穿越不同密实度饱和砂土地层的盾构隧道地震响应三维数值分析

地震液化对隧道结构有重大威胁,且位于不同抗液化能力地层交界处的盾构隧道段更易发生严重的地震破坏。采用三维数值方法研究穿越不同密实度状态饱和砂土地层的盾构隧道的地震响应规律。饱和砂土用一种描述不同密实度砂土液化行为的边界面模型进行模拟,首先通过隧道液化上浮的振动台试验结果验证该本构模型的合理性。其次,应用多自由度连接弹簧表征管片环间相互作用,采用文献中的拼装管片的逐级加载试验结果验证该方法的可行性。最后,建立穿越两种不同密实度饱和砂土地层的盾构隧道三维数值模型,研究相对密实度、输入加速度峰值和交界面倾角对砂土地层-盾构隧道系统动力响应的影响。结果表明,可液化地层中隧道结构位移模式是水平地震激励下产生的水平位移与由于液化上浮效应产生的竖向位移的耦合作用,加之隧道在不同土层中变形存在差异,从而导致隧道呈现扭转的变形形态。在靠近交界面处,隧道整体上浮量急剧变化且该处结构上浮量随着交界面倾角增大而增大,同时管片结构弯矩出现突变,接头螺栓的环间剪切和拉伸位移也显著增加。分析结果进一步印证地震作用下盾构隧道在不同性质饱和砂土地层交界面处更易破坏,在设计阶段应予以重点关注。     

Analytical approach for circular-jointed shield tunnel lining based on the state space method

This paper presents a new analytical solution to the circular segmental tunnel lining subjected to overburden and surrounding earth pressures. The governing equations are derived by adopting the curved Euler beam theory and the principle of minimum potential energy. Based on the state space method, the displacements and the relevant energy-conjugated internal forces are treated as the fundamental unknown state vector and can be obtained by solving the state function. The inter-segment joints on the lining are modeled by a set of linear springs, including shear, compression, and rotation. The presented method allows for the arbitrary distribution of the segmented joints and loads along the circumferential direction. The most striking advantages of the proposed method include the rigid body displacement treatment, lining-displacement-dependent soil reaction, and internal force direction dependency of the joint stiffness. Using this method, the displacements and internal forces of the entire lining can be obtained conveniently and simultaneously under the arbitrary loading and joint distribution conditions. The verification of the analytical solutions is provided by several examples.     

A new numerical approach to the hyperstatic reaction method for segmental tunnel linings

This paper proposes a numerical approach to the hyperstatic reaction method (HRM) for the analysis of segmental tunnel linings. The influence of segmental joints has been considered directly using a fixity ratio that is determined on the basis of the rotational stiffness. The parameters necessary for the calculation are presented. A specific implementation has been developed using a FEM framework. This code is able to consider the three‐dimensional (3D) effect of segment joints in successive rings on the tunnel lining behaviour. The present HRM allows one to take an arbitrary distribution of segment joints along the tunnel boundary into consideration. In addition, the rotational stiffness of segment joints has been simulated using nonlinear behaviour, as it is closer to the true behaviour of a joint than linear or bilinear behaviour. The numerical results of three hypotheses on ring interaction, which allow the 3D effect of a segmental tunnel lining to be taken into account, have been compared with data obtained from the shield‐driven tunnel of the Bologna–Florence high‐speed railway line project. The numerical results presented in the paper show that the proposed HRM can be used to effectively estimate the behaviour of a segmental tunnel lining. Copyright © 2014 John Wiley & Sons, Ltd.     

Generalized displacements of a rigid elliptical anchor embedded at a bi-material geological interface

The present paper examines the class of problems related to a flat rigid anchoring region which is embedded at a geological interface. The analysis focuses on the evaluation of the elastic stiffness of the embedded anchor. A boundary element technique is used estimate the axial, rotational and translational stiffnesses of the anchor. These estimates are compared with a set of bounds which are evaluated in exact closed form. These bounds are obtained by invoking kinematic and/or traction constraintsat the geological interface. The numerical results presented in the paper illstrate the manner in which the various stiffnesses of the anchoring region are influenced by the elastic properties of the surrounding geological media.     

Laboratory Estimation of Rock Joint Stiffness and Frictional Parameters

Numerical modeling of complex rock engineering problems involves the use of various input parameters which control usefulness of the output results. Hence, it is of utmost importance to select the right range of input physical and mechanical parameters based on laboratory or field estimation, and engineering judgment. Joint normal and shear stiffnesses are two popular input parameters to describe discontinuities in rock, which do not have specific guidelines for their estimation in literature. This study attempts to provide simple methods to estimate joint normal and shear stiffnesses in the laboratory using the uniaxial compression and small-scale direct shear tests. Samples have been prepared using rocks procured from different depths, geographical locations and formations. The study uses a mixture of relatively smooth natural joints and saw-cut joints in the various rock samples tested. The results indicate acceptable levels of uncertainty in the calculation of the stiffness parameters and provide a database of good first estimates and empirical relations which can be used for calculating values for joint stiffnesses when laboratory estimation is not possible. Joint basic friction angles have also been estimated as by-products in the small scale direct shear tests.     

爆炸地震波作用下盾构隧道动力响应分析

盾构隧道衬砌由于各种类型接头的存在而与整体式衬砌的力学特性存在较大差异。将盾构隧道衬砌结构看作由弹塑性铰链连接的刚性管片组成,考虑围岩介质的黏弹性,提出了爆炸地震波作用下盾构隧道动力分析的简化计算方法。采用该方法对南京地铁盾构段典型横断面进行了动力分析,研究了爆炸地震波入射角度、围岩介质特性及管片厚度对结构受力与变形的影响规律。分析结果表明:波入射角度对盾构隧道有很大影响,斜入射时结构的动力响应要大于垂直入射时结构的动力响应;围岩介质等级越高,围岩对隧道结构的约束越强,隧道的抗爆性能越好;管片厚度的增大会增大结构的内力,合理设置管片厚度有利于提高盾构隧道抗爆性能。     

Transitional–tensile fracture propagation: a status report

One model for the development of hybrid shear fractures is transitional–tensile fracture propagation, a process described as the in-plane propagation of a crack subject to a shear traction while held open by a tensile normal stress. Presumably, such propagation leads to a brittle structure that is the hybrid of a joint and a shear fracture. Crack–seal veins with oblique fibers are possible candidates. While these veins clearly show shear offset, this is not conclusive evidence that a shear traction was present at the time of initial crack propagation. Many recent structural geology textbooks use a parabolic Coulomb–Mohr failure envelope to explain the mechanics of transitional–tensile fracturing. However, the laboratory experiments cited as demonstrating transitional–tensile behavior fail to produce the fracture orientation predicted by a parabolic failure envelope. Additional attempts at verification include field examples of conjugate joint sets with small acute angles, but these conjugate joints form neither simultaneously nor in the stress field required by the transitional–tensile model. Finally, linear elastic fracture mechanics provides strong theoretical grounds for rejecting the notion that individual cracks propagate in their own plane when subject to a shear traction. These observations suggest that transitional–tensile fracture propagation is unlikely to occur in homogeneous, isotropic rock, and that it is not explained by a parabolic Coulomb–Mohr failure envelope as several recent structural geology textbooks have suggested.     

穿越黏滑断层分段接头隧道模型试验研究

数次大地震震害调查表明,隧道穿越断层处是受地震破坏较为严重的区域。为此,基于地震动能量的传播与释放特征,建立了一种穿越断层隧道结构抗减震的设计理念,并提出了一种穿越断层隧道节段接头形式。以跨断层龙溪隧道为依托,采用振动台模型试验研究了单一错动方式与断层错动-震动综合加载方式下带有接头的衬砌结构响应。研究结果证明：强震作用下,地震波对穿越断层隧道的影响是不可忽略的,断层错动-震动综合加载方式是合理的;新型接头能够自身适应性变形协调减轻隧道结构震害,节段间接头的设置改变了隧道的变形形态,提高隧道整体抗震能力;同时减小了衬砌的环向破坏,消弱了节段间地震力的传递,实现了衬砌震害的局部化。由于接头的设置,上盘隧道结构震害集中在距断层1.8倍洞径的范围内,下盘处隧道衬砌震害集中在距断层1.2倍洞径范围内;上盘的衬砌震害主要是由错动-震动联合作用造成的,而下盘衬砌震害主要受地震动的影响。     

An analytical solution for a jointed shield‐driven tunnel lining

This paper presents an analytical solution for the prediction of internal forces and displacements of a jointed segmental precast circular tunnel lining. The effects of joint stiffness on the performance of the tunnel lining are discussed. The ‘force method’ is used to determine the internal forces and displacements of jointed tunnel lining. Five shield‐driven tunnel cases are adopted to study the effects of joint stiffness, soil resistance, joint distribution and joint number on the internal forces and displacements of circular tunnels. Laboratory model tests are conducted to verify the proposed analytical solution. Copyright © 2001 John Wiley & Sons, Ltd.     

盾构下穿非连续管线变形特性及预测方法研究

城市地下管线采用承插式接口连接,管线结构的连续性与否取决于接口刚度。然而,现有研究大都假定地下管线为连续结构,忽略了接口转角对管线变形的影响。开展土工离心模型试验和两阶段有限元参数分析,系统研究了盾构下穿不同接口刚度管线的变形特性。发现非连续管线的薄弱接口导致其整体抗弯刚度明显小于连续管线,且接口转动导致非连续管线具有更好的与土体协调变形能力。因此,盾构下穿施工引起的非连续管线沉降明显大于连续管线。非连续管的结构连续性假定将大大低估管线沉降。盾构下穿引起的接口转角与地层损失呈线性关系。基于系统的有限元参数分析,建立了区分相对刚性、柔性管线的无量纲组。针对相对刚性、柔性的非连续管线,分别建立了管节相对长度、管-土相对刚度与接口转角的预测方法,利用离心模型试验结果验证了预测方法的合理性。新方法能有效地预测盾构穿越地下管线的接口转角,研究成果可应用于城市地下管网改造工程。     

盾尾非对称推力作用下盾构隧道纵向变形分析

盾构机在沿曲线掘进或轴线纠偏过程中,盾尾非对称推力会在管片端部产生附加弯矩,从而引起隧道发生纵向变形。现有解析方法多是将盾构隧道简化为等效连续梁,不能考虑隧道管片环间接头的弱化。首先,建立一种能够同时考虑环间张开和剪切错台的简化纵向梁-弹簧盾构隧道模型（simplified longitudinal beam-spring shield tunnel model,简称SLBSM）;其次,将在建隧道简化为Winkler地基上的SLBSM,采用状态空间法推导了非对称推力作用下盾构隧道纵向变形解析解答。通过与既有文献有限元及现有两种连续梁模型计算结果进行对比,验证了所提方法的可靠性和适用性,并对部分参数进行敏感性分析。研究结果表明：连续梁模型计算得到的隧道纵向位移表现为连续特征,而所提方法得到的隧道纵向位移表现为非连续特征,隧道纵向位移在接头处会发生突变;通过参数分析可知：增大接头转动刚度可有效降低隧道隆起和环间张开量;增大接头剪切刚度可有效降低环间错台量,但会导致隧道隆起和剪力的增加;增大地基刚度能显著降低隧道环间张开量和隆起,但会导致环间错台量的增加;管片始端轴力对隧道纵向变形的影响不可...     

挖填交界区格栅加筋路堤的试验和数值模拟分析

在对半挖半填路堤病害及成因分析的基础上,分析了加筋路堤格栅工作机制。通过现场试验,对采用格栅加筋法处理的路堤挖填交界区域进行了原位观测,观测了路堤填土完成时路面沉降、竖向土压力及格栅变形情况。通过建立有限元分析模型,对路堤填筑完成时格栅的拉力及位移进行了分析,并对不同路面荷载和格栅刚度条件下,格栅的拉力与位移进行了计算。结果表明：路堤挖填交界处铺设格栅后,路面局部差异沉降较小。填方区域格栅底部土压力与填土自重应力相当,格栅存在有效加筋长度,在挖填交界面附近产生较大变形和拉力。上层格栅比下层格栅沉降曲线平缓,下层格栅的拉力在交界区域会陡然增大。路面荷载对格栅拉力和位移有一定影响,随埋深增加影响减小,格栅的竖向位移随着荷载增大略有增大,格栅在挖填交界面附近拉力增大。随格栅刚度增大,其拉力也增大,而位移变化很小。     

A complex variable solution for a deforming buoyant tunnel in a heavy elastic half‐plane

An analytical solution is presented for a buoyant tunnel in an elastic half‐plane. The tunnel undergoes a prescribed displacement along its boundary, and the surface of the half‐plane is stress‐free. The solution uses the complex variable method and consists of conformally mapping the hole and half‐plane to an annular region. The complex potentials each contain two logarithmic terms due to the resultant buoyancy force acting on the tunnel, and as a result the displacements at infinity are unbounded. An example is presented for the case of a rigid buoyant tunnel in a half‐plane with gravity loading. Even though the tunnel does not deform, the buoyancy effect can be clearly seen in the contours of the displacements and stresses. Copyright © 2002 John Wiley & Sons, Ltd.     

Multiscale method for long tunnels subjected to seismic loading

A multiscale method for the dynamic analysis of underground structures is proposed, which involves the concurrent discretization of the entire domain with both coarse‐scale and fine‐scale finite element meshes. The coarse‐scale mesh is employed to capture seismic response characteristics of the integral system, whereas the fine‐scale mesh describes in detail the dynamic response in positions of potential damage or interest. For both the coarse‐scale and fine‐scale meshes to overlap, a bridging scale term is introduced so that compatibility of dynamic behavior between the coarse‐ and fine‐scale models is enforced. Both material and contact nonlinearities are considered in the multiscale model. As an application, the model is used for large‐scale seismic response of a newly built long‐distance shield tunnel. Results show that this multiscale method does not have spurious wave reflections at the fine/coarse interface and does not need filtering procedures, which is an advantage compared with the displacement coupling method. Stress and deformation response in lining segments and their connecting bolts are investigated and analyzed within the fine‐scale model, and the capacity of critical structural components, such as bolts and joints is evaluated. Copyright © 2011 John Wiley & Sons, Ltd.     

水下盾构隧道渗流场应力场耦合效应研究

在高水压条件下施工水下盾构隧道,渗流场对于结构及围岩应力场有很大影响。结合重庆主排水过江盾构隧道的修建,针对不同水压情况下的盾构隧道,采用有限元法对围岩及结构的渗流场和应力场进行耦合分析,获得施工期管片应力、位移及孔隙水压力分布。重点研究了管片的水压力分布规律,并与现场试验进行相互验证。结果表明：耦合效应下隧道管片需要承担更大的拉力,在设计中应按更不利工况进行配筋。所得结论为类似工程的设计施工提供有了益参考及依据。     

盾构隧道衬砌结构受力分析的梁—弹簧系统模型

盾构隧道衬砌结构由若干管片及其间的连接螺栓组成。在其断面受力的工程设计中,目前普遍采用梁-弹簧系统模型来模拟其受力性态。其中,梁可分成直梁和曲梁两类。本文在考虑弹簧刚度的轴向、切向和转动效应的同时,从卡氏（Castigliano）第二定理出发,给出了梁-弹簧模型的矩阵式,并论证了直梁-弹簧模型与曲梁-弹簧模型的一致性关系。在数值模拟计算过程中,还考虑了地层反作用力非线性情形和管片接头转动刚度正、负弯矩时的非对称性问题。     

横向载荷作用下刚性桩变位规律研究

目前对横向受载刚性桩的研究主要集中在其承载力方面,对变化规律研究很少。为此提出了利用刚性桩上两点位移求桩上任意一点位移、桩回转中心位置及转角的方法。通过对粉质黏土中的刚性桩进行模型试验与数值计算发现,回转中心位置随位移和载荷的增大,先是急剧下降,然后变缓,最后基本趋于稳定,而且桩埋置参数与土力学参数对回转中心位置的变化规律影响很小;而桩的转角随位移增大近似线性变化。比较发现,由试验和数值计算得到的回转中心极限位置与由极限地基反力法得到的结果相差不大     

考虑接头力学特性的盾构隧道衬砌结构计算方法研究

基于盾构隧道衬砌结构接头的构造特征,建立了接头的力学模型,将接头位置管片间的相互作用离散为一系列由剪切弹簧和法向弹簧组成的组合弹簧,根据得到的节点弹簧应力或法向位移在计算过程中动态调整弹簧刚度参数,将接头模型应用到衬砌结构计算中。该方法可以综合考虑衬砌结构的横向和纵向结构性能,计算管片和接头的内力与变形以及接缝的张开量。采用上海长江隧道衬砌结构整环试验结果对计算模型进行了验证,结果表明该模型能比较合理地模拟衬砌结构的变形特性。     

The application of energy principles to the determination of the sliding resistance of rock joints

Summary Energy principles have previously been applied to the analysis of rock joints in order to determine the shear strength of dilatant joints (Ladanyi and Archambault, 1970). This work was based on the analysis of regular triangular asperities and assumed that the asperities were rigid. In recognition of the difficulty of measuring a representative asperity angle in natural, complex rock joints, Ladanyi and Archambault extended their results to natural joints by assuming the equality of joint dilation rate and the effective joint asperity angle. It is shown that the assumption of this equality is not universally valid, and that it may lead to an underestimation of joint shear strength. Further, the effective friction angle for joints in an elastic rock mass, for joints comprising asperities of varying inclination, for post-peak shear displacements and for joints in degradable rock are all analysed using extensions of Ladanyi and Archambault's approach.     

多节理岩体裂纹扩展及变形破坏试验研究

为了研究不同倾角下多节理岩体力学行为,采用10 MN微机控制电液伺服大型多功能动静力三轴仪,开展包含较多预制非贯通节理类岩石试件的单轴压缩试验,研究了多节理岩体裂纹的特征、贯通模式、破坏模式、应力-应变特征等与节理倾角之间的关系。试验结果表明,（1）多节理岩体的裂纹类型主要有翼裂纹和次生共面裂纹,翼裂纹的扩展路径与单个节理情况下的扩展路径差异较大,翼裂纹起裂后沿起裂方向存在较长的扩展长度,直接与相邻节理或翼裂纹形成贯通,并且裂纹的贯通表现出四种不同的模式;（2）多节理岩体的破坏模式归纳为3种类型：平面破坏、块体转动式破坏和台阶式破坏;（3）根据多节理岩体的应力-应变曲线在应变软化阶段所表现出的不同非线性变形行为特征,可以将曲线归纳为4种类型;（4）多节理岩体的强度和变形各向异性特征非常显著,强度和弹性模量均在节理倾角30°时最小,90°时最大。