Misorientations of garnet aggregate within a vein: an example from the Sanbagawa metamorphic belt, Japan     

A. OKAMOTO  K. MICHIBAYASHI 《Journal of Metamorphic Geology》2006,24(5):353-366

In this study, the chemistry and microstructure of garnet aggregates within a metamorphic vein are investigated. Garnet‐bearing veins in the Sanbagawa metamorphic belt, Japan, occur subparallel to the foliation of a host mafic schist, but some cut the foliation at low angle. Backscattered electron image and compositional mapping using EPMA and crystallographic orientation maps from electron‐backscattered diffraction (EBSD) reveal that numerous small garnet (10–100 μm diameter) coalesce to form large porphyroblasts within the vein. Individual small garnet commonly exhibits xenomorphic shape at garnet/garnet grain boundaries, whereas it is idiomorphic at garnet/quartz boundaries. EBSD microstructural analysis of the garnet porphyroblasts reveals that misorientation angles of neighbour‐pair garnet grains within the vein have a random distribution. This contrasts with previous studies that found coalescence of garnet in mica schist leads to an increased frequency of low angle misorientation boundaries by misorientation‐driven rotation. As garnet nucleated with random orientation, the difference in misorientation between the two studies is due to the difference in the extent of grain rotation. A simple kinetic model that assumes grain rotation of garnet is rate‐limited by grain boundary diffusion creep of matrix quartz, shows that (i) the substantial rotation of a fine garnet grain could occur for the conditions of the Sanbagawa metamorphism, but (ii) the rotation rate drastically decreased as garnet grains formed large clusters during growth. Therefore, the random misorientation distribution of garnet porphyroblasts in the Sanbagawa vein is interpreted as follows: (i) garnet within the vein grew so fast that substantial grain rotation did not occur through porphyroblast formation, and thus (ii) random orientations at the nucleation stage were preserved. The extent of misorientation‐driven rotation indicated by deviation from random orientation distribution may be useful to constrain the growth rate of constituent grains of porphyroblast that formed by multiple nucleation and coalescence.  相似文献   

Mapping an aggregate extraction site off the Eastern English Channel: A methodology in support of monitoring and management     

Silvana N.R. Birchenough  Siân E. BoydKoen Vanstaen  Roger A. CogganDavid S. Limpenny 《Estuarine, Coastal and Shelf Science》2010

Each year approximately 23–28 million tonnes of sand and gravel are removed from offshore sediments around England and Wales. This study was located in a licensed marine aggregate extraction site off Shoreham in the Eastern English Channel (EEC thereafter). Results from the multibeam survey showed the presence of dredged pits created by suction hopper dredging and elongated furrows created by trailer suction hopper dredging in the area where sand and gravel had been excavated. Electronic Monitoring System (EMS) contained the dredging intensity recorded annually at the site; this information was combined with particle size data providing interpreted maps, which informed the status of the sediments at the site.  相似文献   

具有空间关系约束的时空数据聚集查询语义理论     

刘新  李成名  刘文宝 《测绘科学》2009,34(3)

由于时空数据集变得越来越庞大,逐个研究数据库中的实体变得非常困难,分析数据库中具有共性元组集的聚集信息变得越来越重要。具有空间关系约束的聚类信息隐含了信息的变化趋势,这些信息对于制定决策是非常重要的。本文根据时空数据库中时空聚集查询,研究了具有空间关系(拓扑关系、方向关系、距离关系和位置关系)约束的聚集查询理论,解决了在某一时刻,与给定元组具有某种空间关系的元组集的聚集查询。  相似文献   

软弱砂岩骨料碾压混凝土的配制及其特性研究          下载免费PDF全文

刘伟宝  陆采荣  梅国兴  戈雪良  王珩  杨虎 《海洋工程》2014,32(6):105-110

在东南亚和我国西南地区由于缺乏合适的原材料,必须采用软弱骨料配制混凝土。以东南亚某工程现场的软弱砂岩为原材料,开展碾压混凝土配制和性能试验工作,探讨了该骨料配制碾压混凝土的可行性。采用软化系数为0.71的软弱砂岩,配制强度等级分别为C18020的二级配碾压混凝土和C1807.5的三级配碾压混凝土。结果表明,采用该砂岩骨料可以配制出满足强度要求的碾压混凝土,其用水量比常规骨料高15~20 kg/m3,拌和物密度和抗压弹模较低。其中,二级配碾压混凝土采用50%粉煤灰掺量、0.55水胶比;三级配碾压混凝土采用60%粉煤灰掺量、0.65水胶比。骨料抗碾压破碎模拟试验表明该骨料在碾压过程中破坏程度很低,说明采用该软弱骨料配制碾压混凝土具有可行性。  相似文献   

Seismic health monitoring of RC frame structures using smart aggregates     

Wen-I Liao  C.H.Lin  J.S.Hwang  G.Song 《地震工程与工程振动(英文版)》2013,12(1):25-32

Structural health monitoring of RC structures under seismic loads has recently attracted much attention in the earthquake engineering research community. In this study, a piezoceramic-based device called "smart aggregate" was used for the health monitoring of RC frame structures under earthquake excitations. Three RC moment frames instrumented with smart aggregates were tested using a shaketable with different ground excitation intensities. Distributed piezoceramic- based smart aggregates were embedded in the RC structures and used to monitor their health condition during the tests. The sensitivity and effectiveness of the proposed piezoceramic-based approach were investigated and evaluated by analyzing the measured responses. The displacement ductility demand of the structural members was calculated and compared with the damage index determined from the health monitoring system. The comparison shows that the damage index is compatible with the calculated ductility demand.  相似文献   

Aggregate accessibility to population at the county level: U.S. 1940–2000     

M.E. O'Kelly  M.W. Horner 《Journal of Geographical Systems》2003,5(1):5-23

 A classic study by Harris (1954) shows a map of U.S. national accessibility. Harris argued that access to population and income represents a critical factor for location analysis. Such maps and analyses are now readily produced by geographical information systems, allowing experimentation with various parameters, and explorations of changes. By comparing changes in these measurements we can develop a synthetic picture of the impacts of population redistribution. This paper offers a comprehensive review of these calculations and illustrates their use with maps from county population in the continental U.S. from 1940 through to 2000. Received: September 2002 / Accepted: January 2003 RID="*" ID="*" Previous versions of this paper were presented to the Initiative in Population Research (IPR) workshop at the Ohio State University (Horner) and to the Center for Spatially Integrated Social Sciences (CSISS) Summer Workshop in Accessibility (O'Kelly). Thanks to the referees for helpful comments.  相似文献   

土石混合体原位水平推剪试验   总被引：5，自引：0，他引：5  

吴旻硕  李晓  赫健明 《岩土工程技术》2007,21(4):184-189

在长江三峡库区沿岸普遍存在着由于滑坡、崩塌、风化卸荷、残坡积和冲洪积等复杂成因而形成的第四纪松散堆积体,其力学特性介于土体与碎裂岩体之间,为了强调其组成及结构上的特点,称之为"土石混合体"。在大量现场调查的基础上,对三峡库区土石混合体的成因进行了总结。在滑坡现场对土石混合体进行了原位压剪以及推剪试验研究,揭示土石混合体在原位受剪情形下的变形与破坏规律。  相似文献   

Presidential Address 2003: Why concrete cracks — geological factors in concrete failure     

William J. French 《Proceedings of the Geologists' Association. Geologists' Association》2005,116(2):89-105

  相似文献   

Use of a Probabilistic Neural Network to Reduce Costs of Selecting Construction Rock   总被引：2，自引：0，他引：2  

Donald A. Singer  James D. Bliss 《Natural Resources Research》2003,12(2):135-140

Rocks used as construction aggregate in temperate climates deteriorate to differing degrees because of repeated freezing and thawing. The magnitude of the deterioration depends on the rock's properties. Aggregate, including crushed carbonate rock, is required to have minimum geotechnical qualities before it can be used in asphalt and concrete. In order to reduce chances of premature and expensive repairs, extensive freeze-thaw tests are conducted on potential construction rocks. These tests typically involve 300 freeze-thaw cycles and can take four to five months to complete. Less time consuming tests that (1) predict durability as well as the extended freeze-thaw test or that (2) reduce the number of rocks subject to the extended test, could save considerable amounts of money. Here we use a probabilistic neural network to try and predict durability as determined by the freeze-thaw test using four rock properties measured on 843 limestone samples from the Kansas Department of Transportation. Modified freeze-thaw tests and less time consuming specific gravity (dry), specific gravity (saturated), and modified absorption tests were conducted on each sample. Durability factors of 95 or more as determined from the extensive freeze-thaw tests are viewed as acceptable—rocks with values below 95 are rejected. If only the modified freeze-thaw test is used to predict which rocks are acceptable, about 45% are misclassified. When 421 randomly selected samples and all four standardized and scaled variables were used to train aprobabilistic neural network, the rate of misclassification of 422 independent validation samples dropped to 28%. The network was trained so that each class (group) and each variable had its own coefficient (sigma). In an attempt to reduce errors further, an additional class was added to the training data to predict durability values greater than 84 and less than 98, resulting in only 11% of the samples misclassified. About 43% of the test data was classed by the neural net into the middle group—these rocks should be subject to full freeze-thaw tests. Thus, use of the probabilistic neural network would meanthat the extended test would only need be applied to 43% of the samples, and 11% of the rocks classed as acceptable would fail early.  相似文献   

微团聚体分析在工程地质研究中的应用   总被引：6，自引：2，他引：6  

吴芝兰  曲永新 《工程地质学报》1997,5(3):282-288

微团聚体是天然粘性土的基本结构单元, 微团聚体的组成、水稳性和强度是粘性土工程性质形成的重要原因。本文通过对黄土与海相软土这两种典型的粘性土颗粒分析与微团聚体分析结果的对比, 研究了水稳性与非水稳性微团聚体的形成原因, 并在此基础上探讨它们的工程特性的形成。  相似文献