• Journal of the Korean Geotechnical Society
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• v.39 no.5
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• pp.13-26
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• 2023

This study examined the soil-water characteristic curve (SWCC), considering the volume change, using wetting curves on the field monitoring data of a wireless sensor network. Special attention was given to evaluating the landslide vulnerability by deriving a matric suction suitable for the actual site during the wetting process. Laboratory drying SWCC and shrinkage laboratory tests were used to perform the combined analysis of landslide and debris flow. The results showed that the safety factor of the wetting curve, considering the volume change of soil, was lower than that of the drying curve. As a result of numerical analyses of the debris flow simulation, more debris flow occurred in the wetting curve than in the drying curve. It was also found that the landslide analysis with the drying curve tends to overestimate the actual safety factor with the in situ wetting curve. Finally, it is confirmed that calculating the matric suction through SWCC considering the volume change is more appropriate and reasonable for the field landslide analysis.

• The Journal of Engineering Geology
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• v.22 no.2
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• pp.145-155
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• 2012

The matric suction and volumetric water content of Jumunin standard sand with a relative density of 60% were measured using an Automated Soil-Water Characteristic Curve (SWCC) apparatus during both drying and wetting processes. The test time for the drying process was longer than that for the wetting process, because the flow of water is likely to be protected by air trapped in voids within the soils during the drying process. Based on the matric suction and volumetric water content, the SWCC was estimated using the model proposed by van Genuchten (1980). For the drying process, the unsaturated fitting parameters ${\alpha}$, n, and m were 0.399, 8.586, and 0.884, respectively; for the wetting process, the values were 0.548, 5.625, and 8.220, respectively. The hysteresis phenomenon occurred in the SWCCs, which means the SWCC of the drying process is not matched with the SWCC of the wetting process. Using these unsaturated parameters, we estimated the Suction Stress Characteristic Curve (SSCC), based on the relationship between suction stress and the effective degree of saturation. The suction stress showed a rapid decrease when the matric suction exceeds the Air Entry Value (AEV). Therefore, the effective stress of unsaturated soils is different from that of saturated soils when the matric suction exceeds the AEV. The suction stress of the drying process exceeds that of the wetting process for a given effective degree of saturation. The hysteresis phenomenon was also recognized in SSCCs. The hysteresis phenomenon of SSCCs arises from that of SWCCs, which is induced by the ink bottle effect and the contact angle effect. In the case of a sandy slope, the suction stress is positive and acts to enhance the slope stability as the water infiltrates the ground, but is negative when the suction stress exceeds the AEV. The results obtained for the wetting process should be applied in analyses of slope stability, because the process of water infiltration into ground is similar to the wetting process.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2369-2379
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• 2013

The Soil-Water Characteristics Curve (SWCC) is affected by the initial density of soil under unsaturated condition. Also, the characteristic of hydraulic conductivity is changed by the initial density of soil. To study the effect of initial density of unsaturated soil, SWCC and the Hydraulic Conductivity Function (HCF) of Jumoonjin sand with various relative densities, 40%, 60% and 75% were measured in both drying and wetting processes. As the results of SWCC estimated by van Genuchten (1980) model, the parameter related to Air Entry Value(AEV), ${\alpha}$ in the wetting process is larger than that in drying process, but the parameters related to the SWCC slope, n and the residual water content, m are larger than those in wetting process. The AEV is increased or Water Entry Value (WEV) is decreased with increasing the relative density of sand. The AEV is larger than the WEV at the same relative density of sand. As the results of HCF estimated by van Genuchten (1980) model which is one of the parameter estimation methods, the unsaturated hydraulic conductivity maintained at a saturated one in the low level of matric suctions and then suddenly decreased just before the AEV or the WEV. The saturated hydraulic conductivity in drying process is larger than that in wetting process. The saturated hydraulic conductivity is decreased with increasing the relative density of sand in both drying and wetting processes. Also, the hysteresis in unsaturated HCFs between drying and wetting process was occurred like the hysteresis in SWCCs. According to the test results, the AEV on SWCC is decreased and the saturated hydraulic conductivity is increased with increasing the initial density. It means that SWCC and HCF are affected by the initial density in the unsaturated soil.

• Conservation Science in Museum
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• v.2
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• pp.19-25
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• 2000

In order to studies proper conservation treatment condition of waterlogged archaeological wood excavated from wetland in Shinchang-dong, Kwangju, 2 kinds of wooden objects were treated with PEG(Poly-Ethylene Glycol), sucrose and lactitol and their size stability and relative humidity were analyzed and compared each other. The result showed that Quercus spp. had the highest size stability in 2 Step-PEG treatment using PEG#200(MW:200) and PEG#4000 (MW:3,350) and Acer spp. was the highest in treatment using only PEG#4000. In relative humidity test after treatment 2 Step-PEG treatment showed the lowest size stability. In the meantime, sucrose and lactitol-treated sample was fast for penetration, sucrose-treated sample showed a sharp increase for penetration in as high as 84% humidity condition and medicine flew out a lot and lactitol-treated sample got enlarged with fine cracking(splitting) in relative humidity test. In relative humidity test, the samples showed cracking(splitting) in all treatment materials except for 2 Step-PEG treatment. This study showed that waterlogged archaeological wood excavated from Shinchang-dong had the highest size stability and highest adaptation to humidity change in case of treatment with 2 Step-PEG.

• Korean Journal of Agricultural Science
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• v.3 no.2
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• pp.207-213
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• 1976

In order to obtain the prediction of the maximum dry density and the optimum moisture content of soil without soil moisture test, compaction test results from 157 different places either under construction or already completed were analyzed. The analyzed results were as follow The relationship between the maximum dry density and the optimum moisture content of the soil showing a correlation coefficient of 0.96 indicated that there was a high correlation between them. From the above relationship we obtained the equation, ${\gamma}_{dmax.}={\frac{1}{0.4193+0.00937W_{opt.}}$ Equation between the optimum moisture content and the maximum wet density of the soil was $W_{opt.}={\frac{0.4193{\gamma}_{tmax.}}{0.937_{\gamma}_{tmax.}-0.01}$, and the values of the optimum moisture content being predicted with the maximum wet density of the soil showed a little difference between those and tested values. The values of the maximum dry density being predicted with the moisture content estimated by the maximum wet density of the soil were within the range of ${\pm}5%$ of its tested values. The relationship between the dry density and the void ratio showed a high correlation between them (${\gamma}=0.9706$). From the above relationship, we obtained the equation, ${\gamma}_{dmax.}={\frac{1}{0.3938+0.3426e}}$.

• Korean Journal of Remote Sensing
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• v.33 no.6_1
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• pp.931-946
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• 2017

The purpose of this study is to observe and analyze soil moisture conditions with high resolution and to evaluate its application feasibility to agriculture. For this purpose, we used three Landsat-8 OLI (Operational Land Imager)/TIRS (Thermal Infrared Sensor) optical and thermal infrared satellite images taken from May to June 2015, 2016, and 2017, including the rural areas of Jeollabuk-do, where 46% of agricultural areas are located. The soil moisture conditions at each date in the study area can be effectively obtained through the SPI (Standardized Precipitation Index)3 drought index, and each image has near normal, moderately wet, and moderately dry soil moisture conditions. The temperature vegetation dryness index (TVDI) was calculated to observe the soil moisture status from the Landsat-8 OLI/TIRS images with different soil moisture conditions and to compare and analyze the soil moisture conditions obtained from the SPI3 drought index. TVDI is estimated from the relationship between LST (Land Surface Temperature) and NDVI (Normalized Difference Vegetation Index) calculated from Landsat-8 OLI/TIRS satellite images. The maximum/minimum values of LST according to NDVI are extracted from the distribution of pixels in the feature space of LST-NDVI, and the Dry/Wet edges of LST according to NDVI can be determined by linear regression analysis. The TVDI value is obtained by calculating the ratio of the LST value between the two edges. We classified the relative soil moisture conditions from the TVDI values into five stages: very wet, wet, normal, dry, and very dry and compared to the soil moisture conditions obtained from SPI3. Due to the rice-planing season from May to June, 62% of the whole images were classified as wet and very wet due to paddy field areas which are the largest proportions in the image. Also, the pixels classified as normal were analyzed because of the influence of the field area in the image. The TVDI classification results for the whole image roughly corresponded to the SPI3 soil moisture condition, but they did not correspond to the subdivision results which are very dry, wet, and very wet. In addition, after extracting and classifying agricultural areas of paddy field and field, the paddy field area did not correspond to the SPI3 drought index in the very dry, normal and very wet classification results, and the field area did not correspond to the SPI3 drought index in the normal classification. This is considered to be a problem in Dry/Wet edge estimation due to outlier such as extremely dry bare soil and very wet paddy field area, water, cloud and mountain topography effects (shadow). However, in the agricultural area, especially the field area, in May to June, it was possible to effectively observe the soil moisture conditions as a subdivision. It is expected that the application of this method will be possible by observing the temporal and spatial changes of the soil moisture status in the agricultural area using the optical satellite with high spatial resolution and forecasting the agricultural production.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.474-474
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• 2015

Horton 지수는 유역에 대한 수문순환의 특성을 정량화하는 지수로서 유역의 습윤량과 기화량의 비로 산출된다. 습윤량과 기화량은 토양 수분과 밀접한 관계를 가지므로 추계학적 거동에 따른 토양수분의 동역학모형을 파악하여 Horton 지수를 산출할 수 있다. 본 연구에서는 추계학적인 토양수분수지 모형을 이용하여 서울, 부산, 대구, 제주 지역을 대상으로 30년간 일 기상자료(강우량, 일 평균기온, 풍속, 상대습도, 일조시간)을 이용하여 Horton 지수를 각각 산출하였으며 Horton 지수에 대한 변동성 분석을 실시하였다. 분석 결과, 모든 대상 유역에서 기후의 계절성에 의하여 Horton 지수가 작아짐을 확인할 수 있었다. 하지만 습윤한 기후를 가진 서울과 건조한 기후를 가진 대구에서는 각각 연 강우량이 많거나 연 강우량이 적은 해에 Horton 지수에 미치는 기후의 계절성의 영향력이 줄어듦을 살펴볼 수 있었다.

• Horticultural Science & Technology
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• v.29 no.1
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• pp.16-22
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• 2011

In developing soil wetting agent using polyoxyethylene nonylphenyl ether (PNE) and polyoxyethylene castor oil (1:1; v/v), the effect of application rates on changes in concentration of PNE, initial wetting of peatmoss + perlite (7:3) medium, and growth of hot pepper (Capsicum annuum L. 'Knockwang') plug seedlings were investigated. The elevation of application rates of wetting agent increased the amount of water retained by the root media. The treatment of 2.5 $mL{\cdot}L^{-1}$ showed similar water retention to + control ($AquaGro^L$ 3.0 $mL{\cdot}L^{-1}$). Most of the liquid wetting agent (LWA) incorporated during the medium formulation leached out in the first and second irrigation, then it decreased gradually until 10 times in irrigation. In investigation of the influence of LWA on position of water infiltrating into root media, the vertical water movements in treatments of 0.5, 1.0, and 1.5 $mL{\cdot}L^{-1}$ were much faster than those in 0.0 $mL{\cdot}L^{-1}$ (-control), but relative speed of water movement decreased by the elevation in application rate of LWA to 2.0 or 2.5 $mL{\cdot}L^{-1}$. The evaporative water loss of root media that to contained various rate of LWA and irrigated to reach container capacity was the fastest in -control among the treatments and it delayed as the application rate of LWA was elevated. The plant height of 22.2 cm in 0.5 $mL{\cdot}L^{-1}$ and stem diameter of 3.26 mm in 1.0 $mL{\cdot}L^{-1}$ were the highest among the treatments tested. The treatment of 1.0 $mL{\cdot}L^{-1}$ also had the heaviest fresh and dry weights such among treatments tested as 3.08 g and 0.861 g per plant, respectively. The elevated application rate over than 1.5 $mL{\cdot}L^{-1}$ resulted in decreased seedling growth. The results mentioned above indicate that optimum application rate of LWA is 1.0 $mL{\cdot}L^{-1}$.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.407-408
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• 2009

Drying shrinkage have influence on the durability of concrete structure. Various models have been suggested to predict the drying shrinkage, experimentally. In this study, the drying shrinkage with Concrete strength and Curing condition was measured, and compared with representative model code. As a result, drying shrinkage was reduced as W/C ratio decrease, and total shrinkage greatly reduced in 4 week wet curing case. The test results agreed with EC2 model better than the other.

• The Korean Journal of Applied Statistics
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• v.5 no.2
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• pp.123-137
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• 1992

We analyzed a time series composed of the annual precipitations of Seoul based on the measurements of a Korean raingage and a modern raingage. The precipitations measured with a Korean raingage for the period of 1771 to 1907 are followed by the precipitations with a modern raingage for the period of 1908 to 1990. The latter part of the time series of annual precipitations were obtained from a book for annual precipitations of Korea by Korea Meteorological Administration and the former from Wada's table 1 for monthly precipitations reproduced from the daily rainfall measurements by a Korean raingage for the period of the Yi Dynasty. In our analysis three different precipitation regimes clearly stand out of the entire period. In order to define objectively the period of each precipitation regime we made a time series of 9 year moving averages from the above time series. By taking into account the shapes of the moving average time series and by using a threshold value of annual precipitation 1050 mm, we defined three precipitation regimes of wet period 1(WP1), dry period (DP), and wet period 2 (WP2). The WP1 and WP2 show very similar characteristics in out statistical analyses. On the other hand, DP is very different from the two periods in many statistical aspects. The strong similarities of the WP1 and WP2 regimes in the magnitudes of statistical parameters and in the shapes of their power spectrum distribution are supporting very positively the soundness of precipitation amounts measured with a Korean raingage in spite of numerous conceivable errors which might have been introduced into measurements of precipitation due to changes of observation site and environment, the scale of units employed, and urbanization of Seoul, etc. However, the annual precipitation amounts are not enough to examine throughly the characteristic of precipitation variations during the two regimes. It is definitely necessarly to recover the daily amounts of precipitation, based on two or three times measurements of rainfall with a Korean raingage, scattered in various ancient documents such as the official diary of 'Seungjeong-weon'