Gotthard Base Tunnel Research Articles

Seismic prediction of geological structures ahead of the tunnel using tunnel surface waves

ABSTRACTIn order to keep up with the economic and safety demands of modern tunnel construction projects, especially in urban areas, there is a need to detect safety threats in real time while the construction is advancing. Tunnel prediction methods accompanying the drilling process can help to correlate and update a priori information on expected geological structures with their actual spatial location or even existence ahead of the tunnel face. We recently presented a seismic prediction approach using tunnel surface waves, which has already proven its potential during field surveys. However, common tunnel seismic data interpretation, regardless of the prediction method, requires human interaction. Either a specially trained field technician have to be present at the construction site or the data has to be uploaded to an office for further interpretation. In this work we present a simple but stable approach to automatically detect major geological structures ahead of the tunnel face. We focus on the accurate determination of the distance of fault zones or lithological boundaries from the tunnel face without any a priori information. By 3D seismic finite difference modelling we simulated a synthetic tunnel seismic survey that includes typical features encountered in tunnel construction. The developed prediction sequence was tested on these data and later successfully applied to two different tunnel data sets acquired at the Gotthard Base Tunnel (Switzerland) and during the construction of the ‘Neuer Schlüchterner Tunnel’ close to Fulda (Germany).

Gotthard Base Tunnel – Tunnelling in the influence zone of two concrete arch dams /

AbstractThe determination of the alignment of the Gotthard Base Tunnel made sure not to tunnel directly under the dams of the Vorderrhein AG power stations. The Gotthard Base Tunnel will, however, have to be driven through the zone, which could affect the three arch dams at Nalps, Santa Maria and Curnera.The Zeuzier dam in Wallis (Valais) suffered severe damage in 1978 as the result of drainage of the rock mass for an investigation tunnel being driven in the vicinity. The cracks in the dam led to years of operational limitations and required extensive repair works.A whole range of measures was undertaken for the Gotthard Base Tunnel in order to avoid a repetition. The construction of the tunnel near the dam was the subject of years of preparatory work. Since the end of 2005, the southward drive from Sedrun has been near the Nalps dam and since the middle of 2009, that from Faido has been within the zone influencing the Santa Maria dam. Long‐term safe operation of both dams has to be ensured despite the near approach of the tunnelling works. Although the task is the same for both dams, completely different solutions were chosen. The following paper explains the reasons for thisBei der Festlegung der Linienführung für den Gotthard Basistunnel wurde darauf geachtet, dass die Stauanlagen der Kraftwerke Vorderrhein AG nicht direkt unterfahren werden. Der Gotthard Basistunnel muss jedoch im Einflussbereich der drei Bogenstaumauern Nalps, Santa Maria und Curnera vorgetrieben werden.Die Staumauer Zeuzier im Wallis erlitt im Jahr 1978 als Folge der Gebirgsentwässerung eines in der Nähe vorgetriebenen Sondierstollens schwere Schäden. Die Risse in der Mauer führten zu jahrelangen Betriebseinschränkungen und lösten umfangreiche Sanierungsmaßnahmen aus.Am Gotthard Basistunnel wurde somit eine ganze Anzahl von Maßnahmen getroffen damit ein solcher Zwischenfall sich nicht wiederholt. In jahrelangen Vorarbeiten wurde der Tunnelbau in der Nähe der Stauanlagen vorbereitet. Seit Ende 2005 befindet sich der von Sedrun ausgeführte Südvortrieb im Bereich der Stauanlage Nalps und seit Mitte 2009 jener von Faido aus im Einflussbereich der Stauhaltung Santa Maria. Bei beiden Mauern muss langfristig ein sicherer Betrieb der Stauanlagen, unter Berücksichtigung des in der Nähe vorgenommenen Tunnelvortriebs, gewährleistet werden. Obwohl die Aufgabenstellung in beiden Fällen identisch war, wurden schließlich für die zwei Mauern zwei komplett unterschiedliche Lösungsansätze gewählt. Der nachfolgende Beitrag zeigt die Gründe dazu auf.

The Interaction Between Shield, Ground and Tunnel Support in TBM Tunnelling Through Squeezing Ground

When planning a TBM drive in squeezing ground, the tunnelling engineer faces a complex problem involving a number of conflicting factors. In this respect, numerical analyses represent a helpful decision aid as they provide a quantitative assessment of the effects of key parameters. The present paper investigates the interaction between the shield, ground and tunnel support by means of computational analysis. Emphasis is placed on the boundary condition, which is applied to model the interface between the ground and the shield or tunnel support. The paper also discusses two cases, which illustrate different methodical approaches applied to the assessment of a TBM drive in squeezing ground. The first case history—the Uluabat Tunnel (Turkey)—mainly involves the investigation of TBM design measures aimed at reducing the risk of shield jamming. The second case history—the Faido Section of the Gotthard Base Tunnel (Switzerland)—deals with different types of tunnel support installed behind a gripper TBM.

On the propagation characteristics of tunnel surface‐waves for seismic prediction

ABSTRACTTo increase the safety and efficiency of tunnel constructions, online seismic exploration ahead of a tunnel has become a valuable tool. One recent successful forward looking approach is based on the excitation and registration of tunnel surface‐waves. For further development and for finding optimal acquisition geometries it is important to study the propagation characteristics of tunnel surface‐waves. 3D seismic finite difference modelling and analytic solutions of the wave equation in cylindrical coordinates reveal that at higher frequencies, i.e., if the tunnel‐diameter is significantly larger than the wavelength of surface‐waves, these surface‐waves can be regarded as Rayleigh‐waves confined to the tunnel wall and following helical paths along the tunnel axis. For lower frequencies, i.e., when the tunnel surface‐wavelength approaches the tunnel‐diameter, the propagation characteristics of these surface‐waves are similar to S‐waves. We define the surface‐wave wavelength‐to‐tunnel diameter ratio w to be a gauge for separating Rayleigh‐ from S‐wave excitation. For w > 1.2 tunnel surface‐waves behave like S‐waves, i.e. their velocity approaches the S‐wave velocity and the particle motion is linear and perpendicular to the ray direction. For w < 0.6 they behave like Rayleigh‐waves, i.e., their velocity approaches the Rayleigh‐wave velocity and they exhibit elliptical particle motion. For 0.6 < w < 1.2 a mixture of both types is observed. Field data from the Gotthard Base Tunnel (Switzerland) show both types of tunnel surface‐waves and S‐waves propagating along the tunnel.

Materials management at the Gotthard Base Tunnel – experience from 15 years of construction

AbstractThe management of the handling of approximately 25 m tonnes of spoil material from the Gotthard Base Tunnel was and still is an enormous challenge. A permit system for concrete mixes and continuous testing of the excavated raw material and the grading of the broken rock ensure that as much spoil material as possible can be reused for the production of high‐quality concretes and shotcretes for the construction of the tunnel.Although a generous margin has been applied to forecasts in materials management since the start of the project, extensive alterations were necessary to the plans and facilities for materials management to deal with the actual development of the project. The main reasons for this were changes to the schedule of material production and requirements and changes of material quantities within and between the individual sections. It has proved possible so far to avoid materials management becoming a factor holding back the performance.Die Bewirtschaftung der rund 25 Mio. Tonnen Ausbruchmaterial des Gotthard‐Basistunnels war und ist eine enorme Herausforderung. Ein Zulassungssystem für Betonrezepturen sowie laufende Prüfungen am ausgebrochenen Rohmaterial und den aufbereiteten Gesteinskörnungen stellen sicher, dass möglichst viel Ausbruchmaterial wiederverwertet wird und damit hochwertige Betone und Spritzbetone für den Tunnelbau hergestellt werden. Obwohl seit Projektbeginn in der Materialbewirtschaftung mit großzügigen Prognosebandbreiten gearbeitet wurde, waren aufgrund der tatsächlichen Projektentwicklung umfangreiche Anpassungen an den Konzepten und Anlagen der Materialbewirtschaftung erforderlich. Die Hauptgründe dafür sind zeitliche Verschiebungen von Materialanfall und ‐bedarf sowie Veränderungen der Materialmengen innerhalb und zwischen den einzelnen Teilabschnitten. Bisher ist es gelungen die Materialbewirtschaftung nicht zum leistungsbestimmenden Faktor werden zu lassen.

The use of open tunnel boring machines in squeezing rock in the Gotthard Base Tunnel

AbstractIn the Faido section of the Gotthard Base Tunnel (GBT), two open gripper tunnel boring machines (TBM) with a bored diameter of 9.4 m are each driving about 11 km of single‐track tunnel. No extensive fault zones were expected in the entire section except for the Piora‐Mulde. A special tunnel was driven to investigate the Piora‐Mulde, from which investigation boreholes were drilled down to tunnel level. Because of the finding of sugar‐grain dolomite, the tunnelling work was tendered by drilling and blasting as well as mechanically, but the tenders led to the award being based on TBM tunnelling.In the course of construction, a stretch some hundreds of metres long unexpectedly had to be bored through squeezing rock, where the temporary support was destroyed and the West TBM and backup almost became jammed. This article describes the experience from the mechanical tunnelling of the Faido section and then gives details about the intended support, the design of the TBM, the difficulties that arose and the experiences gained.Im Teilabschnitt Faido des Gotthard Basis Tunnels (GBT) fahren zwei offene Gripper Tunnelbohrmaschinen (TBM) mit einem Bohrdurchmesser von 9, 4 m und einem Achsabstand von 40 m eine Strecke von zweimal rund 11 km Einspurtunnel (EST) auf. Im gesamten Teilabschnitt wurden mit Ausnahme der Piora‐Mulde keine mächtigeren Störzonen erwartet. Zur Erkundung der Piora‐Mulde wurde ein eigener Stollen vorgetrieben, von dem aus Erkundungsbohrungen auf Tunnelniveau abgeteuft wurden. Aufgrund des Ausschlusses von zuckerkörnigem Dolomit wurde sowohl Sprengvortrieb als auch maschineller Tunnelvortrieb ausgeschrieben. Die Offerten führten zu einer Beauftragung des TBM‐Vortriebs.Im Zuge der Ausführung wurde unerwartet ein mehrere hundert Meter langer Bereich mit druckhaftem Gebirge aufgefahren, in dem die Außenschale zerstört wurde und es nahezu zum Verklemmen der TBM West und deren Nachläuferkonstruktion kam. Im vorliegenden Beitrag werden die Erfahrungen des bisherigen maschinellen Vortriebs im Teilabschnitt Faido beschrieben. Im Detail wird auf den vorgesehenen Ausbau, die Auslegung der TBM, die aufgetretenen Schwierigkeiten und auf die daraus gewonnenen Erfahrungen eingegangen.

Geomechanics and Tunnelling 5/2009

AbstractProceedings of the 58th Geomechanics ColloquiumGrouting in RockJ. Linortner, G. Jung & G. Zenz: Design and construction of the grout curtain for Ermeneck HPP DamI. Reichl, J. Seegers, M. Lotter & N. Prosser: Ground improvement in carstic rock (Irlahüll Tunnel, DB Nürnberg‐Ingolstadt)A. Vigl & R. Gerstner: Grouting of pressure tunnels for Hydro Power PlantsB. Stille, H. Stille, G. Gustafson & S. Kobayashi: Experiences with a ”Real Time Grouting Control Method”K. Breit: Complex grouting projects in Austria and abroad; a Contractor's view R. Pollard: The use of TPA at the Dounreay shaft isolationProjects in AustriaP. Schwab, B. Präsent & J. Dissauer: Motorway Bruck S35 BL22 ”Tunnel excavation in serpentinite”C. Gamper: H8 Tunnel Jenbach, Brenner railway axis northern feeder line to the Brenner Base Tunnel, hydroshield excavationH. Westermayr, M. Höllrigl, J. Daller & V. Mihailov: Construction of the 2nd tube of the Pfänder Tunnel by tunnel boring machine (TBM)K. Czopak & E. Neumüller: Contract LT 33 Tunnelling in hard rock on the middle section of the new Lainzer Tunnel in ViennaH. Goldberger & A. Stärk: Lainzer Tunnel Lot LT31 – side wall drift in ViennaM. Bauer, F. Püringer & M. Eder: Tram Line Harter Plateau – Tunnelling beneath Linz Central StationDeep TunnelsM. John & B. Mattle: Review of determining rock mass behaviour for tunnels with high overburdenA. Preh & R. Poisel: Cherry pit failure of tunnels – new understanding of the failure mechanismS. Kainrath‐Reumayer, G. Gschwandtner & R. Galler: The convergence‐confinement‐method as an auxiliary tool for the design of deep tunnelsN. Radoncic, W. Schubert & B. Moritz: Ductile lining design G. Lombardi, M. Bettelini, M. Neuenschwander & A. Pancierer:Gibraltar tunnel: design update and geomechanical challengesJ. Gollegger, M. Rausch & A. Priller: Application of open TBMs under squeezing ground conditions in the Gotthard Base TunnelG. Harer, D. Handke& L. Herwig: Tunnelling methods for zones of squeezing rock mass behaviour at the KoralmbahnReuse of Tunnel Excavation MaterialD. Resch, R. Galler, F. Ebner & K. Lassnig: Excavation material in tunnelling – High quality raw material?R. Lieb: Material management at the Gotthard Base Tunnel – findings from 15 years of experienceG. Harer & P. Pichler: Effectively decreasing the requirement for landfill sites at the Koralmtunnel – SolutionsA. Fromm, B. Schreitl & C. Kitzler: S1 Tunnel Donau‐Lobau – Recycling the excavation materialH.‐G. Haid, H. Hammer: Katzenbergtunnel – conditions for recycling excavation material from the environmental and authorization point of viewJ. Burdin: Material management for the project Lion‐Turin‐RaillinkK. Mittermayr, M. Steiner & W. Ramspacher: A26 – excavation material, transport, recycling

Consolidation settlements above deep tunnels in fractured crystalline rock: Part 2—Numerical analysis of the Gotthard highway tunnel case study

A recent high precision levelling survey several hundred metres above the Gotthard highway tunnel in central Switzerland has revealed up to 12 cm of subsidence. Subsidence of this magnitude in relation to a deep tunnel excavated in fractured crystalline rock is unexpected and appears to be related to large-scale consolidation resulting from groundwater drainage and pore-pressure changes around the tunnel. This is a concern for the 57 km long Gotthard Base Tunnel currently under construction, as its alignment will pass through similar rock mass conditions and under several important concrete dams. Thus, the assessment and prediction of potential surface displacements are of paramount importance. This paper, the second of two parts, presents results from an extensive and thorough numerical modelling study focussing on the hydro-mechanical processes responsible for the measured subsidence above the Gotthard highway tunnel. Results derived from 2-D continuum and discontinuum numerical models (i.e. finite- and distinct-element, respectively) show that discrete fracture deformation and poroelastic consolidation of the intact rock matrix both contribute to the observed subsidence. Moreover, the explicit inclusion of geological structures in the distinct-element models enabled a better fit of the width and shape (asymmetry, small-scale inflections, etc.) of the measured subsidence profile to be achieved. Continuum models, although able to reproduce the maximum settlement when constrained by field observations, could not reproduce the asymmetric shape of the subsidence profile leading to under prediction of vertical displacements away from the centre of the subsidence trough.

Consolidation settlements above deep tunnels in fractured crystalline rock: Part 1—Investigations above the Gotthard highway tunnel

Surface subsidence associated with tunnelling in fractured crystalline rock masses is rarely considered to be large enough to be a cause for concern. Recent high precision levelling measurements along the Gotthard Pass road in Central Switzerland, however, have revealed up to 12 cm of subsidence along sections that pass several hundred metres above the Gotthard highway tunnel. Large-scale consolidation associated with pore-pressure reduction in the rock mass arising from tunnel drainage is believed to be the contributing mechanism. Although these settlements may appear to be small compared to those associated with groundwater or oil and gas withdrawal from more compliant porous media, they are large enough to adversely affect the structural integrity of sensitive concrete structures on the surface (e.g. thin-arch concrete dams). This is a concern for the 57 km long Gotthard Base Tunnel, which is currently under construction, as it will pass through similar geological conditions as the Gotthard highway tunnel and underneath several important dams. The prediction of the expected settlements requires a more complete understanding of the processes underlying the settlements than exist at present. This paper (Part 1) and a companion paper (Part 2) are a contribution towards this end. In Part 1 we examine the question of consolidation in fractured crystalline rock, introduce the geodetic data and the geological setting of the subsidence associated with the Gotthard highway tunnel. Possible mechanisms for the consolidation are described and estimates obtained for the key hydro-mechanical parameters that govern their action, such as the normal stiffness of fault zones. These data are used to condition analytical scoping calculations of expected subsidence based upon poro-elastic theory, and to provide input for a series of numerical models used to obtain a more detailed understanding of the data, which are presented in Part 2.

Rayleigh-to-shear wave conversion at the tunnel face — From 3D-FD modeling to ahead-of-drill exploration

For safe tunnel excavation, it is important to predict lithologic and structural heterogeneities ahead of construction. Conventional tunnel seismic prediction systems utilize body waves (P- and S-waves) that are directly generated at the tunnel walls or near the cutter head of the tunnel boring machine (TBM). We propose a new prediction strategy that has been discovered by 3D elastic finite-difference (FD) modeling: Rayleigh waves arriving at the front face of the tunnel are converted into high-amplitude S-waves propagating further ahead. Reflected or backscattered S-waves are converted back into Rayleigh waves which can be recorded along the sidewalls. We name these waves RSSR waves. In our approach, the front face acts as an S-wave transceiver. One technical advantage is that both the sources and the receivers may be placed behind the cutter head of the TBM. The modeling reveals that the RSSR waves exhibit significantly higher amplitudes than the directly reflected body waves. The excavation damage zone causes dispersion of the RSSR wave leading to multimodal reflection response. For the detection of geologic interfaces ahead, RSSR waves recorded along the sidewalls are corrected for dispersion and stacked. From the arrival times, the distance to the S-S reflection point can be estimated. A recurrent application, while the tunnel approaches the interface, allows one to quantify the orientation of the reflecting interfaces as well. Our approach has been verified successfully in a field experiment at the Piora adit of the Gotthard base tunnel. The distance to the Piora fault zone estimated from stacked RSSR events agrees well with the information obtained by geologic surveying and exploratory drilling.

Spatial predictions of geological rock mass properties based on in-situ interpretations of multi-dimensional seismic data

The article presents a statistical approach to characterize and predict engineering geological conditions in the up to 2000 m deep Faido tunnel and Gotthard base tunnel in Switzerland. Seismic investigations were conducted to improve the technology of interpreting seismic tomographic images. Overall, the goal of this study was to predict spacial maps of geological rock mass properties, such as, uniaxial compressive strength or total fracture spacing, by using up to six seismic features in combination, e.g., compression-wave and shear-wave velocities and dynamic Poisson's ratio. Self-Organizing Mapping (SOM), an artificial intelligent method, was used for the purposes of interpreting multi-dimensional geophysical attributes derived from seismic profiles of tomographic images along tunnel sidewalls. The SOM-method was applied in the Faido tunnel to delineate complex physical relations between the geological and seismic parameters. Then, the method was applied to predict geological properties around a segment of the Gotthard base tunnel with unknown geological–geotechnical conditions. The results illuminate that correlation analyses (pairwise parameter classification) are substantially less powerful than the SOM-method (multi-parameter classification) in order to interpret geological features from seismic in-situ data. Moreover, predicted spatial distributions of the total fracture spacing and the uniaxial compressive strength, for example, corresponded well with drill core and tunnel mapping results. The SOM-approach was a helpful tool for practitioners in predicting zones of instabilities and geological complexity during underground excavation processes of the Gotthard base tunnel. It is suggested to use such an interpretation method as decision support for purposes of sub/surface exploration and long-term geophysical monitoring of large-scale geoengineering projects, such as, disposals of nuclear waste and greenhouse gases or geopower plants for renewable energy (geothermal, biosoils).

Seismic investigations of the Piora Basin using S-wave conversions at the tunnel face of the Piora adit (Gotthard Base Tunnel)

Seismic investigations of the Piora Basin using S-wave conversions at the tunnel face of the Piora adit (Gotthard Base Tunnel)

Estimation of the rocks statistical parameters from traveltime measurements

In this paper the method for estimating the statistical parameters of the medium from traveltime measurements of refracted waves is applied to study the statistical characteristics of crystalline rocks at the Multifunctional Station Faido (Gotthard Base Tunnel, Switzerland). The method is based on the geometrical optics (GO) approximation. A covariance function for traveltime fluctuations has been obtained by considering quasihomogeneous fluctuations of sound velocity in a plain-stratified medium. Strongly anisometric (having unequal dimensions in different directions) random inhomogeneities were embedded in this medium. To estimate the statistical parameters around the tunnel, the traveltime fluctuations are calculated. It is assumed that each observation of traveltime-distance relation for a given shot-receiver group corresponds to a particular realization of a medium statistical ensemble. By calculating the variance and the zero cross intervals of the first derivative of traveltime fluctuations, the standard deviation of the velocity fluctuations and the characteristic horizontal scale of the inhomogeneities are estimated. Although the method allows to obtain the characteristic lengths of the inhomogeneities in vertical as well as in horizontal direction, the limited offset of the field data made it only possible to measure the latter. The estimated horizontal characteristic scale is about 13 m, which is reasonably close to the direct geological measurements in the studied region, where quartz lenses are dominant among the inhomogeneities. The standard deviation of the velocity is estimated as 4.5%, which might be caused by the fractured structure around the tunnel and also by the fault zone near the study area.

In situ seismic investigations of fault zones in the Leventina Gneiss Complex of the Swiss Central Alps

Abstract Underground seismic tomography investigations have been carried out in the Faido access tunnel of the Gotthard Base Tunnel, Switzerland. Velocity measurements were made over a total length of 2651 m of the adit with the tunnel seismic prediction system, ISIS (Integrated Seismic Imaging System). ISIS provides high-resolution seismic imaging, using an array of rock anchors equipped with 3D-geophones. The first onsets of the compressional and shear waves were used for tomographic inversion. Two-dimensional seismic-velocity models reveal a disturbed zone between 2 and 3 m inward from the tunnel wall, characterized by strong variations from 3500 to 5800 m s −1 in compressional wave velocity V P , and from 2000 to 3000 m s −1 in shear-wave velocity V S . High-velocity zones correspond to quartz lenses, and low velocities mainly indicate fractured rock. Beyond the excavation disturbance zone, the variations in seismic velocities are generally smaller. The tomographic image of the rock mass also revealed two major fault zones composed of cataclastic shear planes surrounded by wider fracture zones. These structural characteristics are also useful for the prediction of cataclastic zones at other sites.

Tunnelling in high overburden with reference to deep tunnels in Switzerland

Due to its topographic conditions, Switzerland has a long and fairly broad history of experience with tunnelling in high overburden. Railway tunnels built between 1870 and 1900 like the first Gotthard, the Simplon and the Loetschberg tunnel had overburden of more than 1500 m. The Furka Base Tunnel, built in the early 1980s, and the recently commissioned Vereinatunnel also experienced overburden in the order of 1500 m. Both the Loetschberg Base Tunnel and the Gotthard Base Tunnel presently under construction will reach overburden of more than 2000 m, what not only imposes high in situ stress in the rock, but also results in other phenomena such as high temperatures, high water pressures, etc. Based on thorough geological investigations which already pay attention to the future excavation method the setting up of so-called hazard scenarios lay at the base of all rock mechanical investigations. For the Gotthard Base Tunnel hazard scenarios were defined which are typical for deep tunnels, such as (among others) rock burst, squeezing, face instability, fault zones. These hazards were already encountered in the construction of the Furka Tunnel but the tunnelling technologies have since seen a remarkable development especially in the use of TBM. The definition of the adequate rock support means and their application in relevance to the expected deformation behaviour is far more critical with TBM than in conventionally bored tunnels. First experience with a TBM was gained at the Vereinatunnel, where both technologies were applied, based on a yielding/resisting principle for the rock support, which was developed based on the experience made at the Furkatunnel, and which afterwards also was used for the Gotthard Base Tunnel. At the Gotthard the longer part will be excavated with TBMs thus underlining the increasing importance of this technology, a tendency taking place for deep tunnels also outside Switzerland. Together with the increased importance of TBMs in the excavation of deep tunnels one also sees a substitution of the classical rock support means for the yielding/resisting principle like sprayed concrete, rockbolts and steel arches with precast elements - introducing specific new problematics such as a high stiffness of the rock support/lining with no yielding potential, etc. Aside from the rock mechanical issues deep tunnelling has additional specific problems, such as ie special climatic conditions due to the hot rock temperature and water inflows - quite often loaded with aggressive dissolved contents - under high pressure. To tackle both fields a new approach has been developed at the Gotthard Base Tunnel: materials and systems permanently applied in the tunnel must run a prequalification test, designed for these very specific conditions. The test procedure not only reflects the demanding conditions but also the requested life cycle of 100 years without major maintenance and may be therefore find its application also for other deep tunnels. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

New developments in automated tunnel surveying systems

Surveying requirements for tunnel construction have changed little since the first tunnels were dug many centuries ago, such as leaving and arriving at the required place. Over the years the techniques and facilities to achieve this have developed considerably and also the cost constraints within which they should be achieved. One of the most critical factors for the successful construction of a tunnel is that the finished excavation is fit for the purpose for which it was designed. For this to be achieved the tunnel must follow the designed axis (route) and be of the correct size and shape. Nowadays these factors are easy to design in an engineering design office with the latest CAD facilities, which can produce precise designs for complex shapes and exact three-dimensional axes with precise absolute coordinates. However to translate this complex design data into a finished tunnel still relies on the application of surveying technology which due to the underground environment and confined spaces is a unique challenge in itself. The development of computerised total stations with increased functionality such as automatic target recognition, automatic target tracking, power search and remote controls has provided the hardware for increasingly accurate traditional survey tasks such as the base survey over land for the start and end reference points of the tunnel and the establishment of reference stations within the tunnel as the tunnel progresses. But what about the actual tunnel construction? TBM manufacturers have always been at the forefront of tunnel guidance systems due to the critical nature of the control of the direction and elevation of the TBM and associated support in the backup. The complexity of ring build and alignment correction has been helped immensely by the advent of computer software to work out the correct order and design alignments. The more varied and flexible methods of tunnelling have traditionally still relied on the old fashioned methods for setting out the direction and dimensions of the tunnel. However, this has been steadily changing over a number of years with the latest systems being very technically advanced. The latest of this type of systems is the tunnel measurement system (TMS) from Leica Geosystems. This system can be divided into two packages, firstly the LEICA TMS SETOUT and secondly the LEICA TMS PROFILE. This software is designed as a package to be used together during the tunnelling process to provide continuously updated records of progress and performance. At the construction stage the system provides a seamless translation of the complex design data into practical set out information at the face. This information is available to the tunnelling crew at anytime through the creation of task orientated software for the total station and the use of the remote control unit. The other area of advance is in the use of laser scanning technologies for the measurement of the tunnel at various phases through the construction. On the Gotthard Base tunnel in Switzerland this technology is being used to evaluate the waviness of the shotcrete before the application of the waterproof membrane and cast in situ concrete lining. One additional factor for the successful application of all modern surveying technologies is the handling of data through imports and exports between the various different applications. For the hardware to really effective it should be able to use a standard system or format so that all applications can use the same absolute data for the more efficient and safer excavation of underground space. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

The construction of Gotthard Base Tunnel for high speed rail

Switzerland's national government and parliament have approved construction of two new railway axes through the Alps. This is the 'New Alpine Transversal (NEAT)' scheme with the Gotthard and Loetschberg axes. The project will provide a vital link between the high speed rail networks of Germany and Italy, and produce a much-needed reduction in the heavy road traffic over the Alps by switching it to the rails. The longest NEAT tunnel, the Gotthard Base Tunnel (GBT), is about 57 km long. The tunnel consists of two parallel single-track tubes, which are connected by crosscuts at about 300 m intervals. The exceptional length of the GBT requires that special consideration be given to achieving both efficient construction and adequate ventilation under traffic. In order to achieve an acceptable over-all construction time, intermediate points of attack were conceived. Besides providing additional points for concurrent tunnel heading, they will serve as ventilation inlets and outlets once the tunnel is under traffic. The three intermediate points of attack have been topographically arranged to divide the tunnel into sections of roughly equal length and to geologically difficult sections to be tackled at an earlier stage of the tunnel project. The Sedrun and Faido sections each include a multifunctional station (MFS). In the event of an accident they provide safe rooms for passengers. Fresh air will reach them via the access galleries. Smoke can be extracted the same way, separated from the fresh air. In the MFS's special emergency train stops are linked by a gallery system to enable passengers to transfer from one tube to the other. Trains will be able to switch from one tube to the other by using a tunnel crossroad. It will also to be possible to close individual sections of the tunnel tube between the portal and the emergency stop or between the emergency stops themselves for maintenance. The maintenance schedule and the high demands to be met by the rail technical equipment are designed to reduce disturbances to a minimum. At the Gotthard axis, not only the Base Tunnel, but the entire axis had to be planned and designed to enable high-speed passenger trains to travel at speeds of 200-250 km/h, and freight trains to travel at 140 km/h. As a result the tunnel portals must be built at an elevation of 600-800 m lower than those of the existing Gotthard Railway Tunnel. This leads to a maximum overburden of up to 2300 m, one of the geotechnical challenges of this tunnel. Nearly 90% of the entire drive can be headed by using tunnel boring machines. The remaining part of the section in Sedrun will be excavated by conventional means, due to unfavorable geotechnical conditions in this section. In 1996 the construction began at the Sedrun intermediate access-gallery. Since 2001 the four main lots of the tunnel tubes are under construction. The paper deals with the latest stage reached as well as what the future will bring. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Tunnelling in changing geology

Permanent technological improvements in mechanized tunnelling enabled new tunnelling projects, which were not realizable only a few years before. Considered to be the greatest challenges are projects consisting of mixed geologies, of high-strength abrasive hard rock, as well as unstable loose rock with clogging tendencies and high groundwater pressure. This requires a regular and professional maintenance concept for all tunnelling components participating directly and indirectly as well as an efficient construction operation for the support of the tunnel boring machine. Projects crossing soil, weathered and massive rock are challenging because of totally different machinery requirements between EPB and rock drilling. On one hand the tunnel boring machine should support the tunnel face to avoid settlements using a cutterhead which allows soil to enter the excavation chamber easily. On the other hand, the hard and massive rock requires a close cutter disc spacing and strong cutter head structure. Problems were encountered especially in mixed ground conditions when soil and rock run through the tunnel face. The result is extremely high wear on cutting tools as well as on the cutterhead structure itself and finally long downtimes for tool changes and cutterhead repair. New wear phenomena on the cutter discs were encountered and technical solutions developed. The design of a TBM in such conditions is a compromise between both excavation methods. To improve job site performance, all geological parameters and machine behavior have to be permanently analyzed. Possible measures like certain design features, conditioning of soil, special cutter and driving parameters will be pictured. Paris, Singapore, Porto and St. Gotthard/Switzerland are only some examples, where - through intensive technical support from the side of the TBM supplier - mechanized tunnelling is managed in extremely difficult geological and hydrological conditions. A sophisticated road tunnel is currently built west of Paris, which will complete the freeway circuit A86. Designed as a two-story road tunnel it is approximately 10 km long with a bore diameter of 11.57 m. Geological conditions of this area consist of heterogeneous soils, which cover the entire spectrum of cohesive and rolling soil to hard rock. The machine concept provides a combination of Mixshield and EPB-Shield that can host both conveyor systems at the same time - screw conveyor as well as feeder and pressure lines for the liquid operation. Singapore is currently replacing the existing sewage system (DTSS) up to 50 m deep, to comply with the requirements of a world metropolis in the 21st century. It is located in very difficult heterogeneous ground conditions: granite of up to 190 MPa, slightly to strongly disturbed clay, silt and sandstones as well as conglomerates, Kallang formation, consisting of soft clays and loose sands, old alluvium, additionally the hydro-static water pressure is of up to 4 bar. The Joint Ventures ordered Herrenknecht EPB-Shields equipped with cutterheads specially for hard granite formations. A 70 km extensive metro system is currently constructed in Porto, partially running underneath the city center of Porto. The tunnel boring machines have to face changes between very hard granite and loose rock as well as difficult hydrological conditions. In Switzerland four Herrenknecht tunnel boring machines are tackling the Gotthard from the north and the south for a distance of 75 km. After its completion in 2014, the Gotthard Base Tunnel with its 2 · 57 km will be the longest traffic tunnel of the world. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Fuzzy rule-based expert system for short-range seismic prediction

In Switzerland, the 57 km long Gotthard base tunnel is being built as part of the AlpTransit project with a maximum overburden of 2000 m . Because of the difficult geological situation, an exploratory tunnel was set up to explore the Piora-Mulde, a possibly unstable carbonate rock zone in south Central Switzerland. A geophysical forecast system called tunnel seismic prediction has been designed by Amberg Measuring Technique Ltd. to explore the geology during the tunnelling process. But several difficulties occurred in interpretation of the seismic data in terms of geological forecasts. This paper describes a simple approach to geological interpretation of seismic diffraction stack images by using fuzzy logic. A fuzzy rule-based expert system was developed to classify lithologic and tectonic rock units by interpreting those seismic images.

Numerical modelling of three-dimension stress rotation ahead of an advancing tunnel face

As underground excavations and construction works progress into deeper and more complex geological environments, understanding the three-dimensional redistribution of excavation-induced stresses becomes essential given the adverse consequences such stresses will have on the host rock strength and the subsequent excavation stability. This paper presents the results from a detailed three-dimensional finite-element study, which explores near-field stress paths during the progressive advancement of a tunnel face. These results demonstrate that as the tunnel face approaches and passes through a unit volume of rock, the spatial and temporal evolution of the three-dimensional stress field encompasses a series of deviatoric stress increases and/or decreases as well as several rotations of the principal stress axes. Particular emphasis is placed on the rotation of the principal stress axes as being a controlling factor in the direction of fracture propagation. If this orientation changes in time, i.e. during the progressive advancement of the tunnel face, the type of damage induced in the rock mass and the resulting failure mechanisms may also vary depending on the type and degree of stress rotation. The significance of these effects is discussed in terms of microfracture initiation and propagation, brittle fracture damage and rock strength degradation. Further analysis is also presented for varying tunnelling conditions including the effects of tunnel alignment with respect to the initial in situ stress field, excavation sequencing and elasto-plastic material yielding. Implications with respect to the new Gotthard base tunnel, currently under construction in Switzerland, are presented using examples from the nearby Furka tunnel.