Deformational responses of operated shield tunnel to extreme surcharge: a case study

A field case of operated shield tunnel disrupted by unexpected extreme surcharge in Shanghai is reported in this paper. The deformational responses of segmental lining, in terms of convergences, settlements and joint open width, are highlighted. The surcharge caused by unexpected dumped soils with a maximum height of 7 m is six times larger than the design value of surcharge. Three hundred and sixty segmental lining rings of the operated metro shield tunnel below this surcharge are severely affected. The measured horizontal convergence to outer-diameter ratio (ΔD/D_out) ranges from 16.6 to 35.7‰, which is far beyond the averaged value for normal condition, i.e. 5.1‰. The trend of tunnel deformation (e.g. horizontal convergence and settlement) varying with surcharge level is found to be significantly non-linear. Correspondingly, the longitudinal joints are also severely disrupted and have large open widths. The rubber packer for joint near-tunnel springline loses its function of waterproof due to the release of 6 mm pre-compressive deformation. The majority of steel bolts of joint near-tunnel crown have passed yield state, while some are fractured. However, the circumferential joints are found to be in a sound workability.     

地震作用下盾构隧道衬砌结构动力响应分析

盾构隧道衬砌结构在地震载荷作用下的安全越来越受到重视,本文运用有限元软件数值模拟地震作用过程,分析地震作用下不同管片接头模型中管片性能的变化规律,结果表明：盾构隧道在地震横向作用下产生较大的横向位移,不同管片接头模型中管片的位移时程曲线趋势基本一致,且随着管片刚度减小而增大,但均比地表土体横向位移小很多|地震作用下不同管片接头模型中管片和连接螺栓的内力分布情况相类似,随着管片刚度减小,管片横向方向和剪切方向的应力均减小,连接螺栓的轴力、剪力和弯矩均增大,其中剪力增加的幅度最大,弯矩最大值位于隧道两拱腰处。     

盾构隧道衬砌的设计方法分析

针对盾构隧道衬砌管片的内力及变形受多种因素影响的情况,结合工程实例,从衬砌管片方面分析了衬砌的内力及变形,得出衬砌管片的内力及变形随其自身因素变化的一些规律,以供设计人员参考。     

双圆盾构隧道衬砌结构设计及参数研究

评价了盾构隧道衬砌结构设计模型及其发展现状,指出不同计算模型的特点和适用范围,通过上海地铁M8线实际工程对不同计算模型进行了分析和对比,重点讨论了双圆DOT(Double-O-Tube)盾构隧道结构计算中各种设计参数对计算结果的敏感性。研究结果表明,双圆盾构隧道结构计算中,目前常用的几种计算模型(修正惯用法、梁-弹簧模型等)都能满足工程设计的具体要求,关键在于计算参数选择的合理性和匹配性。不同的设计参数对结构计算结果的影响程度各不相同,对于中浅埋双圆盾构隧道,拱背土压力的影响不能忽略,否则计算结果将偏不安全。     

盾构隧道通用装配式管片衬砌结构计算分析

采用梁 -非线性弹簧模型 ,对盾构隧道通用装配式管片衬砌在基本拼装方案下各典型计算点进行最大截面内力及变形计算 ,确定管片设计控制荷载点 ;并在通用管片衬砌环布置时可能出现通缝及错缝拼装情况下进行多种方案组合计算 ,进而确定控制管片设计的拼装组合 ,并发现不同拼装组合条件下截面内力及变形的变化趋势     

地铁盾构隧道衬砌管片密封槽尺寸优化分析

文中以天津市地铁Z2号线衬砌管片密封槽截面尺寸为基础,根据经验公式提出了一种密封垫断面形式,从弹性橡胶密封垫防水机理及防水失效影响因素出发,提出不同密封槽尺寸对应的密封垫修改方法,并根据此方法建立不同工况下的二维数值模型。通过数值计算,得到张开量为零时密封垫表面平均接触应力、闭合压力,分析密封槽尺寸对密封垫防水性能影响规律,并提出密封槽尺寸设计及优化建议。     

Deformation and mechanical characteristics of tunnel lining in tunnel intersection between subway station tunnel and construction tunnel

Deformations and stress distributions in tunnel intersection areas are more complicated than those in common tunnels. The literature on deformations and stress distributions in tunnel intersections, in which the intersecting tunnel is in a different section, is limited. The Shangxinjie subway station in Chongqing, China, was selected to investigate the deformation, stress and plastic zone responses of a tunnel intersection using numerical simulations. Based on the numerical results, the scopes of influence with respect to the deformation, stresses and possible failure modes of the tunnel lining were further studied. The numerical results show that the deformation in a section close to the tunnel intersection was larger than the deformations in distant sections. Compared with the common section, the crown settlement reached the maximum value at the tunnel intersection, and the maximum rate of increase was approximately 28%. The range of the plastic zone at the tunnel intersection was much larger than that in the other areas, and it was mainly located in the side wall and tunnel crown. In the longitudinal direction, the lengths of the scopes of influence were 2.4 B and 1.6 B with respect to the deformation and stress, respectively. The magnitudes of the internal forces in the longitudinal and circumferential directions were almost equal. The bending moments of the tunnel lining within 135° and 225° significantly changed, but the axial force decreased dramatically. Tensile and compressive failures may occur at the tunnel intersection and in a section 5 m away. Locally thickening the supporting structures is suggested to improve the stability of the tunnel.     

The study of seepage forces acting on the tunnel lining and tunnel face in shallow tunnels

In this paper, the seepage force problems arising from the flow of groundwater into a tunnel were studied. Firstly, the effect of seepage forces acting on the tunnel lining was studied for the case of shallow drainage-type tunnels and these results were compared with the lining stresses developed for waterproof-type tunnels. This model was then reviewed through a comparison with an actual case study of the Seoul Subway Line No. 5. Secondly, the effect of seepage forces on the tunnel face stability was studied. In this study, two factors were considered simultaneously. The first factor considered was the effective stresses acting on the tunnel face, calculated from the upper bound solution of limit analysis and the other factor was the seepage forces, calculated from a numerical analysis under a steady-state of groundwater flow conditions. Consequently, reasonable design concepts applicable to the design of tunnel lining and to the evaluation of the support pressure required for maintaining the stability of the tunnel face were suggested for underwater tunnels.     

Simplified nonlinear simulation of shield tunnel lining reinforced by epoxy bonded steel plates

A high-efficiency simplified modeling approach based on fiber-beam elements and discrete elements is proposed for investigating the nonlinear response of shield tunnel reinforced concrete linings. The proposed approach focus on following main features: modeling simplicity and computational efficiency, the considerations of critical material and geometric nonlinearity associated with the entire loading process, including the stage of reinforcing the deformed concrete lining by steel plates. Comparison between the analysis results of the proposed numerical model and the experimental results from the full-scale structural test are presented to validate the developed model. The results show that the proposed model can capture the essential characteristics of the nonlinear load–deformation response of segmental tunnel lining. The modeling approach presents a balance between simplicity and accuracy, and serves as a viable alternative to detailed finite elements analysis.     

Repair of displaced shield tunnel of the Taipei rapid transit system

A section of completed shield tunnel of the Panchiao Line of the Taipei Mass Rapid Transit (TRTS) was deformed and displaced due to an adjacent excavation. It was observed that the segments in the invert were separated from the concrete behind, and cracks were formed in the crown. In order to ensure that the shield tunnel section would meet the structural safety requirements set out by TRTS, the tunnel underwent repair work. This paper describes the damage, discusses the selection of repair methods, and outlines steel segment erection operations. It is the authors’ hope that the case presented would serve as a reference for other similar cases.     

Design and optimisation of the lining of a tunnel in the presence of expansive clay levels

This paper describes the study made of the Trasvasur tunnels (Canary Islands, Spain), which were excavated in rocky formations of volcanic origin presenting metric levels of expansive clays. The building of these tunnels had to be abandoned 30 years ago, owing to the problems caused by the expansivity of the ground. It was subsequently decided to resume the project, making joint use of geotechnical investigation campaigns, convergence measurements and numerical simulations, thereby contributing towards the optimisation of the cross-section of the tunnelled area, support and lining. The work done has shown that when building tunnels in the presence of expansive clays it is advisable to use circular or similar cross-sections. It has also been found to be advisable to seal off the excavation as quickly as possible to prevent alteration due to the decompression of the expansive clay levels and their absorbing water from the tunnel itself.     

Failure mechanism of tunnel lining joints and bolts with uneven longitudinal ground settlement

To simulate the failure mechanism of tunnel segmental lining joints and longitudinal bolts under uneven longitudinal ground settlement, a numerical model with 3D lining rings and bolts was established. The loads were divided into two parts: the soil pressure around the tunnel just after construction and a displacement loading according to field measurements of uneven longitudinal ground settlement. The interactions between the lining tenons, bolts and their holes, were determined. The results indicated that the deformation of the circumferential joints consisted of opening and dislocation, but the dislocation was dominant. The progressive failure of bolts and waterproofing measures were also revealed. The evaluation of structural integrity of circumferential joint and the mitigate measures were proposed in order to ensure the operational safety of a metro tunnel.     

Dynamic responses and damage analyses of tunnel lining and errant large vehicle during collision

Collision accidents between errant vehicles and tunnels occur frequently, causing serious loss of life and property as well as the damage to the tunnel lining. Damage analysis of the tunnel lining under collision loads is still a lack of research at present. Based on dynamic finite element method, this study simulates and analyzes the interaction between errant large vehicles and tunnel lining structure and their dynamic response processes under various collision cases. It is noted that the lining structure mainly suffers tensile damage and its value increases with the increases of the collision angle and the vehicle speed. The larger the vehicle speed and the collision angle are, the bigger accelerations the passengers experience. A series of in-situ damage detections and sampling tests of the tunnel lining in a real collision accident that occurred in the Panlong Tunnel on Jinghu Highway in China in 2009 strongly approve the numerical simulation results. This study provides technical supports to the optimal design and operations management of tunnels.     

Voids delineation behind tunnel lining based on the vibration intensity of microtremors

In-situ microtremor measurements and numerical simulations were carried out to study the microtremor characteristics of tunnel linings. Power spectrum density (PSD) of microtremor signals measured from three spans of a tunnel lining with or without defects (cracks and voids) was calculated and analyzed. The results revealed that the normalized ratio of comparative power spectrum density (NRPSD) obtained by calculating the ratios RPSD, which is the ratio of PSD between different orientations (axial, radial and circumferential), of damaged spans to that of the healthy span, can be used as an indicator for the void delineation. For a damaged lining where voids exist, the vibration intensity is enlarged greatly in the radial direction, resulting in a pronounced value of NRPSD by comparing the NRPSD of the radial orientation to that of other orientations. Influences of properties of rock–concrete interfaces, geometric properties (location, arc length, and depth) of voids, and mechanical properties of rocks and concrete on the values of NRPSD were estimated via numerical simulations. As a preliminary study, these results provide clear evidence that the vibration intensity characteristics of microtremors have a strong correlation with the existence of voids located between lining concrete and surrounding rock masses, which has high potential to be developed to an effective approach for health assessment of tunnel linings in the future.     

Design of shield tunnel lining taking fluctuations of river stage into account

Fluctuations of river stage are expected to induce changes in loads acting on the tunnel linings and cause readjustments of member forces in the segmental linings subsequently. Therefore, the evaluation of impacts of time-dependent river levels on the loads acting on the tunnel linings is of great importance in design of shield tunnel linings situated beneath the rivers. However, the loads acting the tunnel linings are generally considered as constant in most design methods available, taking no account of the influences of constantly changing river stage. In this study, the influences of river stage on design of shield tunnel linings are evaluated with respect to two common ground conditions: (a) impermeable overburden strata of low permeability and (b) permeable overburden strata of high permeability. Two earth pressure calculation models are correspondingly established. In addition, field observations in the Hangzhou Qiantang River Tunnel are described in detail to present the responses of tunnel linings to fluctuations in river stage and validate the established design model for the former case.     

隧道二衬渗漏水浅析

结合多年的隧道施工及管养经验,对隧道二衬出现的渗水情况作了简要介绍,就二次衬砌渗水原因进行了分析,并根据渗水情况给出相应的渗水处治原则和方法,以保证隧道运营安全。     

隧道衬砌混凝土裂缝控制施工技术与应用

结合工程实践,分析了岩坑尖隧道群隧道施工二次衬砌混凝土裂缝的成因,并对此提出了具体的控制措施,解决了高温季节隧道衬砌施工的裂缝问题,对同类工程有一定的参考意义。     

基于Spreadsheet法的盾构衬砌截面可靠度分析

采用Spreadsheet法这一可靠度计算方法计算盾构衬砌截面可靠度,该方法可避免相关变量的独立变换以及极限状态方程对基本变量求偏导这两个问题。承载能力极限状态下,建立衬砌截面的正截面偏心受压破坏和斜截面受剪破坏失效模式下的功能函数,采用Spreadsheet法计算相应的可靠度指标,并计算这两种失效模式串联导致衬砌截面破坏的失效概率。正常使用极限状态下,建立截面开裂、纵缝张开和直径收敛失效模式下的功能函数,采用Spreadsheet法计算相应的可靠度指标。同时,采用Monte Carlo法计算不同失效模式下部分截面的可靠度指标,并与Spreadsheet法的相应计算结果进行比较。结果表明,Spreadsheet法与Monte Carlo法计算的可靠度指标误差最大不超过4%,但是Spreadsheet法节省了大量的计算时间。因此,采用本文建立的承载能力极限状态和正常使用极限状态功能函数,并采用Spreadsheet法求解可靠度指标,提供了一种分析盾构隧道衬砌截面可靠度快速、准确、便捷的方法。     

Experimental research on temperature field and structure performance under different lining water contents in road tunnel fire

An important feature for distinguishing tunnel lining structure and structure on the ground is the obvious difference of water content. In order to realize the difference between lining structure temperature characteristic and damage which are caused by different water content, a large-scale model test is carried out in this paper through studying the fire entity engineering in Xinqidaoliang to research the temperature field distribution and damage of road tunnel lining structure under different water content. The result shows that the heating rate and the highest temperature of lining internal surface are closely related to the distance to fire and water content of lining. The farther away from the fire, the slower the heating rate is and the lower the highest temperature becomes; for the sections that are equidistant from the fire, the higher the water content is, the slower the heating rate becomes and the lower the highest temperature on lining surface is. As it is closer to the inner of lining, the time needed to reach the highest temperature increases multiply; for the sections that are equidistant from the fire, the higher the water content is, the lower the highest temperature becomes and the longer the time needed to reach the highest temperature is. Due to the water evaporation inside lining structure, there is a stagnation period on the temperature rising curve. The time of stagnation is relevant to water content of lining, the distance from fire sections and the surface depth. When each part of lining structure is equidistant from the fire, the higher the water content is and the lower the temperature of each part is. Besides, for the lining structure with higher water content, the reduced temperature gradient along the lining thickness is apparently higher, as compared with the one with lower water content. The concrete damage of the tunnel lining structure with higher water content is apparently more serious than the one with lower water content. Though the moisture can reduce the temperature inside the lining, the damage of lining is exacerbated. This research can provide reference for further similar projects.