节理倾角对公路隧道围岩塌落拱影响分析

文章主要通过室内石膏块模型试验对节理间距为0.5 m的隧道围岩在节理倾角分别为0°,30°,45°,60°和90°时无支护开挖情况下围岩的塌落拱跨度、高度和塌落面积的探讨,得出了在不同节理倾角下得到的结果 ,并与普氏理论值进行了对比分析,发现塌落高度、塌落宽度以及塌落面积均与节理倾角呈非线性变化关系,其极小值介于45°~60°之间;同时利用离散元软件UEDC对上述工况进行二维数值分析,室内试验结果与数值分析结果一致;依据数值计算和室内试验综合分析,得到了在不同节理倾角下塌落拱高度的计算方法。     

不同节理位置及倾角对隧道围岩稳定性的影响分析

文章以黄土含节理地区隧道开挖为例,采用有限元软件Midas建立模型,并考虑不同节理位置和节理倾角两种工况,对隧道围岩变形以及应力变化规律进行了分析。结果表明:(1)考虑不同节理位置时,对于水平位移,节理的存在会略减小靠近节理一侧拱腰的最大水平位移;对于竖向位移,节理的存在使得最大竖向位移向节理处靠近。节理在拱腰、拱肩和拱顶时,其最大竖向位移比无节理时分别大8.8%、10.3%和0.3%,节理在拱肩处应力比拱腰和拱顶时围岩应力分别大3.2%和4.0%。(2)节理倾角为30°、45°、60°和90°时的最大竖向位移值比无节理时分别大23.0%、14.8%、9.3%和7.4%,随着节理倾角的增大,最大竖向位移值逐渐减小;节理倾角为45°、60°和90°时的最大应力比节理倾角为30°时分别小0.4%、1.1%和2.0%,随着节理倾角的增大,最大围岩应力逐渐减小,但整体变化趋势不大。     

不同围压下节理岩体中TBM滚刀破岩效率研究

为提高TBM掘进效率,降低TBM施工成本,有必要研究节理岩体中的滚刀破岩效率。为此,文章采用二维离散元软件UDEC研究在不同围压下,节理间距、节理倾角、滚刀间距及贯入度对破岩效率的影响规律。研究表明:(1)节理倾角以30°附近为界向上增加或向下减小,比能耗随围压增加而减小的趋势变缓,并且在接近90°和0°时,围压的增加对滚刀破岩呈现不利影响;(2)节理岩体节理间距越小,比能耗受围压影响越明显。随着节理间距的增加,围压对比能耗的影响逐渐弱化,直至消失;(3)节理倾角0°附近,在满足安装要求的情况下滚刀间距宜取小值;节理倾角30°附近,刀间距100 mm左右时比能耗最小;节理倾角60°时,刀间距120 mm左右比能耗最小;(4)在滚刀之间裂隙贯通的前提下,节理岩体取较小贯入度时破岩效率较高。     

冻结裂隙砂岩的力学特性研究

为得出围压、裂隙倾角、冻结温度等因素对砂岩力学性能的影响规律,采用三轴压缩试验方法和理论分析方法,研究了不同围压下,无裂隙0°,15°,30°和45°倾角裂隙砂岩在-5℃,-10℃和-15℃冻结时的强度、内摩擦角和粘聚力变化特征。结果表明:无裂隙和有裂隙砂岩的强度,随冻结温度的降低而非线性增强,随围压的降低而近线性降低,随裂隙倾角的增大而减小;粘聚力随冻结温度的升高而减小,内摩擦角和粘聚力均有随裂隙倾角的增加而先减小后增大的变化趋势;无裂隙,0°,15°倾角裂隙砂岩的内摩擦角均随冻结温度的升高而减小,30°倾角裂隙砂岩的内摩擦角随冻结温度的降低先增大后减小,45°倾角裂隙砂岩的内摩擦角则随冻结温度的降低先减小后增大。     

三轴压缩条件下千枚岩力学及扩容特征分析

岩石在变形破坏中具有扩容特征.文章以千枚岩为研究对象,通过室内岩石常规三轴压缩试验,揭示了节理夹角为5°～45°影响下小角度节理千枚岩的强度与扩容特征.结果表明:(1)岩石的特征点应力随围压的增大而增大,其扩容特征随之减弱;(2)岩石的峰值应力随节理面与最大主应力夹角的增大而减小;在节理夹角为5°～45°范围内,闭合应...     

不同节理倾角对红层地区偏压隧道围岩稳定性的影响

以达州至万州高速公路沙坝湾隧道靠近洞口偏压段为研究对象,采用数值模拟的方法,研究了红层地层不同节理倾角下隧道围岩力学响应、变形特性。研究表明:红层地层中节理倾角对围岩应力和变形有较大的影响;当节理倾角与偏压坡面垂直时,隧道周边围岩水平方向应力与变形最大;当节理倾角与偏压坡面平行时,隧道周边围岩竖直方向应力最大。     

浅埋黄土隧道土石分界高度对初期支护结构安全性的影响分析

为获得浅埋黄土隧道土石分界高度对初期支护结构安全性的影响,文章以临县隧道为工程背景,采用数值模拟的方法研究了浅埋土石分界高度及土石分界面位置对隧道初期支护结构安全性的影响。结果表明:土石分界致使隧道初期支护结构安全系数发生突变,分界面倾斜时安全系数分布不对称。同一种埋深条件下,随着土石分界面位置的下移,土石分界面以上部分偏压减弱,分界面以下的部分偏压增强。同一界面深度条件下,隧道初期支护结构左右断面偏压情况随着埋深增加而增大。当土石分界面分别位于隧道上导坑和中下导坑、分界面倾角为10°时,可通过增加20%隧道左侧荷载或减小20%右侧抗力系数来进行荷载计算。     

不同因素对立体交叉隧道施工的影响规律分析

针对围岩级别、交叉角度和岩柱高度3个影响因素,设计100个试验工况进行数值建模计算,分别从新建隧道施工引起的既有隧道拱顶沉降和初期支护内力变化两方面探讨了该3种因素对立体交叉隧道施工的影响规律。研究结果表明:受新建隧道下穿施工的影响,既有隧道拱顶沉降和喷混凝土轴力均有增大的趋势,且随交叉角度的增大,增幅更为显著;当立体交叉隧道岩柱高度增加、围岩变差时,引起的既有隧道拱顶沉降变化加大,而喷混凝土轴力的增大比率反而逐渐减小。可见对于立体交叉隧道而言,既有隧道结构变形为较敏感的物理量,可作为施工设计的重点考察指标。     

水平、垂直节理发育条件下的隧道稳定性分析

文章依托内蒙古呼和浩特市窑沟隧道工程实例,对典型断面所在区段的节理特征参数进行了采集,得到了实际地层中存在的近水平、垂直发育节理的详细参数;通过综合运用现场监测、室内模型试验、数值模拟手段,分析了隧道开挖后的上覆岩层运动行为与结构受力特征,研究了该类地层中围岩的变形特征与失稳模式,为后续的支护设计及其优化提供了参考。研究结果表明,在窑沟隧道所处的典型地层,即近水平、垂直节理发育工况下:(1)无支护开挖时,地层稳定性极差,塌落区与松动区集中分布于拱顶上方,最大塌落高度为0.48倍洞宽,塌落面积为0.51倍断面面积,拱顶等效荷载为0.084 MPa,松动区延伸至地表,近似呈三角形分布;(2)按设计方案施作初期支护后,地层松动范围明显缩减,高度降为1.1倍洞宽,拱顶最大沉降为7.7 mm,边墙收敛为3.4 mm,结构安全储备足够。     

基于遍布节理模型的超大断面隧道开挖优化研究

为优化节理发育岩体条件下超大断面隧道开挖方法,文章以天峨至北海公路(巴马至平果段)山贡隧道为工程依托,通过引入遍布节理模型开展隧道开挖过程数值分析,并建立0.5 m、1.0 m、1.5 m、2.0 m、2.5 m、3.0 m共6种中隔壁法循环开挖进尺数值模拟工况,从围岩变形及塑性区分布的角度分析循环开挖进尺对围岩稳定性...     

The Impact of Container Type Diversification on Regional British Port Development Strategies

Abstract

Despite a concentration of container traffic in the southeast of the UK over the last few decades, regional ports are attempting new development strategies to capture or retain specific traffic segments. These include intra-European short-sea traffic and a potentially increasing feeder market. These trends are reflected in the movement of different container types, which result in a number of planning challenges related to changing infrastructural and operational requirements. This paper uses highly disaggregated data on container type movements to address three issues that can inform these planning challenges. First, the imbalance of trade resulting in empty container repositioning; second, the requirement for gauge-cleared rail routes to cater for the increasing proportion of high-cube containers; and third, the specialisation of European short-sea traffic at secondary UK ports. The results reveal the disproportionate repositioning of empty containers at Scottish ports and the importance of 45?ft, high-cube and pallet-wide containers at regional ports, highlighting their focus on intra-European short-sea traffic and raising difficulties relating to their lower quality of landside infrastructure (particularly rail) in comparison to the large south-eastern ports. The potential repercussions on hinterland infrastructure development raise questions about both public and private sector responses to regional port development.     

Survey of R&D in PRT systems

A survey of research and development in advanced transit has been made by Chalmers University of Technology in Gothenburg in cooperation with Trans21 in Boston. Summary findings are reported for fourteen academic research programs and ten development programs for PRT. An earlier version of this paper was presented at the International Conference of PRT and other Emerging Systems held in Minneapolis in 1996.     

Modular route bus design – A method of meeting transport operation and vehicle manufacturing requirements

This research examines the problem of route bus specification and vehicle manufacturability. In order for bus operators to provide transport services, a range of vehicle configurations must be available from bus manufacturers, generating variety which has a negative impact on the manufacturing process. Larger part inventories, uncontrolled labour tasks and more troublesome maintenance are known impacts of this variety. This research identifies the functional necessities in route bus interior design and reduces the problems in bus manufacture and operation caused by specification diversity by proposing a modularised system of bus design. In particular, it makes recommendations as to how bus configuration should be carried out, ensuring an optimum mix of operational and manufacturing needs:

• 1.Determine user needs before the bus specification process.
• 2.Designs to be developed by the manufacturer in response to user needs.
• 3.This design should be standardised where possible, as suggested by the user needs.
• 4.Where user needs dictate product variations, apply a mass customisation approach to accommodate these needs.

The recommendations are communicated in design proposals for a modular bus interior, demonstrated by four cases designed to meet the present status quo of bus interior design and predictions for the future of the field.     

Productive efficiency and ownership of urban bus services

The established ownership mix of urban bus operations in Australia provides a unique opportunity to investigate the productivity differences between public and private bus service supply. Using duality theory in economics which links economic indices of factor productivity to the cost structure of a firm, we develop empirical measures of total and partial productivity of inputs, and adjust the differences for the effects of ownership status and operating environment. The evidence supports the notion that private supply of public passenger transport in general has performed more efficiently in the past than public supply, although the differences in productivity need not continue in the future.     

Optimization of bus stop locations for improving transit accessibility

A mathematical model is developed in this paper to improve the accessibility of a bus service. To formulate the optimization model, a segment of a bus route is given, on which a number of demand entry points are distributed realistically. The objective total cost function (i.e. the sum of supplier and user costs) is minimized by optimizing the number and locations of stops, subject to non‐additive users' value of time. A numerical example is designed to demonstrate the effectiveness of the method thus developed to optimize the bus stop location problem. The sensitivity of the total cost to various parameters (e.g. value of users' time, access speed, and demand density) and the effect of the parameters on the optimal stop locations are analyzed and discussed.     

Determinants of modal choice in freight transport

In the next few years, exciting developments in the field of freight transport are likely to occur. The Channel Tunnel will be perceived as giving railways much greater distance of operation, compared to the current train ferry to/from Great Britain. The further development of swap-body technology will allow easier modal transfer and the creation, in 1992, of a single market in Europe will transform the pattern of trade. All of these are likely to have significant impacts on modal choice, and hence modal split, in freight transport. Reappraisal by many firms of the modes of transport used is likely but will it result in a net transfer of freight from road to rail and, if so, to what extent? To answer such questions, an accurate and reliable method of predicting modal split is required. Research in the past has concentrated on the development of modal split models based on generalised costs. These fail to explain adequately the prevalence of road freight in the UK. From surveys of freight managers within industry, it is clear that models to date rely too heavily on the economic cost factor and too little on behavioural factors (Jeffs 1985). This paper derives from a recent study of freight transport modal choice from the standpoint of the transport decision-maker within the firm. It attempts to shed light on the actual parameters which should be incorporated into a modal split model. Many variables appear to exert an influence on modal choice decision-making process. However, it is possible to categorise them into six main groups, namely: customer-requirements; product-characteristics; company structure/organisation; government interventions; available transport facilities; and perceptions of the decision-maker him/herself. It is the interactions and inter-relationships between these which ultimately determine freight modal split. This study has shown that the relationship between the outcome of the transport decision process and the values of particular determinants of modal split is not straight-forward, due to the complexity and variety of interactions involved. Perhaps one of the main reasons for researchers' failure hitherto to develop a successful modal-split model has been the preoccupation with techniques that rely on the development of common metric (e.g. generalised cost), which has led to the exclusion of some important explanatory variables along quite different dimensions. Another important issue concerns the appropriate level of aggregation. In order not to reduce the explanatory power of the key variables, it is important to work at a disaggregate level, although this does make substantial demands on data. The use of factor analysis enables both the aggregation of information without loss of behavioural reality and the specification of variables in terms of a common metric. In conclusion, freight transport has usually been examined within too narrow a framework. It must be placed firmly within the context of the total industrial process. The demand for freight transport is directly influenced by the level, composition and geographical distribution of production and consumption activities. Freight flows are complex and so it is highly unlikely that a universal mode-choice model can ever be developed. Future research should, therefore, be directed towards developing partial models in response to specific needs of those involved in decision-taking in the freight sector.     

管道风险分析指数评分法中分值调整初探

管道风险分析指数评分法中重要步骤之一就是确定影响管道事故因素的权重,各个管道风险因素在整个管道事故中所占的权重是不相同的。针对目前管道风险分析指数评分法基本假设之一（各因素的分值范围都是0～100分）,为了更加客观、准确、合理地反映各个风险因素对于管道事故的影响程度,提出并论述了依据层次分析法的数学逻辑性进行综合计算得出管道风险因素的权重,然后对评分法中各个因素的最高分值,根据其权重不同进行相应调整,从而增强评价者对风险因素的认识和评判能力,提高管道风险评价结果的准确性。     

天然气站往复式压缩机活塞失效分析

针对天然气站往复式压缩机活塞的断裂事故,运用失效分析方法,开展了活塞断口扫描电镜分析、能谱和金相分析。根据断口形貌的电镜和金相观察结果,结合理论知识,分析确定了该活塞发生断裂事故的主要原因,即在特定工况下该活塞的材料缺陷是造成断裂的主要因素。