddies. Adoption and expansion of intermittent irrigation of SRI/AWD may require costly public and private investments in irrigation infrastructure that can precisely make irrigation control, and the involvement and upgrading of water management agencies and farmer organizations to enhance management capabilities. Private and public collaboration as a means of earning carbon credit under the clean-development mechanism (CDM) with SRI/AWD for industries to meet as a part of their GHG emission quota as well as a social contribution and publicity program could contribute to adopt intermittent irrigation and rural investment and development. Also, inclusion of SRI and AWD in programs designed under CDM and/or in official development assistance (ODA) projects could contribute to climate-change mitigation and help to achieve UN sustainable development goals (SDGs).

• Journal of the Korean Geotechnical Society
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• v.40 no.1
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• pp.47-54
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• 2024

In current slope stability analysis techniques, slope stability is evaluated based on the saturated-soil theory. However, soil-water characteristics change frequently depending on the climate. Therefore, because the saturated soil theory has limitations, the application of the unsaturated soil theory is necessary for slope stability. It is also important to evaluate the engineering properties of unsaturated soil because the capillary absorption capacity is reduced due to heavy rain, thereby causing a reduction in slope stability. In this study, soil-water characteristic tests were performed using four samples with different fine contents (0%, 10%, 20%, and 30%) using granite-weathered soil in domestic production areas. In particular, to consider the previously conducted drying process as well as the evaluation of stability due to heavy rain on the actual slope, a wetting process was conducted, in which the water content was increased. In addition, the van Genuchten (1980) model, which is the most consistent theoretical equation for the experiment, was used with various theoretical equations, and the parameters were analyzed according to the fine content of the granite-weathered soil for the drying and wetting processes.

• Korean Journal of Weed Science
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• v.16 no.3
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• pp.200-209
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• 1996

It is assumed to be an efficient method for keeping a germinability of weed seeds as long as possible, if a secondary dormancy is not induced by transferring the seeds of which dormancy was broken in wetting condition into drying condition. To investigate its validity, two experiments were carried out on seeds of 9 weed species ; to find out the most effective storage condition in breaking the dormancy of each weed species and to know whether there is a decrease in the germinability by transferring into drying storage condition. The dormancy of Chenopodium album and Stellaria aquatica was released well under the drying condition, but that of Echinochloa crus-galli var. oryzicola by soaking in water. Other weed species were released from dormancy by storage in wetting condition. When the seeds stored in the wetting or soaking condition, are air-dried and then restored at room or low temperature, a decreasing tendency of germinability which might cause a trouble in using them practically, was not observed except on the seeds of Persicaria vulgaris. In the case of Persicaria vulgaris, the low germination since 3 month-storage seemed not to be caused by drying, because a decrease of its germinability was observed with increasing storage period in all of the storage conditions. In contrast, high germination was induced as the seeds of Echinochloa crusgalli var. oryzicola, which were not germinated during the storage in low temperature and wetting condition, were transferred into the room temperature and drying condition. These results suggest that this approach can be one of the efficient methods for keeping a good germinability as long as possible in most weed seeds.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.770-771
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• 2005