Shotcrete for underground support: a state-of-the-art report with focus on steel-fibre reinforcement

This paper reviews current trends in shortcreting, primarily based on the Status Report of a Working Group of the International Tunneling Association and the most recent U.S. Engineering Foundation conference on the theme (held in Uppsala, Sweden, in 1990). Of special interest is the increasing use of fibre reinforcement, which implies increased safety and substantial cost savings. The need for scientific collaboration and exchange of ideas between concrete and rock mechanics specialists is emphasized as a tool for a better understanding of the support behaviour of shotcrete linings.     

Wind loads on low-rise buildings: a review of the state of the art

This paper refers to the most recent research on wind loads on low-rise buildings. Novel measurement techniques and methodologies are reviewed, and selected experimental results from various studies are presented. Particular emphasis is given to works aimed at the formulation of codified data, i.e. results appropriate for incorporation into design standards and codes of practice. Only either full-scale studies or those done under conditions simulating the earth's atmospheric boundary layer have been considered. Comparisons between full-scale and laboratory results are discussed. Areas requiring additional research and analysis are identified.     

Planning history in Australia: The state of the art

Over the last two decades, planning history in Australia has firmed as both a specific research field and pragmatic endeavour geared to planning practice. The emergence of an identifiable planning history strand across the borders of such disciplines as planning, political science, human geography, and history in the mid‐1970s gained much of its rationale from other developments at this time, including the academic legitimation of urban studies and urban history, an unprecedented level of governmental interest in urban and regional development, reassessment and reaction to traditional land use planning, and the benevolent imprimatur of the British Planning History Group. From the vantage point of the early 1990s, a substantive literature can now be critically surveyed. Diverse if not fragmented, parochial and sometimes quirky, the general nature of this body of work partly reflects the spatial isolationism and parochialism that have been hallmarks of Australian cultural and political development. Beyond the straitlaced general surveys of state, city and metropolitan planning, several established lines of inquiry are evident, notably colonial town layout, civic design, the impact of planning movements, evaluations of metropolitan planning, political conflict, and federal urban policy. The links with cognate fields such as housing, landscape architecture and, increasingly, environmental studies, are close. Alongside these general themes have come more distinctively Antipodean preoccupations like the planning of Adelaide and Canberra as well as the work of Walter Burley Griffin. Future challenges lie in more original research, integration, theory development, and policy relevance.     

A new energy-absorbing bolt for rock support in high stress rock masses

An energy-absorbing rock support device, called a D bolt, has been recently developed to counteract both burst-prone and squeezing rock conditions that occur during underground excavation. The bolt is a smooth steel bar with a number of anchors along its length. The anchors are firmly fixed within a borehole using either cement grout or resin, while the smooth sections of the bolt between the anchors may freely deform in response to rock dilation. Failure of one section does not affect the reinforcement performance of the other sections. The bolt is designed to fully use both the strength and the deformation capacity of the bolt material along the entire length. The bolt has large load-bearing and deformation capacities. Static pull tests and dynamic drop tests show that the bolt length elongates by 14–20% at a load level equal to the strength of the bolt material, thereby absorbing a large amount of energy. The impact average load of a 20 mm D bolt is 200–230 kN, with only a small portion of the load transferred to the bolt plate. The cumulative dynamic energy absorption of the bolt is measured to be 47 kJ/m. D bolts were tested in three deep mines. Filed measurements show that D bolts are loaded less than rebar bolts. This paper presents the layout and principle of the D bolt, and corresponding results from static, dynamic, and field tests.     

切坯机使挤出更完美——切坯技术现状

<正>切坯机是挤出机的主要部分,因为它是黏土泥条连续地通过切坯机制作最终产品的唯一方法。同时,切坯机也是切割后坯体全自动托盘处理、码坯、输送设备的一部分。从第一台人工切坯机到现在电子控制自动化切割设备,切坯机已经经历了快速和全面的发展。     

Design and performance of shotcrete-bolting support for a tunnel in a special weak rock

This paper deals with a special condition of weak rock, i.e. a hard rock that includes developed and concealed microcracks in a highly geostressed region. The basic properties of a rockmass in a highly geostressed region and the tunnelling method used with this type of rock are discussed.     

Analysis of the behaviour of a yield-control support system in squeezing rock

Recent innovations in yield-control support systems allow to increase the rate of advance when tunnelling in difficult conditions is associated with severely squeezing rock. Such systems which imply the insertion in the lining of highly deformable concrete elements are being adopted successfully in tunnelling projects using conventional excavation methods. The Saint Martin access adit excavated in a Carboniferous Formation along the Base Tunnel of the Lyon-Turin rail line is presented as a case study. Numerical analyses are discussed to compare the results of computed and measured performance of a typical monitored section and to find out possible optimizations of the support system adopted.     

基于分权状态下的授权艺术

授权与分权是现代组织中权力分散的两条基本途径,两者既相互区别又相互联系。分权是一条组织工作原则,授权是一门领导艺术。在新的历史时期,面对复杂多变、竞争激励的外部环境,组织内部决策的复杂性和时效性已空前提高,此时,作为管理组织的领导者,已不可能事必躬亲、事无巨细,必须正确地认识授权的重要性、掌握授权的艺术。敢于授权又善于授权已成为现代领导活动的重要特征及目标追求。在现代组织中,权力的分散一般可以通过两条基本途径来实现:一是组织层级化设计中的分权(即制度分权);二是作为管理组织的领导者在工作过程中的授权。尽管授…     

Determination of the stress state in a rock mass subjected to excavation

This paper develops a model that allows the variation in the stress state in an area of ground to be determined, especially in the rock mass, as a consequence of human activity. It does so through the basis of measurements carried out at three boreholes that are neither co-linear nor co-planar and which are oriented towards the area in which the stress state is to be determined. More specifically, the method uses the data obtained from the measurement of the variations in diameter in each of the boreholes as a result of the alteration of the stress state of the rock mass, and calculates the deformation in three directions, perpendicular to one another. An elastic behaviour is assumed to obtain the state of stress. Finally, the paper reports a practical application of the method in an underground coal mine in Asturias (Spain), where it was possible to measure the stress states of the rock walls of the mined seam.     

三车道隧道喷锚支护施工技术总结

结合沂源隧道工况,阐述了锚喷支护的特点及其设计,重点介绍了沂源隧道喷锚支护的施工要点,提出了一些有益于施工实践的建议,为三车道隧道初期支护施工提供了参考借鉴。     

Restructuring and privatization : viable strategies for state enterprises in developing countries?

Too often, State oil companies are inefficient monopolies, vulnerable to government interference and tempted to consume an inordinate part of the oil rent they generate. While outright privatization may not be feasible for political, cultural or economic reasons, selling part of the company's ownership to local or foreign stockholders, transnationalization, and entering into joint ventures with foreign companies could be ways to increase the efficiency of these Stateowned enterprises. In every case, the solution lies in increasing the competition to which the company is exposed.     

Principles and methods of rock support for rockburst control

This paper presents the principles of rock support for rockburst control and three rockburst support systems used in deep metal mines.Before the principles of rock support are presented,rock fracture related to strain burst is first discussed with the help of photos taken on site,and the energy sources and transformations during bursting are illustrated through conceptual models.Surface parallel extension fracture usually occurs in the ejected and surrounding rocks in a strain burst event,while the ejected rock in a fault-slip rockburst is often already pre-fractured before the event.There must be excessive release energy available for rock ejection.The excessive release energy comes from both the ejected rock itself and the surrounding rock.To prevent rock ejection in a rockburst,the support system must be able to dissipate the excessive release energy.All support devices in a support system for rockburst control must be able to dissipate energy,be firmly linked,and be compatible in deformability.A support system for rockburst control comprises surface-retaining devices and yield rockbolts as well as yield cablebolts when needed.Laying mesh on the top of shotcrete liner is a good practice to enhance the surfaceretaining capacity of the support system.Energy-absorbing yield rockbolts dissipate energy either by stretching of the bolt shank or by sliding of the inner anchor in the borehole.Mesh,mesh strap and shotcrete are the surface-retaining devices widely used in the current rock support systems.The three types of rock support used for rockburst control at present are soft support system using Split Set bolts,hybrid support system using rebar and two-point anchored yield bolts,and entirely yieldable support system using strong yield bolts.     

Between the state and market: Electricity sector reform in developing countries

Developing countries have had to reform technically and financially less efficient electricity sectors than developed countries with less resources and weaker institutions. This paper examines the reform experience and lessons in these countries. The paper reviews private participation and key reform steps such as restructuring, competition, and regulation. The role of contextual factors such as system size, institutional endowment, and international organizations are then discussed. It then argues that there is a need for redefining the role of the state rather than a full withdrawal from the sector and that many countries should adopt simpler reform models and gradual implementation.     

不同围压下软岩巷道全长锚固支护优化研究

以淮南矿区丁集矿西三采区地质条件为背景,采用FLAC 3 D计算软件对深井软岩巷道全长锚固支护条件下围岩稳定性进行模拟计算,获得不同围岩应力和支护强度作用下巷道围岩稳定性影响规律.得知,随着围岩应力环境增大,巷道顶帮下沉量和底板底鼓量增大,巷道顶底板变形位围岩移量变化趋势与巷道两帮变形趋势基本一致,在10 MPa围岩环...     

铝合金空间网格结构研究现状及关键问题

相比于钢结构,铝合金结构由于其自重轻、耐腐蚀和易加工等优点,在结构工程中备受关注,其应用也日益增多。从铝合金作为建筑结构用材与钢材的特性对比出发,列举了国内外大量具有代表性的铝合金空间网格结构,综述了国内外对于铝合金单、双层网壳和网架等铝合金空间网格结构及节点体系的研究现状,并指出目前试验研究、理论研究和设计应用的主要不足之处;通过进一步探讨,提出铝合金空间网格结构的研究与应用中需解决的若干关键技术问题,这些问题集中在节点刚度和杆件初始缺陷对铝合金单层网壳结构整体稳定性的影响、新型节点形式的研究以及铝合金空间网格结构的抗震、抗火性能研究等方面。     

地震作用下钢筋混凝土柱纵筋屈曲研究进展

阐明钢筋受压屈曲的概念,从单根钢筋和钢筋混凝土柱纵筋两个方面对地震作用下钢筋混凝土柱纵筋屈曲的研究进展进行论述。分析影响钢筋屈曲 的主要因素,介绍具有代表性的几个考虑屈曲的钢筋本构模型;讨论纵筋屈曲试验研究中存在的问题及解决方法,论述考虑纵筋屈曲的钢筋混凝土柱设计及 抗震性能数值分析方法。最后,总结出纵筋屈曲需要进一步研究的问题。