提高土压平衡盾构掘进效率研究

为了在确保工程质量及施工安全的同时,进一步提高盾构掘进施工效率,获取更大的经济效益,根据土压平衡盾构施工特点,从盾构掘进的施工工序进行综合研究,以石家庄地铁1号线一期工程和平医院站-烈士陵园站区间施工为例,确定了影响盾构掘进效率的主要因素,并对掘进影响因素进行分析总结。得出了： 1)盾构掘进时间、管片拼装时间工序较为单一,主要和地质情况和作业人员熟练程度有关; 2)管片吊运下井时间、渣土吊运出井时间、其他外部原因对现场施工的影响等会受施工场地布置影响,在盾构施工前应进行合理的施工场地布置; 3)对盾构、后配套设备维修保养及易损件更换时间、盾构施工测量及移站影响时间的优化,能进一步提升施工效率。     

印度应对城市机动化策略

为应对快速的城市机动化进程及其带来的负面影响,印度政府早期采取诸如修建立交桥和拓宽道路等办法,结果却导致了更多的机动车数量增加和更严重的交通拥堵。为此,印度政府实施了＂国家城市交通政策＂,重点投资公共交通和非机动交通方式;同时还制定了＂国家城市更新计划＂,以此建立鼓励地方政府执行国家政策的激励机制,提高对城市基础设施的投资水平。这些创新政策的实施,推动了一系列公共交通项目的发展,也促进了城市内部交通体制改革和城市综合交通发展规划的制定。     

天津地铁盾构隧道四线交汇掘进数值分析

为解决多条近接隧道施工时后行隧道开挖对先行隧道结构造成的不利影响,以天津地铁5、6号线四线交汇隧道为研究对象,选取典型复杂断面,采用数值软件FLAC3D,模拟富水地层中四线交汇隧道开挖时隧道结构之间的相互影响规律。结果表明： 该复杂断面处,后行隧道施工使先行隧道整体位移具有偏向开挖隧道移动的牵引趋势,且先行下部隧道竖向整体位移较横向整体位移变化更为显著。在渗流作用下,先行下部隧道施工产生的地表沉降量及沉降范围相比后行上部隧道较大,验证了富水地层中渗流作用对土体变形影响程度及范围均远大于开挖应力释放的影响。     

基于两阶段算法的运行图与天窗协同优化

列车运行图铺画与天窗设置存在相互影响,相互制约的耦合关系,为了达到优化列车运行图结构,合理配置铁路运力资源的目的,在分析天窗与列车运行动态影响关系的基础上,以天窗设置对列车运行线铺画影响最小为目标,建立了列车运行图与天窗协同优化的混合整数规划模型. 考虑问题复杂性,设计了包含初步优化和综合优化的两阶段求解算法. 初步优化阶段采用基于专家经验的启发式算法得到列车运行图的大体框架,综合优化阶段利用禁忌搜索算法获取全局最优解. 最后以宝成线（阳平关—成都）为例进行有效性验算. 结果表明,相较于人机交互编制所得运行图,优化得出的运行图中所有客货列车在途经车站的总停留时间降低了6.19%,共减少1 355 min,其中旅客列车和货物列车在站停留时间分别降低了3.08%和7.40%,减少总时间分别为189 min和1 166 min.      

盘点保时捷对大众控股的深远意义

控股大众的现实意义2005年9月保时捷宣布收购大众的18．5%股权。从而宣布两家公司的关系回到了费迪南德先生开发大众甲壳虫车的30年代。围绕Ferdinand Piech(费迪南德·保时捷的孙子)的角色问题,这一控股行动倍受股东和金融机构的质疑。     

Use of the box and Jenkins time series technique in traffic forecasting

This paper explores the use of recently developed time series techniques for short term traffic volume forecasts. A data set containing monthly volumes on a freeway segment for the years 1968 through 1976 is used to fit a time series model. The resulting model is used to forecast volumes for the year 1977. The forecast volumes are then compared to actual volumes in 1977. The results of this study indicate that time series techniques can be used to develop highly accurate and inexpensive short term forecasts. A discussion of the ways in which such models can be used to evaluate the effects of policy changes or other outside impacts is included.     

Economic policies and seaports: Strategies for port authorities

This paper discusses the strategies which might be adopted by port authorities, given that modern port technologies have considerably limited the scope for competition. It therefore analyses the several forms of competition relevant to ports, any or all of which may apply in any given instance.

It describes the 'minimalist strategy, which consists of recognizing that public sector bodies have many faults, may make many mistakes and that well-intentioned attempts to rectify faults in the private sector may make matters worse. Second, it describes the 'pragmatic' strategy, which involves establishing committees to examine problems and to recommend actions, if they can reach a consensus. Third, it describes the 'public sector' strategy, which involves the port authority taking over all port functions. Finally, it describes the 'competitive' strategy, which involves a careful reproduction of the circumstances of competition, even though there may be room for only one efficiently-sized operator at a time. Franchising, or short-term leasing on any of a variety of competitive bases, so as to produce serial competition is described. Each of these strategies is presented as having its own advantages and disadvantages, and each may be suitable to particular circumstances.     

Economic policies and seaports: The economic functions of seaports

This paper argues that the economic functions of seaports are to benefit those whose trade passes through them, i.e. through providing increments to consumers' and producers' surpluses. Whilst recent developments in the technologies of seaports (containers, bigger ships, more rapid handling of bulk cargoes) have increased technical efficiency, they have also provided such economies of scale as to reduce some opportunities for competition and, therefore, the probability that cost reductions are actually passed on in this way. For this purpose port costs need to be considered in their entirety, i.e. as generalized transport costs per tonne, comprising money, time and the risks of loss, damage and delay. Such cost reductions will lead to expanded trade in a variety of ways.

This statement of the economic function of seaports is contrasted with views that they should try to increase employment in their locality, or that they should maximize profits.     

Passing sight distance on two-lane highways: Review and revision

Several models have been developed to determine the minimum passing sight distance required for safe and efficient operation on two-lane highways. The American Association of State Highway and Transportation Officials has developed a model assuming that once the driver begins a pass, he/she has no opportunity but to complete it. This assumption is believed to result in exaggerated passing sight distance requirements. Considerably shorter passing sight distance values are presented in the Manual of Uniform Traffic Control Devices and are used as the marking standards in Canada and the U.S.A. More appropriate models have been developed considering the driver's opportunity to abort the pass, and are based on a critical sight distance which produces the same factor of safety whether the pass is completed or aborted. However, these models need to be revised to determine the passing sight distance requirements more accurately and to closely match field observations. In this paper, a revised model for determining the minimum required passing sight distance was developed, based on the concept of critical sight distance and considering the kinematic interaction between the passing, passed, and opposing vehicles. The results of the revised model were compared with field data and showed that the revised model simulates the passing manoeuvre better than the currently-available models which are either too conservative or too liberal. The results showed that the passing sight distance requirements recommended in the Manual of Uniform Traffic Control Devices are sufficient at low design speeds (50–60 k.p.h.) and for manoeuvres involving passenger cars only. For higher design speeds, the Manual of Uniform Traffic Control Devices standards are less than the passing sight distance required for safe and comfortable passes. The deficiency was found to increase with the increase in design speed, and reaches about 36% at a 120-k.p.h. design speed. Based on these results, major revisions to the current Manual of Uniform Traffic Control Devices marking standards are recommended.