• Geomechanics and Engineering
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• 제31권2호
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• pp.167-181
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• 2022

Soil liquefaction has been one of the most important concerns in geotechnical earthquake engineering in recent years, due to its damages to structures and its destructive effects. The cyclic liquefaction of silty sands, in particular, remains of great interest for both research and application. Although many factors are known that affect the liquefaction resistance of sands, the effect of fine grain content is perhaps one of the most studied and still controversial. In this study, 48 deformation-controlled cyclic simple shear tests were performed on BS and CS silt samples mixed with 5%, 15% and 30% by weight of Krk085, Krk042 and Krk025 sands in constant-volume conditions to determine the liquefaction potential of silty sands. The tests were carried out at 30% and 50% relative density and under 100 kPa effective stress. The results revealed that the liquefaction potential of silty sand increases with increasing average particle size ratio (D_50sand / d_50silt) of the mixture for a fixed silt content. Furthermore, for identical base sand, the liquefaction potentials of coarse grained sands increase with increasing silt content, while the respective potentials of fine grained sands generally decrease. However, this situation may vary depending on the silt grain structure and is affected by the nature of the fine grains. In addition, the variation of the void ratio interval was shown to provide a good intuition in determining the liquefaction potentials of silty sands, while the intergranular void ratio alone does not constitute a criterion for determining the liquefaction potentials of silty sands.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.993-998
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• 2009

This study was conducted to propose the model that is able to predict long-term settlement of sands containing carbonates. We can observe that in addition to the initial elastic compression, a considerable additional compression occurs with long-term period in some sands. The compressibility of sands is significantly dependent on particle characteristics. Some sands have many pores and particularly has an angular shape. To predict of long-term settlement of these sands which contain carbonates, first of all a variety of tests which are to assess chemical, physical and compression characteristics of these sands were conducted. Second, in order to know settlement with time, the time parameter was determined by analyzing the measured data obtained from $\bigcirc\bigcirc$ area. The measured settlement of this area shows that in addition to the initial elastic compression, a considerable additional compression occurring with time. It was caused by the crushing, shattering, and rearrangement of particles, which were real phenomena in sandy soils under loading condition. Based on this case study, we proposed that a simple method is able to predict settlement with time of sandy soil containing carbonates.

• 미생물학회지
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• 제50권4호
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• pp.376-380
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• 2014

경상북도 영덕군과 포항시에 위치한 해수욕장 주변에서 생활하수나 생활쓰레기 등의 환경조건이 해변모래에 서식하는 미생물 분포에 어떤 영향을 미치는지를 조사하기 위하여, 10월 중순에 12곳의 해변모래를 채취하여 16S rRNA 유전자를 pyrosequencing 방법으로 분석하였다. 해수 부근의 청결한 모래에는 Acidobacteria, 담수 부근의 모래에는 Proteobacteria, 생활하수 부근의 모래에는 Cyanobacteria, 해변공원 부근의 모래에는 Bacteroidetes 그룹이 20-90% 정도로 높게 분포하였고, 생활하수가 해수와 합해지는 해변모래에서는 Actinobacteria, Chlorobi, Deferribacteres, Deinococcus-thermus, Firmicutes, Gemmatimonadetes, Nitrospirae, Verrucomicrobia 그룹이 1-5% 정도로 낮게 분포하였다.

• 한국건설순환자원학회논문집
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• 제4권4호
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• pp.99-104
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• 2009

폐주물사의 재활용을 위하여 최근 연구자들은 매립에 의존하지 않고 리사이클링하기 위해 노력하고 있으며, 폐주물사의 효율적인 재활용방법으로 시멘트와 결합하여 각종 건설용 자재로 사용하는 방법을 연구하고 있다. 본연구에서는 폐주물사를 대체 잔골재로 사용하여 1:2, 1:3, 1:5의 배합으로 부 빈배합의 예비실험을 통해 폐주물사의 성상을 실험적으로 검토하여 폐주물사를 적용할 수 있는 범위를 배합비 1:3의 W/C 43%와 50%의 2개 수준에 대한 실험으로 폐주물사의 적정 대체율을 찾아 활용할 수 있는 방안을 제안한다. 실험결과 굳지않은 모르타르의 특성으로 유동성은 폐주물사의 대체율이 증가 할수록 플로우는 감소하는 것으로 나타났으며, 공기량도 유동성과 유사한 경향으로 폐주물사의 대체율이 증사 할수록 감소하는 것으로 나타났다. 경화모르타르의 강도특성은 폐주물사를 치환 할수록 강도는 증가하는 것으로 나타났고, 폐주물사를 치환함으로써 초기강도가 증가하는 것을 알 수 있다. 수밀특성으로 투수량과 흡수량은 폐주물사의 미립분에 의해 공극충전효과로 투수량이 감소하는 것으로 나타나 수밀성을 요구하는 구조물에 폐주물사의 치환은 효과적일 것으로 사료된다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2005년도 추계 학술논문 발표대회
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• pp.17-20
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• 2005

This study investigates mock-up test of the concrete containing crushed sands with improved quality and following could be draws as conclusions. The slump satisfies the target value. The air content reaches the goal, however, it decreases by the occurrence of loss with elagse of age. In normal strength region, the setting time of CS24 member is shorter than that of SS24 member. In high strength region, the setting time of SS50 member is make only slower than that of CS5O because of the use of retarding AE agent. The compressive strength of the concrete using crushed sands is little higher than the concrete using washed sea sands, and the compressive strength of core sample increases at lower part. Drying shrinkage of the concrete using crushed sands is larger than that using washed sea sands. At water caring condition, both the concrete using crushed sands and using washed sands expand at first, exhibit to be swelled and with elagse of age, they remain relatirely constant. Also, the drying shrinkage occurred greatly when the width and thickness of a member are small because it is easy to evaporate the inner part vapor in the small width and thickness of a member. there can be little different according to the location of a contact gauge, however it is similar to the change of specimen's length change. The concrete using crushed sands, of which grading, grain shape and fine particle is improved, are comparable to the quality of the concrete using washed sea sand.

• Geomechanics and Engineering
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• 제22권2호
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• pp.165-171
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• 2020

Laboratory determination of strength and deformation behavior of clean sands and gravels has always been challenging due to the difficulty in obtaining their undisturbed samples. An alternative solution to this problem is to develop correlations between mechanical properties of cohesionless soils and their gradation characteristics. This study presents database of 3 natural sands with 11 varying particle size gradation curves to allow investigating relationships between mean particle size, maximum and minimum void ratio, relative density and shear strength of the test soils. Direct shear tests were performed at relative densities of 50, 75 and 95% to explore the effects of gradation and density on the angle of internal friction of the modeled sand samples. It is found that the mean grain size D₅₀ bears good correlations with void ratio range (e_max - e_min) and peak angle of internal friction 𝜙'_peak. The generated regression models are in good agreement with published literature and can be considered as reliable for natural sands in Pakistan. These empirical correlations can save considerable time and efforts involved in laboratory and field testing.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 가을 학술발표회 논문집
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• pp.605-612
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• 2002

The objective of this study is to investigate the behavior of Visco-Elasto-Plastic materials of Silicate Grouted Sands due to external load. Uniaxial compression strength of silicate grouted sands was increased accordingly with curing time, but it was almost unchanged after 7days. A series of uniaxial compression creep tests were peformed for $\sigma$/$\sigma$$\sub$f/ = 8%,16% and 24%. The tested Silicated Grouted Sands exhibits three types of strains : elastic, plastic, viscoelastic. It is seen that the magnitude of the instantaneous recoverable strains $\varepsilon$$\sub$r/(o) is approximately independent of the unloading time. In this tests, The total creep strains( elastic, plastic, viscoelastic) are proportional to the stress level. Based on the constant creep test results, relationships between the time and the creep compliance are developed.

• 한국안전학회지
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• 제15권3호
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• pp.83-87
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• 2000

Combustion characteristics of immobilized benzene and toluene in sands were studied. Experiments were performed by burning benzene and toluene immobilized on sands(particle size 0.1~0.5mm) to measure combustion rate and combustion temperature. The longer time from ignition to extinguishment was resulted from the larger particle size exhibited the higher mass burning rate. Of aromatic compounds tested the relative magnitude of facilitation of combustion was benzene and toluene. Combustion temperature of benzene and toluene without regard to the types of benzene and toluene was not increased with smaller sand. However, with larger sands, combustion temperature of benzene and toluene were increased by 50~$100^{\circ}C$ and the highest combustion temperature was obtained with larger sands.

• 한국제4기학회:학술대회논문집
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• 한국제4기학회 2005년도 추계학술대회
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• pp.34-39
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• 2005

A 120-cm core recovered from Lake Hovsgol, the northern Mongolia provides evidence for climate variability since the Marine Isotope Stage 3, representing a sharp lithological change. The lowermost part of the core consists of diatom-barren calcareous silty clay without coarse sands, framboidal pyrite, and biogenic components deposited during the MIS 3. Following the last glacial maximum, in-situ moss is included in the sediments, as lake-level was retreated by cold and dry environment with low precipitation. The AMS radiocarbon ages of the plant fragments match a marked lithologic boundary between 14,060 and 14,325 $^{14}C$ yr BP. The contents of coarse sands abruptly increase, indicating probably wind-derived sandy dust or coarse grains contributed from floating icebergs. And abundant framboidal pyrite grains were deposited in an anoxic environment, as reflected by high accumulation of organic matters at a low lake stand. During the deglaciation, quantities of coarse sands, ostracod, shell fragments, framboidal pyrite, and diatom markedly varies by regional and global scale climate regimes. Some allochthonous coarse sands were probably ice-rafted debris derived from floating icebergs. A rapid increase in diatom productivity probably marked the onset of Bolling-Allerodwarming. Subsequent high concentration of framboidal pyrite probably represents a dry and cold condition, such as Younger Drays events. Consistent warm period with high precipitation at Holocene is documented by diatomaceous clayey ooze without framboidal pyrite, coarse sands, and ostracod.

• 유기물자원화
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• 제18권4호
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• pp.38-44
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• 2010

주물사는 규사에 벤토나이트나 resin 등의 점결제를 첨가한 것으로써 주물제품의 생산을 위한 주형에 사용되고 있다. 주물업체에서 반복적으로 사용된 주물사는 결국 열에 의해 파쇄되어 그 기능을 상실하며 폐주물사로 전락된다. 폐주물사는 점결제의 성분 및 함량에 따라 지정 또는 일반폐기물로 처분되고 있지만 주물사의 주종을 이루는 규사는 열에 의해 변성되지 않는 성질로 인하여 적절한 처리를 통하여 재사용이 가능하다. 본 연구에서는 국내 외 폐주물사의 발생 및 처리, 재활용현황, 그리고 재활용에 관련된 제도 및 재활용을 저해하는 요인 등을 조사하여 문제점을 도출하고 폐주물사의 재활용 활성화 방안을 제시하였다.