走滑断层黏滑错动下隧道破坏的模型试验研究

为了探究断层错动对隧道及围岩的损伤机理及破坏特性,以滇中引水工程香炉山隧洞为依托,通过开展隧道穿越断层破碎带的黏滑错动模型试验,并采用ABAQUS进行数值建模,对试验结果进行验证分析.研究结果表明:断层错动过程中,衬砌主要发生受拉破坏,局部位置衬砌受压破坏;衬砌发生变形及破坏的区域,主要集中在破碎带范围内,以错动面处衬砌变形、破坏最为突出,衬砌的变形随距错动面距离的增大而减少,衬砌横断面内拱顶、右腰位置破坏最为严重;断层错动起始时刻,破碎带中间部位拱顶处衬砌拉损伤已经达到较高量级,衬砌局部开裂破坏,随着断层错动量的增加,损伤不断累积,当错动量达25 mm(相当于实际错动量1 m)时,衬砌整体损伤已累积到较高量级,此时衬砌的破坏接近试验的最终状况.岩体的破裂区域主要集中在距错动面两侧30 cm范围内,围岩变形随着距错动面距离的增加而逐渐减小.

隧道稳定性分析与设计方法讲座之一:隧道围岩压力理论进展与破坏机制研究

本文作为一个讲座对以往研究成果做一个综述,回顾了围岩压力理论的发展过程与隧道破坏机制研究的进展,通过模型试验与弹塑性有限元强度折减法,得出浅埋拱形隧道的破坏在拱顶,深埋隧道的破坏在侧壁的破坏机制,并可求出隧道围岩破裂面位置与形态。分析了矩形隧洞与拱形隧道破坏机制随埋深增加而变,矩形隧道可划分为浅埋顶部破坏阶段、深埋压力拱破坏阶段和深埋两侧破坏阶段3个阶段,而拱形隧道不存在压力拱破坏阶段。

砂土层中盾构隧道局部破坏引发连续破坏的机理研究

盾构隧道由混凝土管片拼接而成,接缝部位薄弱,在建设和运营过程中存在大量风险。国内外发生过多起因隧道管片局部损坏演变为隧道大范围破损甚至连续坍塌并导致地表沉陷等灾害。通过对隧道管片接头的受力分析,建立了接头的极限承载力M-N包络图,作为管片接头的破坏准则。以隧道联络通道施工时,隧道腰部设置洞门作为隧道局部破坏的背景,利用离散元软件PFC,通过FISH语言二次开发研究了隧道腰部管片局部破坏引发的隧道连续破坏机理。研究表明,隧道腰部局部破坏引起土体进入隧道内从而引起隧道腰部外土体松动,并且松动区外围产生的土拱的拱脚支承于隧道顶部区域,这都导致隧道内力急剧增大,直至超过管片及接头的极限承载力,隧道局部破坏发生扩展。由于隧道环间螺栓的作用,破坏环过大的变形引起邻近环横向变形增大,进而引发邻近环的破坏,破坏沿纵向传递,隧道发生大范围连续破坏。最后,初步提出并对比分析了多种隧道防连续破坏措施。

紧邻隧道条件下基坑开挖变形破坏模式分析

目前基坑开挖对邻近既有隧道的影响主要集中于隧道变形及应力的变化,对于紧邻隧道条件下基坑开挖的破坏模式以及机理仍缺乏较深入的理解。研究了不同隧道埋深、不同隧道与地连墙水平间距和不同地连墙埋置深度下,在紧邻隧道情况下基坑不同计算步的破坏模式,分析了变形破坏机理及易发生破坏的开挖步。研究结果表明,潜在破坏面可分为3种形式:直线形破坏面、圆弧形破坏面、U形破坏面;随着基坑的开挖以及内支撑的建设,剪切带逐渐变为绕地连墙墙趾的深层剪切带,与隧道的交叉部分从右侧肩部逐渐向下转移到右侧腰部或右下侧近腰部;基坑破坏易发生在开挖后未设置内支撑及开挖至坑底后设置内支撑的情况下。

“5.12”大地震对酒家垭隧道造成的破坏和隧道恢复重建方案选择

四川汶川"5.12"大地震对正在建设中的酒家垭隧道造成严重破坏,而破坏最严重的部位大部分发生在区域性断裂带上,因此在灾后重建方案设计时应将隧址区断层构造带作为处治的重点,才能保证隧道的安全。对酒家垭隧道震害最严重区域的恢复重建提出了四个处治措施进行比较后,认为拱部拆除重建措施可保证原设计建筑限界,虽施工难度较大,但整治效果好,可作为推荐方案。

山体滑坡对隧道变形破坏的影响

山岭隧道的变形破坏与山区边坡是否稳定密切相关,山体滑坡会对隧道的结构产生影响较大的危害。由于特殊的地理条件,我国每年因为滑坡造成的损失数量巨大,是世界上隧道受滑坡危害最严重的国家。以陕西省略阳县共青团嘉陵江隧道变形为例,分析滑坡与隧道变形的相互关系和作用机理,制定有针对性的治理措施,避免因山体滑坡造成重大损失,对于今后类似工程的设计和施工有一定的工程参考价值。

烧结砖隧道窑破坏原因及修复

烧结砖吊平顶隧道窑是生产线中重要的热工设备,投资较高,运行条件严格,需要满足产量高、质量好,服务年限较长的要求。然而,部分企业没有按照项目建设程序对隧道窑设计及施工方案进行评审,最终因该隧道窑质量事故,造成较大的经济损失。

连拱隧道边坡耦合作用:滑坡连拱隧道

由于连拱隧道结构复杂,施工工序较多,一般用于中短隧道,不可避免地要遭遇到边坡问题。一旦边坡出现蠕动变形或滑动,连拱隧道的结构难以抵抗此下滑力,此时连拱隧道可称之为滑坡连拱隧道。滑坡连拱隧道的破坏形式和边坡变形、运动方式有关,滑坡可直接破坏连拱隧道的主体结构及其附属结构。在施工影响下边坡(错落)缓慢蠕动时,其破坏方式主要有不均匀偏压变形、拱圈错位、衬砌裂缝、中墙偏移以及内支撑焊点跳开等。本文结合两座典型滑坡连拱隧道的现场监控量测工作,讨论了滑坡连拱隧道的破坏规律和特征,对于连拱隧道的设计、施工和监测都具有重要参考意义。

浅埋黄土隧道围岩压力计算方法

结合浅埋黄土隧道实际的破坏形式,构建浅埋黄土隧道的破坏模式,基于极限平衡理论推导围岩压力的计算公式,并根据围岩滑裂面上的应力状态推导围岩破裂角的计算公式。将此方法得到的破裂角、围岩压力计算值分别与现场实测值和既有的谢家烋法、太沙基法、易小明法的破裂角计算值进行对比,以验证所用计算方法的正确性和有效性,并分析不同参数对围岩破裂角、围岩压力的影响规律。结果表明:围岩破裂角和围岩压力的本文计算值均与实测值最接近;围岩破裂角随侧压力系数、内摩擦角和隧道埋深的增大而减小,随矢跨比的增大而增大;围岩压力随侧压力系数、土体内摩擦角和黏聚力的增大而减小,随矢跨比、隧道埋深和土体重度的增大而逐渐增大。本文围岩压力和破裂角的计算方法克服了既有研究方法的不足,充分考虑了侧压力系数、矢跨比、埋深、内摩擦角、黏聚力及重度对围岩压力的影响。

华蓥山隧道围岩位移与边界元计算

本文通过对华蓥山隧道新奥法施工过程中Ⅲ、Ⅳ、Ⅴ类洞身围岩的位移时变特性分析，给出了不同类别围岩稳定位移量和平均达稳时间，并用边界元程序进行了力学模型计算，指出了隧道破坏域的范围。

马岭头隧道膨胀性围岩的工程地质分析与治理

马岭头隧道通车3年后，发现K40＋700-K40＋950段左侧墙出现裂缝，经调查和勘察，揭露该段存在一层全风化泥岩，为软弱夹层，具有膨胀性，全风化泥岩的空间分布和裂缝位置等相当吻合，随后的分析和计算证实了全风化泥岩是导致隧道破坏的地质因素。有限元计算证实，全风化泥岩产生的变形压力和膨胀力直接作用在衬砌上，使衬砌受力严重不均匀，导致了隧道破坏。膨胀性岩作为一类特殊性围岩，其软弱性和膨胀性往往给工程造成较大的危害，工程建设应做到预防在前，治理在后，避免遭受更大的经济损失。

山体滑坡对公路山岭隧道影响的数值分析

依托川藏公路102隧道工程,在收集整理102隧道勘察设计资料、总结国内外已有隧道—滑坡体系相互作用机理的基础上,根据2#滑坡与隧道的相对位置关系,采用了FLAC3D三维数值模拟分析方法,对于运营期间滑坡体发生滑动对隧道结构的影响进行了模拟分析。通过对比分析在隧道拱顶距滑动面不同最小距离(1D-4D)条件下,由于降雨导致滑坡发生滑动时,隧道的二次衬砌受力特征及其安全性,为今后类似条件下隧道工程建设提供借鉴经验和工程依据。

Blasting induced dynamic stress concentration and failure characteristics of deep-buried rock tunnel

In this study,the dynamic stress concentration factors(DSCF)around a straight-wall arch tunnel(SWAT)were solved analytically utilizing the complex variable function methods and Duhamel’s integral.The effects of wavelength,incident angle,and blasting rising time on the DSCF distribution were analyzed.Theoretical results pointed out dynamic disturbances resulting in compressive stress concentration in the vertical direction and tensile stress in the incident direction.As the wavelength and rising time increased,there was a tendency for the amplitude of stress concentration to initially rise and then converge.Moreover,a series of 3D FEM models were established to evaluate the effect of different initial stress states on the dynamic failure of the tunnel surrounding rock.The results indicated that the failure of the surrounding rock was significantly influenced by the direction of the static maximum principal stress and the direction of the dynamic disturbance.Under the coupling of static and blasting loading,damage around the tunnel was more prone to occur in the dynamic and static stress concentration coincidence zone.Finally,the damage modes of rock tunnel under static stress and blasting disturbance from different directions were summarized and a proposed support system was presented.The results reveal the mechanisms of deep-buried rock tunnel destruction and dynamically triggered rockburst.

Catastrophe stability analysis for shallow tunnels considering settlement

Limit analysis of the stability of geomechanical projects is one of the most difficult problems.This work investigates the influences of different parameters in NL failure strength on possible collapsing block shapes of single and twin shallow tunnels with considering the effects of surface settlement.Upper bound solutions derived by functional catastrophe theory are used for describing the distinct characteristics of falling blocks of different parts in twin tunnels.Furthermore the analytical solutions of minimum supporting pressures in shallow tunnels are obtained by the help of the variational principle.Lastly,the comparisons are made both in collapsed mechanism and stability factor with different methods.According to the numerical results in this work,the influences of different parameters on the size of collapsing block are presented in the tables and the limit supporting loads are illustrated in the form graphs that account for the surface settlement.

Model test to investigate failure mechanism and loading characteristics of shallow-bias tunnels with small clear distance

Based on the similarity theory,a tunnel excavation simulation testing system under typical unsymmetrical loading conditions was established.Using this system,the failure mechanism of surrounding rock of shallow-bias tunnels with small clear distance was analyzed along with the load characteristics.The results show that:1) The failure process of surrounding rock of shallow-bias tunnels with small clear distance consists of structural and stratum deformation induced by tunnel excavation; Microfracture surfaces are formed in the tunnel surrounding rock and extend deep into the rock mass in a larger density; Tensile cracking occurs in shallow position on the deep-buried side,with shear slip in deep rock mass.In the meantime,rapid deformation and slip take place on the shallow-buried side until the surrounding rocks totally collapse.The production and development of micro-fracture surfaces in the tunnel surrounding rock and tensile cracking in the shallow position on the deep-buried side represent the key stages of failure.2) The final failure mode is featured by an inverted conical fracture with tunnel arch as its top and the slope at tunnel entrance slope as its bottom.The range of failure on the deep-buried side is significantly larger than that on the shallow-buried side.Such difference becomes more prominent with the increasing bias angle.What distinguishes it from the "linear fracture surface" model is that the model proposed has a larger fracture angle on the two sides.Moreover,the bottom of the fracture is located at the springing line of tunnel arch.3) The total vertical load increases with bias angle.Compared with the existing methods,the unsymmetrical loading effect in measurement is more prominent.At last,countermeasures are proposed according to the analysis results: during engineering process,1) The surrounding rock mass on the deep-buried side should be reinforced apart from the tunnel surrounding rock for shallow-buried tunnels with small clear distance; moreover,the scope of consolidation should go beyond the midline of tunnel(along the direction of the top of slope) by 4 excavation spans of single tunnel.2) It is necessary to modify the load value of shallow-bias tunnels with small clear distance.

Comprehensive health assessment of shield tunnel structure based on prototype experiment

Health state of shield tunnels is one of the most important parameters for structure maintenance.Usually,the shield tunnel is extremely long in longitude direction and composed by many segments.It is difficult to quantify the relationship between the structure damage state and shield tunnel structure deformation by the model test because of unpredictable effects of different scales between model test and prototype tunnel structure.Here,an in-situ monitoring project was conducted to study the excavation induced shield tunnel structure damage,which could be considered a prototype test on the tunnel deformation.The disaster performance of tunnel leakage,segment crack,segment dislocation and segment block drop-off during longitude deformation and cross-section ovality developments was analyzed.The results indicate that instead of the longitude deformation,the ovality value has the strongest correlation to the rest disease performance,which could be used as the assessment index of the tunnel health.For this tunnel,it is in health state when the ovality is less than 0.5%,and the serious damage could be found when the ovality value is higher than 0.77%.The research results provide valuable reference to shield tunnel health assessment and help complete the standard of shield tunnel construction.

Determination of minimum cover depth for shallow tunnel subjected to water pressure

Prediction of the state of roof collapse is a big challenge in tunnel engineering, while the limit analysis theory makes it possible to derive the analytical solutions of the collapse mechanisms. In this work, an exact solution of collapsing shape in shallow underwater tunnel is obtained by using the variation principle and the upper bound theorem based on nonlinear failure criterion. Numerical results under the effect of river water and supporting pressure are derived and discussed. The maximum water depth above the river bottom surface is determined under a given buried depth of shallow cavities and the critical depth of roof collapse is obtained under a constant river depth. In comparison with the previous results, the present solution shows a good agreement with the practical results.

Safe range analysis of clear distance of twin shallow tunnels based on limit analysis and reliability theory

A method of analyzing the stability of twin shallow tunnels was presented using both limit analysis with nonlinear failure criterion and reliability theory.In the condition of nonlinear failure criterion,the critical clear distancesof twin shallow tunnels were obtained by analyzing the change of surrounding pressure.A reliability model was established based on limit state equation,and the failure probability was solved by virtue of Monte Carlo method.Safety factor and corresponding clear distance of different safety levels were obtained by introducing a target reliability index.The scope of clear distance for different safety levels is described,which can be used as a supplement and improvement to the design codes of tunnels.

Mechanical response features and failure process of soft surrounding rock around deeply buried three-centered arch tunnel

Due to the extreme complexity of mechanical response of soft surrounding rock(SR) around a tunnel under high geostatic stress conditions, the integration of physical and numerical modeling techniques was adopted. Based on the similarity theory, new composite-similar material was developed, which showed good agreement with the similarity relation and successfully simulated physico-mechanical properties(PMP) of deep buried soft rock. And the 800 mm×800 mm×200 mm physical model(PM) was conducted, in which the endoscopic camera technique was adopted to track the entire process of failure of the model all the time. The experimental results indicate that the deformation of SR around a underground cavern possessed the characteristics of development by stages and in delay, and the initial damage of SR could induce rapid failure in the later stage, and the whole process could be divided into three stages, including the localized extension of crack(the horizontal load(HL) was in the range of 130 k N to 170 k N, the vertical load(VL) was in the range of 119 k N to 153.8 k N), rapid crack coalescence(the HL was in the range of 170 k N to 210 k N, the VL was in the range of 153.8 k N to 182.5 k N) and residual strength(the HL was greater than 210 k N, the VL was greater than 182.5 k N). Under the high stress conditions, the phenomenon of deformation localization in the SR became serious and different space positions show different deformation characteristics. In order to further explore the deformation localization and progressive failure phenomenon of soft SR around the deeply buried tunnel, applying the analysis software of FLAC3 D three-dimensional explicit finite-difference method, based on the composite strain-softening model of Mohr-Coulomb shear failure and tensile failure, the calculation method of large deformation was adopted. Then, the comparative analysis between the PM experiment and numerical simulation of the three centered arch tunnels was implemented and the relationship of deformation localization and progressive failure of SR around a tunnel under high stress conditions was discussed.

Kinematical analysis of highway tunnel collapse using nonlinear failure criterion

For different kinds of rocks,the collapse range of tunnel was studied in the previously published literature.However,some tunnels were buried in soils,and test data showed that the strength envelopes of the soils followed power-law failure criterion.In this work,deep buried highway tunnel with large section was taken as objective,and the basic expressions of collapse shape and region were deduced for the highway tunnels in soils,based on kinematical approach and power-law failure criterion.In order to see the effectiveness of the proposed expressions,the solutions presented in this work agree well with previous results if the nonlinear failure criterion is reduced to a linear Mohr-Coulomb failure criterion.The present results are compared with practical projects and tunnel design code.The numerical results show that the height and width of tunnel collapse are greatly affected by the nonlinear criterion for the tunnel in soil.