The influence of seepage forces on ground reaction curve of circular opening

When a tunnel is excavated underneath a groundwater table, groundwater flows into the tunnel and consequently, seepage forces act on the cross-section of the tunnel. Such seepage forces significantly affect the ground reaction curve, which is defined by the relationship between the internal pressure and displacement of the tunnel wall. From a practical point of view, a simplified analytical solution of the ground reaction curve accounting for the seepage forces with steady-state flow was developed in this study based on ground reaction curve theories from earlier studies. The simplified analytical solution derived in this study was validated by numerical analysis. The changes in the ground reaction curve according to various ground and groundwater table conditions were investigated. Finally, the simplified analytical solution of the ground reaction curve developed in this study can be used for approximate design of circular openings such as tunnels excavated underneath a groundwater table with seepage forces.     

金沙江虎跳峡河段水电开发中存在的主要地质问题

虎跳峡梯级电站是金沙江中下游河段梯级开发的“龙头”，除其自身具有巨大的效益之外，对下游各梯级也将产生很大的补偿调节作用。研究认为，该河段地形地质条件复杂，处于Ⅷ～Ⅸ度地震烈度区，区域及近场活动断裂发育；各拟选坝址多存在高陡边坡问题，同时也不能完全排除水库及岩溶渗漏的可能性，河床深覆盖层的存在将使坝基防渗处理十分困难。峡谷左岸存在两家人及核桃园两巨型崩滑体，就目前所掌握的资料来看，两崩滑体特别是核桃园崩滑体整体稳定性较好，但下峡口水库蓄水后，仍不能排除存在局部失稳的可能性。峡谷左岸引水隧洞及地下厂房施工将可能遇到的复杂高地应力及边坡稳定问题也是应进一步研究的重要内容。     

The electronic origins of alloy phase stability

The program entitled Accelerated Supercomputer Initiative (ASCI) aims at the utilization of state-of-the-art computational architecture for the study and simulation of materials properties relevant to the enduring stockpile. In order to carry out these calculations, it is necessary to have in hand a well-developed theoretical understanding of the corresponding computational algorithms. In this paper, we review some central elements of such theoretical developments as they relate to the study of phase stability of metallic alloys. These developments are based on the determination of the electronic structure of the alloys and related properties, such as total energies at zero temperature (ground-state energies). Parameters extracted from such calculations are then used to carry out the study of thermodynamic quantities such as ordering tendencies of the alloys and concentration–temperature–pressure phase diagrams. The results of numerical calculations carried out with respect to alloys of the transition metals are used to illustrate the methodology described here. When the methodology is extended to the materials of relevance to the stockpile it becomes evident that the difficulties of its numerical implementation increase rapidly, soon demanding the capabilities of massively parallel architectures and large memory capacity, thus being ideally suited for the framework of ASCI. This revised version was published online in July 2006 with corrections to the Cover Date.     

Model for In Situ Perchloroethene Dechlorination via Membrane-Delivered Hydrogen

A one-dimensional contaminant fate and transport model was developed to simulate reductive dechlorination of perchloroethene (PCE) in an anaerobic aquifer supplied with hydrogen via a gas-permeable membrane curtain. The model predicted that providing hydrogen at transfer rates equal to the reducing-equivalent demand associated with the groundwater PCE flux would mineralize 75% of the PCE-bound chlorine to chloride and, furthermore, that 0.55 moles of chloride would be released per mole of hydrogen transferred. Supplying higher hydrogen transfer rates was predicted to result in slightly lower dechlorination efficiencies and significantly lower dechlorination yields due to greater methanogenic growth and concomitant displacement of dehalorespirers away from the hydrogen-supply membranes. The model also predicted that high hydrogen-utilizing biomass concentrations would develop near the membranes, resulting in minimal hydrogen dispersal. Model predictions were qualitatively similar to results attained in experimental soil column studies; however, incorporation of homoacetogenesis and acetate utilization by dehalorespirers, as well as hydrogen production via fermentation of biomass decay products, would have improved agreement between model simulations and experimentally observed dechlorination performance.     

高速电路的板层设计

本文给出了高速电路的板层设计方法，重点研究了信号的高频回流和电源层的设计。在电源设计中研究了电源的分割和数模电源设计。文中给出了电源分割模型，并根据这个模型结合信号源的设计实例进行了详细的叙述，具有重要的工程实践意义。     

关于小接地电流系统中接地现象的探讨

电力系统单相接地故障是运行中经常发生的故障，其表现形式不尽相同．本文分析各种故障现象的发生原因与处理方法，有助于电网的安全运行。     

群发性高压开关跳闸原因分析与处理

本文围绕河南蒲山电厂#1炉#2磨煤机开关启动后故障跳闸,导致引风机、排粉风机、送风机等高压开关群发性误跳这一异常现象,介绍故障的产生原因、分析、诊断以及处理过程。根据热工信号受干扰情况及干扰源的发展,相应制订出了三次试验进行排查,最终查出群发性开关误跳闸的根本原因为热工D/O端子板受强电干扰引起,实施了隔离措施。     

小官庄西区地压显现宏观调查及地压控制

通过对西区—230～-250m三个水平的巷道、炮孔和溜井等采准工程的破坏状况的调查结果,揭示了影响巷道和炮孔破坏的主要因素,并得到了采场地压活动的定性规律。基于上述认识,在-260m水平采取了一系列利用和控制地压的技术工艺和措施,使该水平的矿体回采获得较好的社会效益和经济效果。可为其他采区乃至类似矿床的回采提供经验。     

Common Ground in Australia: An Object Lesson in Evidence Hierarchies and Policy Transfer

Developed in New York City in 1990, the Common Ground model of supportive housing has recently been embraced in Australia as a high-profile solution to chronic homelessness. Combining on-site support services with a congregate housing form accommodating ex-homeless people and low-income adults, Common Ground is presented as an innovative model which permanently ends homelessness, enhances wellbeing, and strengthens communities. This article critically examines the process of transferring the model into Australia's social housing sector, drawing on the perspectives of the high-level stakeholders closely involved. It argues that, despite official commitments to evidence-based policy, the ‘advocacy coalition’ driving this international policy transfer employed a ‘knowledge hierarchy’ wherein professional intuition and personal experience were afforded a higher status than formal evaluative evidence. The article provides an example of the contested nature of what ‘counts as evidence’ in housing and homelessness policy, and considers what role academic research – as well as other knowledge sources – should play in the policy development process.     

考虑淤泥处置场荷载特点的软土地基处理方法

淤泥处置场占地面积较大,对深厚的软土地基,若采用常规的复合地基处理方式无疑将大规模增加工程投资。本文考虑淤泥处置场的荷栽特点,将淤泥的处置过程当作分级加载的过程,分析地基在处置场运行期间地基承载力的提高,通过控制作业程序,使淤泥堆填的速度和荷载与地基承载力随时间的增长相适应,同时设置加筋砂石垫层,为软土地基提供排水层,减小库区的不均匀沉降,提高地基承载力,。最后结合某淤泥处置场工程,分析了该地基处理思路的可行性,对淤泥处置场的方案提出了优化建议。本文的计算方法和地基处理方式可为软土地区污泥处置和垃圾填埋等工程提供有益的参考,