Probabilistic simulations of TBM tunnelling in highly fractured and faulted rocks

Despite the potential excellent performance of TBMs in favourable ground conditions, the presence of fault zones or heavily jointed rocks represents important geological hazards encountered during tunnel excavation. The effects of these challenging environments on the final tunnel construction time and costs can be investigated through a specific computer code: the Decision Aids for Tunnelling (DAT). In this framework the DAT simulate the tunnel excavation in several geological profiles, where changing ground scenarios are described in terms of different “fault zone” classes (from highly fractured rocks, to faulted and crushed material). For each class a certain reduction of the TBM advance rate is specified based on real data analyses. Although the great uncertainty, the results give a reliable estimation of the effect of degrading rock mass conditions on the tunnelling performance. Finally, a real case-study has been simulated by DAT in order to validate the use of the “fault zone” classes (and the relative advance rate reductions) in the estimation of the final time of tunnel construction. The predicted time values prove to be very close to the ones recorded on the field, confirming the importance of a more detailed and comprehensive characterisation of difficult ground conditions such as fault and highly fractured zones.     

徐家梁子隧道围岩分类

徐家梁子隧道是西攀高速公路的一个重要控制点,根据该隧道围岩岩性特征、岩体强度、岩体结构特征、风化程度、结构面发育分布特征及岩体完整性等特征,对其进行了围岩分类,其结果对隧道施工和衬砌类型的选择提供了依据。     

Numerical evaluation of strength and deformability of fractured rocks

Knowledge of the strength and deformability of fractured rocks is important for design, construction and stability evaluation of slopes, foundations and underground excavations in civil and mining engineering. However, laboratory tests of intact rock samples cannot provide information about the strength and deformation behaviors of fractured rock masses that include many fractures of varying sizes, orientations and locations. On the other hand, large-scale in situ tests of fractured rock masses are economically costly and often not practical in reality at present. Therefore, numerical modeling becomes necessary. Numerical predicting using discrete element methods(DEM) is a suitable approach for such modeling because of their advantages of explicit representations of both fractures system geometry and their constitutive behaviors of fractures, besides that of intact rock matrix. In this study, to generically determine the compressive strength of fractured rock masses, a series of numerical experiments were performed on two-dimensional discrete fracture network models based on the realistic geometrical and mechanical data of fracture systems from feld mapping. We used the UDEC code and a numerical servo-controlled program for controlling the progressive compressive loading process to avoid sudden violent failure of the models. The two loading conditions applied are similar to the standard laboratory testing for intact rock samples in order to check possible differences caused by such loading conditions. Numerical results show that the strength of fractured rocks increases with the increasing confning pressure, and that deformation behavior of fractured rocks follows elasto-plastic model with a trend of strain hardening. The stresses and strains obtained from these numerical experiments were used to ft the well-known Mohr-Coulomb(MC) and Hoek-Brown(H-B) failure criteria, represented by equivalent material properties defning these two criteria. The results show that both criteria can provide fair estimates of the co     

Geomechanical characterisation of fault rocks in tunnelling: The Brenner Base Tunnel (Northern Italy)

The goal of this study is to characterise the rock faults involved in the excavation works of the Brenner Base Tunnel, which crosses one of the main tectonic alignments of the alpine area, the Periadriatic fault. The characterisation was carried out at different scales from macro (through drillings and geomechanical surveys) to meso (lab tests on specimens) and micro-scale (through thin sections), in order to find a correlation between the different scales properties of the rock masses. Finally, a relation between the voids ratio at the micro-scale and the fault rocks conditions at the meso and macro-scale was pointed out. As a result, by means of the Hoek–Brown method, an estimation of the fault rock strength was achieved, tending to avoid quite a typical overestimation arising from the use of literature values.     

Slope stability problems of the weak rocks in the Asarsuyu pass of the Anatolian motorway

 The Anatolian motorwaythrough the Asarsuyu Valley passes across landslides formed in amphibolites, metagranites and metadiorites which have been extensively disturbed by past fault movements. The investigations indicated that the instabilities in the valley could affect the proposed motorway. An attempt was made to establish the shear strength values of the 1200×750×130 m Kom Rock Slide using the Hoek and Brown equation. The work indicated that this was not applicable in the highly sheared material along the major fault zones. 28 February 1998 · Accepted: 9 June 1998     

Theoretical estimation of loosening pressure on tunnels in soft rocks

This paper presents a theoretical method predicting the development and progress of plastic zones around tunnels in soft rocks and determining the loosening pressure which has to be taken by rock bolts or linings. Influence effects of the mechanical properties of soft rocks on the loosening pressure are examined and discussed. The judgment method used to assess the extent of rock failure is presented according to the ground characteristic curve. The ground characteristic curve shows a lowest point that refers to the minimum support pressure and the controlled tunnel wall strain when the competency factor (i.e. ratio of compressive strength to the initial in-situ pressure) is smaller than a critical value, which can be estimated from the proposed theoretical equations.     

Models for estimation of TBM performance in granitic and mica gneiss hard rocks in a hydropower tunnel

Bulletin of Engineering Geology and the Environment - The risk of excavation operations due to high capital costs can be reduced by correct estimation of machine performance. Many models have been...     

TBM隧道在不同围岩条件下的数值模拟分析

通过利用ANSYS有限元分析软件，对TBM法隧道施工的过程进行数值模拟分析，结合隧道的工程地质情况，通过分析其应力应变的状态，提出了ANSYS模拟TBM在不同围岩条件下开挖隧道时围岩应力变化的可行性，得出了TBM隧道在不同围岩条件下的一些基本特征。     

围岩变形内表比及一种新的巷道围岩分类法

根据现场实测资料和数值模拟计算结果,研究了几种不同类型巷道围岩变形规律,提出更能反映围岩变形规律和变形状态的"内表比"概念,进而考虑依据巷道围岩表面变形量和内表比值两个参数,提出一种新的巷道围岩分类法,并根据各种支护所容许的极限变形量,给出相应的合理支护形式。     

An appraisal of TBM performances in Turkey in difficult ground conditions and some recommendations

The geology of Turkey is very complex and major Northern and Eastern Faults including minor faults associated to these faults create tremendous problems, like squeezing of the TBM, excessive water ingress, TBM face collapses, as encountered in the Kargi power tunnel, the Dogancay energy tunnel, the Gerede water tunnel, and the Nur Dagi railway tunnel. Mixed ground conditions with ophiolites, graphitic schists and melanges with boulders are other fundamental difficulties leading to squeezing and blocking of the TBMs or even causing complete failures of the segments and abandoning of the tunnel. A typical example for tunnel abandoning is the Kosekoy high speed tunnel and an example for excessive TBM squeezing is the Uluabat energy tunnel. The affects of dykes in the Istanbul region is known well by practicing tunnel engineers. These andesitic rocks, make fractures in the country rock and cause several problems during TBM excavation like blocking the cutterhead and excessive disc cutter consumption. Typical examples are the Goztepe-Kadıkoy Metro tunnels, and the Melen water tunnel. The Beykoz utility tunnel is one of the most difficult tunnelling projects in Istanbul. Presence of clay minerals existing within the geologic formations is also one of the main reasons clogging the cutterhead of TBM as encountered in the Suruc water project. The effects of complex geology on the excavation efficiencies of different type of TBM’s used in the ten projects mentioned above are explained in this paper and some recommendations with a ground classification system for proper use of TBMs in faultyzones are given.     

软弱围岩小净距隧道动态施工力学行为分析

基于新奥法施工理念,结合某大跨度、小净距隧道工程浅埋段施工过程,根据采取的双侧壁施工方法,建立了数值模型,对其施工过程进行了三维有限元弹塑性模拟。分析了施工过程中随着各部的开挖,隧道周边各点竖向位移的变化;通过对开挖后地表沉降、支护受力和塑性区的模拟计算以及隧道拱顶沉降监测值与计算值的对比分析,进而对施工过程中隧道结构的安全性及围岩稳定性作出评价。数值计算结果表明,在软岩浅埋隧道中,超前小导管的设置可起到加固围岩和抑制隧道变形的作用,有效控制双线隧道开挖引起的反复扰动是小净距隧道施工成败的关键。     

Analysis of longitudinal profile of the tunnels in the active faulted zone and designing the flexible lining (for Koohrang-III tunnel)

This paper presents a method of designing flexible lining for tunnels within the regions of active faults. The design criterion is based on the allowable longitudinal deflection and/or angular distortion. Besides the design of flexible joints, the longitudinal deformation profile is also determined within the active faults region. This analysis indicates that if the lining is designed to tolerate an angular distortion about 1–2° along its length, a circular tunnel of 4 m diameter can stand safe and without any damages for the assumed life time. This requirement can be satisfied by introducing some flexible joints between two consequent rigid parts of lining to make it flexible enough to be able to tolerate the moment and shear which may happen in it. It is worth mentioning that the present approach is basically for a particular case in Iran that should be considered as a very risky and critical position.     

津巴布韦大岩墙铂族矿床分布特征及成因分析

津巴布韦大岩墙是一套铁镁质和超铁镁质的层状基性-超基性岩体,是铂族元素主要成矿地带。本文通过对大岩墙中铂族矿床的分布规律进行研究得出,本区铂族矿床主要产于岩体中硫化物带（MSZ）的底部,矿体呈层状、似层状赋存于辉石岩中,其埋深具有在大岩墙的两翼浅、核部深的特征。电子探针分析表明,铂族元素主要产于以磁黄铁矿、镍黄铁矿、黄铁矿为主的硫化矿物组合中,镍和钴的含量均较低。成因分析表明,矿床中铂族元素的富集与基性-超基性的岩浆分异作用关系密切,原始岩浆来源于地幔,成矿环境为低氧逸度和高硫逸度的还原环境,并具有多期成岩成矿特征。     

Applicability of the geological strength index (GSI) classification for very weak and sheared rock masses. The case of the Athens Schist Formation

 The Athens Schist Formation includes a wide variety of metasedimentary rocks, varying from strong or medium strong rocks such as sericite metasandstone, limestone, greywacke, sericite schist through to weak rocks such as metasiltstone, clayey and silty shale and phyllite. The overall rock mass is highly heterogeneous and anisotropic owing to the combined effect of advanced weathering and severe tectonic stressing that gave rise to intense folding and shearing followed by extensional faulting, which resulted in highly weathered rock masses and numerous shear and/or mylonite zones with distinct downgraded engineering properties. This paper is focused on the applicability of the GSI classification system to these highly heterogeneous rock masses and proposes an extension of the GSI system to account for the foliated or laminated weak rocks in the lower range of its applicability. Received: 5 March 1998 · Accepted: 13 July 1998     

北羌塘地区冬布勒山基性、超基性岩特征及构造意义

冬布勒山基性、超基性岩产于若拉岗日逆冲断裂带北侧,近东西向展布,岩石组合为超镁铁岩及变质玄武岩,与千枚岩、硅质岩、碳酸盐岩共生,呈岩块状镶嵌于上三叠统若拉岗日岩群砂泥质复理石、中基性火山岩及灰岩中。超镁铁岩浆来自亏损的地幔,并受壳源物质混染;玄武岩贫钾富钠,属钙碱性、碱性系列,为过渡型洋脊玄武岩,它们为蛇绿岩残片,与西侧大横山、弯岛湖蛇绿混杂岩带、东部康特金—岗齐曲蛇绿混杂岩带处于同一构造带,东连金沙江蛇绿岩带,是古特提斯洋壳向北俯冲消减过程中形成的增生楔。     

SNS柔性防护系统在震裂危岩防护中的应用

结合汶川地震,分析了震裂危岩的特点,阐述了SNS柔性防护系统的优点,介绍了SNS柔性防护系统的施工方法,提出了震裂危岩的治理措施,以提高工程技术人员对SNS柔性防护系统的认识,推广该防护系统的应用。     

一种岩体裂隙时效扩展的数值模拟方法及验证

 鉴于岩体中存在大量的微缺陷,假定数值模型中每个单元均含有一条长度和倾角具有正态分布的无厚度虚拟微裂纹。通过断裂力学理论及裂隙扩展模式,判定这些微裂纹的扩展速率及模式,当微裂扩展至单元边界,则此单元破坏。这些破坏的单元相互搭接连通,则形成宏观破裂面。以改进的Burgers模型为例,将上述方法嵌入FLAC数值软件,对完整岩石、单裂隙岩体及双裂隙岩体进行单轴压缩和双轴压缩蠕变数值试验。将数值模拟结果与试验结果对比,验证所提出的岩体裂隙时效扩展数值模拟方法的有效性。     

桂林市某中学后山危岩破坏机理及其防治

根据桂林市某中学后山危岩的实际情况，在充分调查分析其发育的地质环境条件基础上，有针对性地采取SNS被动防护系统治理措施，同时加强排水和监测工作，以成功地进行危岩治理。     

略阳白雀寺-石瓮子双峰式侵入岩锆石U-Pb定年、地球化学特征及意义

在碧口地体东段勉略宁地区,发现侵位于碧口群双峰式火山岩中的白雀寺-石瓮子杂岩体具有双峰式侵入岩的特征,其主体由辉长岩与二长花岗岩组成。二者的锆石U-Pb年龄分别为836. 2 Ma与835. 1 Ma,年龄非常接近且略晚于碧口群火山岩(850～840 Ma)。与碧口群双峰式火山岩类似,该双峰式侵入岩中酸性端元所占比例较少,以基性端元为主,且二者岩石地球化学特征存差异并非巨大,据此初步推断二者可能具有相同的岩石圈地幔源区。辉长岩具有的碱性玄武岩与拉斑玄武岩特征,以及二长花岗岩具有的弧向板内过渡特征,并非绝对的陆内(板内)裂谷特征,而为陆间裂谷所特有;其形成于陈家坝岛弧(或弧后)的局限裂解环境,这与碧口群双峰式火山岩、以及在区内苍社-太阳岭一带的岩浆成因碳酸岩在时空上高度耦合,共同代表了新元古代扬子北缘碧口局限洋盆俯冲(会聚)作用过后的弧后(局限)伸展构造体制下幔源岩浆事件。