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51.
Several theoretical, empirical and semi-empirical methods are available in the literature to predict settlement of drilled
shafts in sandy soils. In the Arabian Gulf countries, specifically in the United Arab Emirates, equations and procedure from
the rest of the world are being used in analysis and design of drilled shafts without proper validation. It is the aim of
this study to assess the applicability and evaluate the accuracy of two well known, and commonly used methods for pile prediction
in the United Arab Emirates (UAE), namely Vesic (1977) and Poulos (1979), via comparison with data from field pile load tests
conducted on shafts drilled in the region. Some of these tests were conducted for the purpose of this study, while others
were made available through the courtesy of International Piling Contractors who are active in the region (e.g. Bauer International
and Swiss Borings). Pile load test data were analyzed to back-calculate the model parameters related to settlement under different
loading stages. Geological data and soil properties were obtained from studies conducted at the relevant sites. An effort
is made to correlate soil properties with the prediction models. Statistical analysis is conducted to assess the accuracy
of the results obtained from the two methods at different stages of loading via those obtained from pile load tests. Moreover,
a detailed parametric study is conducted to assess the effect of the related parameters on the predicted pile settlement and
the estimated settlement at different stages of loading. The study concluded with a recommendation of the most appropriate
models and procedures to be followed for predicting the settlement of drilled shafts in the UAE, together with useful charts
and correlation relations. Results showed that settlement values predicted by Vesic (1977) and Poulos (1979) overestimates
the true values.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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An experimental study on reduction of U (Ⅵ) by anaerobic bacteria, Shewane//a putrefaciens, is first reported here in China. The experimental conditions were: 35℃ and pH =7.0-7.4, corresponding to a physicochemical environments in which the sandstone-hosted interlayer oxidation-zone type uranium deposit formed in Northwest China's Xinjiang. Bacteria adopted in the present experiment, Shewanella putrefaciens, occur extensively in natural environment. Our study shows that nano-crystal precipitates of uraninite quickly occurred on the surface of the cells within one week. It was found that the pitchblende was characterized by a random arrangement of uraninite nanocrystals (2-4 nm) in it, significantly different from natural pitchblende in which uraninite nanocrystals are arranged in order. Finally, a possible mechanism of uranium biomineralization by microorganisms in the deposits is discussed. Our investigation may supply a technical train of thoughts for bioremediation of nuclear-contaminated water environments and for underground dissolving extraction of the sandstone-hosted uranium ores. 相似文献
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Olivier Regnault Vincent Lagneau Hubert Catalette Hélène Schneider 《Comptes Rendus Geoscience》2005,337(15):1331-1339
Carbon dioxide sequestration in deep aquifers and depleted oilfields is a potential technical solution for reducing green-house gas release to the atmosphere: the gas containment relies on several trapping mechanisms (supercritical CO2, CO2(sc), dissolution together with slow water flows, mineral trapping) and on a low permeability cap-rock to prevent CO2(sc), which is less dense than the formation water, from leaking upwards. A leakproof cap-rock is thus essential to ensure the sequestration efficiency. It is also crucial for safety assessment to identify and assess potential alteration processes that may damage the cap-rock properties: chemical alteration, fracture reactivation, degradation of injection borehole seals, etc. The reactivity of the host-rock minerals with the supercritical CO2 fluid is one of the potential mechanisms, but it is altogether unknown. Reactivity tests have been carried out under such conditions, consisting of batch reactions between pure minerals and anhydrous supercritical CO2, or a two-phase CO2/H2O fluid at 200?°C and 105/160 bar. After 45 to 60 days, evidence of appreciable mineral-fluid reactivity was identified, including in the water-free experiments. For the mixed H2O/CO2 experiments, portlandite was totally transformed into calcite; anorthite displayed many dissolution patterns associated with calcite, aragonite, tridymite and smectite precipitations. For the anhydrous CO2 experiments, portlandite was totally carbonated to form calcite and aragonite; anorthite also displayed surface alteration patterns with secondary precipitation of fibrous calcite. To cite this article: O. Regnault et al., C. R. Geoscience 337 (2005). 相似文献
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胡志毅 《云南地理环境研究》2005,17(Z1):26-28
随着西部大开发战略的深入实施,如何全面认识旅游业对西部经济落后地区经济的影响,成为旅游学界关注的热点问题之一。通过对石林县社会经济统计数据的综合分析以及实地调研,证实了旅游业对促进石林县国民经济总量扩大、推动产业结构高级化和带动相关产业发展等方面具有积极作用。同时,针对当前石林旅游内部结构和发展质量中存在的旅游产品单一、景区发展失衡和社区受益不足等主要问题,提出了以推动区域经济总体发展和带动农村居民脱贫作为旅游发展的两大基本任务和实现旅游产业增长模式从数量型向内涵型增长转变的基本思路,以及相应的对策。 相似文献
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我国土地利用/覆被研究的热点与应用发展问题 总被引:2,自引:0,他引:2
本文回顾了国内土地利用调查和土地利用/覆被变化(以下简称LUCC)的研究历程,认为20世纪80年代前的半个世纪,我国以土地调查为主的土地利用研究发展缓慢。到了80年代后,由于遥感技术由实验走向实用、地理信息系统技术的普及,加之IGBP和HDP两大组织发起的土地利用/覆被变化研究,这一领域的研究得到了极大地推动。目前,该领域存在着技术潮流、驱动力研究潮流、环境效应研究潮流、景观生态学潮流等热点,这对于推动LUCC的多学科深入研究具有积极作用;指出了土地利用/覆被变化研究中存在的"重技术轻学理"现象、微观机理研究不足、忽视土地利用替代性研究、土地可持续利用评价针对性不够、研究的服务对象单一等问题,LUCC研究要在克服这些问题中发展;由此提出,在经过一定的领域拓展、案例积累、技术准备等基础工作之后,我国土地利用/覆被变化研究应针对前述问题,加强理论建设,探索模型建立,拓展区域应用,发挥多学科核心作用,在理论建设、数学模型表达、机理探讨等方面,为现代地理学做出贡献,为地理学的社会作用和应用拓展更加广阔的空间。 相似文献
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