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通过室内双层地基模型试验,研究上部硬土层在不同强度和厚度条件下的双层地基承载性能,并拍摄数码图像分析了双层地基的变形场。分析荷载p-基础沉降s 曲线,双层地基极限承载力随上部硬土层强度和厚度的增大而增加,双层地基极限承载力下对应的基础垂直位移随上部硬土层强度和厚度的增加而降低;当模型试验中的上部硬土层的水灰比为10%、厚度为30 mm,以及上部硬土层的水灰比为20%、厚度为60 mm 时,后者的极限承载力是前者的3.01 倍,后者的极限承载力下对应的基础沉降是前者的基础沉降的0.11 倍。利用数字照相变形量测DPDM (The digital photogrammetry fordeformation measurement) 技术对双层地基变形的数码图像进行变形场分析,通过网格图的变形分析,土体的初始变形出现在下部软土层中,随着荷载的增大,网格的变形区域逐渐向上部的硬土层及软土层下部发展,同时在水平方向扩展;双层地基破坏模式为上部硬土层的锥台型整体剪切和下部软土层冲剪的综合型破坏形式。对上部硬土层的强度、厚度的优选设计可大幅度提高软土地基处理的效能。 相似文献
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针对海上勘察硬土层静力触探数据难以获取的工程现状,基于国内首次大规模应用的大贯入力海床式孔压静力触探仪,采用国内外静力触探解译公式,对比分析三亚近海地区硬土层静力触探试验成果与室内土工试验、标准贯入试验的物理力学指标。分析表明:海床式静力触探试验解译得到的砂土内摩擦角、黏性土不排水抗剪强度等指标略大于室内试验与标准贯入试验,对硬土地区大贯入力孔压静力触探的分析研究,为类似工程提供了宝贵的经验与参考。 相似文献
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城陵矶外贸码头是目前长江中游最大水位差的高桩梁板式码头,水文与地质条件复杂,土层紧硬,在设计中,从整体,单体,空间,平面,动力,静力多种模型结合分析,提出了目前国内较大水位差地区斜桩斜度5:1的高桩梁板式码头结构方案和在坚硬土层条件下的锤击沉桩可行性等工程措施,突破了常规设计的局限。 相似文献
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《水道港口》2018,(6)
应用有限元数值模拟方法,研究了自升式钻井船的桩靴在复杂层状地基土中贯入一定深度时的地层响应情况,取得了桩靴贯入过程中地基土破坏形式、荷载影响深度、不同承载力计算方法的适用性等多方面认识。在上硬下软及上软下硬的层状土中,所有公式的计算结果无论在数值还是趋势方面都与有限元模拟成果相差较大,这主要是由于单一的公式未考虑到插桩荷载影响深度内下伏不同地层对总承载力的贡献。有限元模拟成果显示,在3. 0B深度范围插桩荷载影响较大;桩靴自上覆硬土层贯入软土层时,会有一定厚度的硬土被压入到软土层,且厚度随插入深度变化,导致出现地层结构的动态重分布。根据层状地层中有限元模拟成果,提出了考虑到3. 0B深度范围所有地层的强度贡献、并考虑地层结构动态重分布的桩靴下地基土极限承载力计算方法,其计算结果与有限元模拟成果最为接近。工程实例计算表明,得出的计算结果以及有限元模拟结果都与实际插桩深度较为接近。 相似文献
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针对福州港可门作业区1#~3#泊位工程排洪沟护岸存在深厚软土地基,但场地表层被块石覆盖而难以进行下卧层软基处理的问题,提出采用引孔结合沉管碎石桩法进行软基处理的方案。该方案成功解决了穿透硬土层处理下卧软土层的技术难题,取得了良好效果。该设计方案及施工方法可为类似工程的设计及施工提供借鉴。 相似文献
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复杂地质条件下,大长细比超深沉井在超软土层中下沉采取阻沉技术,在硬土层中下沉采取助沉技术,并在下沉过程中采取防倾斜、纠偏和防突沉较难技术措施,使得大长细比超深沉井垂直、均匀下沉到位,取得了较好的经济效益和社会效益。 相似文献
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基于埃及塞得东港集装箱码头二期工程,研究分析超过60 m深T形地下连续墙在上软下硬且软弱土层深厚、临海水位高的复杂地层情况下的关键施工技术,包括地下连续墙成槽技术、防止槽壁坍塌技术、垂直度控制技术、钢筋笼的"抬架垂直转体法"吊装技术、热带沙漠高温下C50水下混凝土配制与灌注等关键技术。实践证明该施工技术适用于临海地区复杂土质的超深异形地下连续墙施工,施工工期相对较短,成本低,能够保证工程质量和施工安全。 相似文献
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Georgina Santos Hannah Behrendt Tara Shirvani 《Research in Transportation Economics》2010,28(1):2-629
Road transport imposes negative externalities on society. These externalities include environmental and road damage, accidents, congestion, and oil dependence. The cost of these externalities to society is in general not reflected in the current market prices in the road transport sector.An efficient mobility model for the future must take into account the true costs of transport and its regulatory framework will need to create incentives for people to make sustainable transport choices. This paper discusses the use of economic instruments to correct road transport externalities, but gives relatively more weight to the problem of carbon emissions from road transport, as this is particularly challenging, given its global and long-term nature.Economics offers two types of instruments for addressing the problem of transport externalities: command-and-control and incentive-based policies.Command-and-control policies are government regulations which force consumers and producers to change their behaviour. They are the most widely used policy instruments. Examples include vehicle emission and fuel standards in the US as well as driving or parking restrictions in Singapore. The implementation cost of these instruments to the government is small. Although from an economic perspective these policies often fail to achieve an efficient market outcome, the presence of political constraints often make them the preferred option, in terms of feasibility and effectiveness.Economic theory shows how policies, which affect consumption and production incentives, can be used to achieve the optimal outcome in the presence of externalities. Incentive-based policies function within a new or an altered market. We first examine incentive-based policies, which cap the aggregate amount of the externality, such as carbon emissions, by allocating permits or rights to the emitters. The emitters are then free to trade their permits amongst them. The permit allocation mechanism is important-although market efficiency would be satisfied by an auction, political influences usually favour a proportional allocation based on historic emissions. We discuss EU ETS as an example of a cap-and-trade system, however, no such policy for CO2 emissions in road transport has been implemented anywhere in the world to date.Fiscal instruments are, like command-and-control, widely used in road transport, because they are relatively cheap and simple to implement. They include the use of taxes and charges in order to bridge the gap between private and the social costs and, in principle, can lead to an efficient market solution. Registration, ownership, fuel, emissions, usage taxes, and parking and congestion charges have been implemented in many countries around the world. On the other side of the spectrum, subsidies can be given to those scrapping old cars and buying fuel-efficient vehicles. Some cities, such as London, have implemented congestion charges and many states in the United States have introduced high occupancy lanes. Other interesting possibilities include pay-as-you-drive insurance and other usage charges. However, the size and scope of taxes and subsidies are determined by governments, and because of their imperfect knowledge of the market the outcome is still likely to be inefficient.Governments have many effective economic instruments to create a sustainable road transport model. These instruments can be used separately or together, but their implementation will be necessary in the nearest future. 相似文献
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注浆减摩技术在顶管施工中的应用 总被引:1,自引:0,他引:1
结合工程建设实例,论述顶管施工中注浆减摩的原理,介绍注浆减摩的工艺和措施、注浆材料的选择、孔的布置、泵的选用、注浆压力的大小等,指出注浆减摩技术在长距离顶管施工中的重要性. 相似文献
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Nathan J. Bennett 《Coastal management》2019,47(1):67-87
The world’s oceans and coasts are awash in a sea of politics. The marine environment is increasingly busy, changing, and a site of degradation, marginalization, injustice, contestation and conflict over declining resources and occupied spaces at local to global scales. Themes of political ecology, such as power and politics, narratives and knowledge, scale and history, environmental justice and equity, are thus salient issues to understand in ocean and coastal governance and management. This subject review examines research on these themes of political ecology in the ocean and coastal environment and reflects on how the insights gained might be applied to governance and management. Political ecology provides important insights into: the influence of power in ocean management and governance processes; the manner in which narratives, knowledge, and scale are used to legitimize and shape policies and management efforts; the effects of historical trajectories on present circumstances, options, and practices; and the nature of inequities and environmental injustices that can occur in the marine environment. Moreover, ocean and coastal researchers, practitioners, and decision makers ought to engage with the political processes and injustices occurring in the ocean. Moving from critical insights to constructive engagements will ensure that political ecology helps to plant seeds of hope in the Anthropocene ocean. 相似文献
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论现代综合物流新概念及其“虚拟化”发展趋势 总被引:1,自引:0,他引:1
现代综合物流是信息流、管理流、资金流和货物流四位一体的有机联系和协调运动的综合体系。确定现代综合物流的概念定义,研究揭示这一体系的运动规律及运作虚拟化的发展趋势将会对物流理论、物流实践乃至整个经济管理产生重大变革和深远影响,同时,引导航运承运人和物流经营人采用“虚拟”方式,通过市场合理配置社会资源,真正使信息流、管理流、资金流和货物流成为协调运动的综合体系。 相似文献
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中国修船业在国家改革开放的浪潮中,经历了三十多年的快速发展,如今已稳居世界修船大国的国际地位,而中国修船企业正在引领世界绿色修船科技的进步,也引起了国际修船业的高度关注.然而,在人类社会生态环境面临严峻挑战的当下,作为世界贸易和港口经济重要组成部分的修船产业,如何形成发展新格局,从生态层面推进绿色、低碳、数字"一体化"... 相似文献
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The brackish Baltic Sea has been seen as particularly suitable for studies of food webs. Compared to fully marine ecosystems, it has low species diversity, which means fewer trophic linkages to analyse. The Baltic Sea is also one of the best-studied areas of the world, suggesting that most data requirements for food web models should be fulfilled. Nevertheless, the influence of physical and biological factors on trophic interactions and biogeochemical patterns varies spatially in the Baltic Sea, adding considerable complexity to food web studies. Food web structure and processes can be described and compared quantitatively between areas by estimating the flow of matter or energy through the organisms. Most such models have been based on carbon, though studies of complementary flows of other elements limiting production, such as nitrogen and phosphorus would be desirable. However, since ratios between carbon and other elements are used in calculating these flows, it is crucial, as a first step, to quantify the flows of carbon as accurately as possible.In this study, we used the EcopathII software (ver 3.1) to analyse models of carbon flow through the food webs in the three main areas of the Baltic Sea; the Baltic proper, Bothnian Sea and Bothnian Bay. A previously published study on carbon flow in the Baltic Sea [Elmgren, R. 1984. Trophic dynamics in the enclosed, brackish Baltic Sea. Rapp. P.-V. Reun. — Cons. Int. Explor. Mer. (183) 152–169.] was complemented with the data on respiration and flow to detritus [Wulff, F., Ulanowicz, R. 1989. A comparative anatomy of the Baltic Sea and Chesapeeake Bay ecosystems. In: F. Wulff, J.G. Field, K.H. Mann (Eds.), Flow Analysis of Marine Ecosystems: Theory and Practice. New York: Springer-Verlag.] in order to present complete mass balance models of carbon. The purpose of re-evaluating previous models with new analytic tools was to check how well their carbon flows balance, and to provide a basis for improved mass balance models using more recent data, including nutrients other than carbon.The resulting mass balance networks for the Baltic proper, Bothnian Sea and the Bothnian Bay were shown to deviate from steady state. There was an organic carbon surplus of 45, 25 and 18 g C m−2 year−1 in the pelagic zones of the Baltic proper, Bothnian Sea and Bothnian Bay, respectively. The Ecopath network analysis confirmed that the overall carbon flow was highest in the Baltic proper, somewhat lower in the Bothnian Sea and much lower in the Bothnian Bay. The only clear differences in food web structure between the basins was that the average trophic level was lower for demersal fish in the Bothnian Sea and higher for macrofauna in the Bothnian Bay, compared to the other basins. The analysis showed weakness in our current understanding in Baltic Sea food webs and highlighted areas where improvements could be made with more recent data. 相似文献