• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.25-34
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• 2013

This paper presents the results of a reduced-scale physical model investigation into the behavior of retaining walls subject to cycles of wetting and drying due to rainfall infiltration. Reduced-scale model walls equipped with a water spraying system that can simulate the wetting process were first constructed and a series of tests were conducted with due consideration of different rainfall intensities and backfill soil types. The results indicate that cycles of wetting and drying process have adverse effects on the wall behavior, increasing wall deformation as well as earth pressure acting on the wall, and that the first cycle of wetting and drying process has more pronounced effect on the wall performance than the ensuing cycles. It is also shown that the degree to which the wetting and drying cycles affect the wall behavior depends greatly on the backfill soil type, and that the larger the fine contents, the greater is the effect of cycles of wetting and drying on the wall behavior. Practical implications of the findings from this study are discussed in great detail.

• Journal of the Korean Geosynthetics Society
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• v.10 no.4
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• pp.19-28
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• 2011

This paper presents the results of an investigation into the effect of cyclic wetting-drying on the compressive strength characteristics of decomposed granite soils. A series of plane strain compression (PSC) tests were performed on test specimens with varying fine contents under different wetting-drying cycles to investigate the change in compressive strength under the process of wetting-drying cycles. The effect of wetting-drying cycles on the structural particle rearrangement at a micro-scale level was also examined using scanning electron microscope (SEM) tests. It was shown that the soil containing larger fines showed more significant decrease in compressive strength compared with the soils with less fines. Also found was that the wetting-drying cycle did not have significant effect on the particle arrangement.

• Journal of the Korean GEO-environmental Society
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• v.15 no.10
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• pp.29-34
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• 2014

In order to examine strength properties depended on climate changes of solidified soil amended by porosity silica which enhance harms of cement, this study conducts a wetting and drying repetition test and then, attempts to verify strength properties before and after solidified soil gets environmental influence. Test pieces for the unconfined compression test changed the mixing ratio of solidified soil compared to mixed soil weigh to 5 %, 10 % and 15 %. For each step, it was created by mixing 0.5 %, 1.0 % and 1.5 % of wood chips, and curing period for 7, 14, and 28 days. Then, the wetting and drying repetition process was repeated 0, 3, 6, and 12 cycles to analyze mechanical properties. To also evaluate changes of relative dynamic elastic modulus before and after the wetting and drying, dynamic elastic modulus tests were conducted when each cycle was completed.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.13-22
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• 2013

This paper presents the results of a numerical investigation into the behavior of retaining wall subject to cycles of wetting and drying due to rainfall. The stress-pore pressure coupled finite element modeling strategy was first established for stimulating the wall behavior. A series of finite element analyses were then performed on a range of conditions including different rainfall and backfill conditions. The results indicated that the rainfall intensity was the primary influencing factor for the wall behavior. Also revealed was that the pre-rainfall condition determines the magnitudes and the distribution of matric suction which in fact has a significant impact on the behavior of wall during a major rainfall. This result demonstrates the importance of incorporating the pre-rainfall condition for numerical modeling of walls during heavy rainfall. Practical implications of the findings from this study are discussed in great detail.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.527-527
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• 2016

최근 급증하는 이상기후 등으로 인하여, 가뭄 및 홍수 등의 자연재해가 반복적으로 발생하는 등 수자원관리에 어려움이 증대되고 있다. 본 연구는 토양수분량, 강우량, 수위관측 및 증발산량 관측이 수행되고 있는 용담-구량천 유역을 대상으로, PDM 토양저류 함수 모형을 습윤(6월~9월) 및 건조(10월~5월)기로 분리 적용하여 기간에 따른 유역 유출 특성을 분석하였다. 습윤 및 건조기의 유출률(유량/총강우량)은 각각 0.61~0.65와 0.31~0.42으로 서로 다른 유출 특성을 나타내고 있다. 2014~2015년 유역의 관측 토양 수분 자료(심도 100~200mm)와 PDM 토양저류 함수를 활용한 모의 결과가 습윤기에서 유사한 경향성을 보이고 있다(R2=0.9). 이를 바탕으로 용담-구량천 유역의 토양 저류 및 유출 특성을 분석한 결과, 기간을 습윤기 및 건조기로 분리하여 각각의 유역 유출 모형을 구축하는 것이 필요하다고 판단된다. 향후 단기 홍수 사상의 분석을 통한 홍수 유출 및 토양 저류 분석을 위한 모형을 제시하고자 한다.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.57-64
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• 2003

The liquefaction potential of saturated sands under seismic loading conditions has been carefully considered by many investigations. Typical of these investigations is the laboratory determination of cyclic strength of sands by means of cyclic triaxial tests. This study was conducted to investigate the effects of the method of sample preparation on the liquefaction characteristics of remolded samples of saturated uniform sands. Cyclic triaxial tests were performed on saturated uniform sand compacted to the same density by 3 different procedures of pluvial compaction through air, pluvial compaction through water and vibratory compaction. It was validated that the cyclic stress ratio of remolded saturated uniform sands by different compaction procedures at the same density was very different.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1023-1026
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• 2008

과거에 수문자료 시계열 모의기법은 수자원시스템 설계에 사용되는 일강수량 모의에 주로 이용되어 왔지만 최근에 기후변화에 따른 수문사상의 변동성을 평가하기 위한 기본 자료 모의를 위한 방법론으로 많이 이용되고 있다. 수문시스템에서 강수는 현상의 발생여부에 따라 건조일과 습윤일이 교대로 반복되는 과정으로 구성되어 있으며 건조일, 습윤일 등으로 구분하고 습윤일의 강수량을 상태별로 분류하여 각 상태별 천이확률을 계산함으로써 장래에 발생 가능한 강수사상의 모의 발생이 가능하다. 기후변화 영향 평가 연구에서 가장 중요한 문제 중의 하나는 기후변화로 기인하는 수문사상의 전체적인 거동의 변동사상을 추정하는 것이며 이를 기존 모형들과 연계시키는 방법이라 할 수 있다. 이러한 관점에서 본 연구에서는 천이확률 및 강수 모의에 이용되는 Gamma 확률분포와 같은 분포형의 매개변수들이 우리가 목적으로 하는 월강수량 또는 계절강수량의 총량을 유사하게 모의할 수 있도록 CWGEN(Cross-validated Canonical Correlation Analysis-Weather Generator)를 도입하였다. 이를 국내 강수 지점을 대상으로 검토 평가하였다.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.27-37
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• 2001

본 연구에서는 지금까지 수행한 건조토 지반에 대한 말뚝의 수평거동 연구의 연속된 연구로서 지반내에 함수비가 존재하는 포화토 및 습윤토 지반에서의 수평거동에 대한 지반내 함수비의 영향성을 평가하고자 함이 목적이다. 말뚝의 수평거동을 고찰하기 위하여 각각 다른 함수비를 갖는 네 종류의 지반과 말뚝의 두부 및 선단 구속조건이 다른 네 종류의 말뚝조건으로 모형실험을 수행하였다. 본 연구에서 1회의 지하수 상승과 하강을 반복하는 모형실험결과에 의하면, 포화토와 습윤토 지반의 수평지지력은 건조토 지반에 비하여 각각 26%~45% 감소와 20%~36%정도 증가하는 것으로 나타났다. 말뚝두부 고정과 선단 자유조건의 경우, 동일 수평변위 1mm에서의 최대 휨모멘트는 건조토 지반에 비하여 25%의 함수비를 갖는 습윤토 지반에서 약 48% 증가하나, 34.06%의 함수비를 갖는 포화토 지반에서는 반대로 68% 감소하였다. 이는 지하수의 존재로 인한 입자간 인력에 의한 유효응력과 겉보기강도의 증가 그리고 단위중량의 증가로 설명할 수가 있다. 지속수평하중에 대한 수평변위와 최대 휨모멘트의 변화를 포화토 및 습윤토 지반에서 관찰할 수 있었다.

• Water for future
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• v.29 no.6
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• pp.179-188
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• 1996

The chronical sequences of daily precipitation are of great practical importance in the planning and operational processes of water resources system. A sequence of days with alternate dry day and wet day can be generated by two state Markov chain model that establish the subsequent daily state as wet or dry by previously calculated vconditional probabilities depending on the state of previous day. In this study, a synthetic generation model for obtaining the daily precipitation series is presented by classifying the precipitation amount in wet days into multi-states. To apply multi-state Markov chain model, the daily precipitation amounts for wet day are rearranged by grouping into thirty states with intervals for each state. Conditional probabilities as transition probability matrix are estimated from the computational scheme for stepping from the precipitation on one day to that on the following day. Statistical comparisons were made between the historical and synthesized chracteristics of daily precipitation series. From the results, it is shown that the proposed method is available to generate and simulate the daily precipitation series with fair accuracy and conserve the general statistical properties of historical precipitation series.

• Water for future
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• v.21 no.2
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• pp.193-201
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• 1988

A simplified model for higher order scanning curves in the soil water characteristic function is suggested. The conceptual hysteresis models developed by $Mualem_{8,9}$ are simplied for higher order scanning curves. Higher order drying curves are regarded as primary drying curves and the last wetting reversal point is assumed to be on the main wetting curve by moving that point vertically downward. For the higher order wetting curves, it is assumed that these curves can be regarded as primary curves and the last wetting reversal point sits on the imaginary main drying curve which passes through the last wetting reversal point. The water content computed from the simplified model are compared with those obtained from Mualem's original model for second order scanning curves. It is found that absolute differences between the two methods aree relatively small and the simplified model always underestimates for higher order drying curves while it overestimates for higher order wetting curves. Hence, those two tend to compensate each other for repeated drying-wetting processes. The simplified model approximates higher order scanning curves well and reduces computation considerably.