Study on dented hemispheres under external hydrostatic pressure

This paper is dedicated to the comprehensive investigation on dented hemispheres under external hydrostatic pressure. A total of 20 stainless steel hemispheres are fabricated, which have a nominal radius of 60 mm and a nominal wall thickness of 0.76 mm. These fabricated hemispheres are divided into four groups with five samples in each group. Wherein, three groups are dented using conical, spherical, and cylindrical indenters respectively, while the remaining group is designated as undented one. Both dented and undented hemispheres are hydrostatically tested into collapse to examine the effects of indention on the collapse characteristics of hemispheres. Additionally, all tested hemispheres are semi-analytically and numerically evaluated based on the measured geometric data and tested material properties. The experimental, semi-analytical, and numerical results are compared in figures and tables.     

隧道塌方处治支护参数选取

塌方是隧道建设时经常遇到的技术难题,塌方处治的支护参数往往凭经验选取,那么凭经验选出的支护参数是否安全合理就成了设计人员必须思考的问题。本文详细介绍了塌方体的荷载计算方法,计算中如何考虑钢支撑对喷射混凝土的加强作用,钢筋混凝土受压构件安全系数的计算方法,隧道初期支护与二次衬砌极限承载力的计算方法。并最终基于以上四点给出了塌方体支护参数的选取方法,该方法在广元至巴中高速公路兴隆山隧道塌方段的支护参数选取中得到了成功应用,为隧道塌方处治的设计提供了参考。     

跨铁路桥施工受火车振动影响的研究

以跨铁路线连续刚构桥施工过程中受火车行驶振动影响的实际工程为背景，通过现场测试、模型和试块的模拟振动试验、加载破坏试验、现场减振隔振试验及施工工艺研究等一系列工作，深入研究了现浇混凝土受火车行驶振动的影响，取得了一些具有工程参考价值的研究成果。     

Ludwig?s Ratchet and the Collapse of New England Groundfish Stocks

The stocks of principal groundfish species off New England have collapsed, creating economic hardship and dislocation in fishing communities from Rhode Island to Maine. In this article we analyze the causes of this collapse using the ?ratchet effect? described by Ludwig, Hilborn, and Walters (1993) as a framework. According to Ludwig, Hilborn, and Walters, powerful economic and political interests drive fisheries to overcapitalize and overexploit despite scientific evidence that stocks are declining. When the fishery is no longer economically viable, governments provide financial assistance to minimize economic hardship. When stocks increase there is another rush to invest, and the cycle repeats itself. The history of groundfish management in New England conforms well to this model. Optimism among fishers and government over U.S. control of this fishery in 1977 stimulated successive rounds of investment that built up excessive fishing capacity despite warnings from scientists that stocks were becoming weaker. Management regimes designed by the New England Fishery Management Council were ineffective in constraining fishing effort. Collapse of the stocks has led to severe restrictions on fishing and to government assistance. We suggest that the integration of science, management, and harvesting sectors through ecosystem-based management offers the best means of avoiding similar situations in the future.     

百丈隧道穿越流塑状富水破碎带施工措施及其安全性评价

百丈隧道左洞ZK152+433~ZK152+463段穿越流塑状富水破碎带施工时反复出现变形侵限、塌方等情况,给工程施工带来前所未有的挑战。文章详细阐述了施工过程中采取的各种处治措施,总结了不同处治方案和效果,并采用数值分析方法对隧道结构安全性进行了分析。结果表明:(1)对于流塑状富水破碎带,加密超前支护是防止开挖时围岩出现较大变形或者坍塌的最有效措施。百丈隧道流塑状富水破碎带最终采用了每榀钢架(钢架间距50 cm)都打设一环3.5 m长?51自进式锚杆的超前支护方式,即每个断面都有7层超前支护,最终有效控制了开挖后围岩变形,避免衬砌侵限与塌方;(2)对于流塑状富水破碎带,加固围岩尤其是边墙与基底处围岩非常重要,可有效减少开挖过程中衬砌的整体式下沉。采用抛石挤淤+注浆的方式进行边墙与基底围岩加固,其效果比采用单纯注浆方式好得多;(3)对于外部荷载较明确的隧道,采用计算分析结合工程经验的方式确定衬砌支护参数,既能保证隧道结构安全,又使其经济合理;(4)在双车道隧道施工中,采用三台阶法施工,应尽量缩短台阶长度,使初期支护及时封闭成环,从而可以较好地控制围岩变形。     

罗圈背隧道坍方分析及处理

以XXX高速公路工程罗圈背隧道施工为背景,阐述了罗圈背隧道发生塌方的过程和状况,分析了塌方原因,并就塌方处理方案及技术进行了论述,以供类似工程参考。     

Experimental assessment of the ultimate strength of a box girder subjected to severe corrosion

The objective of this paper is to describe the experimental assessment of the ultimate strength of a severely corroded box girder subjected to a uniform bending moment resulting from four-point loading. Three box girders that could simulate the behaviour of midship sections have been deteriorated in corrosive seawater environment to simulate different levels of corrosion degradation of ageing ship structures. During the deterioration process, various parameters have been controlled and the total weight lost was registered. Corroded plate thicknesses have been measured in 212 points and a statistical analysis has been performed. The resulting corrosion wastage has been fitted by a non-linear time variant degradation model. The experimental results of the ultimate strength test of a severely corroded box girder subjected to a four-point loading have been analysed. The load-displacement and moment-curvature relationship is discussed, different failure modes are identified, and the strain gauges readings are analysed.     

长短大管棚法处理隧道塌方施工技术

文章以重庆开县龙安隧道为例,分析了该隧道塌方的原因,提出了长短大管棚处置方案,并详细阐述了长短大管棚法处理隧道塌方的施工技术,指出了施工注意事项,评述了采用该方法进行隧道塌方处置的效果。     

塌方地铁车站的后续施工方案研究

暗挖地铁车站断面较大,通常埋深较浅,施工时常发生塌方事故,且塌方纵向影响长度多达数十米。为提高塌方后续施工的安全性,结合塌方事故实例,利用风险分析和有限元计算方法,并结合现场监控量测数据,研究塌方事故影响段后续施工问题。研究结果表明:在后续施工中采用双侧壁导坑法安全可靠,"变大跨为小跨"有效控制后续施工引起的变形;从施工工法、支护措施及施工工艺等多方面制定措施,改善岩体物理性能,提高支护体系和围岩承载能力,有效控制后续施工风险。     

Effect of non-symmetrical corrosion imperfection on the collapse pressure of subsea pipelines

The effects of non-symmetrical corrosion defects (about the major or minor axis of the ellipse) on the collapse modes and collapse pressures of subsea pipelines are studied using the Finite Element (FE) method. The corrosion defects are represented by a groove of a given length, width, and depth which is created by the “element death” technology. Parametric studies are conducted and the influences of corrosion location angle, length, width, and depth on the collapse pressure are discussed. Several significant and interesting results are achieved: (1) The collapse modes are mainly affected by the corrosion location angle, width, and depth; (2) The collapse pressure of a pipe may increase as the corrosion length, width, or depth increases when the corrosion location angle is small; (3) The longer the corrosion length, the larger the effect of corrosion location angle on the collapse pressure; (4) For collapses controlled by corrosion defect (0.3≤h/t ≤ 0.7), the relationship between the collapse pressure and corrosion location angle follows a simple cosine function. For collapses controlled by the ovality (h/t < 0.3), the relationship can be expressed by the combination of straight-line and cosine function.