Study on the tunnel shape and soil-lining interaction influencing the lining behavior under seismic loading

The response of tunnels subjected to seismic loading is a complex mechanism and depends not only on the seismic nature but also on tunnel structure and surrounding soil properties.The individual behavior of circular,rectangular,and sub-rectangular tunnels subjected to seismic loadings has already been studied in the literature.In the present research,two case scenarios of circular,rectangular tunnels and four sub-rectangular shaped tunnels,with similar cross-section areas,were adopted to perform a comprehensive numerical investigation.The purpose of the study was to determine the mechanical behavior of tunnels of different shapes,depending upon seismic conditions.Analyses were performed by considering the influence of soil-lining interaction,soil parameters,and lining thickness,as well as lining rigidity.Computations were performed for no-slip and full-slip conditions.The results indicate that the tunnel shape design is of great importance when regarding the mechanical behavior of the surrounding soil.This concerns no-slip as well as full-slip soil-lining interaction,especially when the lining is subjected to seismic loading.Moreover,it is shown that changes in incremental bending moments for circular,rectangular and sub-rectangular tunnels that depend upon the soil-lining interaction conditions differ significantly.

Determination of minimum overburden depth for underwater shield tunnel in sands:Comparison between circular and rectangular tunnels

With the development of global urbanization,the utilization of underground space is more critical and attractive for civil purposes.Various shapes of shield tunnels have been gradually proposed to cope with different geological conditions and service purposes of underground structures.Generally,reducing the burial depth of shield tunnel is conducive to construction and cost saving.However,extremely small overburden depth cannot provide sufficient uplift resistance to maintain the stability and serviceability of the tunnel.To this end,this paper firstly reviewed the status of deriving the minimum sand over-burden depth of circular shield tunnel using mechanical equilibrium(ME)method.It revealed that the estimated depth is rather conservative.Then,the uplift resistance mechanism of both circular and rectangular tunnels was deduced theoretically and verified with the model tests.The theoretical uplift resistance is consistent with the experimental values,indicating the feasibility of the proposed equations.Furthermore,the determination of the minimum soil overburden depth of rectangular shield tunnel under various working conditions was presented through integrated ME method,which can provide more reasonable estimations of suggested tunnel burial depth for practical construction.Additionally,optimizations were made for calculating the uplift resistance,and the soil thickness providing uplift resistance is suggested to be adjusted according to the testing results.The results can provide reference for the design and construction of various shapes of shield tunnels in urban underground space exploitation.

Mechanical Behavior and Shape Optimization of Lining Structure for Subsea Tunnel Excavated in Weathered Slot

Subsea tunnel lining structures should be designed to sustain the loads transmitted from surrounding ground and groundwater during excavation. Extremely high pore-water pressure reduces the effective strength of the country rock that surrounds a tunnel, thereby lowering the arching effect and stratum stability of the structure. In this paper, the mechanical behavior and shape optimization of the lining structure for the Xiang＇an tunnel excavated in weathered slots are examined. Eight cross sections with different geometric parameters are adopted to study the mechanical behavior and shape optimization of the lining structure. The hyperstatic reaction method is used through finite element analysis software ANSYS. The mechanical behavior of the lining structure is evidently affected by the geometric parameters of crosssectional shape. The minimum safety factor of the lining structure elements is set to be the objective function. The efficient tunnel shape to maximize the minimum safety factor is identified. The minimum safety factor increases significantly after optimization. The optimized cross section significantly improves the mechanical characteristics of the lining structure and effectively reduces its deformation. Force analyses of optimization process and program are conducted parametrically so that the method can be applied to the optimization design of other similar structures. The results obtained from this study enhance our understanding of the mechanical behavior of the lining structure for subsea tunnels. These results are also beneficial to the optimal design of lining structures in general.

Optimization of ambipolar current and analog/RF performance for T-shaped tunnel field-effect transistor with gate dielectric spacer

A new T-shaped tunnel field-effect transistor(TTFET) with gate dielectric spacer(GDS) structure is proposed in this paper. To further studied the effects of GDS structure on the TTFET, detailed device characteristics such as current-voltage relationships, energy band diagrams, band-to-band tunneling(BTBT) rate and the magnitude of the electric field are investigated by using TCAD simulation. It is found that compared with conventional TTFET and TTFET with gate-drain overlap(GDO) structure, GDS-TTFET not only has the minimum ambipolar current but also can suppress the ambipolar current under a more extensive bias range. Furthermore, the analog/RF performances of GDS-TTFET are also investigated in terms of transconductance, gate-source capacitance, gate-drain capacitance, cutoff frequency, and gain bandwidth production. By inserting a low-κ spacer layer between the gate electrode and the gate dielectric, the GDS structure can effectively reduce parasitic capacitances between the gate and the source/drain, which leads to better performance in term of cutoff frequency and gain bandwidth production. Finally, the thickness of the gate dielectric spacer is optimized for better ambipolar current suppression and improved analog/RF performance.

低空封闭连廊的表面风压和整体体型系数

采用刚性模型测压风洞试验研究低空封闭连廊的风压分布和整体体型系数,分析连廊4个表面测点的体型系数和非高斯分布特性,研究连廊整体体型系数随风向角和连廊长度的变化,给出低空封闭连廊的正迎风整体体型系数和角度风分配系数,基于极值分析方法给出连廊的全风向极值风压系数,最后给出连廊抗风设计的建议值.研究表明,低空封闭连廊在正吹情况下背风面的体型系数约为-1.04~-0.86,绝对值均大于规范中方柱的-0.6,导致连廊的整体体型系数大于规范中方柱的1.4,30 m长低空封闭连廊的整体阻力系数为1.61;正吹情况下连廊中间截面的整体体型系数大于其他截面,正吹风向角的整体体型系数大于其他风向角,连廊越长正迎风整体体型系数越大;在正吹情况下,连廊迎风面风压主要为高斯分布,其他表面主要为非高斯分布;给出正迎风整体体型系数和角度风分配系数以用于低空封闭连廊主体结构的抗风设计.

公路隧道箱型预制仰拱变形破坏的模型试验研究

基于自主设计的新型箱型预制仰拱结构,采用室内物理模型试验,结合数字照相量测技术,研究该箱型预制仰拱的力学特性及破坏模式,通过数值模拟研究实际工况中衬砌与仰拱共同作用的受力规律.结果表明:竖向荷载作用下产生的拉张效应是预制仰拱裂纹产生及发展的主要原因,水平压力对预制仰拱的裂纹发展作用不明显.预制块接缝处以及各个预制块中柱转角处是预制仰拱结构的最薄弱部位,接缝处和转角处影响预制仰拱结构的安全.预制仰拱位移变化关于中轴部位呈对称分布,位移由大到小依次为中间预制块、左1预制块、左2预制块、左3预制块.箱型预制仰拱破坏可以分为加载压密、弹塑性变形和塑性破坏3个阶段.当仰拱与衬砌共同作用时,仰拱的上部主要承受拉应力,仰拱的下部主要承受压应力.试验结果表明,所设计仰拱结构具有良好的受力性能.

抽蓄电站无压隧洞交叉区体型优化试验研究

交叉无压隧洞交汇区域水流的水力特性复杂,无压隧洞交叉区体型及交汇口水流水力特性的研究对确保水利枢纽的安全运行具有重要的工程意义。基于物理模型试验,对某抽水蓄能电站下水库高落差泄洪排沙洞和放空洞交叉区体型进行优化,最终确定圆弧连接+交叉角21°的交叉区体型。对比分析圆弧连接+交叉角21°的交叉区优化体型下特征试验工况的水力特性。结果表明,6种特征试验工况下,泄洪排沙洞和放空洞交叉口及下游均为急流,明流泄洪且流态较稳定,均在交汇口下游右边直墙处形成最大水深,水深低于直墙高度,满足水面线不宜超过直墙范围的要求。

Evolution of crescent-shaped sand dune under the influence of injected sand flux:scaling law and wind tunnel experiment

This paper studies the evolution of crescent-shaped dune under the influence of injected flux. A scaling law and a wind tunnel experiment are carried out for comparison. The experiment incorporates a novel image processing algorithm to recover the evolutionary process. The theoretical and experimental results agree well in the middle stage of dune evolution, but deviate from each other in the initial and final stages, suggesting that the crescent-shaped dune evolution is intrinsically scale-variant and that the crescent shape breaks down under unsaturated condition.

半U形隧道火灾补气速度和最高烟气温升的机器学习预测

半U形隧道是考虑火灾发生在水下隧道变坡点前而简化得到的隧道结构,通过理论推导很难建立有关烟气运动参数预测模型。因此,借助于FDS数值模拟和机器学习对320组火灾工况进行模拟分析和机器学习预测。结果表明:纵向风速的增大对于空气补充速度会有一定的抑制效果,BP神经网络在测试集和训练集上的预测效果较其他机器学习模型更为精确,决定系数R~2能够达到0.99;通过Shap值对影响隧道内空气补充速度的特征因素按重要性从高到低排序依次为高度效应、热效应、风效应;最高烟气温升受风速影响,坡高小则温升随风速减小剧烈,坡高大时风速影响不显著,并且相较于其他机器学习方法,BP神经网络和理论计算均能准确预测烟气最高温升,R~2均大于0.9。研究结合数值模拟与机器学习,为高效预测隧道火灾动力学行为及通风排烟系统优化设计提供了新方法。

边箱式π型断面涡振性能及导流板措施参数研究

π型断面因构造简单与受力性能好,被广泛应用于桥梁建设中,但其抗风性能差,易产生涡激振动问题.本文以边箱式π型断面桥梁为研究对象,采用宽高比10∶1的π型断面刚体节段模型进行同步测振测压试验,并且通过计算流体力学方法加以对比验证,研究π型断面涡振性能与导流板抑振机理.试验结果表明:边箱式π型断面在0°、±3°风攻角下发生显著涡激振动,通过在断面两侧加设特定形式及尺寸参数的导流板措施可抑制断面竖弯及扭转涡振.其中,倒L型导流板措施气动优化效果显著,可有效消除涡振振幅,而水平导流板措施的抑振效果有限,相较于竖弯涡振,扭转涡振对于水平导流板尺寸参数更为敏感.通过对比数值模拟结果与表面气动压力分布,表明倒L型导流板措施能够优化断面气动外形,削弱断面上下表面旋涡脱落尺度和能量,同时降低断面所受的周期性气动力,从而有效抑制断面涡振.

高流速、大流量无压洞掺气设施体形优化模型试验研究

高水头、大流量、高流速的泄水建筑物,往往需要设置掺气设施来降低空蚀破坏。结合新疆某水利枢纽工程实例,通过开展泄洪冲沙洞水工模型试验研究,对1号、2号掺气设施挑坎高度、通气孔面积、坡比及型式进行优化设计。结果表明:体形优化后,在各种工况下,掺气设施掺气效果良好,掺气空腔完整而稳定,坎下未出现较大回水等不利流态;通气孔通气顺畅,整体水流流态平顺,无水翅溅到洞顶等不利现象;沿程余幅均满足要求;过流能力和流量系数基本与原设计一致。研究结果可为类似工程的掺气设施体形研究提供指导与技术支撑。

周边孔聚能装置间隔装药在光面爆破中的应用研究

隧道光面爆破工程的周边孔需要采用间隔装药方式,而大部分间隔装药方式采用“导爆索+雷管”联合起爆技术,此技术具有一定的局限性且经常发生拒爆现象。如何在保证隧道掘进效率的前提下提高光面爆破效果成为目前亟待解决的难题,从现场试验方面开展相关研究,提出“聚能装置+数码电子雷管”新型联合起爆技术,将其应用于高原某隧道,通过与原始的“导爆索+数码电子雷管”联合起爆技术的爆破后效果进行对比分析。实验结果表明:对比原始技术,新技术炸药单耗降低了0.2 kg/m^(3),半孔留痕率提高了5%,平均装药时间由原来的1.3 h降为1.0 h,稳定循环进尺的同时极大降低了耗材费用,提高了隧道光面爆破效果。

沈阳恒隆市府广场超高层塔楼风荷载分析研究

为了确定高度350.6m沈阳恒隆市府广场塔楼结构设计的风荷载,采用刚性风洞试验与风洞数值模拟相结合的方法分析塔楼的风荷载,风洞试验研究给出楼层剪力与扭矩及风致加速度。采用四种湍流模型进行风洞数值模拟,分析建筑平均风压系数、体型系数、基底剪力及倾覆力矩,并与风洞试验进行比较,得出适用于超高层建筑风洞模拟的湍流分析模型,利用该分析模型的数值风洞模拟技术,分析塔楼13个风向角的风压系数、体型系数和基底剪力,为结构风荷载取值提供依据。研究结果表明:相比于《建筑结构荷载规范》(GB 50009—2012)对近似矩形平面建筑物的体型系数的规定,RSM模型迎风面0.83、背风面-0.56,与规范矩形截面迎风面0.8、背风面-0.6最为接近;RSM模型与试验吻合最好;选取RSM模型来分析超高层等大型复杂结构风荷载,能够得到较为准确的结果。

典型峡谷Ⅴ型地貌下桥址区风特性

为得到山区峡谷典型Ⅴ型地形下的桥梁抗风设计的关键风特性参数,通过“数值风洞试验”建立模型,以实桥为工程背景构建三维地形网格,基于3种典型湍流模型和流体壁面粗糙度对桥位的风场特性进行分析,选取最优湍流模型和流体壁面粗糙度对该地形桥位处的风场特性进行分析;围绕两个影响桥址区风特性的地形参数(山体高度和夹角),阐明Ⅴ型峡谷地形下风特性参数的变化规律,并与现行规范进行对比,推算桥面设计基准风速。结果表明:该Ⅴ型峡谷地形的最佳湍流模型和流体壁面粗糙度分别为RNG k-ε和20 m;随着山体高度及山体夹角两参数的变化,风速增加幅度分别为2.37%~12.56%和1.24%~6.98%;山体高度及山体夹角两变参数下,梯度风高度分别为700 m和800 m左右;实际湍流强度大于规范中四类地表规范值,在离地高度40 m范围内,湍流强度更接近于D类地表。实际Ⅴ型峡谷桥址区不能简单按规范归为C类或D类地形,在设计风参数计算时应综合考虑规范和经验公式,还可借助模拟手段来提高其准确性。

槽形钢箱梁涡振性能及抑振措施试验研究

为提高槽形钢箱梁桥的抗风性能,对槽形钢箱梁的涡振性能及抑振措施进行试验研究。以某人行景观桥槽形钢箱梁为背景,通过主梁节段模型风洞试验,研究+3°、0°、-3°风攻角下均匀流与紊流风场中槽形钢箱梁的涡振性能,分析交替封闭栏杆、将栏杆楔形扶手改为圆形扶手、提高阻尼比等措施的抑振效果。结果表明:原槽形钢箱梁断面涡振性能不满足规范要求,均匀流风场中,3个风攻角下均出现了超限的竖弯涡振,+3°和-3°风攻角下出现了不同程度的扭转涡振,最不利风攻角为-3°;紊流风场中,最不利风攻角下原断面竖弯涡振振幅降低了23%,未见明显扭转涡振;楔形扶手栏杆交替封闭使结构竖弯涡振振幅增大,主梁涡振性能降低;单独改变栏杆扶手形状为圆形对主梁涡振性能影响不大,在此基础上交替封闭栏杆能够有效抑制主梁涡振;提高结构阻尼比能有效抑制主梁涡振,阻尼比为7‰时,主梁竖弯涡振振幅可降至规范限值的一半左右。

基于正交试验的旋流竖井泄洪洞衔接段体型参数敏感性分析

竖井式泄洪洞的衔接段体型直接影响退水隧洞的流态、竖井的振动特性和消能效果。对衔接段体型的研究目前以单因素居多,多因素研究较少,在工程设计实践中对竖井体型进行优化多参考类似工程经验,尚无较为系统的优化方法。通过数值正交试验,以出口湍动能为指标,对衔接段长宽比、出口压坡收缩比、压坡坡比等衔接段体型参数进行了敏感性分析。研究表明:衔接段长宽比对出口湍动能的影响最为显著,压坡坡比次之,收缩比最低。研究成果可在工程设计中对竖井泄洪洞衔接段体型优化提供一定的参考。

新建暗挖隧道下穿既有铁路U型槽的施工影响研究

为了给涉铁工程的设计施工提供参考,基于北京市某电力隧道下穿丰沙铁路U型槽结构的工程案例,建立“土体-U型槽结构-电力隧道”三维数值模型,计算并分析新建电力隧道施工对既有铁路轨道及U型槽结构的变形影响,研究表明铁路轨道沉降最大值为-3.592 mm,水平位移最大值为3.496 mm;U型槽沉降最大值为-3.974 mm,水平位移最大值为4.142 mm,可满足安全要求,并进一步提出必要的工程措施建议。

单坡度V字形隧道火灾中等效纵向风速及温度场研究

火灾发生在水下隧道的变坡点附近时,隧道结构可简化为单坡度V形隧道。在单坡度V形隧道发生火灾时,烟气运动会受到一侧倾斜隧道烟囱效应的影响。采用FDS数值模拟研究方法,对自然通风状态下单坡度V形隧道火灾中的等效纵向风速以及隧道温度场进行研究,并建立了预测模型。结果表明,火灾产生的等效纵向风速与隧道坡高和热释放速率有关,其数值大小与热释放速率的1/3次幂和无量纲坡高成正比;单坡度V形隧道顶板下烟气的最大温升随着坡度的增加而线性递减,整个火灾下游的烟气温度分布呈指数衰减,且坡度越大,纵向烟气温度在火源周围的衰减越明显,衰减曲线也更陡峭。

高超声速火箭橇气动特性优化与风洞试验

为研究如何在不额外增加稳定装置的基础上提高超声速条件下火箭橇的在轨运行稳定性,基于数值分析方法开展了高超声速火箭橇气动特性优化设计,并通过风洞试验对优化后的橇体进行了不同工况下的气动特性研究。建立了基于SST湍流模型、N-S控制方程的火箭橇气动特性数值分析方法,通过经典双椭球模型对计算方法的准确性进行验证。基于气动特性数值分析方法开展橇体气动外形设计,对整流板俯仰角、侧偏角以及前、后滑靴的位置进行优化。通过风洞试验对优化后的橇体进行不同工况下的气动特性研究,分析马赫数、雷诺数以及轨道和地面效应的影响。研究结果表明:火箭橇高超声速气动特性数值分析方法的精度约为86.94%,可以用来模拟火箭橇在高超声速流场中的气动特性;在Ma=5时,优化后的模型相较于优化前的模型,气动阻力减小了约23.57%,气动升力减小了约38.49%;随着马赫数的增加,橇体阻力系数呈下降趋势,当Ma从4增加到6,橇体的阻力系数下降约19.98%;橇体升力系数与俯仰力矩系数均随着雷诺数的增大而增加,Ma=5,当雷诺数从1.80×10^(7)变化到3.60×10^(7)时,橇体的阻力系数与俯仰力矩系数分别增加约8.95%和13.09%;轨道和地面会导致橇体阻力系数、升力系数和俯仰力矩系数同时增加,其中俯仰力矩系数的变化最为显著,3组对比试验的俯仰力矩系数平均增量约为992%。该研究可为高超声速火箭橇设计提供数据支撑,具有一定的工程应用价值。

截面型式及槽宽比对高填明洞土压力影响分析

利用离散元软件PFC2D,考虑到土体的离散性与不均匀性,通过分析洞顶平均竖向土压力、内外土柱相对沉降差以及颗粒间接触力链的变化规律,探讨截面型式(矩形、1/4拱形、1/2拱形)及槽宽比(B/b=1.5∶1,2∶1,3∶1,4∶1)变化对高填黄土明洞土压力的影响,结合顾安全公式,分析高填明洞沉降差与土压力间的函数关系,并修正该函数,使其可以适用与不同的截面型式与槽宽比下的高填明洞。结果表明:(1)B/b确定,明洞采用矩形截面时,接触力链在洞顶分布,平均土压力更大,明洞采用拱形截面时,平均土压力更小,但拱顶存在局部应力集中现象;(2)明洞截面型式一定,随着B/b的增大,洞顶平均竖向土压力与沉降差均随之增大,当B/b较小时,边坡作用增强,外侧土柱沉降降低,对内土柱的作用力变小,从而导致明洞顶竖向土压力更小;(3)内外土柱沉降差与附加土压力呈线性相关,相对于矩形截面,拱形截面下较小的沉降差会产生相同的附加土压力,更有利于结构的稳定。