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Huang Z.Wu J.Zhang Y.Liu S. 《现代隧道技术》2018,(5):61-71
In order to study the impacts of the transient seepage on the stability of tunnel excavation face during the installation of lining segments, the fluid-solid coupling effect based numerical model of the tunnel excavation face was developed by the finite element software PLAXIS. With adoption of the variablecontrolling approach, the influences of the depth/diameter ratio (the ratio of the buried depth to diameter of the tunnel) and the support pressure ratio (the ratio of the face support pressure to water and soil pressures ahead of the excavation face) on the face stability and ground settlement were investigated, respectively. At same time, the failure modes of the excavation face under the fluid-solid coupling analysis were also discussed. The results show that:1) the transient seepage leads to the development of the soil arching at the front of the excavation face, in which the smaller deformation at the excavation face is achieved, and so less support pressure for the face stability is allowed. While for the plastic analysis without taking into account the effect of transient seepage, a higher support pressure is required to maintain the stability of the excavation face; 2) in the fluid-solid coupling analysis, the depth/diameter ratio has less impacts on the stability of the excavation surface, but has larger impacts on the ground settlement. The larger the depth/diameter ratio, the larger the ground surface settlement and the settlement profile; 3) however, with the combination of the decrease of the support pressure and the impact of transient seepage on the settlement of ground surface, the soil arching effect in front of the excavation face is gradually reduced. The deformation zone at the ground surface is then connected with the deformed part ahead of the tunnel face to form a wedge-shaped soil sliding zone. It is also observed that the wedge-shaped body tends to have a larger funnel-shaped failure mode than that in the plastic analysis without considering the transient seepage. The results show that the transient seepage has a great impact on the stability of tunnel excavation face in the soil condition with high permeability ratio. The fluid-solid coupling analysis should be adopted to evaluate the deformation of excavation face and ground settlement. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved. 相似文献
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José Manuel Vassallo 《Transportation Research Part A: Policy and Practice》2010,44(10):806-814
Flexible-term highway concessions are becoming quite popular around the world as a means of mitigating the traffic risk ultimately allocated to the concessionaire. The most sophisticated mechanism within flexible-term concession approaches is the least present value of the revenues (LPVR). This mechanism consists of awarding the concession to the bidder who offers the least present value of the revenues discounted at a discount rate fixed by the government in the contract. Consequently, the concession will come to an end when the present value of the revenues initially requested has been eventually reached. The aim of this paper is to evaluate the effect that the discount rate established by the government in the bidding terms has on the traffic-risk profile ultimately allocated to the concessionaire. To analyze this effect, a mathematical model is developed in order to obtain the results. I found that the lower the discount rate the larger will be the traffic risk allocated to the concessionaire. Moreover, I found that, if a maximum term is established in the contract, the lower the discount rate, the less skewed towards the downside will be the traffic-risk profile allocated to the concessionaire. 相似文献
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波纹管膨胀节是一薄壁挠性元件,在内压作用下能够吸收热膨胀或机械运动引起的位移,U形膨胀节应用最广泛。膨胀节材料选用主要取决于工作条件、环境和经济性;应力校核应满足各项条件,否则需调整结构尺寸,重新进行应力计算,同时给出了膨胀节参数与其性能之间的影响规律;膨胀节的制造以液压成形为好,尽量采用整体成形,且按照要求进行相关热处理,焊接时根据材料不同选择合适的焊接方法,以保证波的形状和表面质量。 相似文献
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Sun L.Huang Y.Wang Q.Zhou H.Dai C. 《现代隧道技术》2018,(5):140-145
Based on the background of the first phase project of the R3 line of Jinan Rail Transit, and in view of the metro shield tunnel passing under the existing railway bridge and subgrade, this paper uses Abaqus to establish a numerical model to simulate the deformation of the existing bridge and subgrade of the Jiaoji railway line under the two conditions of non-active reinforcement and reinforcement. The results show that under the condition of no reinforcement, the maximum settlement of the top bridge on the pier is -5.88 mm, and the maximum settlement difference is 5.16 mm, which exceed the deformation control requirements of the 5 mm regarding the bridge pier of the railway with ballast track. The maximum lateral displacement and longitudinal displacement of the pier are 0.28 mm and -3.01 mm, respectively. After the reinforcement measures of the bored piles are adopted, the maximum settlement of the top bridge on the pier is -1.71 mm, and the maximum settlement difference is 1.16 mm, which fully meet the bridge pier deformation control standard. The maximum lateral displacement and longitudinal maximum displacement are -0.245 mm and -2.83 mm, respectively, which meet the requirements of the control standard. The vertical settlement of the railway subgrade is relatively small. The maximum settlement values under the two working conditions are -12.31 mm and -11.97 mm, respectively, which meet the subgrade settlement control requirement of 20 mm. It is proved that the reinforcement effect of the bored pile is good, and the reinforcement scheme is safe and feasible. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved. 相似文献
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走滑断层错动容易使穿越活动断裂带的隧道结构遭受严重的破坏。以某铁路隧道穿越某断裂带为工程背景,采用有限差分数值模拟手段,通过分析不同走滑断层错动量下隧道结构的位移、应力和应变,对隧道结构的安全性进行评判。研究表明:走滑断层错动时,除纵向位移外,随着错动量的增加,隧道结构位移越大,且走滑断层错动对在断层区和上盘区域的隧道结构影响最大;在走滑断层错动量>0.6 m后,隧道结构应力受错动量的影响较小,且隧道结构开始破坏,随着错动量增加,破坏范围增大。 相似文献
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地下结构施工不当会对邻近既有地铁盾构隧道结构产生巨大影响。文章以广州市某地铁线路下穿施工导致既有运营地铁盾构隧道产生较大变形的工程实例为背景,分析了既有隧道结构因地层损失产生不同椭圆度变形情况下管片结构的受力情况。基于工程实测数据,运用三维有限元分析软件,考虑了管片接头处的螺栓孔等细部构造,研究了管片椭圆度与结构应力状态之间的量化关系,并分析了结构的塑性变形情况及其发展趋势。结果表明:随着盾构隧道管片椭圆度的增大,结构最大主应力值与最大剪应力值均增大,且盾构隧道结构最大剪应力与椭圆度呈线性相关关系;盾构隧道结构最大主应力随椭圆度变化更加明显,与椭圆度呈非线性相关关系。 相似文献
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文章对箱梁腹板竖向预应力钢绞线和精轧螺纹钢筋进行对比试验,研究钢绞线和精轧螺纹钢筋竖向预应力的规律,分析了两种不同竖向预应力体系的特征和预应力损失,结果表明钢绞线和精轧螺纹钢筋的第一次张拉预应力损失率和两者长期损失率基本相同,竖向预应力钢绞线的第二次张拉效果明显,预应力损失率较第一次张拉减小近1/2,对于控制主拉应力较大的高腹板的竖向预应力可靠度较大,证明了钢绞线作为竖向预应力筋的实际意义,为工程设计提供参考. 相似文献
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针对老年人下肢行动功能衰退的问题,提出通用设计理念与SAEA模块化功能设计方法的研究思路,及辅助型轮椅的创新设计成果。利用STS生物力学实验法分析老年人使用轮椅过程中的问题,采用调研法分析下肢行动不便的老年人对辅助出行产品的需求重点,作为辅助型轮椅开发研究的切入点;通过SAEA模块化设计矩阵形式逐级解决辅助出行产品开发对用户需求及服务功能的方案,以通用设计思维模式对SAEA模块化设计矩阵分析成果进行方案优化;用计算机辅助设计看板模型整合最终方案,完成多功能辅助型轮椅设计成果。结论表明以通用设计理念对老年人辅助型轮椅开发进行STS实验和SAEA模块化研究所获得数据成果,可以为老年人辅助出行产品的研发提供技术参考及理论依据。 相似文献
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This study explores the optimal investment in the length of an expanded section of road to mitigate the congestion on a transportation corridor. It is assumed that one end of the road is in the central business district (CBD) and that the households are uniformly distributed along the road. Each individual makes trips from his/her residence to the CBD. Trip demand is elastic and depends on the cost of the trip (including congestion costs). During the first stage, the government determines the length of the expanded section given the width of that section. In the second stage, road users determine their trip demands by taking into consideration the trip cost function. In the process of solving this problem, the equilibrium traffic volume is first solved using differential equations. The optimal length of the expanded section is then solved by maximizing the social welfare. The analysis is then applied to the case of the Tucheng city – Banciao city – Taipei CBD corridor in the Taipei metropolitan area. The scheme of road expansion without tolling performs closely to the first-best scheme for the case of a high potential demand. This study’s approach can serve as valuable reference for city planners engaged in road planning in a transportation corridor between the CBD and satellite cities in a metropolitan area. 相似文献
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文章以重庆绕城高速公路上的走马互通式立交为例,分析了群体优化思路在城市立交群规划布局和方案选择中的应用,总结了城市路网节点处互通式立交选型的一些经验,供同类工程参考。 相似文献
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中夹岩柱是小净距隧道围岩稳定控制的关键部位,判别中夹岩的安全性是工程设计和施工过程中的重难点。文章通过分析不同围岩级别、埋深情况下中夹岩的破坏模式,建立Ⅳ级围岩条件下水平小净距隧道中夹岩力学分析模型,并确定中夹岩破裂面位置。根据中夹岩上部滑块体形状的不同分为两种情况,通过边坡稳定性原理、极限平衡假设及普氏压力拱理论推导中夹岩上部滑块体的抗滑力、下滑力以及安全系数的计算公式,从而建立起评判中夹岩安全性的安全系数法,并结合数值模拟对其进行验证。将经验证后的安全系数法应用于某实际隧道工程,判断其中夹岩安全性,得出该隧道中夹岩破坏临界厚度为6 m,进而对6 m以下的中夹岩使用锚杆进行加固。 相似文献