Three-dimensional numerical modelling for TBM tunnelling in consolidated clay

This paper presents a new field to analyze three-dimensional (3-D) coupled linear flow for Tunnel Boring Machine (TBM) tunnelling in saturated porous medium. This is important to control ground deformation and excess pore water pressure due to the process of shield tunnelling in three-dimension and time-dependent. A numerical model to simulate explicitly the behaviour of excess pore water pressure mobilization and its dissipation in time is presented. For the TBM tunnelling techniques, the positive pressure is applied to support the tunnel face and the grouting material is injected to decrease the deformation into the tail void gap behind the shield. Hence, this study is employed on 3-D model to investigate the impact of the most important parameters, which are slurry pressure and grouting pressure. The governing equations are derived in the light of the generalized Biot theory where displacement and excess pore pressure are the primary unknowns. The excavation stages during the advance of the machine in 3-D consolidation analysis is simulated. An isoparametric quadratic solid consolidation elastic soil model is used for this analysis. Results of this study indicate that a realistic modelling of soil behaviour, especially the distribution shape of the excess pore water pressure around the TBM tunnels during the construction stages and its dissipation during the consolidation time can be assessed. Thus, short-term as well as long-term effects of the TBM tunnelling are predicted. The practical importance of this analysis is the optimization of values and quantities of the slurry pressure and grouting pressure required for TBM technology. A design criterion based on this study can be suggested to tunnelling procedure in consolidated clay.     

On the influence of face pressure, grouting pressure and TBM design in soft ground tunnelling

A three-dimensional finite element simulation model, which includes all relevant shield tunnelling components and allows for the modelling of the step-by-step construction process of the tunnel advance is used to analyse the influence of TBM operation parameters and design parameters for a shallow tunnel advance in homogeneous, soft, cohesive soil below the ground water table. The numerical sensitivity studies presented in this paper focus on the face support pressure, the grouting pressure, the trailer weight and the length, weight and taper of the shield machine. The simulation results are evaluated with respect to the settlements of the ground surface, the shield movement and the loading of the tunnel lining. The evaluation of the sensitivity analyses helps to obtain a more detailed insight into the influence of selected parameters relevant for the design and steering of TBM tunnel advances.     

Pressurised TBM tunnelling in mixed face conditions resulting from tropical weathering of igneous rock

Weathering is a process that turns rock into soil. Deep weathering is prevalent in tropical and sub-tropical areas. The resulting sub-surface conditions can be very onerous for tunnelling, with tunnel drives commonly encountering a significant proportion of mixed face conditions, comprising partly rock and partly soil. Problems that have been encountered have included: inability to maintain the face pressure, ground loss, sinkholes, slow rates of tunnelling, rapid tool wear, damage to tools, mixing arms and other parts of the TBM, very frequent and long interventions, clogging and blow-outs. The nature and extent of the problems on any particular tunnel have depended on the type and design of the TBM, the nature of the rock and the proportion of the tunnel in mixed ground. In Singapore this has resulted in a change from mainly EPB to mainly slurry tunnelling in weathered igneous rock; however, predominantly EPB TBMs have been used in weathered sedimentary rock. Information from EPB and slurry TBM drives is used to illustrate the issues involved.     

Case studies of TBM tunneling performance in rock–soil interface mixed ground

This paper investigates the performance of tunnel boring machines (TBMs) in rock–soil mixed-face ground based on TBM tunneling projects in Singapore. Currently several methods are available to estimate TBM tunneling performance in homogenous rock or soil. However, the existing models cannot be effectively applied to predict TBM penetration rate in mixed ground. The tunnels in this study were excavated in adverse mixed-face ground conditions. The geological profiles and the TBM operational parameters are compiled and analyzed. The influence of different geological face compositions on the performance of the TBMs is studied. The statistical analysis shows that there is a possible correlation between the mixed-face ground characteristics and the TBM advancement. Different approaches are used to find a reliable model. Finally, a method is proposed to predict the TBM performance in mixed-face ground for project planning and optimization.     

Effect of adverse geological condition on TBM operation in Ghomroud tunnel conveyance project

With the planned length of 36 km, Ghomroud tunnel is one of the longest tunnels under construction in central Iran. About half or 18 km of this tunnel was excavated by a double shield TBM. Several adverse geological conditions encountered, consisting of ground squeezing and face collapse, hindering TBM performance, and caused several TBM stoppages and jamming. This paper presents the impact of ground conditions on machine performance based on the information obtained from field observations and geotechnical site investigations. As built geological conditions are described while the method and results of tunnel convergence measurements and their impacts on tunneling operation is examined. Based on the detail study of the available geological information and tunnel convergence measurements, it was evident that the existence of weak structures in rock mass resulted in high rate of the convergence, which was the dominant factor in the TBM jamming. Since it was not possible to make observation and measurements of geological parameters when working in a lined tunnel built by a shielded machine, an attempt was made to correlate TBM operational parameters and ground convergence. The preliminary result of the analysis has indicated a good correlation among machine’s operational parameters and tunnel convergence. If the system is fully developed, these parameters can be used as an indicator of the potential for high rates of convergence. An early warning on ground convergence is essential for taking precautionary measures to avoid TBM from getting jammed by squeezing ground.     

Kinematic behaviour of a Tunnel Boring Machine in soft soil: Theory and observations

State-of-the-art shield tunnelling in difficult ground conditions still involves a trial-and-error approach as a complete understanding of the physics governing the interaction between the Tunnel Boring Machine (TBM)-shield and the surrounding soil is still lacking. This is particularly concerning as it was demonstrated that the shield–soil interaction, and especially the ground displacement around the shield periphery, gives a significant contribution to the overall soil deformation. This paper quantifies the radial soil displacements induced by a TBM-shield driving in soft ground. The displacements have been obtained by means of a model that captures several aspects of the kinematic behaviour of a TBM, based on theoretical and geometrical considerations. The theoretical model has been verified against TBM monitoring data obtained during the construction of the Hubertus Tunnel, a double-tube road tunnel located in The Hague, The Netherlands. Results show the amplitude and spatial distribution of the ground displacement around the shield periphery as they occurred in practice.     

The “penalty factors” method for the prediction of TBM performances in changing grounds

Tunnel construction by TBMs through hard rock is significantly affected by the geological and geotechnical conditions at tunnel level. Ground parameters such as uniaxial compressive strength, fracturing degree and abrasiveness, and factors such as water inflows and stress level may deeply affect the way a TBM will perform. In addition, different types of TBMs will behave differently in a given condition.This paper presents a method for TBM performance prediction in changing grounds, which has been developed in the framework of the European project “New Technologies for Tunnelling and Underground Works” (NeTTUN). The model starts from an optimum TBM performance in best conditions, i.e. when all ground parameters are in their “best state”. A stepwise reduction of the optimum advance rate is then performed, according to “reduction factors” that quantify the effect of degrading ground conditions on the TBM advance rate. By doing so, the “penalty factors” model is able to take into account a very wide range of ground conditions, from very good to very poor. Two types of TBMs commonly employed in rock tunnelling have been considered, i.e. Gripper and Shielded machines, each of them characterized by its own set of reduction factors.In order to consolidate the factor values and to validate the model, a TBM performance database, also developed in the framework of the project NeTTUN, has been used. The database includes a large number of tunnels excavated in different ground conditions with all standard TBM types. The comparison between the values given by the “penalty factors” model and the actual TBM performances observed during construction shows that the developed tool may provide a reliable estimation of the TBM performance based on simple ground parameters.The “penalty factors” model has also been interfaced with the DAT (“Decision Aids for Tunnelling”). The DAT software, co-developed by MIT and LMR-EPFL, is able to compute the probabilistic distributions of the tunnel construction time and – cost in function of the geology – and construction related uncertainties.The model is conceived to be used in its present form. However, the methodology can be easily adapted to match the expertize of the user, who is free to update the optimal performances, the ground parameters and/or the values of the reduction factors according to his/her own experience. The model can also be extended to other TBM types and to conventional excavation methods.     

A methodology for assessing geotechnical hazards for TBM tunnelling—illustrated by the Athens Metro, Greece

Unexpected ground conditions have always been a major problem for the tunnelling industry. As demand for the development of new underground structures, regardless of the ground conditions, has increased, safety and risk considerations have become even more important. The methodology presented in this paper aims at the identification of risk-prone areas, incorporating, at the same time, the uncertainty of ground conditions. It is focused on TBM tunnelling and can be implemented in the early stages of the project. The methodology assesses the hazards by introducing the concept of a vulnerability index, which is based on the principles of rock engineering systems, to identify the weighting of the parameters, and on probabilistic modelling to address the uncertainty in the parameters’ values. The proposed model is illustrated via the Athens Metro case study, used also for validating its performance under actual construction conditions.     

武汉长江隧道盾构过江施工技术措施

武汉长江隧道工程盾构长距离穿越砂层，盾构承受水压高，地质条件和地下水状况非常复杂，江底段隧道最小覆土厚度小于隧道直径，而且水底部分与覆土压力相比水压力更大，特别是武昌深槽段水压力主导的施工。为了确保盾构过江安全，对水土压力设定与控制、泥浆特性、隧道上浮问题和管片变形及软硬不均地层盾构姿态控制等问题进行初步的研究分析。     

Theoretical model of the equivalent elastic modulus of a cobblestone–soil matrix for TBM tunneling

Cobblestone–soil mixed ground is a composite comprising cobblestones surrounded by soil. It is typical mixed-face ground encountered during tunnel boring machine (TBM) tunneling, and it may result in cutter wear, jamming of the roller cutterhead, poor TBM performance and cost overruns. The present paper investigates the deformation problem of cobblestone–soil mixed-face ground during TBM excavation. The ground under study is composed of two components (soil matrix and cobblestones) usually firmly bonded together at the interface, and can be regarded as a continuum. Previous studies have proposed many theoretical models for a composite material with two components. Representative models include the parallel model, series model, and effective medium theory model. Nonetheless, these models are limited by their assumptions and preconditions. In the present study, under an assumption of uniform strain, analytical solutions were derived for the equivalent elastic modulus while the cobblestone is assumed to be perfectly spherical or ellipsoidal. Triaxial compression tests were carried out to validate the analytical solutions. The equivalent elastic modulus derived from the triaxial experiments and theoretical models matched rather closely. The analytical solutions are helpful in clarifying the deformation of such ground and enhancing TBM performance.     

Evaluation of the geological condition ahead of the tunnel face by geostatistical techniques using TBM driving data

In tunnel excavation by Tunnel Boring Machine (TBM), it is difficult to grasp the ground condition ahead of and surrounding the tunnel face because the face cannot be observed during tunnel driving. This is the reason why it has not been possible to make the best use of high-speed excavation capability of the TBM, especially in ground under complex conditions. Thus, the TBM Excavation Control System was developed to realize the accurate prediction of the geological condition ahead of and surrounding the tunnel face simultaneously with excavation. The special feature of this system is that geostatistical techniques are introduced into the data analysis using both drill logging data from pilot boring and TBM driving data obtained during excavation, in order to improve the precision of the ground mapping.     

Estimating torque,thrust and other design parameters of different type TBMs with some criticism to TBMs used in Turkish tunneling projects

It is crucially important to select a proper TBM and define its basic specifications such as installed cutterhead torque and TBM thrust capacities for a special job. Underestimation of these parameters would reduce excavation performance. In order to generate a general guidance on determination of some of TBM specifications, a database including 262 TBMs’ design parameters is established. The statistical relationships between the design parameters of 262 TBMs (72 open, 24 single shield, 41 double shield, 86 EPB and 39 slurry TBMs) manufactured after 1985 in the world are investigated and theoretical concepts behind the relationships between TBM diameter and installed thrust capacity, nominal cutterhead torque capacity, total weight, maximum rotational speed of cutterhead, and number of disc cutters are discussed. Some of the correlations between these parameters are found to be strong. The results are summarized in a table given upper and lower limits of predicted values. At the end, some data obtained in different 30 tunnels excavated in different geological conditions with different TBMs in Turkey are discussed to test the validity of predictor equations developed within the frame of this study.     

软土地层大直径泥水盾构掘进引起的地面变形分析

为了研究大直径泥水平衡盾构施工引起的地层变形,基于Mindlin解,推导了在泥浆重度影响下开挖面不均匀附加压力、不均匀分布下盾壳摩擦力、环向消散下盾尾注浆压力引起的地层变形,叠加地层损失引起的地层变形,获得了大直径泥水平衡盾构施工引起地层变形的计算公式,典型工程实例结果表明:①不考虑泥浆重度、不均匀分布和环向消散等因素会高估地面纵向位移的隆起值而低估沉降值,本文计算方法所得地面纵向位移与实测值吻合较好;②本文方法计算所得的大直径泥水平衡盾构施工引起的地面横向位移与实测变形基本吻合,且符合高斯曲线正态分布。研究成果可为控制和预测大直径盾构隧道施工引起的地层位移提供理论指导。     

超大直径双线泥水盾构施工的三维数值模拟

以上海长江西路隧道工程为背景,基于适合软土的修正剑桥模型并综合考虑盾构开挖、开挖面泥水压力、盾尾注浆以及盾壳刚度和坡度等因素,建立单台超大直径(=15.43m)泥水盾构往返推进的三维有限元模型。分析不同施工步、不同泥水压力下北线盾构施工对地表沉降以及新建南线隧道的横向位移影响。通过数据分析发现,盾构返回推进时的地表位移规律明显区别于单条隧道施工的情况;盾构的反向推进会造成已建隧道管片的挤压变形以及顺指针的旋转;返回推进时,泥水压力的不同取值对已建隧道的横向位移影响显著。根据数值分析结果提出相应的施工建议:盾构返回施工时适当减小泥水压力;密切监控盾构返回推进时切口断面后1倍刀盘直径范围内已建隧道管片的变形量。     

地锚工程中粘结型锚头锚固特性的探讨

粘结型内锚头抗拔力的计算是地锚工程设计中的一个关键问题。本文对现有设计计算方法进行了综合分析,并且运用文献[7]所提出的考虑锚杆、浆体和围岩共同变形的计算模型和计算程序,对地锚设计中浆体切向刚度系数的取值及岩土体变形模量对锚固段内力分布的影响等问题进行了探讨。     

曲线顶管施工环境影响的三维有限元分析

通过建立三维有限元模型,研究了曲线顶管施工过程中地表的变形规律.通过有限元模拟,探讨了泥浆套、机头压力和土体抗力对地表变形的影响,结果表明:泥浆套的完整性和机头压力对曲线顶管施工过程中地表的变形有重要影响;曲线顶管由于附加土体抗力的存在,管轴垂直方向地表变形的最大值偏向顶管平面曲线的圆心一侧,偏移的距离与顶管的平面曲线半径有关.     

深基坑基底注浆加固效果数值模拟分析

采用高压旋喷注浆工艺对软土地区的基坑底部土体进行加固是保证深基坑施工安全与工程稳定常采用的方法。基于某地铁站监测数据,利用PLAXIS 2D软件建立了其数值计算模型并进行模型校核,对加固和未加固两种工况进行了数值模拟,对比分析了地连墙的位移和弯矩、地表沉降等开挖响应。研究表明,对软土地区基坑进行基底注浆加固,能有效减小地连墙的侧向变形和地表沉降。并针对加固区厚度、地连墙嵌入深度及刚度、软土层厚度4个参数进行了分析与讨论,优化了加固区的合理厚度、地连墙的合理嵌入深度,研究了基坑变形受地连墙刚度和软土层厚度影响的敏感性。     

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.     

复合地层中双护盾TBM与围岩相互作用机制三维数值模拟研究

 为研究复合地层中双护盾TBM与围岩之间的相互作用机制,采用FLAC3D建立完整的TBM模型,研究复合地层中以下几种情况对TBM掘进时围岩变形及护盾所受接触力和摩擦阻力的影响：地层(1)为断面内上软下硬、上硬下软;地层(2)为沿洞线方向具有不同软岩长度;地层(3)为沿洞线方向具有不同软硬交替厚度。同时,将不均匀间隙作为函数引入护盾压力计算式中。得出地层(1)条件下受不均匀间隙的影响,围岩纵轴向剖面位移(LDP)曲线自下而上先后与护盾接触,接触部位主要位于隧道腰部及以下区域,接触压力主要集中在前、后盾中后方,且前盾尾部压力值最大;地层(2)条件下,护盾所受摩阻力随软岩长度的增加逐渐增大并最终趋于稳定;地层(3)条件下TBM前后护盾所受摩阻力呈周期性波动,其变化规律与围岩位移曲线变化频率基本对应。而且不论地层(2)或地层(3)中,围岩LDP曲线形态都不同于均匀地层。这些认识对于进一步研究复合地层中TBM与围岩的相互作用及预测卡机有重要意义。     

自行走隧道掘进机施工引起地表沉降规律分析

通过水准测量对自行走隧道掘进机施工过程中地表变形进行了研究，结果表明：横向沉降槽曲线不完全符合Peck理论的正态分布，最大沉降点位于轴线上方。沉降变形集中发生在土体开挖而掘进机尚未到达掌子面时，环向增阻块对土体挤压造成地表轻微隆起。