Effects of tunnelling on existing support systems of perpendicularly crossing tunnels

The interactions between perpendicularly crossing tunnels in the Sydney region are investigated using a full three-dimensional (3D) finite element analysis coupled with elasto-plastic material models. Special attention is paid to the effect of subsequent tunnelling on the support system, i.e. the shotcrete lining and rock bolts, of the existing tunnel. The results of the analysis show that in a region such as Sydney, with relatively high horizontal stresses, installation of the new tunnel causes the shotcrete lining of the existing tunnel to be in tension in the side facing towards the tunnel opening and in compression at the crown and invert. The pre-stressed rock bolts are usually tensioned more in the sections closest to the tunnel opening. For this particular study, if a new tunnel is driven perpendicularly beneath an existing tunnel, significant increases are induced in the bending moments in the shotcrete lining at the lateral sides of the existing tunnel and in the axial forces at its crown and invert. The increase in side bending moments causes further tensile cracking but the crown and invert stresses remain within the thresholds for both compressive failure and tensile cracking for shotcrete lining of typical concrete quality. Moreover, the driving of the new tunnel causes the tensile forces in the existing side rock bolts to increase and those in the existing crown rock bolts to decrease. In contrast, if the new tunnel is driven perpendicularly above the existing tunnel, compressive failure of the existing shotcrete lining is induced at the crown of the deeper tunnel for concrete of typical capacity and a significant tensile force increase of the existing rock bolts around the crown. It is concluded that in order to ensure the stability of the existing tunnel, local thickening is needed at the sides of the existing shotcrete lining if the shallow tunnel is installed first and local thickening is needed at the crown if the deep tunnel is installed first.     

爆炸平面波作用下大跨度洞室稳定性模型试验研究

通过抗爆模型试验,研究了爆炸平面波作用下大跨度毛洞和锚喷衬砌支护洞室的受力变形和稳定状态。介绍了模型试验原理及方法,根据试验实测数据分析了洞室围岩的受力特征、洞壁的运动变形特征、洞室的破坏形态及承载能力等。研究表明：设计工况和超载工况下,锚喷衬砌支护洞室侧墙部位垂直应力、拱顶加速度正峰值、拱顶位移峰值及残余值、洞壁环向应变峰值均明显小于毛洞;超载试验后,毛洞破坏严重,丧失了承载能力,而锚喷衬砌支护洞室破坏明显轻微,承载能力可提高约60%。     

Advanced constitutive modelling of shotcrete: Model formulation and calibration

Shotcrete is one of the main support elements for tunnels constructed according to the principles of the New Austrian Tunnelling Method (NATM). In this paper, a sophisticated constitutive model for the complex mechanical and time-dependent behaviour of shotcrete is presented, which is formulated within the framework of elasto-plasticity. Two independent yield surfaces govern the material behaviour in compression and tension under multi-axial loading conditions, which is further controlled by non-linear plastic strain hardening and softening rules following uniaxial stress–strain curves. The main novelty of the model is the introduction of normalised hardening and softening parameters which enable a more realistic simulation of the shotcrete loading history. In addition, cracking of the shotcrete is treated within the smeared crack concept by applying a fracture energy approach as a regularisation technique, which eliminates the dependency of the results on the size of the elements in a finite element mesh. Furthermore, the model takes into account the gradual change of the main material properties of the shotcrete due to cement hydration during the first 28 days after spraying. Other important time effects such as creep, shrinkage and hydration temperature induced deformations at early ages are considered in the current model formulation. This paper aims to describe in detail the developed structure of the constitutive model and model calibration.     

Blast‐induced rock fracture near a tunnel

Damage in the form of cracks is predicted to assess the susceptibility of a tunnel to failure due to a blast. The material‐point method is used in conjunction with a decohesive failure model as the basis for the numerical simulations. The assumption of a cylindrical charge as the source for the blast allows the restriction of plane strain and two‐dimensional analyses. In the simulation, a further restriction of a single pressure pulse is used as the source of stress waves that are reflected and refracted after reaching the free surface of the tunnel wall. Three critical zones of significant cracking in the vicinity of a tunnel are identified as potential contributors to tunnel failure. Copyright © 2014 John Wiley & Sons, Ltd.     

洞桩法大断面群洞交叉隧道初衬数值模拟

针对采用洞桩法施工的北京地铁10号线工体北路站大断面群洞交叉隧道,介绍了洞桩法大断面群洞交叉隧道施工步序,分析了交叉口衬砌工作的力学机理,采用三维有限元数值模拟方法对其初衬结构力学行为进行研究。结果表明：洞桩法交叉隧道交叉口区域两个方向的衬砌受力存在相互影响,但影响的范围不大,衬砌拱顶沉降总体上表现出中间大,两端小的特征;主线隧道拱部受后期联络通道扣拱的影响,在与联络通道的相交部位出现了受拉状态,产生了与主线其他部位不同的受力特征;交叉口变高部位设置折梁能有效扩散联络通道扣拱时产生的压力,减轻了应力集中程度。研究结论可供洞桩交叉隧道的施工与设计参考。     

Influence of shotcrete composition on load‐level estimation in NATM‐tunnel shells: Micromechanics‐based sensitivity analyses

Displacement measurement‐based estimations of loads and utilization degrees in shotcrete tunnel shells as part of the New Austrian Tunneling Method (NATM), have become standard tools in tunnel practice; their quality, however, may crucially depend on the knowledge of the actual shotcrete composition after spraying. To shed light on this issue, we here determine, based on experimentally validated micromechanical representations of shotcrete, the hydration degree‐dependent elastic, creep, and strength properties of different shotcretes, characterized by water cement ratios (w/c) between 0.4 and 0.6, aggregate cement ratios (a/c) between 3.5 and 5, and Young's modulus of aggregates (E_agg) between 40 and 80 GPa. These properties are fed into a structural shell model of the Sieberg tunnel, and this model is subjected to displacement fields approximated from daily displacement measurements at five selected points along the shell's inner surface. Resulting stresses and forces in the tunnel shell allow for analyzing the influence of shotcrete composition on load‐level estimation in NATM tunnel shells: The magnitudes of circumferential and longitudinal normal forces increase significantly with decreasing w/c, while a/c and E_agg have the inverse and relatively minor effect. The utilization degree is virtually insensitive to changes in w/c(especially at early ages), and only slightly decreases with decreasing a/c and E_agg. The location of maximum loading is unaffected by the shotcrete composition underlying the analysis. Conclusively, location and magnitude of maximum utilization degrees are very robust estimates (not affected by limited knowledge on the shotcrete composition), whereas realistic estimation of stresses and forces does require more accurate consideration of shotcrete composition. Copyright © 2011 John Wiley & Sons, Ltd.     

大断面海底隧道CRD法绝对位移控制基准建立及应用研究

隧道位移控制基准的建立是确保隧道安全施工的一项重要内容。以厦门－翔安海底隧道陆域浅埋暗挖段CRD法施工为工程背景,陆域浅埋段总长约2 525 m,主要穿越全、强风化花岗岩地带,含水率高、自稳能力差。依据全站仪非接触量测获得初期支护三维绝对位移分布规律,确定三维绝对位移基准控制指标,同时对86个围岩位移监测断面的监测数据进行变形正常断面和变形异常或险情断面的位移量统计分析,最终确定CRD法（center cross diaphragm method,交叉中隔壁法）三维绝对位移控制基准。研究结果表明,将CRD1、CRD3部拱顶竖直位移和上中隔墙、下中隔墙水平位移作为CRD法位移控制指标;CRD1部和CRD3部拱顶下沉极限位移分别为200 mm和130 mm;CRD3部拱顶竖直位移约为CRD1部的0.5～1倍;上中隔墙水平极限位移约为100 mm,下中隔墙水平极限位移约为15 mm。通过现场97个断面应用,共发现58次异常和险情,由于发现及时,处置有力,保证了施工安全。     

Nonlinear analysis of NATM tunnel construction with the boundary element method

This paper presents a novel approach to the simulation of NATM tunnel construction using the Boundary Element Method (BEM) as principal numerical method. This new approach has the advantage that only the excavation surface, the possible plastic zones and the tunnel lining have to be discretised. The whole rock mass is represented by the BEM whereas the Finite Element Method (FEM) is used to represent the tunnel lining only. Thus, a general coupling strategy for coupling three-dimensional boundary elements with shell finite elements (shotcrete) and beam finite elements (steel arches) is presented. To achieve realistic results the effect of hydration of the shotcrete and yielding of the steel arches is considered in the excavation process. Furthermore, the nonlinear rock behaviour is modelled more realistically by using a powerful hierarchical constitutive model which considers a large range of rock materials. The combination of these ideas results in higher user-friendliness and efficiency. Some verification tests and practical applications in tunnelling are presented.     

阳坡里隧道纵穿滑坡体段变形破坏机制与加固效应研究

以武罐高速公路阳坡里隧道为依托,深入探讨了隧道纵向穿越滑坡体情况下隧道与滑坡的相互作用机制及变形破坏模式。在理论分析的基础上提出了针对性的综合工程防治设计方案,并采用强度折减有限元法与极限平衡法对隧道穿越滑坡段的开挖加固效应进行了分析研究,对开挖加固前、后滑坡的稳定性进行了对比分析。结果表明：在隧道开挖条件下,滑坡的稳定性满足规范要求,目前该工程正在施工中,安全稳定性良好。另外,研究表明：纵穿滑坡体段的隧道结构对滑坡体来讲是一个重要的“抗滑结构体”,由于受滑坡推力作用隧道衬砌结构所受主应力发生明显偏转,当进入基岩后,随着隧道拱顶距基岩与覆盖层接触面距离的增加,衬砌所受各主应力逐渐转变为正常状态。提出的隧道纵穿滑坡段的分析思路和综合防治方案对类似工程有一定的借鉴和指导意义。     

考虑孔隙水压力及非线性Mohr-Coulomb破坏准则下浅埋土质隧道三维塌落机制的上限分析

浅埋土质隧道的稳定性研究一直是隧道工程的关键问题,而孔隙水压力的存在影响着浅埋土质隧道的安全。构建了隧道顶部为圆弧形的浅埋土质隧道的三维塌落机制,基于非线性Mohr-Coulomb破坏准则和极限分析上限法,并考虑孔隙水压力的作用,推导出浅埋土质隧道的塌落范围及支护力的最优上限解计算公式。通过与既有研究进行对比,验证了所提方法的合理性。分析了不同参数对塌落范围、塌落土体的重力及支护力的影响,结果表明：孔隙水压力对浅埋土质隧道的塌落范围、塌落土体的重力及支护力有着显著的影响;孔隙水压力对塌落范围、塌落土体重力的影响比较复杂,而支护力都随着孔隙水压力系数的增大而增大;不同参数对浅埋土质隧道的塌落范围、塌落土体的重力及支护力的影响规律不同。新方法可为浅埋土质隧道的设计优化提供理论支撑。     

隧道钢纤维喷射混凝土单层衬砌试验研究

为了解决隧道施工中采用单层喷射混凝土作为隧道永久衬砌的问题,对不同钢纤维及外添加剂掺量的混凝土分别进行了抗压、抗拉、抗渗以及弯曲强度等室内试验。结果表明,在喷射混凝土中加入钢纤维材料,其抗拉、抗弯以及抗渗水性能分别提高了65.6 %、94.7 %、98.1 %;并通过现场试喷,选定符合设计要求、经济合理的配合比,在摩天岭隧道通风斜井施作了湿喷钢纤维混凝土,以单层衬砌代替原设计的复合式衬砌。工程实践证明,钢纤维湿喷混凝土,其支护强度达到了设计要求,喷射作业回弹损失量减少7 %～15 %。研究成果可为类似隧道纤维喷射混凝土单层衬砌技术的应用提供参考。     

From micron-sized needle-shaped hydrates to meter-sized shotcrete tunnel shells: micromechanical upscaling of stiffness and strength of hydrating shotcrete

Knowledge on the stresses in shotcrete tunnel shells is of great importance, as to assess their safety against severe cracking or failure. Estimation of these stresses from 3D optical displacement measurements requires shotcrete material models, which may preferentially consider variations in the water–cement and aggregate–cement ratios. Therefore, we employ two representative volume elements within a continuum micromechanics framework: the first one relates to cement paste (with a spherical material phase representing cement clinker grains, needle-shaped hydrate phases with isotropically distributed spatial orientations, a spherical water phase, and a spherical air phase; all being in mutual contact), and the second one relates to shotcrete (with phases representing cement paste and aggregates, whereby aggregate inclusions are embedded into a matrix made up by cement paste). Elasticity homogenization follows self-consistent schemes (at the cement paste level) and Mori–Tanaka estimates (at the shotcrete level), and stress peaks in the hydrates related to quasi-brittle material failure are estimated by second-order phase averages derived from the RVE-related elastic energy. The latter permits upscaling from the hydrate strength to the shotcrete strength. Experimental data from resonant frequency tests, ultrasonics tests, adiabatic tests, uniaxial compression tests, and nanoindentation tests suggest that shotcrete elasticity and strength can be reasonably predicted from mixture- and hydration-independent elastic properties of aggregates, clinker, hydrates, water, and air, and from strength properties of hydrates. At the structural level, the micromechanics model, when combined with 3D displacement measurements, predicts that a decrease of the water–cement ratio increases the safety of the shotcrete tunnel shell.     

Schotcrete as permanent lining for the Furka base tunnel

Summary The lining concept of the 15.4 km long one-track Furka railway tunnel is described with particular emphasis on shotcrete application as a permanent support Altogether 70000 m³ dry aggregate/ cement mix and 115000 rock bolts have been applied. The tunnel was lined at a rate of approx. 400 tunnel metres per month using up to five shotcrete machines simultaneously. Systematic quality control throughout the construction work indicated an average uniaxial compressive strength of shotcrete of 40 N/mm². The support requirements were grouped into 16 different classes and an additional special class accounting for extreme geological conditions in some relatively short stretches.     

Stability of long circular tunnels in sloping ground

Assessment of tunnel stability has become increasingly crucial as more and more tunnels are built in difficult terrains such as sloping ground. The required support pressure on the tunnel walls associates both tunnel stability and liner design considerations. The present analysis attempts to find a uniform internal pressure which can support a circular tunnel built in a sloping ground with a particular level of stability in cohesive-frictional soils. The lower bound finite element limit analysis has been applied to find the required minimum uniform internal support pressure presented as a non-dimensional term p/c; where p is the minimum normal internal pressure on the tunnel boundary to avoid collapse and c is the cohesion of soil. The variation of p/c is presented for a range of normalised embedment depth of tunnel (H/D), stability number (γD/c), internal friction angle of soil (?) and slope angle (β); where H is the crown depth of the tunnel, D is the tunnel diameter and γ is the unit weight of soil. Appropriate comparisons have been carried out with available literature. Failure patterns of the tunnel have also been studied to understand the extent and the type of failure zone which may generate during the collapse.     

均质岩体中隧道围岩破坏过程的试验与数值模拟

采用模型试验与离散元模拟的方法,对均质岩体中隧道开挖后围岩的变形破坏过程进行了研究,并对围岩变形破坏过程中围岩应力及地表位移的变化规律进行了分析,模型试验结果与数值模拟结果取得了较好的一致性。研究结果表明：隧道开挖后,拱顶处围岩变形明显并出现裂缝,围岩破坏从拱顶开始,进而呈渐进式向上发展,最终形成稳定的塌落拱;开挖后,隧道围岩径向应力减小,隧道周边一定范围内围岩切向应力减小,且随隧道变形破坏的发展,围岩切向应力减小的区域逐渐扩大;隧道塌方后,拱底垂直应力增加,开挖结束至塌方开始期间地表位移增量最大,塌方期间地表位移增量最小。     

Practical Estimate of Deformations and Stress Relief Factors for Deep Tunnels Supported by Shotcrete

Summary. Even though ground-support interaction in the vicinity of the tunnel face is a typical 3D problem, tunnel support design is usually based on simplified plane strain models, which are strongly dependent on the assumed degree of ground stress relief at the time of lining installation. The paper focuses on tunnels supported by shotcrete close to the face, where the interaction between the loading process and progressive hardening of the green shotcrete makes the problem time-dependent. A constitutive law characterized by the time-dependent stiffness and strength of the shotcrete is employed herein. The results of an extensive parametric study based on 3D axisymmetric models are presented in the form of non-dimensional design charts, which can provide guidance to a preliminary evaluation of convergences and support loadings. Moreover a strategy is proposed to enhance the capability of simplified design methods (2D models, Convergence-Confinement Method). This consists in a “guided estimate” of stress relief factors, which again is based on the results of 3D time-dependent analyses. Finally, by way of example, the proposed method is applied to two well-documented case-histories.     

A system of monitoring and dimensioning tunnel support

Summary In this paper a general numerical approach is proposed for the identification of loads acting on tunnel linings made by shotcrete, as a temporary lining, and concrete as a permanent one so as to form a system of monitoring and dimensioning these linings. This method requires a set of in situ displacement measurements of shotcrete layer for back calculation, and the constitutive relationship of the structural materials which are shotcrete, and concrete here is assumed to be linear elastic. The advantage of this method is that it avoids those complicated characteristics of rock masses and the loads from back calculation can reflect the combinative effects of rock surrounding the tunnel. An example was demonstrated for this method.     

基于接触应力反分析的隧道初期支护结构内力研究

利用现场监控量测的数据及时分析和评价支护结构的内力是隧道动态设计和施工的关键问题,对保证隧道施工的安全具有重要意义。根据初期支护中喷射混凝土自身特点,将喷层结构视为弹性地基曲梁,并运用弹性地基曲梁理论,通过喷射混凝土与围岩接触应力推求喷层结构内力的解析解,从而得到喷层结构的应力集中部位,方便后续制定施工安全措施。经台阶法开挖的隧道工程实例分析表明,从喷层与围岩接触应力出发来求解喷层结构内力解析式是隧道内力分析一种新的有效方法,为隧道结构的安全评估提供比较可靠的依据     

隧道喷射混凝土支护的曲线结构单元模拟

将一种新的曲线结构单元引入到块体一弹簧算法中,对圆形断面隧道围岩表面喷射不同混凝土衬砌的支护作用机理以及开挖速度对喷射混凝上材料早期强度的影响等进行分析,得出了一些有意义的结论。     

地表超载作用下隧道失稳破坏的上限有限元分析

针对地表超载作用下隧道稳定性和破坏模式问题,基于刚体平动运动单元上限有限元理论编程并计算分析,获得了浅埋隧道失稳临界超载系数上限解和刚性运动块体体系破坏模式。通过与现有的刚性块体极限分析上限法以及极限分析上、下限有限元法计算结果的对比分析,验证了上限解的可靠性。研究结果表明,（1）临界超载系数 黏聚力c之比 随土体内摩擦角 和隧道埋深C与直径D之比( )的增大而相应增大,随土体重度与黏聚力参数 的增大而减小;（2） 和 对隧道破坏模式的影响较明显; 增大,则隧道破坏范围增加;内摩擦角 增大,刚性运动块体破坏模式相互错动更加显著,相比而言, 对破坏模式的影响并不显著;（3）刚体平动运动单元上限有限元上限解精度高,所得刚性运动块体破坏模式具有滑移线形态,能精细地反映隧道失稳破坏特征。