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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] The SDP geothermal research area geographically located in eastern Indonesia where there are geothermal manifestations of hot springs. 3D modeling and vertical-horizontal gradient analysis are used to determine the presence of subsurface structures of the study area. Separation of complete Bouguer anomaly data to obtain regional and residual anomalies has been done by upward continuation. The results of the horizontal and vertical gradients indicate that the presence of the geothermal manifestation of MAP 1 hot spring is controlled by the presence of trending northwest-to-southeast fault. We interpret the emergence of manifestations due to the presence of a permeable zone in the form of the fault structure. 3D modeling shows the existence of alluvium sediment, sedimentary rocks, limestones, ultrabasas (peridotite), granite, metagranite, gneiss and the presence of trending northwest trending to the southeast fault. (paper)
[en] Highlights: • A new relationship between rate of penetration and heating conditions is obtained. • The decrease of jet-impact coefficient can help to reduce the heating conditions. • Sensitivity studies are performed to quantify the key parameters which affect the heating conditions. • Heating conditions for granite, sandstone are compared. Hydrothermal jet spallation drilling (HJSD) is a new drilling method suitable for drilling deep wells in hard rock formations. The characteristics of HJSD are that the rock surface is impinged by a high-velocity hydrothermal jet, causing rock breaking into small spalls. In this study, we develop an analytical model to evaluate the heating conditions (surface temperature and surface heat flux) in HJSD, in which the effect of jet impact on the heating conditions is first considered. Meanwhile, we conduct thermal spallation experiment using sandstone and granite samples. After that, the effects of jet impact on the heating conditions are investigated. Furthermore, the impacts of all physical parameters on the heating conditions are compared to clarify the key factors. Additionally, we compare the rate of penetration and heating conditions between sandstone and granite, which can provide direct understanding about the suitability of HJSD for sandstone and granite. Our study provides a further understanding of critical physic affecting the rate of penetration and heating conditions in HJSD.
[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] Geochemical fingerprinting was used to identify the sources of fine sediments derived from three types of contrasting lithological zones and deposited in a reservoir in a medium-sized catchment over the past 60 years. The impact of grain-size sorting on the source of fine sediments in the reservoir was investigated. Overall, the fine sediment sources identified in the sediment cores indicated changing trends in sediment contribution from the three types of lithological zones during the past 60 years. Although the granite zone covers half of the catchment, has thicker soils, is more prone to soil erosion, and has been subjected to more human disturbance than the limestone and shale zones, it only provided 25% of the fine sediment in the cores. The limestone and shale zones, on the other hand, account for 23% and 15% of the catchment, respectively, but produce 42% and 33% of the fine sediment in the cores. This is due to grain-size sorting in the reservoir system during downstream sediment transit and deposition. These data show that grain-size sorting has had a significant impact on the sediment source. This study provides new insight into the source of sediments deposited in a reservoir system from different lithological zones at the scale of a medium-sized catchment across multi-decadal periods.
[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)