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971.
Weibing Zhu Shengchao Yu Dayang Xuan Zhenjun Shan Jialin Xu 《Arabian Journal of Geosciences》2018,11(18):554
Strip mining was the major method to control surface subsidence when mining under buildings in China; however, its coal recovery ratio was only 30 to 50%, resulting in a large amount of coal resource waste due to the retained strip coal pillars. As such, it is of important significance to recover the retained pillars while guarantee the safety of the buildings at surface. In order to address this issue, excavating strip coal pillars using caving zone backfill technology was proposed in this study. The process of this technology was to grouting backfill the original strip caving zones using high-water content material at first, creating a combined backfill body of caved gangue and high-water content material, the backfill body acted as the temporary support. Then the retained pillars were excavated and the newly produced caving zones were backfilled with one interval, which effectively prevented the movement and deformation of the strata. The backfilling system and technology were designed and trailed to excavate the retained pillars at mining area 911 in Bucun colliery. It was found that the backfilling rate reached 96.8 to 98.7% in the original caving zones, the backfilling body in caving zones was highly compacted, and the maximum surface subsidence was only increased to 67 mm with no growth in the failure depth of floor. The retained coal pillars in three of the mining areas were safely excavated and the safety of buildings on the ground was preserved. 相似文献
972.
973.
Reassessment of Hydrofluoric Acid Desilicification in the Carius Tube Digestion Technique for Re–Os Isotopic Determination in Geological Samples
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Jie Li Pei‐Pei Zhao Jingao Liu Xuan‐Ce Wang Alexandra Yang Yang Gui‐Qing Wang Ji‐Feng Xu 《Geostandards and Geoanalytical Research》2015,39(1):17-30
In this study, Re and Os isotopes were systematically determined in six geological reference materials (RMs; covering a wide range of lithologies) using the Carius tube (CT) digestion technique with and without hydrofluoric acid desilicification. Our results show that the HF desilicification increased the Re extraction efficiency (by 9–15%) evidenced from basaltic and andesitic rocks (e.g., BHVO‐2, TDB‐1 and AGV‐2). This implies that a small proportion of Re resides in silicate phases. For mafic–ultramafic rocks (e.g., BCR‐2, WGB‐1 and WPR‐1), Re extraction efficiencies obtained by the CT digestion with and without HF desilicification were similar. This may indicate that Re in these rocks may dominantly reside in some phases (e.g., magnetite and sulfides) that could be completely dissolved in aqua regia solutions without the aid of HF desilicification. Our results also show that the HF desilicification increased Os extraction efficiency (by 13–99%) in some RMs (e.g., BHVO‐2, WGB‐1 and AGV‐2). This observation suggests that a portion of Os‐rich trace phases may occur as inclusions in the silicate phases that act as isolators at ~ 200 mesh sizes. This study demonstrates that the HF desilicification step prior to CT digestion is important for complete extraction of Re and Os in geological samples. 相似文献
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975.
976.
研究了泾阳5.2级地震前的地壳形变、地下水化学参数、地震分布图象和地震波速比的变化特征,结果表明,在震前该区地壳形变、地下流体和地震活动表现出长期、中期和短期的不同特征,具有一定的前兆异常,作出地震预测是可能的。 相似文献
977.
利用新发表的高精度、高密度天体测量星表UCAC2,对天王星的五颗主要卫星的CCD观测图像重新进行量测,采用不同方法作定标归算,并使用两种理论模型(GUST86和GUST06模型)计算卫星的理论位置。对不同方法所得到的卫星位置的O-C结果的分析和比较表明,本文获得的卫星位置精度,除天卫五(Miranda)有显著提高,其他4颗卫星的位置精度基本相同。本文中天卫一和天卫三的结果与"亮卫星定标法"的结果在精度上相当,天卫二的位置精度与其他天王星卫星的位置精度具有较好的一致性,这从另一方面证明了我们的"亮卫星定标法"的可靠性。此外我们还获得了天卫四的位置与精度。 相似文献
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979.
This study focuses on identifying concrete behavior under severe triaxial loadings (near field detonation or ballistic impacts). In order to reproduce high stress levels with well‐controlled loading paths, static tests have been carried out on concrete samples by mean of a very high‐capacity triaxial press (stress levels on the order of 1 GPa). It is a longstanding fact that the water/cement ratio (W/C), upon entering the concrete composition, is a major parameter affecting the porosity and strength of the cement matrix of hardened concrete. The objective of this article is to quantify the effect of this ratio on concrete behavior under conditions of high confinement. From the composition of a reference ‘ordinary’ concrete (i.e. W/C=0.6), two other concretes have been produced with W/C ratios equal to 0.4 and 0.8, respectively. This article presents experimental results and their analysis regarding the effect of water/cement ratio (W/C) on concrete behavior under high confinement. It shows that when placed under high confinement, concrete behaves like a granular stacking composed of concrete without any influence from the level of cement matrix strength. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
980.
Tam Giang–Cau Hai lagoon wetland directly or indirectly provides the likelihoods for about 300,000 persons living around as well as on the lagoon. Due to expansion of aquacultures, intensive fishing, and lack of an appropriate management scheme, the biological resources in the lagoon are degraded. This study provides information on the direct use values of the lagoon wetland, using market price approach. This information on economic values can be used for designing new policies and making trade-offs among alternative management options for the lagoon wetland. 相似文献