• Title/Summary/Keyword: unsaturated soil.

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A Methylobacillus Isolate Growing Only on Methanol (메탄올만 이용하여 성장하는 Methylobacillus의 분리 및 특성)

  • 김시욱;김병홍;김영민
    • Korean Journal of Microbiology
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    • v.29 no.4
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    • pp.250-257
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    • 1991
  • An obligate methanol-oxidizing bacterium, Methylobacillus sp. strain SK1, which grows only on methanol was isolated from soil. The isolate was nonmotile Gram-negtive rod. It does not have internal membrane system. The colonies were small, whitish-yellow, and smooth. The guanine plus cytosine content of the DNA was 48 mol%. Cellular fatty acids consisted predominantly of large amounts of straight-chain saturated $C_{16:0}$ acid and unsaturated $C_{16:1}$ acid. The major ubiquinone was Q-8, and Q-10 was present as minor component. The cell was obligately aerobic and exhibited catalase, but no oxidase, activity. Poly-.betha.-hydroxybutyrate, endospores, or cysts were not observed. the isolate could grow only on methanol in mineral medium. Growth factors were not required. The isolate was unable to use methane, formaldehyde, formate, methylamine, and several other organic compounds tested as a sole source of carbon and energy. Growth was optimal at 35.deg.C and pH 7.5. It could not grow at 42.deg.C. The doubling time was 1.2h at 30.deg.C when grown with 1.0%(v/v) methanol. The growth was not affected by antibiotics inhibiting cell wall synthesis and carbon monoxide but was completely suppressed by those inhibiting protein synthesis. Methanol was found to be assimilated through the ribulose monophosphate pathway. Cytochromes of b-, c-, and o- types were found. Cell-free extracts contained a phenazine methosulfate-linked methanol dehydrogenase activity, which required ammonium ions as an activator. Cells harvested after the late exponential phase seemed to contain blue protein.ein.

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Shallow landslide susceptibility mapping using TRIGRS

  • Viet, Tran The;Lee, Giha;An, Hyun Uk
    • Proceedings of the Korea Water Resources Association Conference
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    • 2015.05a
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    • pp.214-214
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    • 2015
  • Rainfall induced landslides is one of the most devastating natural disasters acting on mountainous areas. In Korea, landslide damage areas increase significantly from 1990s to 2000s due to the increase of both rainfall intensity and rainy days in addition with haphazard land development. This study was carried out based on the application of TRIGRS unsaturated (Transient Rainfall Infiltration and Grid-based Regional Slope stability analysis), a Fortran coded, physically based, and numerical model that can predict landslides for areas where are prone to shallow precipitation. Using TRIGRS combining with the geographic information system (GIS) framework, the landslide incident happened on 27th, July 2011 in Mt. Umyeon in Seoul was modeled. The predicted results which were raster maps showed values of the factors of safety on every pixel at different time steps show a strong agreement with to the observed actual landslide scars in both time and locations. Although some limitations of the program are still needed to be further improved, some soil data as well as landslide information are lack; TRIGRS is proved to be a powerful tool for shallow landslide susceptibility zonation especially in great areas where the input geotechnical and hydraulic data for simulation is not fully available.

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Experimental approach to estimate strength for compacted geomaterials at low confining pressure

  • Kim, Byeong-Su;Kato, Shoji;Park, Seong-Wan
    • Geomechanics and Engineering
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    • v.18 no.5
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    • pp.459-469
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    • 2019
  • It is important to estimate the shear strength of shallow compacted soils as a construction material. A series of constant water content triaxial compression (CWCC) tests under low confining state in this study were performed on compacted geomaterials. For establishing a relationship of the shear strengths between saturated and unsaturated states on compacted geomaterials, the suction stresses were derived by two methods: the conventional suction-measured method and the Suction stress-SWRC Method (SSM). Considering the suction stress as an equivalent confining stress component in the (${\sigma}_{net}$, ${\tau}$) plane, it was found that the peak deviator stress states agree well with the failure line of the saturated state from the triaxial compression test when the SSM is applied to obtain the suction stress. On the other hand, the cavitation phenomenon on the measurement of suction affected the results of the conventional suction-measured method. These results mean that the SSM is distinctly favorable for obtaining the suction value in the CWCC test because the SSM is not restricted by the cavitation phenomenon. It is expected that the application of the SSM would reduce the time required, and the projected cost with the additional equipment such as a pore water measuring device in the CWCC test.

Dynamic Deformation Characteristics of Sands Under Various Drainage Conditions (간극비를 고려한 흙-수분특성 방정식의 적용성 평가)

  • Lim, Seong-Yoon;Song, Chang-Seob
    • Journal of the Korean Geotechnical Society
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    • v.23 no.11
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    • pp.39-48
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    • 2007
  • The soil-water characteristic curve(SWCC) is a useful tool in the prediction of the engineering behavior of unsaturated soils. Several equations are available in the literature to mathematically represent the experimental behavior of the SWCC. Some equations are based on the assumption that the shape of curve is dependent upon pore-size distribution. Other equations assume that SWCC can be estimated from the grain size distribution and the physical properties of soils. This study evaluated the suitability of using two different SWCC equations for defining the relationship between water content and matric suction. Various parameters that influence the SWCC behavior are also briefly discussed.

Hot Air Injection/Extraction Method for the Removal of Semi-Volatile Organic Contaminants from Soils (토양내 저휘발성 유류오염물 제거를 위한 고온공기 주입/추출기술 연구)

  • Gu Chung-Wan;Ko Seok-Oh
    • Journal of Soil and Groundwater Environment
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    • v.10 no.1
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    • pp.6-12
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    • 2005
  • Contamination of soils and groundwater by leakage of petroleum compounds from underground storage tanks (USTs) has become great environmental issues. Conventional methods such as soil vapor extraction (SVE) used for the remediation of unsaturated soils contaminated with volatile organic compounds might not be applied for the removal of semi-volatile organic compounds such as diesel fuels and PCBs, which have low volatility and high hydrophobicity. The objective of this study is to develop a hot air injection method to remove semi-volatile compounds. Additionally, operation parameters such as temperature, air flow rate, and water content are evaluated. Experimental results show that diesel ranged organics (DROs) are removed in the order of volatility of organic compounds. As expected, removal efficiency of organics is highly dependent on the temperature. It is considered that more than $90\%$ of organic contaminants whose carbon numbers range between 17 and 22 can be removed efficiently by the hot air injection-extraction method (modified SVE) over the $100^{\circ}C$. It is also found that increased air flow rate resulted in high removal rate of contaminants. However, air flow rate over 40 cc/min is not effective for the operation aspects, due to mass transfer limitation on the volatilization rate of the contaminants. The effect of the water content on the decane removal is minimal, but some components show large dependence on the removal efficiency with increasing water content.

Study on the Characteristics of Shear Strength on the Weathered Granite Soil Slope in Accordance with the Rainfall (강우에 따른 화강암질 풍화토 사면의 전단강도 특성에 관한 연구)

  • Shim Tae-Sup;Kim Sun-Hak;Ki Wan-Seo;Joo Seung-Wan
    • The Journal of Engineering Geology
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    • v.14 no.4 s.41
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    • pp.349-360
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    • 2004
  • This study calculated the pore water pressure, the depth of seepage, the constant of the strength in accordance with the slope inclination and the rainfall intensity over the slope built by the weathered granite soil (SP, SM). And, the change of the shear strength in accordance with the rainfall has been compared and analyzed by applying the shear strength formula of the unsaturated soil. As a result, the rainfall intensity is stronger and the slope inclination is gentler the seepage speed in accordance with the rainfall became faster proportionally. As a result of comparing and analyzing both the theoretical value of Lumb and the actual value of the model, it can be said that the actual value is faster. Since SM shows the bigger shear strength than SP, it can also be said that as the granules increase, the coefficient of permeability becomes smaller; and as the seepage rate became smaller, it affects the seepage speed. Likewise, the shear strength within the slope displays the smallest shear strength at the inclination of 1:1.5 the reason of its decrease turned out that it was due to the increase of the pore water pressure.

Concept and Application of Generalized Preferential Flow Model (GPFM) (Generalized Preferential Flow Model (GPFM)의 개념과 적용사례 연구)

  • Kim, Young-Jin;Steenhuis, Tammo;Nam, Kyoung-Phile
    • Journal of Soil and Groundwater Environment
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    • v.12 no.5
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    • pp.33-36
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    • 2007
  • In recent years the convective-dispersive equation has been often discredited in predicting subsurface solute transport under field conditions due to presence of preferential flow paths. Kim et al. (2005) proposed a simple equation that can predict the breakthrough of solutes without excessive data requirements. In their Generalized Preferential Flow Model (GPFM), the soil is conceptually divided in a saturated "distribution layer" near the surface and a "conveyance zone" with preferential flow paths below. In this study, we test the model with previously published data, and compare it with a classical convective-dispersive model (CDM). With three parameters required-apparent water content of the distribution zone, and solute velocity and dispersion in the conveyance zone-GPFM was able to describe the breakthrough of solutes both through silty and sandy loam soils. Although both GPFM and CDM fitted the data well in visual, variables for GPFM were more realistic. The most sensitive parameter was the apparent water content, indicating that it is the determining factor to apply GPFM to various soil types, while Kim et al. (2005) reported that changing the velocity of GPFM reproduced solute transport when same soils were used. Overall, it seems that the GPFM has a great potential to predict solute leaching under field conditions with a wide range of generality.

Experimental Study on the Unsaturated Characteristics of Dredging Soils at Saemangeum Area (새만금지역 준설토의 불포화 특성에 대한 실험적 연구)

  • Song, Young-Suk;You, Seung-Kyong
    • Journal of the Korean Geosynthetics Society
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    • v.10 no.3
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    • pp.25-32
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    • 2011
  • The matric suction and volumetric water content of dredging soils obtained from Saemangeum area were measured by the automated Soil-Water Characteristic Curve (SWCC) apparatus under both drying and wetting conditions. Based on the test result, SWCCs of the dredging soils were estimated by the van Genuchten(1980) model. The matric suction of drying process is larger than that of wetting process at a same effective degree of saturation. The suction stresses for various matirc suctions were estimated using Lu and Likos(2006) model and the Suction Stress Characteristic Curves (SSCC) were predicted using the independent parameter of SWCC. The suction stress of drying path was increased and decreased, while the suction stress of wetting path was continuously decreased with increasing the effective degree. Also, the suction stress of drying path is larger than that of wetting path at a same effective degree of saturation. The Hydraulic Conductivity Function(HCF) was also predicted by the van Genuchten(1980) model. The hydraulic conductivity was increased with increasing the volumetric water content. The hydraulic conductivity of drying path is larger than that of wetting path at a same matric suction. According to the results of SWCCs and SSCCs, the hysteresis phenomenon of suction stress or matric suction during both drying and wetting paths was occurred. The main reason of hysteresis phenomenon is a ink bottle effect of water among soil particles.

Assessment of Continuous Pressurization Method for Soil-water Characteristic Curve (연속 가압 함수특성 시험 평가에 관한 연구)

  • Park, Hyun-Su;Kim, Byeong-Su;Lee, Eo-Ryeong;Park, Seong-Wan
    • Journal of the Korean Geotechnical Society
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    • v.35 no.9
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    • pp.5-13
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    • 2019
  • The soil-water characteristic curve (SWCC) plays an important role in determining the soil suction parameters required to predict the seepage or shear behaviors of unsaturated soils. In addition, path dependency of the SWCC affects the mechanical and hydrologic behaviors. In general, there is a disadvantage that it takes a long time to measure both the drying and wetting paths of the SWCC by a stepwise pressurization method. Thus, the continuous pressurization method as an improved testing method for the SWCC was suggested, and the testing time for two paths of the SWCC was significantly shorter than the conventional methods. For the applicability evaluation of this method, the results of the SWCC obtained by the stepwise pressurization method and the evaporation method in this study were compared to the result obtained from this method. As a result, it was found that the difference among three methods was negligible, and the testing time of the continuous pressurization method was greatly decreased. Therefore, it can be said that it is possible to quickly and accurately measure the SWCC under various conditions by the continuous pressurization method.

Implementation of Barcelona Basic Model into TOUGH2-MP/FLAC3D (TOUGH2-MP/FLAC3D의 Barcelona Basic Model 해석 모듈 개발)

  • Lee, Changsoo;Lee, Jaewon;Kim, Minseop;Kim, Geon Young
    • Tunnel and Underground Space
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    • v.30 no.1
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    • pp.39-62
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    • 2020
  • In this study, Barcelona Basic Model (BBM) was implemented into TOUGH2-MP/FLAC3D for the numerical analysis of coupled thermo-hydro-mechanical (THM) behavior of unsaturated soils and the prediction of long-term behaviors. Similar to the methodology described in a previous study for the implementation of BBM into TOUGH-FLAC, the User Defined Model (UDM) of FLAC based on the Modified Cam Clay Model (MCCM) and the FISH function of FLAC3D were used to extend the existing MCCM module in FLAC3D for the implementation of BBM into TOUGH2-MP/FLAC3D. In the developed BBM module in TOUGH2-MP/FLAC3D, the plastic strains due to change in suction increase (SI) in addition to mean effective stress are calculated. In addition to loading-collapse (LC) yield surface, suction increase (SI) yield surface is changed by hardening rules in the developed BBM module. Several numerical simulations were conducted to verify and validate the implementation of BBM: using an example presented in the FLAC3D manual for the standard MCCM, simulation results using COMSOL, and experimental data presented in SKB Reports. In addition, the developed BBM analysis module was validated by simultaneously performing a series of modeling tests that were performed for the validation of the Quick tools developed for the purpose of effectively deriving BBM parameters, and by comparing the Quick tools and Code_Bright results reported in a previous study.