岩溶区隧道围岩--支护体系稳定性研究

岩溶是地下水地质作用的过程和结果，是隧道建设面临的不良地质现象之一。正在建设中的某高速公路隧道出口段岩溶地质作用强烈，溶隙、孔洞发育，且受构造变形及后期淋滤溶蚀作用强烈，力学强度低，岩性复杂。其角砾状粘土岩和水云母粘土岩多已泥化成粘土，遇水易膨胀。岩溶区隧道围岩——支护体系的稳定性是该隧道建设面临的主要问题。文章结合隧道施工过程中的围岩变形监控量测和三维弹塑性有限元数值仿真模拟对隧道围岩——支护体系的稳定性进行了研究。围岩水平收敛和拱顶下沉位移及速率变化特性表明，在监测时段内隧道围岩无趋于稳定的迹象。施工动态力学数值仿真模拟表明，在初期支护条件下，围岩出现了较大范围的塑性破坏区，两隧道之间(间距45．0m)围岩破坏接近度达到0．70，最大竖向位移达到3．0mm，表明隧道全断面施工时，两隧道相互作用影响程度较大。为确保隧道围岩——支护体系的稳定，选择合理的施工方法，制定切实可行的支护方案提供了信息。     

Excavation Problem in Mixed Ground Conditions at the Kabatas–Mecidiyekoy Metro (Istanbul) Tunnels

Mechanized tunnelling is a well-established tunnel construction method which allows constructing tunnels in various conditions including mixed ground conditions as well as tunnels in vulnerable urban areas. The selection of the excavator suitable for the geological structure is important in terms of realizing an efficient tunnel excavation. Tunnel excavation studies of Istanbul Kabatas–Mecidiyeköy Metro tunnels are implemented as a double tube. Geology in this section is composed of sandstone, siltstone, mudstone interbedded or as separate units along with dyke intrusions. Calcareous clay, clayey limestone, clayey sand are also rarely observed. Between the Kabatas–Mecidiyekoy tunnels includes two types of mechanical excavation methods namely tunnel boring machine (TBM) and new Austrian tunnelling method (NATM). Main purpose of this study is mixed ground and their impacts on mechanized tunnelling. At the end, some issues have been presented which seems to be important for the success of TBM and NATM in the mixed grounds. As the tunnel excavation studies continued, the problem of collapse on the ground surface of Barbaros Boulevard in Besiktas station increased the importance of tunnel excavation under mixed ground conditions.     

A Top Pilot Tunnel Preconditioning Method for the Prevention of Extremely Intense Rockbursts in Deep Tunnels Excavated by TBMs

The headrace tunnels at the Jinping II Hydropower Station cross the Jinping Mountain with a maximum overburden depth of 2,525 m, where 80% of the strata along the tunnels consist of marble. A number of extremely intense rockbursts occurred during the excavation of the auxiliary tunnels and the drainage tunnel. In particular, a tunnel boring machine (TBM) was destroyed by an extremely intense rockburst in a 7.2-m-diameter drainage tunnel. Two of the four subsequent 12.4-m-diameter headrace tunnels will be excavated with larger size TBMs, where a high risk of extremely intense rockbursts exists. Herein, a top pilot tunnel preconditioning method is proposed to minimize this risk, in which a drilling and blasting method is first recommended for the top pilot tunnel excavation and support, and then the TBM excavation of the main tunnel is conducted. In order to evaluate the mechanical effectiveness of this method, numerical simulation analyses using the failure approaching index, energy release rate, and excess shear stress indices are carried out. Its construction feasibility is discussed as well. Moreover, a microseismic monitoring technique is used in the experimental tunnel section for the real-time monitoring of the microseismic activities of the rock mass in TBM excavation and for assessing the effect of the top pilot tunnel excavation in reducing the risk of rockbursts. This method is applied to two tunnel sections prone to extremely intense rockbursts and leads to a reduction in the risk of rockbursts in TBM excavation.     

Investigation of influence of tunneling on existing building and tunnel: model tests and numerical simulations

To investigate the realistic ground behavior during tunneling, a new device has been developed. With the new device, model tests of tunnel excavation considering an existing tunnel and an existing building were carried out. Non-linear finite element analyses corresponding to the model tests were also conducted using FEMtij-2D software where an elastoplastic subloading t _ij model was used to describe the mechanical behavior of soil. Earth pressure distribution around the tunnels and ground movements during tunnel excavation depend on the distance and position between the twin tunnels. There is a significant effect of tunneling on the existing foundation of building even in the case where the tunnel is constructed in deep underground. The numerical analyses capture well the results of the model tests.     

Interaction of longitudinal surface settlements for twin tunnels in shallow and soft soils: the case of Istanbul Metro

Increasing demands on infrastructures increases the attention on shallow soft ground tunneling methods in urbanized areas. Especially, in metro tunnel excavations, it is important to control the surface settlements observed before and after excavation, which may cause damage to surface structures. To solve this problem, earth pressure balance machines (EPBMs) have widely been used throughout the world. This study focuses on surface settlement measurements, the interaction of twin tunnel surface settlement, and the relationship between shield parameters and surface settlement for parallel tunnels using EPBM shields in clay and sand soils. In this study, the tunnels were excavated using two EPBMs. The tunnels were 6.5 m in diameter, as twin tubes with a 14 m distance from center to center. The EPBM in the first tube followed about 100 m behind the other tube. Segmental lining with 1.4 m of length was employed as a final support. The results from this study showed that (1) the most important parameters for the maximum surface settlements are the face pressure and backfill; (2) in twin tunnel excavation with EPBM for longitudinal profile, the settlement rate reached its peak value when the shield came to the monitoring section and this peak value continued until the shield passed the monitoring section; (3) every shield affected the other tunnel’s longitudinal surface settlement profile by approximately 35–36.8 %; (4) S _A, S _B and S _C values were found to be 38.0, 35.8 and 26.2 %, respectively for an EPBM, and (5) ensuring good construction quality is a very effective way to control face stability and minimize surface settlement.     

基于Peck公式的双线盾构引起的土体沉降预测

基于Peck公式,对双线水平平行盾构隧道施工中土体损失引起的三维土体沉降计算方法进行研究。考虑先行隧道施工对后行隧道的影响和两条隧道开挖面的不同位置,建立修正的三维Peck公式;通过分别计算先行盾构隧道和后行盾构隧道施工引起的土体沉降,叠加得到双线水平平行盾构施工引起的总的三维土体沉降。算例分析结果表明：预测值与实测值比较吻合;随着两条隧道开挖面前后距离的逼近,地面最大沉降量会逐渐增大;随着土体深度z的增大,沉降略增大、沉降槽宽度则略减小;当两条隧道轴线水平距离L较小时,地面沉降量较大,符合正态分布规律;随着L的增大,最大地面沉降量会逐渐减小,沉降曲线形状慢慢由V型转变成W型。     

A Review of Seismic Damage of Mountain Tunnels and Probable Failure Mechanisms

Severe cases of damages of mountain tunnels following 1995 Hyogoken-Nanbu (Japan), 1999 Chi-Chi (Taiwan), 2004 Mid-Niigata Prefecture (Japan) and 2008 Wenchuan (China) earthquakes have challenged the traditional belief of tunnel structures being seldom damaged in seismic events. These experiences are a reminder that seismic behaviour of mountain tunnels must be further studied in detail. Such investigations assume greater significance as more number of tunnels are being planned to be constructed to meet the infrastructural needs of mountainous regions all around the world. In this paper, seismic damages of mountain tunnels have been reviewed. Prominent failure patterns have been identified based on the case histories of damages. Damages in the form of cracking of tunnel lining, portal cracking, landslide induced failures, uplift of bottom pavement, failures of sidewalls, shearing failure of tunnel liner and spalling of concrete have been majorly observed. Based on the damage patterns and earthquake data, main factors leading to instabilities have been discussed. Probable failure mechanisms of mountain tunnels under seismic loading conditions have been explained. Seismic analyses of a circular lined tunnel in blocky rock mass have been carried out through discrete element based approach. The significant role of different seismic parameters like frequency, peak ground acceleration has been identified. Moreover, effect of tunnel depth on the seismic response of tunnels has been investigated. It is believed that the present study will help in advancing the present state of understanding with regard to the behavior of tunnels under seismic conditions.     

Effect of Blast-Induced Vibration from New Railway Tunnel on Existing Adjacent Railway Tunnel in Xinjiang, China

The vibrations of existing service tunnels induced by blast-excavation of adjacent tunnels have attracted much attention from both academics and engineers during recent decades in China. The blasting vibration velocity (BVV) is the most widely used controlling index for in situ monitoring and safety assessment of existing lining structures. Although numerous in situ tests and simulations had been carried out to investigate blast-induced vibrations of existing tunnels due to excavation of new tunnels (mostly by bench excavation method), research on the overall dynamical response of existing service tunnels in terms of not only BVV but also stress/strain seemed limited for new tunnels excavated by the full-section blasting method. In this paper, the impacts of blast-induced vibrations from a new tunnel on an existing railway tunnel in Xinjiang, China were comprehensively investigated by using laboratory tests, in situ monitoring and numerical simulations. The measured data from laboratory tests and in situ monitoring were used to determine the parameters needed for numerical simulations, and were compared with the calculated results. Based on the results from in situ monitoring and numerical simulations, which were consistent with each other, the original blasting design and corresponding parameters were adjusted to reduce the maximum BVV, which proved to be effective and safe. The effect of both the static stress before blasting vibrations and the dynamic stress induced by blasting on the total stresses in the existing tunnel lining is also discussed. The methods and related results presented could be applied in projects with similar ground and distance between old and new tunnels if the new tunnel is to be excavated by the full-section blasting method.     

Visco-Plastic Behaviour around Advancing Tunnels in Squeezing Rock

Summary  The visco-plastic behaviour of rocks plays a relevant role in the tunnelling works, especially for deep tunnels subjected to large initial stresses for which squeezing conditions may develop. A rheological model is discussed that accounts for visco-elastic (primary) and visco-plastic (secondary) contributions to rock creep. The effects of tertiary creep are included in the model by way of a gradual mechanical damage governed by the cumulated visco-plastic strains. The parameters of the intact rock are first identified based on laboratory test results presented in the literature. Then, after scaling them to those of the rock mass, the potential applicability of the model is tested through axisymmetric and plane strain finite element analyses of the full face excavation of a deep circular tunnel. The results are discussed with particular reference to the short term redistribution of stresses around the opening and to its convergence. The analyses show the relevant influence of tertiary creep on the tunnel closure. In addition, those based on an axisymmetric scheme turn out to be crucial for the correct long term prediction of the interaction between the rock mass and the supporting structure of the opening.     

平行小净距盾构与CRD法黄土地铁隧道施工力学研究

西安轨道交通工程是目前首例在我国黄土地区修建的地铁隧道,一号线枣园北路站至汉城路站K12+792.744～K12+889.899区间隧道为同时满足双线正常行车和右线停车线扩大断面的功能需要,选取了左线小断面隧道为盾构法与右线大断面隧道为CRD法相结合的施工方案。针对该地铁隧道的施工过程,进行了三维动态数值模拟和施工力学分析,通过分析施工引起的地表变形、中间土体应力和围岩塑性区的特征和规律,从而研究得出CRD法与盾构法隧道先后施工相互影响的规律性成果：先行大断面隧道采取CRD法施工对后行小断面盾构隧道上方地表沉降的影响较后者对前者的影响大;后行隧道的贯通使得先行隧道开挖形成的地表变形轴线向后行隧道侧偏移了约0.5倍净距,并且地表变形的横向影响范围和地表沉降量均有增大,主要表现在靠后行隧道一侧;先行大断面隧道的开挖较后者对中间土体应力影响大,对相邻洞土体的影响在同掌子面处最为显著。结合西安地铁隧道工程实践开展的数值模拟分析研究,可为今后在黄土地区修建地铁隧道提供具有指导意义的研究成果和宝贵的工程实践经验。     

Study on the Influence of Close Distance Construction of Urban Tunnel on the Existing Station

In the construction of the tunnel passing through the existing structure at an ultra-close distance, the existing structure will produce obvious deformation. It is very important to understand the deformation characteristics of the existing upper structure at different positions, especially to ensure the safety of the upper structure and improve the effectiveness of tunnel construction. In this study, the double-line tunnels of Qingdao Metro Line 4 passing under the Cuobuling station were taken as the engineering background, and a detailed 3D numerical model was established. This study comprehensively considered the on-site construction process, including grouting hardening, stress release of the excavated rock mass, grouting pressure and so on. The influence of tunnel excavation on the ground settlement was compared with or without a station structure, and the result was fitted with an empirical formula. Finally, the deformation of the station structure due to the excavation of the double-line tunnels was analyzed. The results of the analysis were as follows: (1) In the presence of the station structure, the excavation of the tunnels had a significant impact on the surface settlement. (2) The settlement of the sidewall caused by the excavation of the left-line tunnel was greater than that of the right-line tunnel, and the settlement at the junction of the sidewall and the bottom plate was smaller than that at other positions of the sidewall. (3) Compared with the roof and middle slabs, the floor of the station was more susceptible to the influence of tunnel excavation. Overall, the research could provide guidance and reference for similar double-line tunnels through existing stations.

     

A new approach for estimating the transverse surface settlement curve for twin tunnels in shallow and soft soils

Increasing demand on infrastructures has led to increased attention to shallow soft ground tunneling methods in urbanized areas. Especially in metro tunnel excavations, it is important to control the surface settlements which are observed before and after excavation, which may cause damage to surface structures. Unlike motorway, sewage and other infrastructure tunnels, metro tunnels generally have to be excavated as twin tunnels and must have a larger diameter. Metro tunnels also have shallow depth. Due to their shallow depth, metro tunnels generally have been constructed in weak rocks or weak soils in cities. The construction of twin tunnels will generate ground movements which have the potential to cause damage to existing surface and subsurface structures. To solve this settlement problem, experts have used the Earth pressure balance machine (EPBM) and the slurry balance machine. In such excavations, especially in twin tunnels, the main challenges for constructers are estimating the maximum surface settlement, controlling the interaction of transverse surface settlement and shaping the settlement curve. Incorrect estimation of these parameters can lead to significant problems above the tunnels and in nearby structures. This paper focuses on surface settlement measurements, on the interaction of twin tunnel transverse surface settlement and on the relationship between shield parameters and transverse surface settlement for parallel tunnels using EPBM shields in clay and sand soils in shallow depth. Also, a new equation is proposed for estimating the transverse settlement curve of twin tunnels. The results from this proposed equation are compared with the results of field observations. The transverse settlement curve values obtained from the proposed equation have good agreement with the actual results for the Otogar–Kirazli metro case studies.     

盾构隧道注浆对既有隧道影响的离心模拟研究

随着地铁网络不断完善,越来越多的新建盾构隧道近距离穿越既有隧道,然而对于盾构隧道近距离穿越既有隧道影响的研究尚不够完善。以上海典型软弱地层为背景,通过离心模型试验,研究了不同注浆率下的盾构上穿越施工对既有隧道以及周围地层的影响。选用排液法在离心场中模拟盾构施工,在不停机状态下成功模拟隧道开挖卸载、地层损失和注浆效应。分析了在不同的注浆率条件下,既有隧道在上穿越施工期和工后长期的位移、周围孔压和纵向应力的变化规律。试验结果表明,新建隧道近距离上穿越既有隧道时,隧道开挖的卸载效应等会导致既有隧道的隆起,但随着注浆率增大,既有隧道的隆起量减小。但过高注浆率对周围土体扰动较大,从而导致工后既有隧道的沉降也越大。     

基坑开挖引起的旁侧盾构隧道横向受力变化研究

为研究运营盾构隧道附近基坑开挖对隧道管片受力的影响,针对基坑开挖引起旁侧盾构隧道围压变化的机制进行了分析,提出了一种能描述隧道受力-位移-再平衡过程的附加围压重分布模型,并推导出附加围压的计算公式。采用修正惯用法计算相应围压作用下的衬砌内力。根据实际工程做算例分析,研究基坑开挖对盾构隧道围压和内力的影响,并进行影响因素分析。分析结果表明：基坑开挖前隧道围压呈“钟形”分布;当基坑开挖后,隧道两侧的围压减小,基坑开挖侧的围压减小量更多;基坑开挖会使旁侧隧道正负弯矩值和正负剪力值增大,拱顶和拱底的轴力减小;随着基坑侧壁应力释放系数的增大,附加围压和附加弯矩的绝对值都会增加,而弯矩对基坑开挖卸载的响应更为明显;埋深较浅的盾构隧道对旁侧基坑开挖的影响更敏感,埋深较大的隧道,尤其是埋深大于基坑开挖深度的隧道,对旁侧基坑开挖影响的敏感度会明显降低;随着基坑与旁侧隧道净距的增加,基坑开挖对隧道的影响也会减小。     

Influence of Rock Mass Parameters on the Performance of a TBM in a Gneissic Formation (Varzo Tunnel)

Summary The paper analyses the influence of rock mass quality on the performance of a double shield TBM in the excavation of a tunnel in a gneiss formation which is characterized by high strength and low fracture intensity.As full observation of the rock conditions was prevented by the use of segmental lining, a geomechanical survey of the face was performed during maintenance downtime and the observed conditions were correlated with the machine performance parameters for that same day. A statistical analysis of the data shows that penetration rate correlates well with a slightly modified RMR index (in which the influence of the water conditions and joint orientation were discounted), but the most important factor is by far the partial rating of the RMR classification related to joint spacing only. However in tunnels characterized by greater variability in rock strength and joint conditions, it could be worthwhile using the complete RMR index.Given the toughness of the rock, failure of the cutter bearings and supports were a frequent occurrence during excavation. Owing to this factor the influence of rock quality on the rate of advance was found to be weak and the correlation more scattered.The results obtained for the Varzo tunnel were compared with those relative to other tunnels in granitic rocks and found to be in good agreement. However the relationships obtained should be considered valid only for this type of rock; machine behaviour could be found to be markedly different in other rock types, even where rock material strength and joint frequency are the same.     

What is the contribution of time-dependent deformation in tunnel convergence?

Tunnel excavation produces stress changes to the ground and strain to the support lining, leading to the closure (convergence) or instability of the excavated area. Convergence recorded after section excavation is assigned to: (i) strain resulting from the progressive tunnel front advance (face advance effect) and (ii) the time-dependent properties of the soil material (ground creep effect). In the present study, based on the geodetic monitoring records of two recent road tunnels in Greece, a simple methodology to estimate the contribution of each of the two effects is presented. Our analysis reveals that at least half of the total deformation of the examined tunnel sections is due to ground creep, indicating that the major portion of tunnel deformation is due to the time-dependent properties of the ground; a result supported by previous studies from other tunnels as well.     

1000－7598－(2003)增1―0001―08

随着地下工程的发展,对于埋置较深和地质环境较为复杂的隧道工程,高地温问题已经成为一个重要的工程问题并引起了国内外学者的广泛关注。研究隧道的温度场分布问题对于解决寒区隧道冻融问题、高温隧道问题、隧道火灾灾害等是十分必要的。针对高地温环境中的圆形隧道,假定其具有一定长度且承受轴对称的温度荷载和地应力作用,建立两端简支的二维稳态的热传导方程和平衡方程。利用无量纲化和微分方程级数求解的方法,得到了包含温度场、位移场及应力场的热弹性理论解。依据上述研究结果,以某包含衬砌的圆形断面隧道为例进行了热弹性分析,并得到了由于隧道开挖而引起的围岩的温度变化范围。研究所得结论可为隧道施工及运营过程中隧道的保温隔热提供重要的理论依据。     

基坑开挖引起下卧隧道隆起变形的实测数据分析

在上跨隧道的基坑工程中基坑开挖常引起下卧隧道发生结构变形,限制隧道的隆起变形成为基坑施工控制的关键。详细介绍了该类工程的特点,包括交叉形式、隧道变形特点、常见控制措施等,对近期国内发生的39例类似工程进行分类总结,分析了隧道纵向最大隆起变形与各影响因素间的关系,并提出了隧道最大隆起变形的预测模型。结果表明,该类工程中工程地质对隧道的隆起变形影响较大,工程地质条件越差隧道的隆起变形越难控制;开挖深度、基坑面积、基坑形状同样是影响隧道隆起变形的重要因素,基坑开挖面积及深度越大,形状越不规则,隧道的隆起变形越大;在软土地区,当基坑开挖面积及深度较大时设置抗拔桩能显著减小隧道的最大隆起变形。     

Elastic Solution for Deep Tunnels. Application to Excavation Damage Zone and Rockbolt Support

Summary  A new formulation is presented for deep circular tunnels in rock with cylindrical anisotropy. The formulation is an exact solution since it satisfies equilibrium, strain compatibility, and the anisotropic constitutive model. Complete solutions have been found for two scenarios: tunnel with excavation damage zone, and tunnel with rockbolt support. The solution is based on the assumption of a deep, circular tunnel in a medium with two homogeneous zones: an inner zone surrounding the tunnel, which is either isotropic or anisotropic, and an outer zone, for the remainder of the medium, which is isotropic. Plane strain conditions, elastic response of rock, rockbolts and support, and simultaneous excavation and support installation are also assumed. For tunnels surrounded by an excavation damage zone with reduced rock properties, the tangential stresses and the radial deformations at the tunnel wall are very sensitive to both the magnitude of stiffness reduction of the damaged rock and the size of the damaged zone. The effect of the rockbolts on the rock is approximated by treating the rockbolt-rock composite as a material with cylindrical anisotropy with stiffnesses related to the properties of the rock and rockbolts, and spacing of the rockbolts. Comparisons between the analytical solution and a numerical method show small differences and provide confidence in the approach suggested.     

Prediction of swelling rocks strain in tunneling

Swelling deformations leading to convergence of tunnels may result in significant difficulties during the construction, in particular for long term use of tunnels. By extracting an experimental based explicit analytical solution for formulating swelling strains as a function of time and stress, swelling strains are predicted from the beginning of excavation and during the service life of tunnel. Results obtained from the analytical model show a proper agreement with experimental results. This closed-form solution has been implemented within a numerical program using the finite element method for predicting time-dependent swelling strain around tunnels. Evaluating effects of swelling parameters on time-dependent strains and tunnel shape on swelling behavior around the tunnel according to this analytical solution is considered. The ground-support interaction and consequent swelling effect on the induced forces in tunnel lining is considered too. Effect of delay in lining installation on swelling pressure which acting on the lining and its structural integrity, is also evaluated. A MATLAB code of “SRAP” is prepared and applied to calculate all swelling analysis around tunnels based on analytical solution.