Failure mechanism of large-diameter shield tunnels and its effects on ground surface settlements

A new technique for the analysis of the three-dimensional collapse failure mechanism and the ground surface settlements for the large-diameter shield tunnels were presented.The technique is based on a velocity field model using more different truncated solid conical blocks to clarify the multiblock failure mechanism.Furthermore,the shape of blocks between the failure surface and the tunnel face was considered as an entire circle,and the supporting pressure was assumed as non-uniform distribution on the tunnel face and increased with the tunnel embedded depth.The ground surface settlements and failure mechanism above large-diameter shield tunnels were also investigated under different supporting pressures by the finite difference method.

Effect of local openings on bearing behavior and failure mechanism of shield tunnel segments

Local failures(loss of concrete or reinforcement)can severely compromise the bearing capacity of shield segments,damaging the tunnel structures.To investigate the effects of local openings on the bearing behavior and failure mechanism,four full-scale bending tests were conducted on specimens with different opening positions and diameters;monitoring of load,displacement,and concrete strain was performed during loading.The test results reveal that both the opening position and diameter significantly influence the bearing characteristics of the segment.The failure process includes four sequential stages distinguished by three critical loads,namely the cracking,failure,and ultimate loads.Subsequently,the numerical model of the local failure segment was established using the elastoplastic damage constitutive relation of the concrete and verified by inversing the full-scale test results.Based on the numerical model,parametric analyses were performed to comprehensively investigate the influences of the opening position,concrete loss,and reinforcement loss on the bending capacity.Furthermore,an analytical model was proposed,indicating that the opening position is the primary factor decreasing the bearing capacity,followed by the opening diameter and reinforcement loss.The results of this study can provide a theoretical basis for the safety assessment and remedial design of subway shield tunnels under extreme breakthrough conditions.

Prototype test study on mechanical characteristics of segmental lining structure of underwater railway shield tunnel

Based on the first unde rwater railway shield tunnel, the Shiziyang shield tunnel of Guangzhou Zhu- jiang River, the prototype test was carried out against its segmental lining structure by using ＂multi-function shield tunnel structure test system＂. And the mechanical characteristics of segmental lining structure using straight assembling and staggered assembling were studied deeply. The results showed that, the mechanical characteristics of segmental lining structure varied with the water pressures; especially after cracking, the high water pressure played a significant role in slowing down the growing inner force and deformation. It also testi- fied that the failure characteristics varied with straight assembling structure and staggered assembling structure. Shear thilurc often occurred near longitudinal seam when using straight assembling.

Tunnel face stability and ground settlement in pressurized shield tunnelling

An analysis of the stability of large-diameter circular tunnels and ground settlement during tunnelling by a pressurized shield was presented. An innovative three-dimensional translational multi-block failure mechanism was proposed to determine the face support pressure of large-shield tunnelling. Compared with the currently available mechanisms, the proposed mechanism has two unique features:(1) the supporting pressure applied to the tunnel face is assumed to have a non-uniform rather than uniform distribution, and(2) the method takes into account the entire circular excavation face instead of merely an inscribed ellipse. Based on the discrete element method, a numerical simulation of the Shanghai Yangtze River Tunnel was carried out using the Particle Flow Code in two dimensions. The immediate ground movement during excavation, as well as the behaviour of the excavation face, the shield movement, and the excavated area, was considered before modelling the excavation process.

盾构隧道衬砌结构偏心破坏转化临界锈蚀率预测

盾构隧道管片中的钢筋锈蚀会对结构的承载性能和破坏形态产生重要影响。一般盾构隧道结构多呈现小偏心受压状态,当钢筋锈蚀发展到一定程度时会出现小偏心向大偏心受力状态的转变,导致结构承载力下降、危及隧道运营安全。基于盾构隧道衬砌结构压弯受荷特点,设计小偏心加载的锈蚀试验柱,等效地模拟隧道衬砌的实际受力状态,分析不同锈蚀程度下试验柱跨中应变、极限承载力及裂缝的全过程演变。随锈蚀程度加重,试验柱承载力、混凝土应变、受压区高度下降速度逐渐加快,最大锈蚀率达到68.32%时,承载力最大降幅达到53.23%。试验发现高锈蚀程度(η≥46.25%)试验柱由小偏心破坏转化为大偏心破坏的现象。基于受弯构件正截面承载力理论分析,提出隧道衬砌结构由小偏心向大偏心破坏转化的临界锈蚀率理论计算方法,通过设计有限元计算流程验证了该方法的正确性。研究结果可为盾构隧道衬砌结构耐久性设计和安全评价提供理论支撑。

超/特高压输电线路雷电绕击分析方法及其适应性

输电线路雷击已成为制约电力系统安全可靠运行的首要因素,而500 kV及以上电压等级的输电线路主要以雷电绕击导线为主。该文在回顾电气几何模型发展历史的基础上,针对电气几何模型忽略大部分雷击物理过程的问题,详细分析先导发展法,包括雷击输电线路物理过程、先导发展模型参数选择、数值方法实现及模型验证,该方法能够全面模拟雷击发展的物理过程;最后,采用先导发展法分析影响线路绕击特性的因素,并讨论不同绕击分析方法的适用范围,对于500 kV及以上的超特高压线路以及同塔多回输电线路,宜采用先导发展法分析雷电绕击。该研究可为输电线路防雷设计及运行事故分析提供关键技术支撑。

计及邻近线路架设方向和屏蔽影响的密集输电通道防雷性能仿真分析

在调研了输电线路防雷设计的研究现状后,针对考虑密集输电通道中线路间屏蔽作用的绕击跳闸率计算问题提出了改进的电气几何模型法并验证其可行性,主要包括了计算思路的优化和地面倾角处理方式的修正。基于所提出的计算方法,针对3条输电线路并行工况进行了计算和规律分析,发现对线路间屏蔽效果占主导作用的为相邻线路,且屏蔽作用的强弱并非随线路间距线性变化,而是存在一个快速变化的区间范围。在此基础上,提出了考虑实际中线路走向和弧垂的线路间距和对地高度计算方法,基于所提出的方法对实际工程进行了计算,证明了方法的可行性,对输电线路的防雷改造具有一定的指导作用。

正交下穿截污管盾构开挖面被动失稳颗粒流模拟研究

目的 对砂土地层土压平衡式盾构下穿截污管施工工况进行研究,以解决由于支护压力过大导致的开挖面被动失稳问题。方法 以沈阳地铁三号线下穿截污管区段为背景,利用颗粒流程序建立数值模型,研究截污管存在下的开挖面被动失稳模式、支护压力变化以及地层应力分布。同时分析了管隧垂直净距与细观摩擦系数对极限支护压力的影响。结果 开挖面失稳模式和极限支护压力均受盾构开挖位置的影响,当开挖面位于管道前方1.0 D时,管道对失稳模式的影响最大;盾构穿越管道前,管道下部土层出现应力增大现象;极限支护压力随着管隧垂直净距、颗粒摩擦系数的增大而增大。结论 在盾构接近且未穿越截污管时,管道对开挖面被动失稳机理产生了显著影响。

输电线路雷电绕击风险评估多源数据融合可视化方法

直观描述超/特高压输电线路的绕击风险分布,展现线路结构、地形地貌、雷电活动等复杂因素的交互关系具有重要的价值,相关研究亟待深化。该文开展了绕击风险评估多源数据融合可视化方法研究。基于输电通道点云数据、EGM模型参数、绕击闪络率等多源数据特征分析,借鉴“以数生智”认知过程,提出了一种数据融合3维可视化框架及关键技术。该方法采用“档距-导线-断面-计算点-暴露弧”层级数据结构,按层级关联整合不同维度表达需求的数据,基于输电通道激光雷达点云空间开展以暴露弧为载体的绕击风险机理可视化,实现绕击闪络率、屏蔽机理、雷电流幅值等多源信息的综合立体展示,通过支持对限定条件的响应,实现了绕击故障分析应用。某500 kV线路档距案例应用结果表明:融合可视化能够发挥3维视图多尺度、多视角的优势,通过暴露弧与点云数据的信息互补,从机理层面揭示避雷线、地面对导线的屏蔽作用,提升数据展示的全面性、直观性。

正断层错动下地铁盾构隧道变形破坏模型试验研究

为揭示跨隐伏断层地铁盾构隧道结构变形破坏特征,采用自主设计的模拟隐伏断层错动加载试验装置,开展1∶25几何比例的跨断层盾构隧道模型试验,分析正断层错动下盾构隧道的力学响应规律及变形破坏特征.试验结果表明:在2 cm正断层错动影响下,隧道纵向差异变形呈现非线性增大趋势,环缝接头张开变形主要位于断层下盘隧道拱顶及断层上盘隧道拱底,且环缝峰值张开量已超过盾构隧道接缝防水限值;断层延长线与隧道交界处管片直径收敛变形较为严重,该处管片呈现拱腰外侧受拉、拱顶及拱底外侧受压的受力状态;管片与地层之间接触压力受断层错动的影响较大,存在围岩挤压区与围岩松散区,但接触压力峰值相对较小;盾构隧道的主要变形破坏特征为环缝接头拉裂破损、管片纵向开裂及环缝接头变形,管片发生斜向剪切破坏及局部压溃破坏的概率较低.基于盾构隧道环纵向变形破坏特征,建议将管片环缝变形及接头混凝土拉裂破损作为界定跨断层盾构隧道结构破坏的主要控制指标.基于隧道的变形破坏模式,提出了跨断层盾构隧道结构设计及应对措施的建议.

盾构隧道混凝土管片接头抗弯与抗剪性能试验研究

混凝土管片的接头部位在使用过程中,会受到轴力、弯曲力矩和剪切力的共同作用,为能够全面了解混凝土管片接头处受不同外力下作用下的力学性能。根据研究特点,设计三组试验分别为极限承载能力、极限弯矩、剪切试验。针对混凝土管片接头有、无斜向螺栓工况,从管片接头受压区高度、最大张开度以及张开角度的试验数据角度,分析混凝土管片接头处轴力和极限弯矩之间的变化关系。采用有斜向螺栓逆剪切、有斜向螺栓顺剪切以及无斜向螺栓剪切的三种对比试验方式,开展管片接头破坏状态和接头相对错动量分析。研究表明,有无斜向螺栓下的混凝土管片接头处受压区高度和极限弯矩均随着轴力的增加呈现线性增长的趋势,最大张开度和张开角均随着轴力的增加呈线性减弱的趋势;有斜向螺栓连接的管片接头,其相对错动曲线存在平台段,同时受顺剪下的平台段要明显长于逆剪下的平台段。通过管片接头顺剪切和逆剪切破坏对比试验的研究,可较为全面地揭示管片接头部位的抗弯、抗剪切性能的宏观变形规律,其研究结果可为盾构隧道管片接头构造的合理选择提供参考。

位移加载法下的盾构隧道开挖面被动破坏数值模拟研究

针对盾构隧道中的开挖面稳定性问题,分析了盾构施工过程中的实力情况,总结了适用于开挖面主动、被动破坏研究的开挖面支护力加载方式。以砂土地层的浅埋盾构隧道的被动破坏为例,详细介绍了数值模拟中位移加载法的使用办法,分析了位移加载法下的极限支护力、开挖面上的支护力分布、开挖面土体位移、地表沉降特点。结果表明:在开挖面稳定性的被动破坏研究中,采用位移加载法更为合理,其数值模拟结果与实际工程中的开挖面被动破坏的特征吻合良好。

地埋金属管材阴极屏蔽防腐失效研究

目前解决地埋金属管材腐蚀问题最常用和最有效的方法是对金属管材进行表面涂层处理,常用的有机涂料存在耐腐蚀性随涂层老化而快速下降的缺点。依托随州管廊项目,通过对管廊内金属设备防腐层进行分析,得到防腐涂层的失效原因,分析阴极保护体系下阴极屏蔽的产生原因,选出合理的涂层施工技术,减少防腐涂层施工中的污染来源,为类似项目提供参考。

断层错动作用下盾构隧道结构易损性研究

为了研究活动断层错动导致盾构隧道结构失效概率模型,考虑断层属性、隧道几何特征以及断层与隧道位置关系等因素对盾构隧道力学响应的影响,以环缝接头变形及管片直径收敛变形率作为结构性能指标,通过一系列跨断层隧道拟静力数值分析以及回归分析,建立盾构隧道各性能指标与地面永久位移的关系,提出跨断层盾构隧道结构易损性分析流程,评估盾构隧道不同性能水准的超越概率,并和已有试验易损性及经验易损性曲线进行对比分析。结果表明:1)隧道与断层的位置关系、隧道所在地层变形模量对跨断层盾构隧道变形破坏程度的影响较大,其中穿越断层工况盾构隧道极易发生变形破坏,其次是上跨断层硬土工况,上跨断层软土工况中盾构隧道抵抗断层错动能力最强;2)针对跨断层盾构隧道结构失效特征,建议在开展结构易损性研究时以环缝接头变形作为主要性能指标。研究结果可为跨活动断层盾构隧道灾害评估及减灾技术提供理论指导。

Bending failure performance of a shield tunnel segment based on full-scale test and numerical analysis

This study focuses on the bending failure performance of a shield tunnel segment.A full-scale test was conducted to investigate deformation and failure characteristics.During the loading,the bending failure process can be divided into four stages:the elastic stage,working stage with cracks,failure stage,and ultimate stage.The characteristic loads between contiguous stages are the cracking,failure,and ultimate loads.A numerical model corresponding to the test was established using the elastoplastic damage constitutive model of concrete.After a comparative analysis of the simulation and test results,parametric studies were performed to discuss the influence of the reinforcement ratio and proportion of tensile longitudinal reinforcement on the bearing capacity.The results indicated that the change in the reinforcement ratio and the proportion of tensile longitudinal reinforcement had little effect on the cracking load but significantly influenced the failure and ultimate loads of the segment.It is suggested that in the reinforcement design of the subway segment,the reinforcement ratio and the proportion of tensile longitudinal reinforcement can be chosen in the range of 0.7%–1.2%and 49%–55%,respectively,allowing the segment to effectively use the reinforcement and exert the design strength,thereby improving the bearing capacity of the segment.

山地风电场35 kV集电线路耐雷水平分析

以某风电场集电线路雷电绕击杆塔为研究对象,采用ATP-EMTP软件建立集电线路雷击电磁暂态分析模型,对杆塔遭受雷击下集电线路耐雷水平进行分析,分别对未安装避雷器及杆塔底部安装避雷器的两种情况进行分析。结果表明,对于未安装避雷器的杆塔,其绕击耐雷水平较低,大幅值雷电流易引起三相同跳问题;对于安装有避雷器的杆塔,避雷器在一定程度上能提高导线绕击耐雷水平,同时给出相应的防护措施建议,为雷电发多地带风电场防雷保护提供技术参考。

输电线路绕击分散性的试验研究

基于输电线路绕击的模拟试验研究，提出了输电线路的绕击概率模型。该模型可根据线路结构参数，分析输电线路旁空间绕击概率的分布情况。成功地说明了ＥＧＭ难以解释的现场事故原因。

山区输电线路雷电绕击跳闸率的计算

准确评估山区输电线路的绕击跳闸率对于防雷措施的合理选用起重要作用。基于输电线路位于山脉的典型位置,推导了其绕击跳闸率计算公式,以220 kV双避雷线输电线路为例,计算了输电线路处于山脉不同位置时的最大绕击雷电流和绕击跳闸率随地面倾角的变化,可为山区输电线路雷击防护提供参考。

云广特高压直流输电线路雷电屏蔽性能研究

为评估、计算输电线路雷电屏蔽性能即绕击性能,基于长空气间隙放电理论建立了特高压直流输电线路雷电屏蔽的先导发展模型,并用该模型计算了拟建立的云广±800 kV直流特高压输电线路雷电屏蔽性能。计算结果表明:随着地面倾角、保护角的增加,线路屏蔽失效率明显增加,特高压直流输电线路最好采用负保护角运行。

山区复杂地形条件下输电线路雷击跳闸故障分析方法

为提高山区输电线路防雷水平,揭示部分已安装塔顶避雷针或避雷线侧针保护失效原因,应加强对雷击点位置的诊断分析。基于雷电定位系统监测数据,利用三维地理信息系统扫描提取的故障杆塔邻近档距精细地形地貌数据,建立全档距三维全景复现防雷性能计算模型,仿真故障时刻状态,分析确定故障性质和雷击点范围,并考虑邻近杆塔绝缘水平差异和防雷措施保护范围的影响校核雷击点区间。运用该方法对发生在山区的典型故障进行三维全景复现,得到的分析结果能够较好地与故障情况吻合,并且量化解释了部分现有防雷措施失效的原因,对后续防雷改造具有显著的工程指导意义。