2D numerical investigation of segmental tunnel lining behavior

The application field of shield tunneling has extended in recent years. Most shield-driven tunnels are supported by segmental concrete linings. Although many well documented experimental, numerical and analytical results exist in literature concerning the functioning of segmental tunnel linings, their behavior under the influence of joints is still not clear.This paper presents a numerical study that has been performed to investigate the factors that affect segmental tunnel lining behavior. Analyses have been carried out using a two-dimensional finite difference element model. The longitudinal joint between segments in a ring has been simulated through double node connections, with six degrees of freedom, represented by six springs. The proposed model allows the effect of not only the rotational stiffness but also the radial stiffness and the axial stiffness of the longitudinal joints to be taken into consideration. The numerical results show a significant reduction in the bending moment induced in the tunnel lining as the joint number increases. The tunnel behavior in terms of the bending moment considering the effect of joint distribution, when the lateral earth pressure factor K₀ is equal to 0.5, 1.5 and 2, is almost similar and differs when K₀ is equal to unity. It has been seen that the influence of joint rotational stiffness, the reduction in joint rotation stiffness under the negative bending moment, the lateral earth pressure factor and Young’s modulus of ground surrounding the tunnel should not be neglected. On the other hand, the results have also shown an insignificant influence of the axial and radial stiffness of the joints on segmental tunnel lining behavior.     

Non-linear description of ground settlement over twin tunnels in soil

Tunneling inevitably leads to ground settlement. The ground settlement trough over a single tunnel is well described by the generally accepted Peck’s formula. A new model of settlement trough is proposed by extending Peck’s formula to the case of horizontally aligned twin tunnels, which is a widely used tunnel configuration in urban metro projects. The feasibility of the new model is demonstrated through exploration of a large amount of ground settlement data accumulated from a metro tunnel project in China. Two numerical methods are implemented in the data exploration process to solve the problem of non-linear curve-fitting and estimation of model parameters. The Levenberg–Marquardt method is shown to be more suitable than the Nelder–Mead method. Based on the new model of settlement trough, a new method for calculating ground loss over twin tunnels is also proposed. The concluded empirical value of the ratio of ground loss is considered to provide an excellent reference for similar urban railway projects in the future.     

On numerical simulation of tunnel installation

The design of tunnels requires a proper estimate of surface settlements and lining forces. In engineering practice different design methods tend to be used, varying from simple empirical and analytical formulations to advanced finite element analyses. This paper begins with a review of empirical and analytical analyses for settlements and lining forces placing emphasis on the sequences of excavation and installation of support. Such installation procedures range from open face to closed face tunnelling and they tend to have a significant effect on deformations and lining forces. Hereafter the focus is on two-dimensional FE-analyses; again both for open face and for closed face tunnelling. Results for different installation procedures will be presented on the basis of two case studies. It is shown that installation procedures are most important to be considered in order to arrive at proper predictions for tunnelling settlements, horizontal deformations and lining forces. For the installation of closed face shield tunnelling a novel simulation method is presented, named the grout pressure method. It is shown that the grout pressure method yields the best predictions for both ground movements and structural forces.     

盾构管片接头简化数值模拟方法

由管片组装的盾构隧道衬砌环刚度分布不均,其薄弱环节为管片接头处。管片接头刚度的合理确定对于盾构隧道施工全过程模拟的合理性、地表沉降槽的确定以及土体损失的准确估算至关重要。根据管片接头受力特点及其构造,考虑对管片接头及其附近区域进行刚度修正,而管片其余区域保持原刚度不变,提出管片接头简化数值模拟方法——局部刚度修正法。基于圣维南原理和变刚度梁理论,推导了确定接头刚度的公式,并给出了相关参数的确定方法。结合室内盾构管片接头足尺试验成果,对不同荷载作用下管片接头的变形情况进行了数值模拟及对比分析。研究成果为盾构三维施工全过程的精细化数值模拟分析奠定了基础。     

Ground surface settlements due to construction of closely-spaced twin tunnels with different geometric arrangements

This paper examines the ground surface settlement profiles due to the construction of closely-spaced twin tunnels using the shallow tunnelling method. In the concerned zone, where the twin-tunnelling was performed in stacked and offset arrangements, the ground surface settlements of in total 18 cross-sections were continually recorded during construction. To cater for different conditions of the twin tunnels in the concerned zone, partial face, full face and forepoling reinforcement schemes were adopted. The recorded surface settlements and settlement troughs of three typical sections are reported and illustrated. The surface settlement troughs induced by each of the twin tunnels are fitted by the Gaussian function. The parameters that characterize the surface settlement troughs induced by each of the twin tunnels, such as the maximum settlement, percentage of ground loss, trough width and empirical trough width parameter are presented and compared.     

台湾软弱岩盘隧道变形预估系统数值模拟研究

基于大变形分析 ,运用三维有限元方法研究了台湾地区Ⅴ、Ⅵ类岩盘隧道在不同的地应力状态、岩石力学参数和开挖方法下 ,隧道围岩变形、受力与诸计算条件的关系 ,为隧道安全合理设计与施工提供依据。     

Interaction of twin tunnels and shallow foundation at Zand underpass, Shiraz metro, Iran

Tunnel construction in urban areas may inevitably require crossing close to adjacent structures. In this paper, the driving of Shiraz metro twin tunnels beneath Zand underpass of a major municipal artery built 15 years ago has been analyzed. The earth pressure balance (EPB) operation parameters consisting of face pressure, grout pressure and thrust force, which are effective on the ground movement and tunnels-underpass interaction, were investigated. For precise analysis, the effects of twin tunnels construction on modification of normal forces and bending moments of the underpass structural members and first tunnel lining were also studied. The results showed that, face pressure as compared to grout pressure and thrust force had a more significant impact on the underpass settlement. The rate of displacement differences because of increasing those EPB operation parameters at tunnel crown was greater than the surface and piles toe of the underpass. The changes in normal forces of the underpass were greater than bending moments, which could be related to high bending moment of the underpass members. The normal forces showed remarkable variations in the upper concrete plate of the underpass. The effects of second tunnel construction on the first one, regarding to the changes in normal forces, bending moments and displacements showed less than 10% increment.     

龙山浅埋大跨连拱隧道施工过程的数值模拟

采用美国MSC公司的大型通用有限元软件MARC对龙山浅埋大跨连拱隧道的施工过程进行数值计算,模拟隧道施工过程中围岩与支护结构的力学行为,结果表明相邻隧道的施工进度、支护方式都将影响隧道围岩的稳定性和支护结构的承载情况,得到一些有意义的结论,指导后续施工。     

软土地区深基坑圆筒支护结构三维数值分析模拟

介绍了国内外现有的地下连续墙的设计情况.重点阐述了上海地区某钢铁企业热轧漩流池圆形深基坑支护二维、三维均匀开挖、非均匀开挖的分析方法和分析过程,以及在不同受力情况下支护墙体的应力、侧向变形、基坑土体的稳定性等.并将二维、三维分析结果与原位测试结果进行对比,提出了圆形地下连续墙的受力模型及变形、配筋等的计算方法,供类似工...     

探地雷达在新建隧道无损检测中的应用

本文通过隧道工程质量检测实例,阐述了不同工程结构的雷达波特征,分析了各种缺陷的异常波特征,总结出隧道衬砌工程质量的判定方法与注意事项,供同行参考、借鉴。     

Evaluating the effect of soil structure on the ground response during shield tunnelling in Shanghai soft clay

When evaluating tunnel-induced ground response in Shanghai soft clay, the soil structure and its degradation behaviour of natural Shanghai soft clay during shield tunnelling should be properly considered. In this paper, a constitutive model that considers the initial soil structure and its destructuration is formulated within the framework of critical-state soil mechanics. The model is successfully calibrated and used to simulate the undrained behaviour of natural Shanghai soft clay. Based on the proposed model, finite-element analyses are conducted to simulate the short- and long-term ground responses induced by tunnelling at Shanghai metro line 2. The comparisons between numerical results and field measurements reported in literature indicate that the soil structure and the tunnel-induced destructuration significantly affects the magnitude and shape of the short-term surface settlement trough and horizontal displacement in Shanghai soft clay. The pore pressure variations around the tunnel are also affected by soil structure, which will significantly influence the long-term ground consolidation settlement in Shanghai soft clay.     

Effects of building three-dimensional modeling type on twin tunneling-induced ground settlement

Buildings are usually modeled as elastic beams in plane strain finite element (FE) simulation of tunnel-building interaction. However, neither tunnel nor surface buildings behave in a plane strain manner. In order to assess the effect of building modeling type on twin tunneling-induced ground settlement, some full three-dimensional FE models were analyzed and the effect of building modeling type was reviewed. Two dimensional (2D) plane strain interaction and green-field situation models were also analyzed to compare the results with the three dimensional (3D) models and assess the influence of modeling type. Outcomes of the studies showed that three-dimensional modeling has great influence on the results and equivalent surface beam, which is used in common practice of two-dimensional plane strain models, over-estimates the stiffness of building and leads to less settlement prediction in comparison with 3D simulation.     

Geotechnical risk management approach for TBM tunnelling in squeezing ground conditions

Historically, attempts to use tunnel boring machines (TBMs) in Himalayan geology have been unsuccessful, particularly where weak rocks exist at the significant depths often required for hydroelectric hydraulic tunnels resulting in squeezing ground conditions. The use of segmental tunnel linings erected by shielded TBMs presents additional risk, such that the advantages of potentially high rates of advance using this form of construction have not previously been realised. Programme demands for the 330 MW Kishanganga Hydroelectric Project in India required that 15 km of the 23 km headrace tunnel be constructed using a double-shield TBM erecting a segmental lining. Preliminary studies suggested difficult ground due to squeezing conditions along the 1400 m deep tunnel through weak meta-sedimentary rocks. To allow planning and construction to commence, a risk management approach to design and construction was formulated with contingency procedures and criteria developed to allow the risks to the TBM and the lining to be managed effectively. Advanced numerical modelling included analysis of the tunnel with the ground represented by a Stress Hardening Elastic Viscous Plastic (SHELVIP) model to take account of time dependent loading. The Kishanganga tunnel represents the first segmentally lined TBM tunnel to be successfully constructed in the Himalaya. This paper describes the risk-mitigation approach, the special measures developed to address the risks, the numerical modelling and laboratory testing undertaken, and includes results from the segmental lining monitoring. Recognition of the risks, the development of an innovative methodology and the provision of the means by which geotechnical risk could be managed effectively during construction, gave confidence to all stakeholders to proceed with a method of construction that had not previously been implemented successfully in the Himalaya.     

Analysis of interaction between tunnels in soft ground by 3D numerical modeling

Tunnels are increasingly being excavated in soft ground conditions when services are required in urban environments, and it is now common to have tunnels crossing at various elevations. As the tunnel excavations are undertaken at different levels, there will be an interaction which can have a significant influence on stress distributions and consequently deformations within the tunnels and surface settlement. As multi-layer tunnelling is a three dimensional phenomenon in nature, 3D numerical solutions must be utilized for perpendicularly crossing tunnels at various levels. This paper reports the investigations into the changes in stress distribution, deformations and surface settlements which may be expected when the twin Tohid Tunnels pass beneath the Line 4 metro tunnel in Tehran.     

盾构隧道双层衬砌结构三维力学分析模型及验证

在已有双层衬砌梁–弹簧模型的基础上,提出了改进的双层衬砌盾构隧道三维壳–弹簧力学分析模型。该模型采用压杆–弹簧组合方式模拟双层衬砌的结合面力学相互作用,并充分考虑了由盾构隧道管片接缝引起的结构刚度沿环、纵向分布不连续效应。依托武汉地铁8号线越江隧道工程进行建模计算分析,将计算得出的内力数据与现场实测的内力数据进行对比,两者具有一定的一致性,验证了该模型模拟双层衬砌盾构隧道结构三维力学行为的准确性和适用性。研究结果表明:(1)管片内力分布受到环缝和纵缝的影响呈现明显的不连续性,且由于地层岩性不均,管片上部与下部的弯矩亦有较大差异;(2)管片受力稳定后施作二衬,管片自身的内力量值变化较小,二衬主要受到自重作用,内力分布呈现"上小下大"分布规律,其量值与管片相比较小,在建设初期仅起到辅助承载作用。     

大断面隧洞施工的数值模拟分析

通过计算和实测特大断面隧洞采用短台阶法施工时的受力,得出隧洞断面位移和应力的变化规律及最不利点,可为大断面隧洞的设计与施工提供重要依据,从而进一步提高大断面隧洞的设计和施工质量。     

Numerical simulation of the uplift behavior of shield tunnel during construction stage

In this study, a new 3D numerical model that considers the circumferential joint, longitudinal bolt, grout pressure, jacking force and the constraint of shield on the linings is developed to derive deeper insights into the lining uplift behavior during shield tunneling. The numerical analysis is conducted using ANSYS, which is verified by a case history in soft soils. Revealed by both the measurements and calculation results, it is found that the lining uplift due to shield tunneling in soft soils can be divided into three stages: dislocation, stretch and steady deformation stages, respectively. In the dislocation stage, the lining deformation attributes principally to the dislocation deformation between neighboring linings. In the stretch stage, the lining deformation is mainly caused by the stretch deformation of circumferential joints. The major uplift is caused during dislocation stage. Thereafter, the impacts of shield-driving parameters including gradient of grout pressure, jacking force and pre-tightening force of longitudinal bolts on the uplift behavior are investigated by a series of parametric studies. The jacking force during segment preparation and assembly shows the most significant impact on the uplift of the tunnel, while the pre-tightening force of longitudinal bolts shows negligible impact. Finally, the control criterion for lining uplift related to the allowable dislocation and opening angle of circumferential joints is proposed.     

Three-dimensional numerical analysis of geocell reinforced shell foundations

The effects of geocell reinforcement on the behavior of shell foundations were studied using PLAXIS 3D finite element software. For this purpose, conical and pyramidal geometries were adopted as shell foundations. The real honeycomb shape of geocell and rigid body behavior of shells were simulated in PLAXIS 3D. The numerical models for shell foundations and geocell reinforced foundations were separately validated using several laboratory studies in the literature. The validated models were extended to the shell foundations resting on geocell reinforced sandy beds. The inclusion of geocell-reinforcement provided more than 70% reduction in the settlement of pyramidal and conical shell foundations. The stress transferred to the sand beds were reduced and distributed a wider area compared to the unreinforced cases. The maximum improvement in the bearing capacity and the settlement were observed in the case of conical shell foundation. The effect of adopted geocell and shell configuration on the foundation behavior was also analyzed for realistic prototype foundation size.     

Assessment the influence of ground stratification,tunnel and surface buildings specifications on shield tunnel lining loads (by FEM)

Urban development and rapid extension of cities have been accompanied by a considerable growth in mechanized shield tunnelling. Commonly precast concrete segments are used as tunnel lining which comprises relatively considerable part of tunnelling cost. The optimum design of lining needs to an accurate evaluation of loads acting on the lining.In this paper, the effects of ground stratification, surface buildings specifications and tunnel depth on lining loads were studied. For this purpose a 3D finite element model was used employing the ABAQUS software (Ver. 6.11). The geometry of tunnel, lining segments, injection grout and the surrounding soil properties were adopted from the under construction Tabriz urban railway line 2 project.The results show that the studied parameters have considerable effects on lining loads. For mentioned case study, surface buildings with 5 and more story have a considerable effect on lining loads, especially for shallow tunnels. The geometry of surface buildings influences the internal forces of the tunnel lining and increase of buildings width and length increases the lining loads. The building width is the most important parameter and with increase of that the influence of other parameters increases. Also by comparison of obtained results in this study with results of 2D analysis, reliability of 2D models was investigated. The comparisons show that 3D analysis is superior to 2D analysis, particularly in the cases of surface buildings presence. The difference between results increases with decrease of building length and increase of tunnel depth and building weight.