함수특성에 근거한 국내 풍화토의 불포화 투수곡선 추정

김윤기,최경림,이성진,이승래,권형석 한국지반공학회 2010 한국지반공학회논문집 Vol.26 No.10

Unsaturated permeability function is an important factor in the design and analysis of various unsaturated soil structures. Generally the permeability characteristics decrease as the matric suction increases and the trend is similar to water retention characteristics of a soil. The permeability of unsaturated soils can be obtained directly by laboratory tests or indirectly by estimation methods from other soil properties. For unsaturated soils sampled from 7 areas in KOREA, SWCCs and unsaturated permeability functions were obtained by experimental tests. The unsaturated permeability results were also compared with the unsaturated permeability functions derived from the SWCCs theoretically. However, the current estimation models of unsaturated permeability function did not express the unsaturated permeability characteristics. Therefore, the FXK-M permeability function was modified to predict more accurate permeability functions for Korean weathered soils using a correction factor that can be calculated from the air-entry value of SWCC. The new estimation model resulted in good agreements for all tested soils.

Modeling the Dependency of Suction Stress Characteristic Curve on Void Ratio in Unsaturated Soils

A. A. Heshmati,M. R. Motahari 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.1

Geotechnical problems associated with unsaturated soils are common in semi-arid climates, where the upper soil layers arenaturally unsaturated. Once a soil becomes unsaturated, its mechanical properties become different from its saturated counterpart. The main part of effective stress in unsaturated soils resulting from the soil moisture can be defined by the Suction StressCharacteristic Curve (SSCC). Although, the suction stress characteristic curve is determined from shear strength tests, but recentworks show that the SSCC can be connected to the Soil Water Characteristic Curve (SWCC). This paper presents a simple and novelapproach to model the effect of void ratio changes on SSCC in unsaturated soils. The proposed approach can be easily utilized withexisting Soil Water Characteristic Curve (SWCC) equations to model any changes in suction stress for unsaturated soils. The mainadvantage of the suggested method is in fact its dependency to just one parameter, simply calibrated by the conventional waterretention tests. This characteristic is so applicable in hydro mechanical constitutive models of unsaturated soils. Finally, theefficiently predicting of the experimental results implicitly demonstrates the applicability of effective stress principle using theconcept of Suction Stress Characteristic Curve (SSCC) for unsaturated soils.

화강풍화토의 확률론적 불포화 지반정수 특성에 따른 사면안정해석

전준서,이승래,윤석,김윤태 한국방재학회 2013 한국방재학회논문집 Vol.13 No.1

The unsaturated soil properties such as soil-water characteristic curve, unsaturated permeability and unsaturated shear strength,always involve uncertainties associated, making it hard to obtain a representative value in analyzing the stability of slopes. Because a deterministic approach use a representative value, soil properties with severe variance sometimes lead to misestimate and hence the consequence also varies from person to person. To address this problem, a probabilistic approach to the analysis of slope stability has been adopted. Even though the probabilistic characteristics of soil are essential for probabilistic approach, it has not been established. Therefore, in this paper, the probabilistic characteristics of the unsaturated soil properties were defined. A simple procedure for the probabilistic approach was proposed to obtain the unsaturated soil properties for the slope stability analysis. Finally, the probabilistic analysis of unsaturated slope stability using monte-carlo simulation method was conducted for the Korean weathered granite soil. 함수특성곡선, 불포화투수곡선, 불포화전단강도와 같은 불포화 지반정수는 필연적으로 불확실성을 내포하기 때문에 사면안정해석에 사용될 대표적인 값을 획득하기 힘들다. 결정론적인 방법은 하나의 대표적인 값을 사용하기 때문에 분산이 심한 지반정수일 경우 잘못된 평가를 초래할 수 있다. 이를 해결하기 위해 확률론적 해석방법이 이용되고 있다. 하지만 지반정수에 대한확률론적 특성 연구가 확률론적 해석을 위해 선행되어야 함에도 불구하고, 불포화 지반정수에 대한 확률론적 특성 연구는 아직부족한 실정이다. 따라서 본 연구에서는 국내 화강풍화토의 불포화 지반정수에 대한 확률론적 특성을 파악하고, 이를 바탕으로사면안정해석을 위한 불포화지반정수를 획득하기 위한 간단한 절차도를 제안하였다. 또한 불포화 화강풍화토 사면에 대하여 몬테카를로 시뮬레이션 방법을 사용한 확률론적 사면안정해석을 수행하였다.

함수특성곡선의 이력현상이 불포화 사면의 안정성에 미치는 영향

백환조,김경만,김대훈 한국자원공학회 2010 한국자원공학회지 Vol.47 No.3

The soil-water characteristic curves for wetting and drying processes of weathered granitic soils was obtained. A numerical study was conducted for stability analysis of unsaturated soil slope on continuous rainfall,and impacts of hysteresis of soil-water characteristic curve (SWCC) were analyzed. Granitic soil samples were prepared in acrylic containers with sensors installed for soil suction and volumetric water content measurements. Soil samples were saturated under direct rainfall, then were dried out at room temperature. Based on the field data, the drying and wetting SWCC’s were obtained adopting the Fredlund and Xing equation (1994), and a numerical study was conducted for unsaturated soil slope stability due to continuous rainfall using equation of Vanapalli et. al. (1996) relating the shear strength of unsaturated soils. Consequently, the hysteresis of SWCC was clearly defined and as result of numerical analysis, factor of safety of slope was different according to the wetting process and drying process of SWCC. Therefore, considering these properties of unsaturated soil, it is desirable to apply the SWCC of the wetting process and drying process respectively to the site conditions. 본 연구에서는 국내 대표적 지반인 화강풍화토의 습윤 및 건조과정의 함수특성곡선을 얻고, 함수특성의 이력현상이 사면의 안전율에 미치는 영향을 분석하기위해 수치해석을 실시하였다. 시료의 함수특성곡선을얻기 위해 체적함수비와 흡수력을 측정할 수 있는 센서를 연결한 토조를 제작하여 강우에 의한 자료를 획득하였으며, 이후 실온에서 건조시키는 과정에서 얻은 자료를 결합하여 국내 화강풍화토에 적합성이 높은 Fredlund and Xing(1994)의 경험방정식을 이용해 습윤 및 건조 과정의 함수특성곡선을 완성하였다. 또한 국내 화강풍화토에 적합성이 높은 불포화토의 전단강도와 관련된 Vanapalli et al.(1996)의 제안식이 적용 가능한 프로그램을사용하여 지속강우시 사면의 안전율에 관한 수치해석적 연구를 실시하였다. 그 결과 함수특성곡선의 습윤 과정과 건조 과정에 따라 침투속도가 달라 안전율의 차이가 나타남을 확인 할 수 있었고 불포화토의 특성을 고려한보다 합리적인 설계나 안정성 검토에는 강우침투사면과 같은 습윤 과정에서는 습윤 과정의 함수특성곡선을,건조 과정에서는 건조과정의 함수특성곡선을 적용하는 것이 합당할 것으로 판단된다.

불포화 준설매립 지반의 흙-수분 특성곡선 및 불포화 투수계수 예측

신은철,이학주,오영인 한국지반공학회 2004 한국지반공학회논문집 Vol.20 No.1

There has been outstanding research on the soil-water characteristic curves of unsaturated soils over the past several decades. Unfortunately, unsaturated soil mechanics has not been considered as an important factor in Korea. In this paper, laboratory test and numerical analysis(SoilVision Professional ver 3.04) were performed to investigate the prediction method of soil-water characteristic curve and unsaturated permeability coefficient in reclaimed ground. The pressure cell, desiccator, and tensiometor tests were conducted on three types of reclaimed soils(dredged soil, sand, weathered granite soil). Numerical analysis was executed to compare the results with the laboratory test results and also compared with the results of each prediction method. Based on the laboratory test, three different types of soils have shown different soil-water characteristic curves. The hysteresis fir these soils is clearly defined. As a result of numerical analysis, Fredlund & Xing's method and Fredlund & Wilson's model proved to worke out well for reclaimed ground soils in Korea. Also, predicting method based on the soil-water characteristic curves from the particle-size distributions is flirty reliable for estimating unsaturated permeability coefficient.

Soil seal development under simulated rainfall: Structural, physical and hydrological dynamics

Armenise, Elena,Simmons, Robert W.,Ahn, Sujung,Garbout, Amin,Doerr, Stefan H.,Mooney, Sacha J.,Sturrock, Craig J.,Ritz, Karl Elsevier 2018 Journal of hydrology Vol.556 No.-

<P><B>Abstract</B></P> <P>This study delivers new insights into rainfall-induced seal formation through a novel approach in the use of X-ray Computed Tomography (CT). Up to now seal and crust thickness have been directly quantified mainly through visual examination of sealed/crusted surfaces, and there has been no quantitative method to estimate this important property. X-ray CT images were quantitatively analysed to derive formal measures of seal and crust thickness. A factorial experiment was established in the laboratory using open-topped microcosms packed with soil. The factors investigated were soil type (three soils: silty clay loam – ZCL, sandy silt loam – SZL, sandy loam – SL) and rainfall duration (2–14 min). Surface seal formation was induced by applying artificial rainfall events, characterised by variable duration, but constant kinetic energy, intensity, and raindrop size distribution. Soil porosities derived from CT scans were used to quantify the thickness of the rainfall-induced surface seals and reveal temporal seal micro-morphological variations with increasing rainfall duration. In addition, the water repellency and infiltration dynamics of the developing seals were investigated by measuring water drop penetration time (WDPT) and unsaturated hydraulic conductivity (K<SUB>un</SUB>). The range of seal thicknesses detected varied from 0.6 to 5.4 mm. Soil textural characteristics and OM content played a central role in the development of rainfall-induced seals, with coarser soil particles and lower OM content resulting in thicker seals. Two different trends in soil porosity vs. depth were identified: <I>i</I>) for SL soil porosity was lowest at the immediate soil surface, it then increased constantly with depth till the median porosity of undisturbed soil was equalled; <I>ii</I>) for ZCL and SL the highest reduction in porosity, as compared to the median porosity of undisturbed soil, was observed in a well-defined zone of maximum porosity reduction c. 0.24–0.48 mm below the soil surface. This contrasting behaviour was related to different dynamics and processes of seal formation which depended on the soil properties. The impact of rainfall-induced surface sealing on the hydrological behaviour of soil (as represented by WDTP and K<SUB>un</SUB>) was rapid and substantial: an average 60% reduction in K<SUB>un</SUB> occurred for all soils between 2 and 9 min rainfall, and water repellent surfaces were identified for SZL and ZCL. This highlights that the condition of the immediate surface of agricultural soils involving rainfall-induced structural seals has a strong impact in the overall ability of soil to function as water reservoir.</P> <P><B>Highlights</B></P> <P> <UL> <LI> X-ray CT was effectively used to quantify soil seal/crust thickness. </LI> <LI> Different micro-morphological zones within seal layers were revealed. </LI> <LI> Rainfall had a strong and rapid impact on water transport and retention in soil. </LI> <LI> The existence of a soil-dependent raindrop impact threshold was hypothesized. </LI> </UL> </P>

A Hierarchical Single-Surface Model for an Unsaturated Soil-Structure Interface

Fei Peng,Xin Li,Meng-fan Lv,Yong-Hui Li,Yuan-Cheng Guo 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.6

In this paper, according to the shear test of the interface between unsaturated soil and steel plate, the modified apparent roughness is used to describe interface roughness. And considering the influence of matrix suction and interface roughness, the stress variable is constructed to improve the yield and plastic potential functions. Then a modified hierarchical single-surface elastoplastic interface constitutive model (HISS-Unsaturated-Int model) is set up. The finite element calculation of HISS-Unsaturated-Int model is achieved by compiling and calling the user subroutine FRIC of ABAQUS. The interface shear test between unsaturated soil and structure with different water contents and the pull-out shear test between unsaturated soil and soil nail are simulated. The calculation results are consistent with those of experiments, which shows the modified interface constitutive model can effectively predict the shear mechanical properties of soil-structure interface under different soil moisture content, normal stress and interface roughness.

불포화토의 흙-수분 특성곡선에 관한 실험적 고찰

송창섭 ( Song Chang Seob ),김명환 ( Kim Myung Hwan ) 한국농공학회 2003 韓國農工學會誌 : 전원과 자원 Vol.45 No.6

The purpose of this paper is to investigate the soil-water characteristic curves for an unsaturated soil. To this ends, a series of suction measured test was conducted on the selected 4 kinds of soils taken from different sites of Korea, using modified pressure plate apparatus. Form the test results, the water contents, degree of saturation and volumetric water contents were analyzed with the suction. And the soil-water characteristic curves of unsaturated soil were drawn from the test results for various factors. The characteristic curves drawn with water content vs matric suction were classified certainly the difference in wet side but were not classified in dry side. The characteristic curves drawn with degree of saturation vs matric suction for unsaturated soil were shown the opposite inclination as compared with the former curve. But the characteristic curve with volumetric water content vs matric suction was described suitably not only in wet side condition but also in dry side. And it was found that the volumetric water contents of loose soil was high at the initial condition but that of dense soil was high at final condition (dry side).

압축파와 전단파를 이용한 불포화토의 간극비 산정

변용훈,조세현,윤형구,추연욱,김동수,이종섭 한국지반공학회 2012 한국지반공학회논문집 Vol.28 No.12

Soils are commonly unsaturated in the near surface. The stiffness of soils is affected by the amount of air and water. The objective of this study is to evaluate the porosity of the unsaturated soils by using the elastic waves including compressional and shear waves. The elastic waves are measured at different degrees of saturation by controlling the matric suction. Thus, the unsaturated soils are characterized at different levels of the matric suction. Shear and compressional waves are measured by using the bender elements and the piezo disk elements, respectively. Both transducers are installed on the walls of the rectangular cell. The unsaturated soils are prepared by using uniform size sands and silts. Test results show that both compressional and shear wave velocities change according to the matric suction. The elastic modulus, the shear modulus, and the Poisson’s ratio are estimated based on the measured elastic wave velocities. In addition, the void ratio of the unsaturated soils estimated using elastic wave velocities matches well with the volume based void ratio. This study demonstrates that the elastic waves can be effectively used for the characterization of unsaturated soils.

불포화 인공 식재 지반의 배수 성능과 식생 가능 조건에 대한 수치해석적 분석

김성민(Sung-Min Kim),김충언(Choong-Eon Kim),정영훈(Young-Hoon Jung) 한국지반환경공학회 2016 한국지반환경공학회논문집 Vol.17 No.6

본 연구에서는 인공 식재 지반의 공학적 배수 성능과 생물학적 식생 가능성을 평가하기 위해 유한요소해석을 실시하였다. 불포화토 해석을 통해 인공 식재 지반의 공학적 성능 평가가 가능하다. 하지만 식생 조경의 관점에서 조경 식물이 생존하기 위해서는 인공 식재 지반이 최소한의 수분을 제공하는지 확인해야 한다. 화강 풍화토로 이루어진 인공 식재 지반을 1m 높이의 사각형토체 기둥으로 모사하여 해석하였다. 해석 결과 토체의 배수 성능이 포화 투수계수와 불포화토 함수특성의 조합에 따라 크게 달라질 수 있음을 보였다. 체적 함수비의 변화가 최소 한계 수분 범위(LLWR) 이내에서 발생하는지 확인하여 식물이 갈수기 동안 생존할 수 있는 최소한의 수분을 인공 식재 지반이 제공할 수 있음을 파악할 수 있다. This study attempted to investigate drain capacity and vegetation potential of made-planting soil via finite element simulations. Engineering drain capacity of made-planting soil can be evaluated by an analysis of unsaturated soils. In a perspective for vegetation landscape, it is necessary to check whether the minimum amount of water in the made-planting soil can be supplied for the survival of plants. Herein, 1-m high soil column covered by made-planting soil were numerically simulated. Numerical results showed that how the coefficient of permeability of saturated soil and soil-water characteristics of unsaturated soil are considered significantly influences the drain capacity of soils. Variation in the volumetric water content within the Least Limiting Water Range (LLWR) provides us with information on whether the soil can contain a sufficient amount of water for the plants to survive the drought.