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RISS 인기검색어
- 검색키워드
- 저자 : Hiroshi Fukuoka (검색결과 5 건)
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Fukuoka, Takaki,Uchida, Kenya,Sung, Young Mo,Shin, Ji‐,Young,Ishida, Shintaro,Lim, Jong Min,Hiroto, Satoru,Furukawa, Ko,Kim, Dongho,Iwamoto, Takeaki,Shinokubo, Hiroshi WILEY‐VCH Verlag 2014 Angewandte Chemie Vol.126 No.6
<P><B>Abstract</B></P><P>The treatment of an antiaromatic norcorrole Ni<SUP>II</SUP> complex with a kinetically stabilized silylene provided ring‐expansion products in excellent yields through the highly regio‐ and stereoselective insertion into the β‐β pyrrolic CC bonds. The resultant Ni<SUP>II</SUP> porphyrinoid monoinsertion product exhibited relatively strong near‐IR absorption bands due to the small HOMO–LUMO gap in spite of the disrupted cyclic π‐conjugation by the silicon atom.</P>
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토석류 유동성 평가를 위한 링 전단시험장치 개발 및 활용
정승원,송영석,Jeong, Sueng-Won,Fukuoka, Hiroshi,Song, Young-Suk 대한토목학회 2013 대한토목학회논문집 Vol.33 No.1
산사태는 토사, 거석, 유목 등 산사태 물질의 중력사면 이동현상이다. 산사태는 수리학적, 지형학적, 지반공학적 요인에 따라 다양한 흐름 및 퇴적특성을 보인다. 흐름특성은 아주 느리게 움직이는 산사태(활동, 이류 등)에서 아주 빠르게 움직이는 산사태(토석사태, 토석류 등)까지 다양하다. 이런 점에서 산사태 발생과 확산 메커니즘의 이해를 위해 전단변형률에 따른 전단강도특성에 대한 연구가 필요하다. 본 연구는 한국형 산사태에 적합한 링 전단시험장치의 개발과 활용성에 대한 것이다. 링 전단시험장치는 산사태 유형별 피해 및 영향성 평가에 사용되는 전단강도를 측정할 수 있으며, 전단속도에 따른 산사태의 유동성을 평가하기 위한 장치이다. 비배수 전단강도 측정용 링 전단시험장치는 기존에 개발된 링 전단시험기의 수정보완형으로 '포화-압밀-배수-전단' 순으로 시험조건을 자유롭게 조절할 수 있다. 링 전단상자내 흙 시료의 전단강도의 정확한 측정을 위해 미끄럼 방지, 밀폐성 및 회전성 향상 기능을 갖춘 시험장치이다. 링 전단시험장치는 모래와 자갈 시료에 대한 예비실험을 수행하였으며 기존 시험결과와 비교하여 신뢰할 만한 결과를 확인하였다. 회전속도 100 mm/sec 로 구속할 때 배수조건에 따른 일시적 액상화 현상으로 인한 강도저하 현상이 관측되며, 전단면에 따른 입자파쇄 현상이 뚜렷하게 나타났다. 마지막으로 토석류 유변학에 기초하여 링 전단시험장치를 이용한 산사태 유동성 평가기법을 제안하였다. Landslides are known as gravitational mass movements that can carry the flow materials ranging in size from clay to boulders. The various types of landslides are differentiated by rate and depositional features. Indeed, flow characteristics are observed from very slow-moving landslides (e.g., mud slide and mud flow) to very fast-moving landslides (e.g., debris avalanches and debris flows). From a geomechanical point of view, shear-rate-dependent shear strength should be examined in landslides. This paper presents the design of advanced ring-shear apparatus to measure the undrained shear strength of debris flow materials in Korea. As updated from conventional ring-shear apparatus, this apparatus can evaluate the shear strength under different conditions of saturation, drainage and consolidation. We also briefly discussed on the ring shear apparatus for enforcing sealing and rotation control. For the materials with sands and gravels, an undrained ring-shear test was carried out simulating the undrained loading process that takes place in the pre-existing slip surface. We have observed typical evolution of shear strength that found in the literature. This paper presents the research background and expected results from the ring-shear apparatus. At high shear speed, a temporary liquefaction and grain-crushing occurred in the sliding zone may take an important role in the long-runout landslide motion. Strength in rheology can be also determined in post-failure dynamics using ring-shear apparatus and be utilized in debris flow mobility.
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Shear and viscous characteristics of gravels in ring shear tests
Sueng Won Jeong,Sung-Sik Park,Hiroshi Fukuoka 한국지질과학협의회 2018 Geosciences Journal Vol.22 No.1
The shear and viscous characteristics of a material are strongly dependent on the material’s properties, such as cementation, density and grain size distribution, as well as the testing conditions, such as drainage and shearing speed. More complex shear behaviors can occur when the tested materials have diverse grain sizes. The shear and viscous characteristics of gravels are examined in terms of drainage and shear velocity under the constant normal stress using a ring shear apparatus, in which the materials used can be sheared under a large deformation. In this study, the materials used are commercial aquarium gravels with mean diameter of 6 mm. Test results show that the materials typically exhibited strain-hardening behavior when subjected to low shear velocity (i.e., ≤ 0.01 mm/sec) and strain-softening behavior when subjected to high shear velocity (i.e., > 0.1 mm/sec) in the ring shear torque measuring system. As expected, higher shear velocities correspond to higher shear stresses, regardless of the drainage condition. For a given shear velocity (V) ranging from 0.01 to 1 mm/sec, a gradual decrease in shear stress is observed in the drained condition; however, a relatively constant shear stress is observed in undrained shear stress. It is clearly exhibited that the vertical displacement is large in the drained condition but relatively unchanged in the undrained condition. The grain crushing is significant for both drainage conditions when the materials experienced a large deformation. There are two regions: (a) non-dominant grain crushing and (b) dominant grain crushing (with a large amount of sand and fine contents) as a function of shear velocity. For both drainage conditions, a large shear resistance occurred when the shear velocity reaches 1 mm/sec. Through the contraction-particle rearrangement-grain crushing process during shear, when V ≥ 1 mm/sec, it appears that the shear stress is easily reached to the residual state of shear. The amounts of fine contents from grain crushing are much larger in the drained condition than in the undrained condition. In the extreme case that grains are highly crushed, it may result in a high mobilization of materials in natural hazards.
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The laboratory evidence of phase transformation from landslide to debris flow
Ogbonnaya Igwe,Fawu Wang,Kyoji Sassa,Hiroshi Fukuoka 한국지질과학협의회 2014 Geosciences Journal Vol.18 No.1
The dominant factors initiating the transformation of landslides into catastrophic debris flow are examined. The research found that a threshold pore pressure determined from theoretical and experimental analysis was enough to initiate liquefaction type of failure in sandy materials. Loading tests to failure on source-area sandy soils from a catastrophic landslide location show that under definite conditions of loading, a threshold state, characterized by the equality and constancy of pore pressure and shear resistance develops in the sands at a threshold density. Sands at this density clearly define the boundary between contractive and dilative specimens under same effective normal stress. Confirmatory experiments were then conducted using silica sand. Analyses showed that samples in which the threshold pore pressure was exceeded readily liquefied while those in which the pore pressure was below the limit dilated. The concept of threshold pore pressure fills the gap created by classical theories of soils liquefaction that have identified densities at which phase transformation and steady state lines can be defined. The new concept shows there is a density at which both lines merge and it is proposed that sands transiting from dense to loose and vice versa will first pass through the threshold state. While the stability of a slope founded on sandy soils may be breached when the pore pressure exceeds a certain limit, it is possible to make estimates of the limit. Where such estimates are accompanied with adequate field measurements, the effectiveness of landslide prevention projects may be enhanced.
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