• Structural Monitoring and Maintenance
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• 제11권1호
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• pp.1-18
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• 2024

Self-compacting concrete is widely used around the globe today due to its special and unique properties. This study examines the effect of natural and crushed gravel combinations in different percentages in short-and long-term properties of concrete. The best utilized sand had a fineness modulus of 2.7. In the mentioned mix designs, silica fume was used with 0 and 7% of the weight of the cement. In order to check the properties of fresh and hardened concrete, 9 and 5 test types were performed, respectively. The carried out tests were slump flow, V-funnel, J-ring, L-box, U-box and column segregation for fresh concrete, and compressive, tensile and flexural strengths for hardened concrete. A mix with only 100% natural gravel was considered as the control mix. According to the results, the control mix design and the one containing 100% crushed gravel with silica fume were the best in fresh and hardened concrete tests, respectively. Finally, using the optimization method, a mix design with 25% natural gravel, 75% crushed gravel and silica fume was introduced as the best mix in terms of the results of both fresh and hardened concrete tests.

• 한국농공학회지
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• 제43권1호
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• pp.116-121
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• 2001

This study is performed to examine the physical and mechanical properties of eco-concrete with polypropylene fiber. Test results show that the strengths are increased with increase of the content of natural gravel, excellent soil compound and polypropylene fiber. The coefficient of permeability is increased with increase of the content of the polypropylene fiber but it is decreased with increase of the content of natural gravel and excellent soil compound. The lowest coefficient of permeability is achieved by eco-concrete which it is 100 times lower than that of the control. The durability factor is increased with increase of the content of natural gravel and excellent soil compound, and decreased with increase of the content of polypropylene fiber.

• 한국도로학회논문집
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• 제20권2호
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• pp.9-17
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• 2018

PURPOSES : The frequency and severity of natural disasters such as torrential rain or typhoons have become increasingly significant worldwide. Events such as summer typhoons and localized torrential downpour can cause severe damages to a residential area and road networks, resulting in serious harm to the daily lives of people, especially in rural areas by isolating residents from road networks. An immediate and emergency repair technology for the collapsed road networks is urgently needed. This study introduces a new technology to repair road bases or slopes. METHODS : The development of new technology for emergency and permanent repair consists of first, packing of cement paste-coated gravel, second, combining appropriate equipment, and third, conducting a field applicability test. In this research, the compressive strength of cement pastecoated gravel, gravel-netting concrete properties, and packing efficiency were determined, and a full scale field mock-up test was carried out. RESULTS : The compressive strength of the cement paste-coated gravel concrete satisfied the required limit for road base of 5 MPa after 7 days. With appropriate netting materials and packing size, gravel-netting concrete was successful up to a slope of 1:1.5. The full scale field mock-up test showed efficiency in the field and penetration resistance performance. CONCLUSIONS : The new technology of emergency and permanent repair for damaged road bases and slopes, introduced in this study, showed satisfactory performance. The technology is expected to be applied in the field when construction procedures and quality specifications are made.

• 한국환경과학회지
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• 제17권11호
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• pp.1203-1210
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• 2008

Flow resistance in a natural stream is caused by complex factors, such as the grains on the bed, vegetation, and bed-form, reach profile. Flow resistance in a generally stable gravel bed stream is due to protrudent grains from bed. Therefore, the flow resistance can be calculated by equivalent roughness in gravel bed stream, but estimation of equivalent roughness is difficult because nonuniform size and irregular arrangement of distributed grain on natural stream bed. In previous study, equivalent roughness is empirically estimated using characteristic grain size. However, application of empirical equation have uncertainty in stream that stream bed characteristic differs. In this study, we developed a model using an analytical method considering grain diameter distribution characteristics of grains on the bed and also taking into account flow resistance acting on each grain. Also, the model consider the protrusion height of grain.

• Geomechanics and Engineering
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• 제37권4호
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• pp.359-370
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• 2024

The primary goal of this study is to evaluate the migration of fine granular materials into overlying layers under cyclic loading using a modified large-scale triaxial system as a physical model test. Samples prepared for the modified large-scale triaxial system comprised a 60 mm thick gravel layer overlying a 120 mm thick subgrade layer, which could be either tailings or railway sand. A quantitative analysis of the migration of fine granular materials was based on the mass percentage and grain size of migrated materials collected in the gravel. In addition, the cyclic characteristics, i.e., accumulated axial strain and excess pore water pressure, were evaluated. As a result, the total migration rate of the railway sand sample was found to be small. However, the total migration rate of the sample containing tailings in the subgrade layer was much higher than that of the railway sand sample. In addition, the migration analysis revealed that finer tailings particles tended to be migrated into the upper gravel layer easier than coarser tailings particles under cyclic loading. This could be involved in significant increases in excess pore water pressure at the last cycles of the physical model test.

• 암석학회지
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• 제26권3호
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• pp.255-269
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• 2017

여러 분야에서 높은 관심을 받고 있으며 무엇보다 지질학적으로 희소성과 순수성을 지닌 독도 천연보호구역의 해빈자갈퇴적층(몽돌 해변)을 대상으로 5년간 외부에서 유입된 역 이 얼마나 분포하는지에 대해 모니터링 하였다. 연구 지역인 동도 선착장 인근 및 서도 어민 숙소 인근 해빈자갈퇴적층에서, 주로 발견되는 몽돌의 종류에는 독도에서 직접적으로 기원한 것으로 판단되는 현무암, 조면암류, 응회암류와 외부에서 유입된 것으로 판단되는 화강암, 유문암, 편마암, 규암, 대리암, 그리고 콘크리트가 있다. 2011년과 2016년의 외래 역 데이터를 비교해 보면 동 서도에서 암종의 변화는 발견되지 않았으며, 각 지역에서 가장 빈번하게 발견되는 외래 역의 순위 역시 동도에서 화강암, 콘크리트, 편마암, 그리고 서도에서 콘크리트, 편마암, 화강암 순으로 동일하다. 그러나 동도와 서도의 전체 조사 면적에 대한 외래 역 면적의 비율은 다소 감소했다. 기존 시설물의 파괴와 외래 건축 자재 유입이 해빈자갈퇴적층에 존재하는 외래 역에 대한 주요한 유입 경로로 예상되는 가운데, 전체적인 오염도가 감소했다는 점은 연구기간 동안 외래 역 유입에 대한 관리가 대체로 개선 또는 최소한 악화되지 않았다는 점을 지시한다. 한편 지속적인 낙석이 몽돌의 분포에 영향을 끼친 것으로 판단되며, 낙석 영향에 대한 지속적인 평가가 요구된다.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2005년도 총회 및 춘계학술발표회
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• pp.110-113
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• 2005

The objective of this study was to examine the effect of proposed permeable eobarrier system for removal of PCE from groundwater. The materials used for the natural geobarrier are gravel bean and silty clay. In addition, the effect of Pyeongtaek soil on PRB assessed in this experiments. It was observed that the adsorption of PCE in natural geobarrier system is eligible for real site. However, natural geobarrier system has various factors based on using materials. Therefore, more laboratory work is needed to study about permeable geobarrier.

• Journal of Species Research
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• 제13권1호
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• pp.10-31
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• 2024

In this study, 11 strains of epilithic cyanobacteria belonging to six unrecorded species in Korea were isolated from gravel submerged in freshwater of seven collection sites in Korea. The morphological characteristics of the six species isolated in this study were consistent with the type strain of each species, and the similarity of the 16S rRNA gene sequences with the type strain of each species were 98.8-100%. In the phylogenetic tree using the 16S rRNA gene sequences, the 11 strains of these six species formed the same cluster as the strains of each species. The habitat of each previously reported species is mainly the soil surface, but all Korean strains appeared from the gravel submerged in freshwater. As a result of the morphological, ecological, and molecular analyses, these six species of cyanobacteria were identified as Geminocystis papuanica, Allocoleopsis franciscana, Ancylothrix terrestris, Klisinema persicum, Scytolyngbya timoleontis, and Shackletoniella antarctica, which were added as newly recorded species in Korea.

• 지구물리
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• 제6권2호
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• pp.71-77
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• 2003

Generally the dynamic characteristics of stone wall structures depend on several factors such as contact, the type of interlocking bonding stones, and the filling materials. This paper describes a non-destructive technique for diagnosis of historic masonry stone structures using the measurement of natural frequency technique. For this purpose, the castle wall of Nag-An Folk Town located in Sunchon, Korea was selected as a model. The Nag-An Town Castle is one of the well maintained historical remains constructed in the Chosun Kingdom of Korea. The construction started in 1397 A.D and was finished in 1626 A.D. The non-mortar castle wall is 1470m long and the average height is 4m with a width of 3 4m. The exterior of the wall is bonded with 1 2 m rectangular rough-faced stone and the inside of the wall is filled with gravel. The traditional village still remains inside the Nag-An Town Castle, and they have a regional food festival every October. Transverse vibrations were measured at 8 points around the castle. The measured natural frequency of the first mode was 26Hz 41Hz, and the shear modulus of filling material was 2.142 x $10^3$ ~ 8.915 x $10^3$kgf/$cm^2$ . With these results, it may be assumed that the filling material is gravel or a sand-gravel mixture. It is expected that the information provided by this paper will be useful for addressing the maintenance problems of the old castle walls.

• 환경생물
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• 제17권4호
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• pp.389-400
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• 1999

본 연구는 북한강 수계에 연계되어 있는 사기막천 및 조종천의 4개 지점을 대상으로 저서 대형 무척추동물을 1년간(1993) 하상별로 채집, 분류하였으며, 이들 저서 대형무척추동물의 출현빈도율 및 종내의 상대 빈도율에 따른 각 분류군의 하상 선호도를 살펴보고자 하였다. 채집된 대부분의 대형 무척추동물들은 cobble과 pebble 하상 선호성을 보였으며, Ephemera orientalis, Davidius lunatus, Tipula KUb, Isonychica japonica and Tabanus amaenus등은 gravel/sand 하상 선호성임을 확인할 수 있었다. 일면, 본 연구를 통하여 cobble과 pebble 하상에서 채집된 대형 무척추동물군의 종수는 gravel/sand 하상에서 채집된 종 수에 비해 현저히 많음을 알 수 있었다.