• The Journal of Engineering Geology
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• v.28 no.4
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• pp.687-699
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• 2018

Understanding rain infiltration into the ground is an important feature of landslide risk evaluation. In this study, a landslide risk index for the study area is suggested, wherein the result of the landslide risk evaluation, based on the factor of safety (FS), is used. The landslide risk index is a landslide risk prediction index that utilizes the saturated depth ratio of the ground. Based on the landslide risk result for the study area, it was found that the FS was first to decrease. However, it gradually became convergent over the 50-year rainfall intensity study period, a result that is similar to the relationship between the saturated depth ratio and soil thickness. Moreover, saturated depth was also found to be deeper on gentle slopes than steep slopes. As such, the landslide risk index, based on the Inhu-ri study result, is thus suggested. Additionally, the suggested landslide risk index was compared and analyzed against the rainfall intensity of previous landslide experience. Results thus revealed that almost all landslides that occurred were over 0.7, which is the second grade, based on the landslide risk index.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.5 s.57
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• pp.160-168
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• 2009

After steel bar was corroded it removes concrete contaminated, it does steel bar corrosion protection, repairing method and corrosion inhibitor spreading method are difficult to secure corrosion protection performance. Accordingly, in this research before Research and Development to penetrate corrosion inhibitor to high pressure by steel bar position, it measures penetration depth through corrosion inhibitor high pressure penetration experiment and amount of nitrite by position and then it predicts penetration depth in accordance with water-cement ratio, pressure, pressure time and it computed water-cement ratio, pressure, pressure time to be more than 0.6 mol ratio of chloride ion and nitrite to have outstanding corrosion protection performance. As a result of experiment, water-cement ratio gives the biggest influence to penetration of corrosion inhibitor and also the more depth of specimen becomes deep, concentration of penetrated corrosion inhibitor does not equal and becomes low.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.796-800
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• 2009

토목구조물 및 사면의 붕괴는 집중호우가 내리는 경우 많이 발생하고 있으며, 특히 사면에서는 붕괴까지의 변형이 급속히 진행되어 이를 사전에 예방하기는 매우 어려운 현실이다. 침투 및 배수과정에서의 사면 붕괴는 강우침투로 인한 지반의 물리적 특성변화가 직접적으로 사면의 안전계수 변화에 영향을 주는 것으로 판단되며, 이때 발생하는 물리적 특성변화로는 침투시 사면 내 지반의 단위 중량은 증가하여 전단응력의 증가 및 전단강도 감소현상이 발생하며, 이와 반대로 사면 내 배수로 인하여 전단응력의 감소 및 전단강도의 증가현상이 발생한다. 따라서 본 연구에서는 강우침투로 발생하는 지반의 포화도 변화를 지반 내 투수계수의 함수로 설명하여 강우로 인한 지반의 침투 및 배수과정을 규명하고자 한다. 일반적으로 지반 내 지하수의 침투과정은 라플라스 공식을 적용한다. 그러나 라플라스 공식은 정상 상태(Steady State)일 경우에만 사용할 수 있고, 강우 등으로 인한 지하수의 수두 변화가 발생한 비정상 상태(Unsteady State)의 경우에는 부적합하므로 사면과 옹벽 등의 토질구조물에서는 안전성 변화를 계산할 수 없다. 이를 위해 사면 내 지반의 침투 및 배수과정을 투수계수의 함수로 나타내어, 강우의 침투과정을 Fourier Series, 변수분리법 및 섭동함수를 사용하여 식으로 유도함으로서 강우에 의한 지반의 침투 및 배수과정에 따른 사면 내 지하수의 분포를 예측한다. 침투과정 해석을 위하여 지표에서 포화대까지의 깊이 10m의 모델사면 및 지표부터 포화대까지의 포화도는 직선으로 비례한다는 가정을 적용한다. 먼저 푸리에 급수를 이용, 시간에 따른 온도를 열전달에 관하여 편미분하여 발생하는 열확산계수를 투수계수로 변환함에 따라 지하수의 시간과 수직방향거리에 대한 지반의 포화도를 산정한다. 변수분리법은 산정된 포화도에 지반의 초기조건과 경계조건를 고려하기 위해 적용하며, 변수분리법에 의해 산정된 지하수 분포를 섭동함수법으로 과도 및 정상상태로 분류한다. 본 연구의 수행으로 인해 얻어진 결과를 요약하면 다음과 같다. 첫째, Fourier Series와 변수분리법, 섭동함수를 이용하여 강우에 의한 지반의 포화도 변화를 수식적으로 나타낼 수 있으며 둘째, 지반에서의 강우침투과정을 식으로 표현함으로서, 깊이별 시간에 따른 포화도의 영역이 상부로부터 하부로 전이되는 과정을 알 수 있다. 셋째, 푸리에 급수를 이용한 지반의 침투계산으로 강우로 인한 지반의 포화영역 및 불포화영역을 명확히 구분할 수 있으며, 각 깊이별 포화도를 계산하여 각 구간에서 불포화구간의 전단강도에 대한 보다 정확한 계산이 가능하리라 판단된다.

• The Journal of Engineering Geology
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• v.22 no.3
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• pp.343-351
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• 2012

This study proposes a modified equation to calculate the factor of safety for an infinite slope considering the saturation depth ratio as a new variable calculated from rainfall infiltration into unsaturated soil. For the proposed equation, this study introduces the concepts of the saturation depth ratio and subsurface flow depth. Analysis of the factor of safety for an infinite slope is conducted by the sequential calculation of the effective upslope contributing area, subsurface flow depth, and the saturation depth ratio based on quasi-dynamic wetness index theory. The calculation process makes it possible to understand changes in the factor of safety and the infiltration behavior of individual rainfall events. This study analyzes stability changes in an infinite slope, considering the saturation depth ratio of soil, based on the proposed equation and the results of soil column tests performed by Park et al. (2011 a). The analysis results show that changes in the factor of safety are dependent on the saturation depth ratio, which reflects the rainfall infiltration into unsaturated weathered gneiss soil. Under continuous rainfall with intensities of 20 and 50 mm/h, the time taken for the factor of safety to decrease to less than 1.3 was 2.86-5.38 hours and 1.34-2.92 hours, respectively; in the case of repeated rainfall events, the time taken was between 3.27 and 5.61 hours. The results demonstrate that it is possible to understand changes in the factor of safety for an infinite slope dependent on the saturation depth ratio.

• Journal of the Korean Geotechnical Society
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• v.16 no.5
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• pp.107-116
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• 2000

강우에 의한 얕은 사면파괴는 우리 나라에서 흔히 볼수 있는 사면파괴의 형태이다. 본 연구에서는 재현기간에 따른 강우강도와 지속시간을 고려한 한계평형법에 의하여 이러한 얕은 사면파괴의 가능성을 평가하기 위함 방법에 대하여 논의하였다. 이를 위해 일차원 침투모델인 Green-Ampt 모델에 바탕을 둔 두 방법을 고려하였다. 즉 침투능에 따른 침투깊이를 산정하는 Pradel과 Raad의 방법과 일정한(uniform) 강우강도가 작용할 경우 폰딩(ponding)에 대해 해를 주는 Mein과 Larson의 방법을 고려하여 함수특성이 알려진 화강풍화토사면에 적용하였다. 연구결과에 의하며 Pradel과 Raad 방법은 실제 적용된 강우강도가 아닌 침투능을 바탕으로 침투깊이를 산정하므로 Mein과 Larson 방법에 비해 보수적인 사면안정 해석결과를 예측한다.

• Journal of the Korean Geotechnical Society
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• v.29 no.9
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• pp.5-15
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• 2013

In this paper, the unsaturated slope stability analysis considering suction stress (Lu and Godt, 2008) was introduced and the results applied for a certain sand slope were analyzed. The unsaturated slope stability analysis considering suction stress can analyze both conditions of steady infiltration and no infiltration, and it can estimate the safety factor of slope as a function of soil depth. Also, the influence of weathering phenomenon at a certain depth from the ground surface can be considered. The stability analysis considering suction stress was applied to the unsaturated infinite slope composed of sand with the relative density of 60%. The suction stress under no infiltration condition was affected by ground water table until a certain influencing depth. However, the suction stress under steady infiltration condition was affected by seepage throughout the soils. Especially, the maximum suction stress was displayed around ground surface. The factor of safety in the infinite slope under no infiltration condition rapidly increased and decreased within the influence zone of ground water table. As a result of slope stability analysis, the factor of safety is less than 1 at the depth of 2.4 m below the ground surface. It means that the probability of slope failure is too high within the range of depths. The factor of safety under steady infiltration condition is greater than that under no infiltration condition due to the change of suction stress induced by seepage. As the steady infiltration rate of precipitation was getting closer to the saturated hydraulic conductivity, the factor of safety decreased. In case of the steady infiltration rate of precipitation with $-1.8{\times}10^{-3}cm/s$, the factor of safety is less than 1 at the depths between 0.2 m and 3 m below the ground surface. It means that the probability of slope failure is too high within the range of depths, and type of slope failure is likely to be shallow landslides.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.703-708
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• 2005

The effects of polymer-cement ratio and antifoamer content on the setting time and durability of high-fluidity polymer-modified mortars using redispersible polymer powder are examined. As the result, the setting time of the polymer-modified mortars using redispersible polymer powder tends to be delayed with increasing polymer-cement ratio, regardless of the antifoamer content. The water absorption, chloride ion penetration depth and carbonation depth of the high-fluidity polymer-modified mortars using redispersible polymer powder decrease with increasing polymer-cement ratio and antifoamer content. The resistance of freezing and thawing and chemicals improvement is attributed to the improved bond between cement hydrates and aggregates because of the incorporation of redispersible polymer powder

• Journal of the korean academy of Pediatric Dentistry
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• v.45 no.3
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• pp.290-298
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• 2018

This study aimed to evaluate surface morphology and resin tag penetration of resin infiltration into primary anterior teeth after enamel deproteinization with sodium hypochlorite (NaOCl) prior to phosphoric acid ($H_3PO_4$) etching. Ninety primary anterior teeth with non-cavitated caries lesion were devided five groups according to enamel pretreatment as follows, group I-15% hydrochloric acid (HCl) 2min. ; group II-5.25% NaOCl 1min., 35% $H_3PO_4$ 1min. ; group III-5.25% NaOCl 2min., 35% $H_3PO_4$ 1min. ; group IV-5.25% NaOCl 1min., 35% $H_3PO_4$ 2min. ; group V-5.25% NaOCl 2min., 35% $H_3PO_4$ 2min. Fifteen teeth were examined etched surface structure using field emission-scanning electron microscope. Seventy five teeth were infiltrated with resin, maximum penetration depth and percentage penetration were analysed using dual fluorescence confocal microscopy. As the application time of NaOCl increased, ratio of enamel type I, II were increased. Percentage penetration (PP) was higher in group V than group II, III (p < 0.05). PP of group IV, V did not show any differences. Non-cavitated caries of primary anterior teeth can be treated with resin infiltration. Enamel deproteinization with NaOCl prior to 35% $H_3PO_4$ etching could be an alternative of 15% HCl etching in resin infiltration.

• Journal of the korean academy of Pediatric Dentistry
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• v.39 no.1
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• pp.1-10
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• 2012

The concept of resin infiltration which was born in an innovative philosophy to arrest the incipient caries. However, the structural changes of resin infiltrated lesions have not yet explained completely. The liquid resin might contribute not only to maximizing the penetration but to deteriorating physical stability. This study was performed to examine some physical and histological features of resin infiltrated incipient carious lesions. With the specimen of resin infiltrated lesions, microhardness by nanoindentation in depth profile, morphology of resin tags were revealed after HCl dissolution, and degree of microleakage were assessed. The percentage of microhardness of surface layer and lesion body of untreated specimen to sound enamel was 64.6% and 24.6% respectively, while that of resin-infiltrated lesions was 72.1%, showing significant difference (p<0.05). The resin tags observed under SEM had relatively homogeneous length of 433(282~501) ${\mu}m$ on the average. Among 20 specimens for microleakage assessment, 13 specimens showed no leakage while 5 and 2 showed leakage into outer and inner half of lesion respectively. It was thought the infiltrant resin penetrates deeply and homogeneously into lesion body and improves its hardness with relatively good physical stability.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.2
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• pp.71-79
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• 2003

The estimation functions were proposed for calculating diffusion coefficient, chloride binding, and evaporable water. The program estimating chloride ion penetration was developed on the basis of these functions and the effects of humidity, curing temperature, water-cement ratio, and $C_3$A on chloride penetration were analyzed. The relative humidity increases the depth of chloride ion penetration and the trend becomes greater with aging. On the contrary, the influence of curing temperature on chloride ion penetration decreases with aging. By the way, the rise of $C_3$A in cement increases total chloride concentration on the surface as the bound chloride concentration increases but it decreases total chloride concentration on the inner part as the diffusion velocity of free chloride decreases. The fall of water-cement ratio decreases the chloride penetration depth rapidly. Therefore, the reduction of water-cement ratio may be the most effective method for reducing of the steel corrosion by chloride penetration.