• Journal of the Korean Society of Hazard Mitigation
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• v.3 no.2 s.9
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• pp.119-125
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• 2003

Water flow in unsaturated soils is affected by two mathematical equations called soil water-characteristic curve and permeability-suction relationship. Soil water-characteristic curve is an equation showing volumetric water content-suction relationship. Many researchers have presented equations for the relationships. This paper illustrates the importance of correctly determining the two relationships when analyzing unsaturated water flows. Results from two methods, Gardner (1958) and Fredlund et al. (1994), are used for comparison purposes. Numerical simulations of water flow by finite element method are performed using the two methods. The results by the numerical simulations are compared with the field data which was obtained from time-domain reflectometry (TDR) probes in Delaware County, Ohio. This data was obtained by the Seasonal Instrumentation Program which is included as a part of the Strategic Highway Research Program (SHRP).

• The Journal of Engineering Geology
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• v.18 no.4
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• pp.523-535
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• 2008

A simulated rainfall system was built, and the unsaturated characteristics were examined by execution of simulated rainfall system test and soil water characteristic curve cell test(SWCC Cell Test) under the various rainfall and slope conditions. With the results, the applicability of infiltration behavior under rainfall and soil water characteristic curve models to the unsaturated weathered granite soil was examined. At the results of comparison the volumetric water content and matric suction measured in the wetting process(under rainfall) with those in the drying process(leaving as it was) of the simulated rainfall system, the volumetric water content showed a difference of $2{\sim}5%$ and matric suction of about $3{\sim}10\;kPa$, indicating the occurrence of hysteresis. In addition, the difference was relatively larger in matric suction than in the volumetric water content, and this tells that the hysteresis behavior is larger in matric suction. When the soil water characteristic curve derived from measurements in simulated rainfall system test were compared with those from the soil water characteristic curve cell test, both methods produced soil water characteristic curves close each other in the wetting process and the drying process, but in both, there was a difference between results obtained from in the wetting process and those from in the drying process. Thus, when soil water characteristic curves are rationally applied to the design and stability analysis considering of the properties of unsaturated soil, it is considered desirable to apply the soil water characteristic curve of the wetting process to the wetting process, and that of the drying process to the drying process.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.212-212
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• 2011

댐 저수지와 같은 대형 저수지는 댐에 의해 만들어진 공간에 홍수를 저류하여 지체 방류함으로서 홍수저감효과를 얻는다. 이러한 홍수저감효과는 저류용량(storage capacity)에 의존적이며, 궁극적으로 저수지의 저류량-유출량 곡선으로 정량화 된다. 저수지의 저류량-유출량 관계곡선은 저수지 홍수추적에 사용되며, 이 곡선의 특성이 저수지 하류 유역에 대한 홍수추적 결과에 큰 영향을 미치게 된다. 일반적으로 저수지 홍수추적의 경우에는 선형저수지 이론이 적용되지 않는다. 일반적인 댐 저수지의 특성은 수심()의 증가에 따른 저류량()의 증가가 유출량()의 증가보다 훨씬 크게 나타난다. 따라서 저류량과 유출량간의 관계를 비선형 함수의 형태로 가정할 수 있다. 비선형저수지 모형의 경우에도 선형저수지 모형에서와 동일한 개념을 적용하여 저수지 홍수추적의 지체 및 저류특성을 유도할 수 있다. 결과적으로 지수함수 형태를 고려한 비선형 함수의 변곡점은 원점으로 나타나 선형저수지 모형에서와 동일하게 지체효과는 없는 것으로 파악되었다. 또한 저류효과는 수치적인 방법을 이용하여 해석하였으며, 변곡점의 위치를 확인하고 아울러 저류상수를 계산하였다. 결과적으로 변곡점의 위치는 고려한 모든 경우에 대해 원점으로 나타났고, 저류상수는 비선형저수지 모형의 매개변수에 관계없이 일정한 값으로 수렴함을 확인할 수 있었다. 즉, 저류상수는 비선형 함수의 매개변수인 와 비교하여 약 72% 증가된 값으로 수렴하는 형태임을 의미한다. 결과적으로, 본 연구에서는 비선형 저수지 모형을 제안하고, 이를 이용하여 저수지의 저류특성을 이론적으로 검토하였다. 먼저, 저수지의 저류량-유출량 관계를 지수함수 형태인 비선형 저수지 모형을 도입하여 정량화하였다. 또한 저수지의 저류특성은 저류상수로 정량화할 수 있으며, 저류상수는 비선형 저수지 모형의 매개변수를 이용하여 쉽게 결정할 수 있음을 확인하였다.

• Journal of the Korean GEO-environmental Society
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• v.4 no.1
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• pp.49-58
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• 2003

The suction of unsaturated soil is one of the important variables to influence on volume change behavior. This research was performed to analyze the soil-water characteristic of decomposed granite soils in Chung Cheong area, and showed relationship with grain-size distribution. Empirical parameters a, n, m are main variables that can be used in the empirical equations in order to predict unsaturated soil. Decomposed granite soils is taken at 12 field, and redistributed due to a, n, m parameters. The result of Extractor test is showed that matric suction is effected by the grain-size distribution curve's left-right location, degree of an angle and fine contents of a soil.

• Journal of the Korean Geotechnical Society
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• v.21 no.2
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• pp.17-26
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• 2005

Soil water characteristic curve (SWCC) is a unique characteristic that should be considered In the analysis of unsaturated soil and prediction of unsaturated properties. However, the volume change of soil specimens that happens in the existing apparatus affects the SWCC, Therefore, In this study, we intended to obtain more appropriate SWCC by measuring the change In the volume of the specimen in the SWCC tests. The measured change of void ratio indicates that the saturation step prior to the test changes the original structure of the soil specimen. Thus we carried out the test far the same specimen omitting the saturation step prior to the test. The change of void ratio by this test procedure is relatively small.

• Journal of the Korean Geotechnical Society
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• v.28 no.4
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• pp.91-100
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• 2012

Soil-water characteristic curves (SWCCs), which represent a physical property in partially saturated soils, show the relation between volumetric water content and matric suction. The SWCCs exhibit hysteresis during wetting and drying, however experimental expressions used to describe SWCCs have generally ignored the hysteresis. In addition, the shape of SWCC may depend on the void ratio which is changed by soil skeleton deformations or hysteretic behavior under various loading conditions. Hence, it is necessary to understand, both empirically and analytically, the relationship between soil skeleton deformations and the SWCCs of various soils. The typical SWCCs experimentally have drying, wetting, and the second drying curve. The measurement of a complete set of hysteretic curves is severely time-consuming and difficult works, then the first drying curve of SWCC is generally determined to estimate the hydraulic conductivity and shear strength function of partially saturated soils. This paper presents the hydraulic-mechanical behavior of partially saturated soils (weathered soil and silty soil) for volume changes and hysteresis in SWCCs regarding the difference between the first drying and wetting curve.

• Journal of the Korean Geotechnical Society
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• v.21 no.1
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• pp.15-27
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• 2005

In this paper, a method reasonably predicting soil water characteristic curve of domestic weathered granite soils was suggested, based on the test results obtained through experiments. In other words, a method to estimate the parameters of Fredlund and Xing's equation using an ANN (artificial neural network) was proposed. The particle size distribution, compacted water content and void ratio were used as input data in the ANN model for predicting the parameters, since it was found that these basic soil properties affect the parameters obtained from the test results and the fitting results of SWCC. The network model proposed in this study to obtain the parameters of Fredlund and Xing's SWCC equation produced reliable predictions, and the precision of the prediction results from the proposed method was high, in comparison with the prediction results of other methods.

• Journal of the Korean Geotechnical Society
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• v.16 no.6
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• pp.15-21
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• 2000

본 논문은 체적이 변하는 흙에 대하여 새로운 흙-수분 특성곡선 이론을 제시하고 이를 실험적으로 규명하였다. 그 결과, 점토와 같이 불포화되는 과정중 체적변형이 발생하는 흙의 흙-수분 특성곡선은 간극비와 흡인력의 함수이므로 체적변화를 무시할 수 없음이 밝혀졌다. 따라서 본 논문에서는 체적변화가 있는 경우 흙-수분특성곡선을 구하기 위하여 두가지 실험법을 채택하였다. 그 첫째는 전통적인 압력판 추출시험과, 중량함수비와 간극비와의 관계를 알 수 있는 수축한계시험을 실시하여 조합하는 방법이며, 둘째 방법은 압력판 셀을 새로인 고안하여 추출시험시에 체적 수축도 측정할 수 있는 수정된 압력판 셀 시험방법을 이용하는 것이다. 이 시험결과를 3차원 상의 면(surface)에서 표현하여, 체적변형을 고려한 흙-수분 특성을 규명할수 있도록 하였다.

• 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 $1.0{\sim}2.0$.

• International Journal of Highway Engineering
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• v.8 no.2 s.28
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• pp.87-93
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• 2006

To evaluate the deformational characteristics of subgrade soils, four subgrade samples in Korea were tested using the RC and TS tests with various dry unit weight and water content. Both the maximum modulus and normalized modulus reduction curves of subgrade soils were affected by the dry unit weight. The normalized modulus was decreased about 20% with increasing of relative compaction of 5%. It was founded that the variations of modulus of subgrade soils in Korea were over 40% with water content variation of $\pm$2%, and those effects can be estimated by exponential model. However, the normalized modulus reduction curves were almost identical and independent of water content. It was also founded that confining pressure, loading frequency, dry unit weight, and water content have an affect on modulus of subgrade soils independently. Therefore, it can be considered that those effects are independent variables.