黄土无衬砌隧道破坏机制振动台试验研究——隧道稳定性分析讲座之二

在参考相关文献以及做了一定数值模拟分析后进行了黄土无衬砌隧道的大型振动台试验的研究.振动台试验的研究结果表明:埋深越深峰值加速度越小,埋深浅的隧道和地下结构要加强抗震措施;隧道洞口部由于刚性变化较大峰值加速度相比沿隧道其它位置要大,在隧道洞口部一定范围内要提高抗震水准;隧道直墙中下部是最易破坏的部位,而隧道仰拱会出现拉...     

逐级加载下浅埋软岩隧道动力破坏振动台试验

浅埋隧道围岩的质量普遍较低,整体稳定性差,隧道震害表明强震作用下浅埋隧道极易发生震动破坏。通过开展V级围岩条件下浅埋隧道在小震下的震动响应和逐级加载下的震动垮塌振动台试验,研究了小震作用下围岩加速度沿地层的分布、衬砌结构的内力变化和围岩内部的水平位移变化规律,强震作用下衬砌结构裂缝开展和围岩震动垮塌。结果表明:围岩加速度随距地表距离的减小而增加,地表加速度约为拱顶处加速度的1.63倍,相同高度平面内靠近隧道的围岩振动具有一定的加强;隧道拱顶围岩内部的水平位移大约是拱腰围岩内部的1.23倍,围岩内部位移随着远离隧道而逐渐减小,随着震动烈度的增加而不断增加;隧道拱顶上方垮塌区形状近似漏斗,震动引起隧道衬砌结构拱脚处的轴力和弯矩变化最大,且拱肩和拱脚处裂缝分布最多,应加强拱肩和拱脚处结构的抗震性能。     

汶川地震公路隧道洞口结构震害分析及震害机理研究

通过对汶川地震公路隧道震害调查资料的统计分析,对隧道洞口结构进行了震害分析,结果表明：洞外结构受次生灾害影响较大,地震惯性力影响明显;硬岩洞口段隧道结构基本无破坏,软岩洞口段隧道结构震害较严重。通过三维有限差分数值模拟计算和现场典型震害分析,研究了公路隧道洞口结构的震害机理。探明了洞外结构震害机理,即洞外结构受次生灾害影响较大,震害的主要原因是地震惯性力,洞门墙结构和基础设计不合理以及隧道洞口所处位置也是影响洞外结构震害的重要因素。探明了洞口段隧道结构震害机理,即正穿坡面洞口段隧道结构存在软硬围岩交界面时,其附近软岩内隧道结构受较大强制位移作用;正穿坡面洞口段隧道结构覆盖层为软岩时,震害的主要因素是地震惯性力。研究成果对公路隧道洞口结构的抗减震技术有着重要的意义。     

Damage observation and assessment of the Longxi tunnel during the Wenchuan earthquake

The Longxi tunnel was one of the most damaged tunnels during the 2008 Wenchuan earthquake in China. What makes the case interesting is that the tunnel crosses a fault zone. Damage from small to heavy cracking was observed both at the portal and inside the tunnel, while sections close to the fault completely collapsed. A full three-dimensional dynamic finite element model of the tunnel and rock system is used to assess the seismic damage observed in the tunnel and to evaluate the influence of the longitudinal and vertical motions on the seismic response. A comparison between the numerical predictions and the damage reported shows a good agreement. The results indicate that the longitudinal earthquake motion has a significant effect on the response of the tunnel structure and should be considered for the structural design of tunnels in seismic zones. In contrast, the vertical seismic motions can generally be neglected.     

紫坪埔隧道小净距段现场监测试验研究

 为节约工程造价,紫坪铺隧道汶川端设计为渐变小净距隧道与整幅修建的泯江大桥相接。该端隧道洞口段左、右线间距较小,围岩较差。为保证隧道的安全施工和积累经验,对紫坪埔隧道小净距段进行衬砌内力、围岩压力、位移及地表沉降等项目的监测工作。现场监测结果表明：(1) 后行洞开挖对中岩墙及先行洞的围岩及结构均产生一定的影响,影响程度视围岩级别不同而不同;(2) 采用上下台阶法施工时,上下台阶交界部位是应力集中和初期支护薄弱之处,施工中应加强对上下台阶交界处的监控量测;(3) 中岩墙是小净距隧道的薄弱环节,为保证施工过程中的安全,应加强对中岩墙应力、位移的监控量测。     

大跨度、浅埋及软弱围岩隧道进洞施工技术

对厦门市机场快速路(仙岳路—演武大桥)JC6合同段钟鼓山隧道改建并线段大跨度、浅埋及软弱围岩隧道洞口段施工工艺、施工方法的控制要点进行了重点阐述,其施工工艺和方法能为同类隧道进洞施工提供借鉴。     

隧道软岩洞口段结构加强抗震#br# 措施振动台模型试验研究

为提高隧道软岩洞口段的抗震性能,依托某隧道洞口段工程,采用大型振动台模型试验,对采取结构加强的抗震措施进行研究。试验结果表明：随着隧道衬砌结构强度/刚度的增强,由于硬岩部分受地震影响很小,结构安全系数最小值增长较快,最高增长了90.16%;随着隧道断面软岩范围的增加,隧道受地震影响逐步增强,支护结构所承受的地震惯性力和强制位移也不断增加,虽然提高隧道衬砌结构的强度/刚度,但软岩部分支护结构安全系数最小值增长百分比远低于硬岩部分,最高仅为44.73%;软岩部分支护结构的刚度大于围岩,单纯通过提高结构的强度/刚度,其抗震性能提高有限,建议采用结构加强+铰接设计的方式进行隧道软岩洞口段的抗震设防设计。研究成果对于隧道软岩洞口段抗震技术的发展有着重要的意义。     

隧道穿越断层破碎带震害机理研究

首先对汶川“5.12”等各次大地震中跨越断层破碎带隧道震害进行了资料调研,然后通过振动台模型试验及数值计算对跨断层破碎带隧道的动力响应进行了研究,研究内容主要包括围岩与隧道结构的加速度响应特性、地层变形及衬砌结构内力分布规律等。分析结果表明：震害调研结果、振动台模型试验和数值模拟结果有较好的吻合性,穿越断层破碎带隧道在地震中易于产生破坏;隧道断层带段围岩有较大的加速度响应特性,加速度响应在断层接触段不连续;地震过程中断层带段隧道结构对地层具有明显的追随性和依赖性;断层带隧道错动破坏主要由断层带隧道围岩与较好段围岩位移不同步性而造成的位移差值引起,且位移差值与断层带和隧道较好围岩类型有关;隧道断层破碎带段与较好围岩段衬砌结构横断面具有基本相同的内力分布规律,衬砌内力在共轭45°方向最大,但断层破碎带段衬砌具有最大的内力峰值,更易于在地震过程中产生破坏等。以上成果对于合理认识跨越断层破碎带隧道的地震响应特征具有重要意义,可为隧道实际工程设计和施工的抗震设防提供宝贵的基础资料。     

侧部岩溶隧道围岩稳定性数值分析与研究

 结合忠垫高速公路岩溶隧道施工过程,利用有限差分软件FLAC3D对侧部含有溶洞的隧道围岩稳定性进行数值模拟研究,并将数值计算结果与现场监测结果进行比较分析。结果表明：隧道开挖后,围岩分别向溶洞内和隧道内变形,溶洞与隧道之间的围岩向2个相反的方向变形,是较危险区域。围岩塑性区主要集中在隧道的周围和溶洞的左右侧部,溶洞的顶部和底部处塑性区较少。隧道与溶洞之间的围岩由于应力集中可能使围岩产生过大的变形和岩体破坏,对其稳定性要给予特别重视。所得结论可为同类隧道的设计、施工和研究提供有益的借鉴和参考。     

跨断层隧道围岩渐进性破坏模型试验及数值模拟

 断层及其破碎带是隧道开挖过程中常见的不良地质现象,也是围岩不稳定且容易出现事故的地段。以山区隧道施工中常见的IV级围岩为参照对象,利用地质力学模型试验和数值模拟研究跨断层隧道施工过程中围岩的渐进性破坏过程及其受力变形特性。研究结果表明：(1) 位于拱顶之上的断层下盘岩体在隧道开挖后呈悬挑状态,且在靠近断层部位易出现拉裂缝;(2) 隧道开挖使得上覆荷载向隧洞左、右两侧转移,从而导致拱腰以下的岩体往往率先剪切破坏,尤以断层下盘一侧岩体为甚;(3) 隧道开挖将引起围岩应力重分布,若调整后的围岩应力超出岩体自身强度极限时,洞周岩体就会塌落成拱,且位于塌落范围内的岩体切向应力呈“跌落式”下降,此特征可用于判断岩体塌落范围;(4) 隧道开挖后,由于断层的阻隔作用,岩体应力在跨越断层上、下盘时呈不连续、非线性分布的特征。     

Shaking table tests on seismic measures of a model mountain tunnel

A series of three dimensional (3D) shaking table tests were carried out to investigate the mechanism and effect of seismic measures of mountain tunnel using a scaled model based on a real tunnel. Key technical details of the experiment, including similarity relations, seismic measures simulation, boundary conditions, sensor layout, modeling methods, and ground motion input were presented. Main seismic measures, including reinforcing surrounding rock with anchors, increasing lining flexibility with steel wire mesh, and installing seismic isolation layer between reinforced surrounding rock and tunnel lining, were investigated in this study. Experiment results show that: (1) adding a layer of steel wire mesh in the tunnel lining can improve the flexibility and seismic performance and also may effectively prevent radial cracks from crossing the lining; (2) installing a geofoam isolation layer between the reinforced surrounding rock and the tunnel lining reduces dynamic earth pressure by 70–90% for the lining without a seismic isolation layer; (3) the flexible joints can effectively avoid global failures of tunnel lining for they reduce dynamic strain and bending force in the tunnel lining and decrease the seismic energy transmission along the lining in axial direction; (4) reinforcing surrounding rock with anchors significantly reduces dynamic earth pressure and strain of the lining by about 50%. In addition, the length of seismic reinforcement for general mountain tunnel portal is recommended to be 50 m from the tunnel portal along the axial direction.     

特大断面大跨度隧道围岩变形的现场试验研究

 结合广州龙头山双洞八车道高速公路隧道工程实践,对特大断面大跨度隧道施工中围岩变形进行相关监测,分析变形随时间变化规律、不同开挖工序引起的纵向和径向空间围岩变形规律。研究结果表明：特大断面大跨度隧道采用双侧壁导洞法施工,能较好地控制围岩变形;在特大断面大跨度隧道施工过程中,右导洞上台阶、左导洞下台阶以及核心土开挖对围岩变形影响较大,是施工主要控制点;特大断面大跨度隧道开挖的纵向影响距离大致为一倍洞径左右,与导洞跨度基本相同,为6～8 m;洞顶垂直向径向影响距离约为25 m,左导洞顶30°方向的径向影响距离约为15 m。该研究结论可为类似条件下特大断面大跨度隧道设计施工和现场监测提供借鉴与参考。     

Effects of rock pillar width on the excavation behavior of parallel tunnels

Most of the road tunnels were designed as a twin tunnel dual-carriage system with one traffic direction in each tunnel. However, for some long road tunnels, three-parallel-tube tunnel was required to meet the needs of construction and operation. The main aim of this paper is to numerically investigate the effects of rock pillar width on the behavior of three-parallel-tube and four-parallel-tube tunnels during excavation. The results showed that the interaction effects were related not only to the geological condition and tunnel cross-section, but also the rock pillar widths. As the pillar width reduces, the interaction effects becomes more evident. When the rock pillar width was less than two and a half times the radii of the main and pilot tunnels in adverse geology section, grouting for rock mass was required to improve the stability of the tunnel. For twin-tube tunnel, if the rock pillar width near the portal section were too narrow then the central-pillar-gallery tunnel may be constructed to reduce this effect.     

Damage to mountain tunnels related to the Wenchuan earthquake and some suggestions for aseismic tunnel construction

Many tunnels along the Dujiangyan to Wenchuan highway, located near the epicenter of the 2008 Wenchuan earthquake in China, were damaged severely. The characteristics of the tunnel failures were analyzed and categorized as avalanches and landsliding near the tunnels, cracking of the tunnel portals, collapse of the liner and surrounding rock, cracking and dislocation of the liner, uplift and cracking of the ground, deformation and cracking of the preliminary bracing. The main geological factors influencing the tunnel damage are secondary fractures of earthquake faults, sudden change in soil and rock type, weak rocks and the variable geo-stresses in the host material. The tunnel portals and their slopes, unless fully integrated into the tunnel structures and sufficiently reinforced, are likely to suffer significant distress as a consequence of seismic events. The main mitigation measures proposed are the use of reinforced concrete in the secondary lining in the area of fault zones and injection grouting to reduce the differences where there are sudden changes in the character of the host material.     

嘎隆拉隧道洞口段地震响应大型振动台模型试验研究

 洞口段为隧道抗震关键位置,极其容易发生地基失效及结构破坏。通过对嘎隆拉隧道洞口段轴向100 m开展大型振动台模型试验研究,研究结果表明：土体对其卓越频率附近的地震波有明显的放大作用,对地震波高频部分有滤波作用;地震时隧道与土体同步振动,不表现出自身的固有振动频率,惯性力对地下结构地震反应影响不大,故隧道抗震研究的重点是地震下围岩的失效防治,结构抗震设计主要目的是减小围岩失效对隧道产生的破坏;减震层和抗震缝的设置都不会改变结构地震反应的频谱特性,但设置减震层后,结构的峰值加速度增加,加速度放大系数不能作为减震效果的评判依据。研究成果对隧道的抗震设计和减震设计有重要工程应用价值。     

城市地铁双护盾TBM工法隧道衬砌结构受力特征研究

以深圳市城市轨道交通8号线一期梧沙区间隧道为依托工程,对“双护盾TBM工法隧道”施工期间管片衬砌外部压力和结构内力开展了现场跟踪测试,总结归纳出“双护盾TBM工法隧道”管片衬砌外部压力和结构内力在施工期内的时变演化规律。研究结果表明：隧道施工期间,管片外侧压力共经历四个发展阶段,注浆压力对管片内力变化影响较大,管片设计应考虑注浆压力的影响,同时应注意TBM施工时的注浆量控制。对于深埋TBM隧道,结构内力与隧道埋设深度不具有明显的对应关系,但随着结构上部围岩风化程度增加,隧道上方垂直荷载对管片结构内力影响加大。研究成果可为城市地铁双护盾TBM施工结构受力分析提供依据。     

公路隧道前置式洞口工法的三维数值分析

以宁(南京)淮(安)高速公路老山公路隧道为依托,对洞口前置式洞口施工过程的力学行为进行了三维数值模拟,分析了洞口段围岩和前置式支护结构体的位移场、应力。计算结果表明:前置支护结构及两洞间土体对洞口山体的支撑作用明显,既可大大减少洞口的边、仰坡开挖量保护洞口环境,又能有利于洞口段稳定和洞口施工安全。     

Behavior of noncircular tunnels excavated in stratified rock masses – Case of underground coal mines

The amount of tunnels excavated along stratified/sedimentary rock masses in Quangninh coal mine area,Vietnam, is gradually increasing. Rock mass in Quangninh is characterized by beddings between rock layers. The behavior of stratified rock masses surrounding the tunnels depends on both the intact rock and the beddings between rock layers. The main characteristics of stratified rock masses that need to be considered are their heterogeneity and anisotropy. Depending on the dip angle of rock layers, movements and failure zones developed surrounding the tunnels can be asymmetrical over the vertical axis of tunnel. This asymmetry causes adverse behaviors of the tunnel structures. The objective of this study is to highlight convergences and yielded zones developed in rock masses surrounding noncircular tunnels in Quangninh coal mine area using a finite element method. The presence of bedding joints is explicitly simulated. The numerical results indicated that with the increase in dip angle of bedding joints, the stress asymmetry over the tunnel vertical axis increases. It gradually leads to an asymmetry of the failure zone surrounding the tunnel. An increase of rock mass quality means a decrease of rock mass sensitivity to the discontinuities. In addition,a dip angle of the bedding joints of approximately 45° could be considered as the critical angle at which the rock mass mechanism changes between sliding and bending.     

煤柱尺寸留设与巷道围岩稳定性关系实验研究

煤柱尺寸大小影响巷道围岩稳定性,通过不同煤柱尺寸软煤巷道围岩变形与应力分布相似模拟实验,研究了不同煤柱尺寸下巷道围岩裂隙、岩层移动的演化特征与巷道围岩应力、支架载荷的分布规律,确定了巷道围岩初始扰动与临界失稳的煤柱尺寸。结果表明:软煤平巷围岩裂隙演化特征表现为两帮煤体裂隙水平扩展后的顶板裂隙产生,围岩失稳诱发点为巷道两帮上角部;当煤柱尺寸小于300 mm后,巷道两帮表现为非对称塑性破坏后顶板裂隙扩展的加剧,顶板下沉量、两帮移近量与巷道围岩应力、支架载荷变化剧烈,围岩与支架最大应力集中系数分别为2.53和1.67;当煤柱尺寸为150 mm时,煤柱两侧的巷道围岩裂隙与采区煤壁裂隙贯通,煤柱呈屈服承载状态,巷道支架载荷右侧大于左侧,巷道围岩稳定性降低;对巷道围岩稳定性产生影响的煤柱尺寸为300 mm,保证巷道围岩稳定性的最小煤柱尺寸为150 mm。     

偏压小净距隧道围岩压力分析

偏压小净距隧道是一种较新的隧道形式,受力状况较为复杂,目前尚没有其围岩压力的理论计算方法.为此作者对偏压小净距隧道围岩压力进行了理论探讨,得出了滑动破裂角、侧压力系数及垂直围岩压力的理论计算公式.分析了隧道间的净距对围岩压力的影响以及地面倾斜角度和净间距对隧道内侧压力系数的影响,可为类似隧道的设计提供参考.