考虑中间主应力的横观各向同性深埋圆隧弹塑性解

平面应变条件下的深埋圆形交通隧道问题一般忽略中间主应力影响,但塑性区围岩的变形与实际情况会产生较大差异。岩土与地下工程中多遇到层状岩体,常将其处理为横观各向同性固体材料。充分考虑中间主应力对深埋圆形隧道的影响,基于平面应变假设得出了与横观各向同性材料相适应的Drucker-Prager准则并将其与Mohr-Coulomb准则精确匹配,在此基础上推导了考虑剪胀特性的横观各向同性理想弹塑性材料在塑性阶段的中间主应力表达式;根据所得的中间主应力表达式,推导出横观各向同性深埋圆形隧道围岩塑性区应力位移解析式;结合实际算例,分析了横观各向同性参数与围岩剪胀角对横观各向同性深埋圆形公路隧道围岩塑性区位移的影响规律。为深埋圆形交通隧道的计算和设计提供更为合理的理论基础。     

Mechanical behavior of a twin-tunnel in multi-layered formations

Model tests of twin circular tunnels in homogenous material, two-layered formations, and three-layered formations are performed. Induced strains and displacements are measured around the tunnel openings during excavation. A two-dimensional numerical simulation based on the fictitious stress method (FSM) is also developed to study the mechanical behavior of a twin-tunnel of circular cross section in multi-layered formations by considering the continuity equation for stress and displacement at the interface. Different values of initial stress, modulus ratio, and coefficient of earth pressure (K) are considered. The distributions of displacement around the unsupported tunnels are analyzed. The fractured zones around the tunnels are determined based on the Hoek and Brown’s failure criterion under various configurations. The numerical results are found in a good agreement with the experimental results within an error of 2–4%, indicating the FSM model could be regarded as a suitable mean to solve the mechanical behavior of a tunnel excavated in the multi-layered formations. The result also shows that the fractured zones are found to develop along the minor principal stress direction, whereas the major displacement is found to occur in the major principal stress direction.     

Finite element analysis of tunnel–soil–pile interaction using displacement controlled model

Significant additional loads could be induced in pile foundations adjacent to new tunnels. Accurate prediction of magnitude and shape of the ground displacements, which define curvature changes, is crucial for the computation of tunnelling induced bending and axial stresses in pile foundations. The finite element simulation of tunnelling by removing forces corresponding to initial stress-state, tend to predict incorrect shape of ground displacement profiles, hence incorrect forces in pile foundations adjacent to tunnels. To overcome this difficulty, this paper describes the development and application of a simple and useful displacement controlled model (DCM) to predict the effects of tunnel excavation on adjacent pile foundations. The DCM simulates tunnelling by applying displacements to the tunnel boundary. A method to determine magnitude and direction of tunnel boundary displacements, based on convergence patterns observed in field and centrifuge test results, is proposed. Back analyses of numerous greenfield tunnel case histories using the DCM indicate good agreement between computed displacement profiles and field/test data. The suitability of the DCM in modelling tunnel–soil–pile interaction problems is demonstrated through back analysis of a centrifuge test and a field case study.     

铁路隧道初期支护极限位移的意义及确定

阐述了隧道支护系统极限位移的意义,系统地介绍了初期支护极限位移的确定方法。采用连续体模型,按铁路隧道衬砌标准设计采用的断面形式和材料参数,对各级围岩中不同埋深条件下铁路隧道初期支护极限位移进行计算模拟,并对计算结果进行统计处理,与允许位移进行比较,单、双线断面相对位移分开,拱顶下沉、拱脚水平位移和墙脚水平位移设不同判据,采用修订前规范所列的埋深档次,确定档次范围值,最后综合确定出一套适于当今铁路隧道位移判别的极限位移数据。     

基坑开挖对邻近隧道纵向位移影响的计算方法

基坑开挖卸荷会对邻近隧道产生影响,因此有必要对隧道的变形进行预测,确保隧道正常运行.针对目前计算模型的分析方法未考虑基坑壁应力卸荷对隧道位移的影响,以及有限元分析过程较为复杂繁琐,提出采用Mindlin解计算基坑壁与坑底卸荷的附加应力.然后将隧道结构视为弹性地基无限长梁,将开挖引起的附加应力施加于隧道结构上,建立隧道结构纵向变形方程,从而得到隧道位移及内力的计算公式.最后,将计算方法与数值模拟算例、工程实测进行对比分析,计算结果与其较为吻合.     

基于改进双剪统一强度理论的围岩松动圈分析

为了研究岩石应变软化、剪胀性质、中间主应力和拉压不等特性对围岩松动圈的影响,基于改进双剪统一强度理论,得到了隧道围岩松动圈半径、围岩应力及洞壁位移的解析表达式。通过与已有方法计算结果的对比,验证了该方法的可行性,并进一步分析了中间主应力大小以及软化程度对结果的影响。研究结果表明:(1)随着软化模量的降低,隧道围岩塑性区、松动区(圈)半径以及洞壁位移均逐渐减小;(2)中间主应力大小对隧道围岩弹塑性行为具有一定的影响,随着中间主应力系数b的增大,围岩的切向应力在塑性软化区、破碎区内变大,而在弹性区内减小,围岩的径向应力在3个区域内均增大;(3)隧道洞壁位移随着中间主应力系数b的增大而减小;(4)考虑中间主应力的影响以及围岩软化的程度,能够充分发挥围岩的强度潜能,合理指导隧道布置、支护设计与施工。该结果为隧道围岩松动破裂分析提供了理论依据,具有一定的工程参考价值。     

考虑应变软化、剪胀和渗流的水工隧洞解析解

基于统一强度理论和弹脆塑性软化模型,考虑不同工况下主应力顺序、岩石应变软化、剪胀和渗流等综合影响,推导了圆形水工压力隧洞应力和洞壁位移解析解。通过工程算例,比较本文方法与传统方法的不同,说明考虑第一主应力的变化和渗流体积力更符合工程实际,并得出统一强度理论参数、软化特性参数和剪胀特性参数对隧洞切向应力和洞壁位移的影响特性。隧洞设计时,应依据围岩材料特性合理地选取统一强度理论参数,并考虑由于软化特性参数和剪胀特性参数的减小对隧洞切向应力和洞壁位移增大的影响。该结果为圆形水工压力隧洞弹塑性分析提供了理论依据,对工程设计有一定的参考价值。     

大断面顶管通道近接穿越下覆既有地铁隧道数值模拟与现场试验

南京某地下步行通道采用非开挖顶管法施工,顶管近距离穿越既有地铁区间隧道及城市主干道。为了保证隧道及主干道安全,施工前建立三维有限元计算模型,模拟施工全过程,预测施工可能引起的隧道及地表变形。根据数值模拟结果提出针对性控制措施,并制定合理的监测方案,分别对隧道竖向位移、水平位移、径向收敛和地表隆沉进行监测。基于监测数据分析隧道及地表变形规律,明确顶管施工期间隧道及地表变形的3个不同发展阶段。研究表明:隧道竖向位移主要表现为隆起,由通道内出土卸荷所引起,工作井基坑开挖对其影响几乎可以忽略;顶管施工过程中,下覆隧道竖向位移先后经历了初始下沉、隆起增强和隆起稳定3个阶段,地表竖向位移先后经历了隆起增强、隆起减弱和沉降3个阶段;同一监测断面内,地表最大沉降位于通道中心轴线上方,距离通道越远沉降越小;采用微欠挖工艺有效控制了隧道最终隆起和地表最终沉降。     

层状地基中隧道开挖对临近既有隧道的影响分析

首次采用弹性层状半空间地基模型,建立了多层地基中隧道开挖对临近既有隧道影响的连续弹性分析方法,改变了过去采用简化分析方法仅能在均质地基中求解此类工程问题的状况。首先,采用Laplace积分变换得到了直角坐标系下单层地基应力和位移的初始函数,在此基础上,运用矩阵递推技术,给出了竖向荷载作用下层状地基中应力和位移的解析表达式并将其作为分析该问题的基本解。然后,采用弹性层状半空间地基模型将既有隧道视为Euler-Bernoulli梁,地基土体连续位移采用弹性层状半空间体系的基本解进行计算,并引入临近隧道开挖引起的土体自由位移场影响建立该问题的连续弹性求解方程,从而可以求得隧道纵向位移和内力。最后,结合离心模型试验和有限元数值模拟算例进行分析,验证了本文方法的有效性。此外,为考察地基土成层性对既有隧道性状的影响,还对几种典型层状地基中的隧道进行了参数分析。成果可为合理制定地下工程施工对临近既有隧道的保护措施提供一定的依据。     

基于黄土联合强度的黄土隧道围岩应力及位移研究

隧道围岩应力及位移计算问题是隧道工程界中传统研究课题之一,但黄土抗拉强度在黄土隧道围岩应力及位移计算中存在的影响需要进行合理性评价。基于建立的可综合考虑黄土抗拉和抗剪特性的联合强度,开展了极限应力平衡分析,重新推导了强度破坏曲线的主应力表达式;然后重新确定了轴对称圆形隧道条件下黄土围岩塑性区半径;最后得到了隧道周边黄土围岩位移表达式。研究结果表明:在围岩塑性区应力计算与比较中,基于联合强度确定的围岩塑性区应力小于基于传统的Mohr-Coulomb理论确定的围岩塑性区应力,而塑性区半径和隧道周边围岩位移相对较大;基于拉强度建立的联合强度理论克服了Mohr-Coulomb理论高估黄土抗拉强度的缺陷,可以合理评价黄土隧道围岩应力及位移。     

Displacement prediction of tunnels based on a generalised Kelvin constitutive model and its application in a subsea tunnel

Soft rock has the characteristic of time dependency, namely, creep or rheology. When the tunnel is located in weak surrounding rock, due to the rheology properties of surrounding rock, the load on the tunnel support and the displacement of tunnel lining may continue to increase. If the tunnel does not receive timely reinforcement and repair, these problems may threaten the safe operation of the tunnel. For tunnel repair and maintenance, we want to install some displacement monitoring sections in the appropriate position. However, tunnels are linear underground structures, and it is challenging to determine the location of the monitoring section and the displacement monitoring standards. In this study, based on the state equation of the generalised Kelvin constitutive model, a tunnel lining displacement analytical expression with a time variable was derived. Using actual data obtained during the construction of a subsea tunnel in Xiamen City and the theoretical research results presented in this paper, the final displacement of the subsea tunnel lining was forecasted and analysed. According to the results of the prediction and when considering the geological conditions along the longitudinal axis of the tunnel, the location of monitoring cross sections and monitoring standards was given. In the end, the measured data and the prediction result were compared, which proves that the conclusion is reliable. This study provides a useful reference for the maintenance and repair of tunnels in rheology rock mass.     

可液化地层中矩形隧道的上浮响应分析

在地震荷载作用下易导致饱和砂土液化从而引起地下结构发生上浮,以往多集中于圆形隧道的研究。文章基于有限差分软件FLAC2D,建立饱和砂土中土体和地下矩形隧道结构相互作用分析模型,充分考虑孔隙水与土之间的耦合,分析地下结构在地震过程中超孔隙水压力变化、加速度反应、上浮位移以及结构周围土体的变形规律。并探讨矩形隧道结构埋深、断面面积和断面长宽比对结构上浮位移的影响规律。分别提出评价矩形隧道上浮位移与结构埋深和断面面积的计算公式,利用此公式可以为类似工程中隧道结构的抗震稳定性分析提供指导和借鉴。     

深埋双隧洞开挖的解析延拓法求解

 将隧洞所处的地下空间转换为平面应变情况下的弹性半空间,考虑两隧洞开挖次序的影响,利用解析延拓法及Schwarz交替法求解出弹性半空间内2个任意形状任意尺寸的双隧洞在任意相对位置下其半空间内任意一点的应力解和位移解的隐式表达式。将双圆形隧洞作为特例,考虑到隧洞埋深与孔径相比比较大,从而不考虑重力梯度的影响,将重力化为作用在边界上的均布外荷载,考虑2个隧洞衬砌法向反力的影响,求解出弹性半空间内圆形双隧洞任意一点处的应力值和位移值解析解的具体显式表达式。最后利用二维有限元分析对理论推导的两圆形孔洞解析解进行验证,表明解的可靠性。     

交叉隧道围岩收敛和应力分布规律研究

交叉隧道数值模拟的研究很多,由于Y型隧道的设计施工复杂,目前还没有人进行数值研究。以南梁隧道中两条单线隧道合并为一条双线隧道的Y型交叉为背景,首先根据非线性Hoek-Brown准则得到岩体参数,然后用FLAC-3D根据该交叉段的施工方法进行三维数值计算,在不同的位置布置不同的观测面,探讨了单线隧道合并为双线隧道过程中各个观测面的变形破坏规律。综合多个观测面分析隧道开挖引起的位移、应力变化发现:随着单线隧道距离缩小,相互影响加剧,围岩压应力拉应力加大,位移变大,并且增加幅度渐渐变大,变化幅度最大为44.8%,合并为双线大概15 m后位移和应力都趋于稳定。     

圆巷开挖围岩偏应力应变能生成的分析解与图解

巷道开挖在围岩中产生偏应力,围岩应力是原岩应力与偏应力的叠加,偏应力或偏应力能控制岩体破坏。在假设静水压力和体积应变等于零条件下,利用文献[1]在弹性、非线性硬化和软化光滑连接的本构模型导得的圆巷围岩弹性、硬化和软化区光滑连接的应力分布表达式,用重积分计算了圆巷围岩弹性、硬化和软化区中的偏应力应变能U d,证明了Ud可以简捷地用地应力关于巷壁位移做一次积分再乘以巷壁周长得到。由此,可通过地应力–巷壁位移关系曲线及其所围面积的几何形式表示围岩偏应力能随巷壁位移变化的情况,此研究结果可以深化由于巷道开挖围岩的力学响应及挖成后巷道围岩工况规律的认识。     

Prediction of tunnel displacement induced by adjacent excavation in soft soil

Deep excavation may have impact on the adjacent tunnels. The interaction between new excavations and existing tunnels has been increasingly serious with the rapid development of underground space and metro system in urban area. It hence creates a high necessity to predict tunnel displacement induced by nearby excavation to ensure the safety of tunnel. In this paper, a semi-analytical method to evaluate the heave of underlying tunnel induced by adjacent excavation is presented and verified by field measurement results. The influence of excavation and the resistance of tunnel are obtained based on Boussinesq’s and Mindlin’s solutions, respectively. Then the soil–tunnel interaction behavior is analyzed based on the displacement coupling condition by assuming the tunnel as an elastic beam. A visco-elastoplastic model (VEP model) is employed to simulate the rheologic deformation of soil. The behavior of the tunnel underneath excavation is studied by the new method to discuss the influence of different factors, including excavation area, relative distance and construction procedure. Results of case studies show a good agreement between prediction and measurements.     

Protection of cement-soil reinforced regions for adjacent running tunnels during pit excavation

In pit excavation,cement is introduced into ground by deep mixing method to form an improved soil raft below final formation level to diminish deflection of retaining wall and effect on surrounding structure.Owning to complicated site conditions and improper workmanship,there are always some regions left untreated in the embedded improved soil raft.In this work,Several schemes of cement-soil mixed piles arrangement are modeled in order to discuss the effect of different cement-soil reinforced regions on protection for adjacent running tunnels.Finite element results show that:when lateral regions above tunnels are not enhanced by cement-soil mixed piles,effect of enlarging vertical enhanced regions around tunnels on diminishing lateral displacement of tunnel is really small;enhancing the lateral regions next to retaining wall is more effective in reducing the deflection of tunnel and retaining wall;uplifting of tunnel under the middle pit mainly depends on lateral reinforced regions and lateral displacements of retaining wall;as cement-soil mixed piles near retaining wall in east pit are removed during east pit excavation,effect of cement-soil mixed piles in east pit on reducing the final wall deflection can be neglected;upward shaft resistances are exerted along left side of diaphragm wall during excavation,which helps to reduce the wall deflection;positive effect of single-head cement-soil mixed piles in east pit is to decreasing the uplifting of soil inside east pit.Double-head cement-soil mixed piles arranged in"T"shape decrease the effect of east pit excavation on tunnels under middle pit apparently.     

近距巷道平行开挖合理错距研究

矿井下运输巷道是矿业生产的重要通道。文中针对极松软地层近距双水平巷道掘进问题,以内蒙古上海庙矿区为工程背景,依据工程区地应力场的实测结果及岩石力学实验参数,运用FLAC^3D三维数值分析计算软件对开拓巷道的合理错距进行了数值模拟研究。通过分析巷道周边应力分布、塑性区变化、位移速率矢量场方向变化以及监测位移数据变化,研究了巷道在分步开挖过程中,不同的开挖错距对已开拓巷道监测端面的影响。结果表明在极松软地质条件下,巷道围岩周边高应力区分布范围较大,新开拓的巷道会对相邻已开拓巷道周边的应力、塑性破坏区及位移速率矢量场产生影响,双近距水平巷道合理开拓错距宜保持在50 m以上。     

大断面公路隧道开挖方法数值分析

依托大连某桥隧建设工程,分别采用导洞法、单侧壁导坑法和双侧壁导坑法模拟大断面公路隧道的开挖过程,详细分析了隧道开挖支护后围岩的位移场与应力场的变化,通过对比研究,得出双侧壁导坑法开挖过程位移变化最小,受力均匀,更有利于维持围岩稳定性的结论。     

A closed-form elastic solution for stresses and displacements around tunnels

A closed-form plane strain solution is presented for stresses and displacements around tunnels based on the complex potential functions and conformal mapping representation. The tunnel is assumed to be driven in a homogeneous, isotropic, linear elastic and pre-stressed geomaterial. Further, the tunnel is considered to be deep enough such that the stress distribution before the excavation is homogeneous. Needless to say that tunnels of semi-circular or “D” cross-section, double-arch cross-section, or tunnels with arched roof and parabolic floor, have a great number of applications in soil/rock underground engineering practice. For the specific type of semi-circular tunnel the distribution of stresses and displacements around the tunnel periphery predicted by the analytical model are compared with those of the FLAC^2D numerical model, as well as, with Kirsch's “circular” solution. Finally, a methodology is proposed for the estimation of conformal mapping coefficients for a given cross-sectional shape of the tunnel.