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[en] To explore the relationship between the dominant direction of micro-cracks and the anisotropy, this research focuses on the micro-crack initiation and propagation mechanism and the anisotropic parameters evolution in the rock under uniaxial compression. Based on the maximum circumferential stress theory and the assumption of shear slip leading to the local tensile stress, the micro-crack initiation and propagation model is established, and the anisotropic parameters of rock is further explored. To verify the theory, the marble limestone, granite porphyry and granite are selected to conduct uniaxial compression experiment. It is indicated that the experimental results of elastic moduli and Poisson’s ratio are well consistent with theoretical analysis. Finally, the relationship between the dominant direction of original and secondary micro-cracks and the effect of the micro-cracks’ dominant direction on practical engineering are discussed. The results show that the dominant direction of micro-cracks is parallel to the maximum principal stress under uniaxial compression, which leads to the anisotropy of rock. With the increase of stress, the axial and transverse elastic moduli would decrease, while the extent of the decrease of axial elastic modulus is larger. The axial Poisson’s ratio would increase and the transverse Poisson’s ratio will decrease. Moreover, the Poisson’s ratio is more sensitive to the anisotropy caused by the dominant direction of micro-cracks.
[en] The Mako bimodal volcanic belt of the Kedougou-Kenieba inlier is composed of volcanic basalts and peridotites interbedded by quartzites and limestones intruded by different generations of granitoids. The early volcanic episode of the belt is constituted of submarine basalts with peridotite similar to those of the oceanic abyssal plains. It is intruded by the Badon Kakadian TTG- granitic batholite dated around 2200 Ma. The second volcanic phase is constituted of basaltic, andesitic, and felsitic flows exhibit structures of aerial volcanic rocks. It is intruded by granites dated between 2160 and 2070 Ma. The general pattern of trace element variation of submarine volcanic rocks is consistent with those of basalts from oceanic plateaus which are the modern equivalent of the Archean greenstones belts. The Nd and Sr isotopic systematics typical of juvenile material indicates that the source of these igneous rocks is derived from a depleted mantle source. These results are consistent with the idea of a major accretion within the West African Craton occurring at about 2.1 Ga and corresponding to an important process of mantle-oceanic. (author)
[en] Prediction of physical and mechanical properties of rock materials using rebound-based hardness test methods is widely preferred in many fields of engineering and in the characterization of rock materials, because they are non-destructive, practical, and economical. In this study, 40 types of rocks with magmatic, metamorphic, and sedimentary origins, represented by travertine, limestone, marble, dolomite, granite, syenite, dunite, andesite, schist, gabbro, tuff, and ignimbrite were selected. First, dry unit weight (γd), open porosity (no), water absorption by weight (WAW), wide wheel abrasion (WA), and uniaxial compressive strength values were determined. After that, Shore C-2 scleroscope (HSC), L-type Schmidt hammer (HSL), and Leeb (HLD) rebound-based hardness tests were carried out on all samples, and then, hardness values by three methods were compared with the obtained parameters. The Leeb hardness test, which is more recent and innovative than the Shore and Schmidt hardness tests, was initially developed for metallic materials. However, the method has become increasingly popular in the determination of hardness of rock materials in laboratory as well as in field. In this study, the Leeb hardness test was found to be more useful due to its quick and precise measurement capabilities compared to Shore and Schmidt hardness tests. The results of the study reveal that the prediction of physical and mechanical properties of rocks can more precisely be determined by the HLD method than the HSL and HSC methods using the proposed equations.
[en] The change in permeability with time of granite, quartzite, anorthosite and gabbro was measured while these rocks were subjected to a temperature gradient. The highest temperature (at the heat source) was fixed at 2500C, while low temperatures ranged from 60 to 1110C, depending on rock type. Permeability reductions of up to two orders of magnitude were observed, with the greatest reactions occurring in the quartzite. These changes are thought to be caused by dissolution of minerals at high temperatures, and redeposition of the dissolved material at lower temperatures. Quartz appears to be an important mineral in this self-sealing process. If very low permeability is desired around a nuclear waste repository in crystalline rocks, than a quartz-rich rock may be the most appropriate host. 10 refs., 3 figs., 2 tabs
[en] In order to understand the effect of nepheline syenite particle size on physico-chemical properties of ceramic Raschig rings, the fluxing agent was grinded at different milling times. The compositions were prepared by blending the illitic-kaolinitic clay and pre-grinded particles. The rings were shaped by a laboratory extruder and then were sintered at 1200 degree centigrade. The mechanical reliability of sintered specimens was mathematically described by Weibull theory and the effect of pre-grinding of fluxing agent on Weibull modulus was evaluated by measuring the diametrical compression strength. Weibull modulus and strength were the criteria for selecting the suitable particle size range of nepheline syenite. It was found that the pre-grinding of nepheline syenite acts as fairly strong parameter on microstructure of rings. The investigation concludes that reliable rings can be fabricated if the particle size of nepheline syenite is arranged between 53 and 75 μm. This enhancement in reliability is valuable in packed towers. (Author)
[en] Dose equivalent rates at 47 major geologies m Korea were measured indirectly using big rock blocks displaying at 'Geologic Time Street of Korea named as Nadeulgil' in Korea Institute of Geoscience and Mineral Resources (KIGAM). The dose equivalent rates at actual geologies were also measured for two sites among these 47 sites. True dose equivalent rates of actual geologic sites were obtained by equation with dose rates on the displaying rocks and the environmental dose at the displaying Geologic Time Street of Korea site of the KIGAM. Obtained results for the Precambrian gneissose area, the Paleozoic calcareous area, the Mesozoic granitic area and the Cenozoic volcanic area are 0.12 ∼ 0.21 μSv/h, 0.01 ∼ 0.04 μSv/h, 0.09 ∼ 0.36 μSv/h and 0.04 ∼ 0.06 μSv/h, respectively. The geographic distribution may be useful to evaluate natural environmental radiation in Korea and for tectonic comparison in geology. (author)
[en] Chafalote Metamorphic Suite is characterized by politic, psamitic, calc-silicate and mafic gneisses, which are affected by a Neoproterozoic granulite facies metamorphism. The rocks derived from semipelite and pelite protoliths show mineral assemblages and textures typical for temperature over 80000C. The metapelite fabrics are described to interpret these protoliths and to better understand the relationships between metamorphism and deformation. The main reference surface is interpreted as a S composite banding (Sb=So/S1/S2). Some layers record graded and crossed bedding preserved in fine-grained quartz-rich semipelites. They contain orthopyroxene. A correlation is presented between thermal peak fabrics and retrograde path derived fabrics, both for meapelites.
[en] The carbonate-siliceouspelitic uranium deposits which widely distributed in South China are more typical stratabound deposits. According to the horizon of ore bearing formation it may be divided into two major types, i.e. Sinian-Cambrian series and upper Palaeozoic group. The formation of uranium source bed was closely related with the crustal evolution of that area. The process of transformation of uranium source bed into uranium deposits being more complexity and variety. Therefore, this kind of deposits was commomly subdivided into three types----sedimentary diagenetic type, leaching precipitation type and hydrothermal reworked type. Among which the former two types are rarely appeared, and the sedimentary diagenetic type is so far not very reliable. The hydrothermal reworked type being the most important one; but they also showing different characteristics in metallogenesis, especially on the relation with granite body situated nearby. Thus, different understandings around their genesis were existed. This paper discusses the geological and geochemical characteristics of several deposits with different processes of mineralization and suggest a scheme for further classification of these of uranium deposits