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ABSTRACT An open gripper TBM continuously records gripper forces. This enables to determine the rock mass stiffness of the surrounding ground by using the gripper as the pressure unit of a plate load test. The gripper tests have been executed in the exploratory tunnel of the Brenner Base Tunnel project in Austria. Two different in situ test procedures have been developed upon constant agreement with the owner, the construction company and the site supervision team of the project. Evaluation of the rock mass stiffness (deformation moduli) indicated good agreement with the characteristic stiffness values for the rock mass from the lab tests. Numerical studies have been executed to validate the depth of influence for the gripper tests. The in situ test data and the results of the gripper test evaluations are discussed and an interpretation on the meaningfulness of the different results are given. Finally, suggested modifications on the gripper-TBM and an outlook on further research requirements on the evaluation of the monitored gripper data are given. 1. INTRODUCTION The Brenner Base Tunnel (BBT) project is a railway tunnel between Austria and Italy through the Alps. Including the Innsbruck railway bypass the entire tunnel system is 64 km long and it represents the longest underground rail link in the world. The system consists of two single-track main tunnel tubes 70 meters apart. A service and drainage gallery lies about 10–12 meters deeper and between the main tunnel tubes (see Fig. 1). This gallery is constructed ahead of the main tunnels and will be used as an exploratory tunnel for them. The construction lot Tulfes-Pfons was awarded to the Strabag/Salini-Impregilo consortium in 2014. The construction lot includes 38 km of tunnel excavation work and consists of several structures such as a 15 km long stretch of the exploratory tunnel, which is excavated by an open tunnel boring machine (TBM) in advance of the main tunnel tubes.
Erharter, G. H. (Institute of Rock Mechanics and Tunnelling, Graz University of Technology) | Marcher, T. (geo.zt gmbh – poscher beratende geologen) | Reinhold, C. (Institute of Rock Mechanics and Tunnelling, Graz University of Technology)
Abstract The past decade has shown a rapid increase in the successful application of Machine Learning techniques for a variety of challenging tasks. Potential for this is also seen in the automatic rockmass behavior classification of tunnel boring machine (TBM) advance-data. This study compares the performance of two kinds of Artificial Neural Networks (ANN) - a Multilayer Perceptron (MLP) vs. a Long-Short-Term Memory (LSTM) Network - for this task. The data originates from the exploratory tunnel Ahrental " Pfons of the Brenner Base Tunnel which is currently under construction. The goal of gathering as much data as possible from the encountered geology is to transfer this knowledge from the exploratory tunnel to the main tunnel tubes. Results show that both ANNs are capable of classifying rockmass behavior only based on TBM advance data, however, the LSTM outperforms the MLP in several of the test-data samples. 1 Motivation The Brenner Base Tunnel (BBT) which is currently under construction, is a flat railway tunnel between Austria and Italy, connecting the cities Innsbruck and Fortezza. Including the Innsbruck railway bypass, the entire tunnel system through the Alps is 64 km long and is therefore the longest underground rail link in the world. The BBT consists of a system of two single-track main tunnel tubes, 70 meters apart, that are connected by crosscuts every 333 meters. A service and drainage gallery lies about 10 - 12 meters deeper and between the main tunnel tubes. During construction the service tunnel serves as an exploratory tunnel, which is driven in advance to gather relevant information about the geology and the expected rockmass behavior for the main excavation. The paper focuses on TBM - data from the 15km long exploratory tunnel "Ahrental – Pfons", which is part of the construction lot "Tulfes-Pfons". This construction lot includes 38 km of tunnel excavation work consisting of several structures such as emergency- and connection tunnels, ventilation structures and parts of the main tunnel tubes. The exploratory tunnel Ahrental-Pfons is driven with an open gripper TBM and 12km are already excavated (January 2019).
Abstract For the Kramer Tunnel, located in the west of Garmisch-Partenkirchen, Germany a reconnaissance tunnel was excavated in advance. This was necessary, because very inhomogeneous and partly very bad rock conditions were assumed and because major sections of the tunnel could not be explored with drillings due to topographic conditions. In the paper, the lessons learned from the reconnaissance tunnel are described. It specifies how to deal with the high water pressure in the main dolomite area, which safety measures are necessary in the Kramer Reverse Fault area (squeezing rock conditions) and how the heading can be carried out in a little explored rockslide area. 1 Project Garmisch-Partenkirchen is a well-known touristic centre in the northern Alps in Germany. In order to reduce the traffic within of Garmisch-Partenkirchen a relocation of the federal road B 23 is planned. The ringroad will pass Garmisch-Partenkirchen to the west under the Kramer mountain massif in the so-called Kramer tunnel. The design of the Kramer tunnel was carried out by the Staatliches Bauamt Weilheim and the ILF Beratende Ingenieure ZT GmbH, Innsbruck. The tunnel is designed as a single-tube tunnel with two-way traffic. With an axial distance of 45 m parallel to the tunnel tube a reconnaissance tunnel is excavated in advance which should be later used as a rescue tunnel. The construction of a reconnaissance tunnel was required in advance, since major sections of the tunnel could not be explored with drillings due to topographic conditions. Figure 1 shows a cross section through the traffic tube (main tunnel) and the rescue tunnel (reconnaissance tunnel) viewing to the south. The reconnaissance tunnel as well as the main tunnel are planned as drained tunnels. Only in the rockslide area both tunnels will be covered with an total sealing in order to avoid a lowering of the ground water level in this area for reasons of nature protection.
Abstract The tunneling industry is abuzz about the upcoming Brenner Base Tunnel Project. The tunnel route will run below the Alps with a maximum cover of 1,600 m. In such conditions, choosing the right tunneling method requires much forethought. Geology in high cover tunnels is often complex and TBM excavation often proves to be the optimal solution versus traditional methods like drill & blast. Both excavation methods are considered for this project. TBMs have proven themselves in deep tunnels worldwide, and are often faster, safer and more cost-effective than their conventional counterparts, as well as more customizable. This paper will explore the advantages of mechanical excavation and the best types of TBMs for the Brenner Base Tunnel Project, a comparison of mechanical excavation versus drill & blast, and important considerations for ground support in high cover conditions. A case study of the high-cover Olmos Trans-Andean Tunnel will also be presented. 1 Project Background 1.1 About the Brenner Base Tunnel The oft-mentioned Brenner Base Tunnel will become the longest underground structure in the world. The 64 km long tunnel will run from Tulfes/Innsbruck, Austria to Fortezza, Italy, making it arguably one of the longest – if not the longest – underground railway tunnels in the world. The tunnel route is a challenging one, traveling below the Brenner Pass in the Alps mountain range with a maximum cover of around 1,600 m. When complete in 2026, twin 8.1 m i.d. tubes will run single-track trains just 70 m apart from one another, connected every 333 m by cross passages. Excavation on the massive scale required to build the Brenner Base Tunnel necessitates customized machinery, skilled crews, and precision planning. Besides the challenges of variable rock types, groundwater and high overburden towards the center of the alignment, it will be prudent to plan for rock bursting and squeezing conditions. The route also crosses a major fault zone where the European and Adriatic tectonic plates press together. These anticipated conditions gave rise to the practical need for an exploratory tunnel, which will provide additional design and programming data for the excavation of the main tubes. Once completed, the exploratory tunnel will be used for drainage during construction and eventually as the service tunnel during operation. The exploratory tunnel could also carry power and data cables.
Küffler, Katharina (ILF Consulting Engineers) | Stackler, Friedrich (ILF Consulting Engineers) | Prager, Christoph (ILF Consulting Engineers)
Abstract Engineering geological and geotechnical experiences obtained from a major NATM-tunnel (BBT Brenner Base Tunnel, exploratory tunnels) and a TBM-tunnel (Stanzertal hydropower plant, headrace tunnel) in phyllitic rocks in Tyrol (Austria) are described herein, focusing on driving method-related challenges and technical solutions. Both tunnels are situated in similar rock masses consisting of thinly laminated quartz-phyllites with brittle fracture and fault zones. The reaction of the rock mass on the tunnel headings have been comparable in the sense of the prevailing failure mechanisms, but had different impacts on the tunnel headings depending on the tunneling method (conventional or mechanized heading). As a centralized résumé, it can be stated out, that the conventional tunnel drives offered great advantages at fault zone crossings, whereas the TBM-headings performed very well within good rock mass conditions attaining advance rates of about 50 m per 24h. 1 Introduction In the Tyrolean Alps (Austria), phyllitic rocks are widely spread and several tunnels for infrastructure and hydropower plants were performed in these kind of rocks, especially in the last 50–60 years. Most of them were built by conventional excavation methods (drill & blast resp. NATM), mechanized driven tunnels have been exceptional cases. However, especially for elongated tunnels the discussion on the most suitable tunneling method - in technical and economic reasons - always arises during planning phase weighing the pros and cons of each method. Decision-making is mostly accompanied with the assumption that the chosen method is indeed fitting for most parts of the geological and geotechnical setting along the tunnel alignment but not for all sections. By describing the experiences from conventionally driven tunnels and a TBM-heading (obtained from geological documentation and geotechnical supervision on site), this paper highlights some advantages and disadvantages of the different underground construction methods. Both above mentioned tunnels (BBT, Stanzertal HPP) have been planned applying the guidelines of Austrian Society for Geomechanics (ÖGG 2008, ÖGG 2013).
ABSTRACT: Extensive field studies show that the occurrence of deep-seated slope instabilities (i.e rockslides) is influenced by the discontinuity network and its intersection in relationship to the slope orientation. Furthermore in similar rock types slope failure can develop even at moderately inclined slopes, whereas the steeper slopes nearby remain stable over a time span of thousands of years. A possible explanation of this slope behavior may be attributed to rock mass anisotropies caused by geological discontinuities i.e. tensile joints, shear fractures, foliation planes and brittle fault zones. A deep-seated paragneissic rockslide located in the Tyrol (Austria) was investigated by means of detailed field investigations and numerical 2-D discontinuum modeling in order to study a) the failure initiation and formation processes of a persistent sliding zone, b) the structural influence on rockslide geometry, c) the interrelationship between the dip angle of the sliding zone and the pre-existing fracture network, d) the sliding mechanisms along this sliding zone and e) the internal deformation behavior that is induced from large-scale shear displacements. 1. INTRODUCTION The growth of settlement areas and new infrastructure projects in mountainous regions (e.g. buildings, traffic routes, tunnels, ski resorts, reservoirs), necessitate that established landslide simulation and prediction methods should be enhanced and new forecasting tools developed. Therefore, a fundamental understanding of the underlying landslide failure and deformation processes is crucial. Furthermore, geological-geotechnical and mechanical models based on limit equilibrium methods or numerical techniques are only reliable if the geometry of a landslide, the failure mechanism and the slope kinematics are sufficiently known. In soils, slope failure is predominately characterized by rotational slides (representing an isotropic material behavior) whereas slope failure in fractured rock masses (i.e. rockslides) often is controlled by geological structures such as foliation and bedding planes, brittle fault zones, meso-scale shear and tensile fractures. Discontinuity properties, i.e. orientation, size, density, persistence and infilling, and their spatial interrelationship to the slope controls the failure mechanism and the failure geometry at scales from meters to kilometers. Furthermore it was observed that in similar rock types slope instabilities often occur in less steeply inclined slopes, whereas the steeper slopes nearby remain stable over a time span of thousands of years. This anomalous slope stability behavior may result from a mechanical rock mass anisotropy which is caused by geological discontinuities. The highly relevant interrelationship between rockslide failure and structural geology was observed in several case studies in the past [1-3]. In this paper a well exposed crystalline rockslide referred to as "Kreuzkopf rockslide" was investigated by means of detailed field mapping, surface deformation measurements and numerical simulations. The Kreuzkopf rockslide comprises a volume of 3.2 million M and is part of several deep-seated landslides in the region of the Kaunertal (Austria). For example, one of them is the large-scale deep-seated creeping slope Hochmais-Atemkopf [4-7] nearby, comprising a volume of 264 million m and reaching a slope height of about 1000 meters. Field investigations and numerical modeling were performed to study processes and mechanisms of rock slide failure and sliding.
Krenn, F. (Geoconsult ZT GmbH) | Brandl, J. (Geoconsult ZT GmbH) | Kurzweil, H.-Ch. (Geoconsult ZT GmbH) | Galler, R. (Chair of Subsurface Engineering, Department Mineral Resources and Petroleum Engineering, University of Leoben)
ABSTRACT The Brenner Base tunnel with its approximately 55 km length is a highly complex and ambitious project. The geomechanical design of such a tunnel system demands flexible tools to be able to cope with adoptions and modifications. The following paper describes the preprocessing of the given data, the setup of the database and the structure of the information processing. The different data are processed in order to get the full information for the tunnel system for each meter. This extensive information is used by the cost estimators. Then the data are condensed to have the information in the structure needed for the geomechanical design reports. 1 INTRODUCTION The Brenner base tunnel with its approximately 55 km length is the main building of the railway corridor between Munich andVerona. The current phase of the project covers the design stage to obtain the approval notifications in Italy and Austria for the construction. The Brenner base tunnel is a twin tube system consisting of two single track tunnels with an axis distance of 70 meters which are connected every 333m via cross passages. Inside the main tunnels the drainage adit is situated approximately 10m deeper (distance top of rail main tunnel and top of track drainage adit). These multifunctional stations include cross-over systems to change the track (i.e. the tunnel tube). In the area of the multifunctional station Innsbruck there are the junctions for the interconnection tunnels to the already operating bypass tunnel Innsbruck. The joint-venture PGBB (Planungsgemeinschaft BRENNER BASISTUNNEL / Progettazione GALLERIA di BASE del BRENNERO) was awarded the main contract for the design in decembre 2004 and works since on this demanding project. 2 TASK AND CHOSEN APPROACH During the preliminary design, which is the basis for the approval documents, the client requested a geomechanical design according to the Austrian guideline (ÖGG 2001). Since the available geotechnical and geological data are under constant refinement by another contractor, and the excavation method, alignment and the projected construction logistics are subjected to adaptions in the ongoing design process, the geomechanical design has to be worked out parallel to the available input data. 2.1 Task The given task comprises the following main items:Primary support design for the subsurface buildings Support classification Preliminary design of the inner linings, especially regarding the reinforcement requirements Distribution of the support classes along the different alignments of the tunnel system according to the geotechnical homogeneous zones and the fault zones Summary of the support distribution The results are then condesed into the respective reports.As mentioned before, these main tasks have to be performed with a changing data basis; that means that the constant updating of the data basis and the results have to be kept in mind when choosing an appropriate approach. 2.2 Chosen Approach Usually the geomechanical design at that design stage is done rather rough – some "representative" cross sections are taken as the basis for the support classification and the support distribution.
Zangerl, C. (alpS - Centre for Natural Hazard Management) | Eberhardt, E. (Geological Engineering/EOS, University of British Columbia) | Schonlaub, H. (TIWAG-Tiroler Wasserkraft AG) | Anegg, J. (Geoinformation, Abteilung der Gruppe Bau und Technik)
ABSTRACT ABSTRACT: Slope deformation of deep-seated rock slides in crystalline rock is often characterized by phases of acceleration and deceleration. In some cases, these phases of low and high activity show a velocity difference of three orders of magnitude. Such slopes appear to present a hazard to inhabitants and infrastructure in the valleys below, but much uncertainty exists as to the nature of the observed episodic behavior and eventual deceleration and selfstabilization of the moving mass following periods of high acceleration, and whether such behavior will continue into the future or whether the potential for a brittle-type, rapid catastrophic failure exists. This paper presents two case studies from the Austrian Alps where the time-dependent/episodic behavior of two well monitored rockslides is analyzed, and the possible mechanisms contributing to their ability to re-stabilize are discussed. 1 INTRODUCTION Deep-seated rockslides located in Northern Tyrol (Austria) were investigated to study their kinematics and deformation behavior. Generally, rockslides are characterized by deformation along one or several shear zones where most of the measured total slope displacement localizes. Such shear zones contain fault breccias or gouges i.e. material that is newly formed through cataclasis and fragmentation of the rock during deformation and shearing, and which possesses soil-like mechanical properties. In some cases, rockslide rupture surfaces have been observed to form through the reactivation of favorably orientated pre-existing brittle fault zones of tectonic origin. The tectonically formed fault breccias or gouges in these cases act to fully or partly reduce the shear strength along the sliding zone. Less frequently, case studies have been presented where a heavily fractured rock slab has slid onto glacial deposits located on the lower half of the slope, suggesting slip magnitudes of several hundred meters (Brückl et al. 2004, Tentschert 1998, Lauffer et al. 1967).
ABSTRACT Glacial erosion brings many alpine valleys to limit equilibrium because of the steepened valley flanks. Instable slopes hold potential dangers, even though slowly creeping landslides as treated below can be observed and do seldom show surprising behavior as long as they do not accelerate. Nevertheless a sudden loss he stability can lead to uncontrollable movements with much higher velocities. Aim of the project presented here is to gain a better understanding of mass movements and the influences of different boundary conditions on slope displacement. A well monitored example for a slowly creeping landslide is the mass movement Hochmais- Atemkopf, situated in the Kaunertal, Tyrol, Austria. Based on a geological model a calculation model including four sliding masses has been developed. In addition, external effects were also taken into account to get a idea of their possible influences on stability and deformation. This paper presents a limit equilibrium analysis and the preliminary results of a numerical finite element study. INTRODUCTION The more than 1000 m high mass movement Hochmais- Atemkopf in the Kaunertal. Tyrol. Austria, see Figure 1 (BEV 1996) is one of several site under investigation The availability for over 40 years of a long-term monitoring program, including geodetical, geophysical, meteorological, geotechnical and geological data, provides a good data basis for a numerical analysis. Beneath the mass movement a hydropower reservoir is located, underlining the importance of the investigations. From geological and geophysical field investigations a geological model was developed (Bruckl et al. 2004). The slope is situated in a foliated, paragneissic rock unit of the Otztal-crystalline basement. Four individual sliding masses, bounded by (Figure in full paper) sliding zones were verified (Fig. 2). Resulting from postglacial sliding of a fractured paragneiss slab, the sliding zone between sliding mass 3 and 4 is situated in moraine deposit. The other sliding zones are located in fractured paragneiss, assuming a zone of densely fractured and crushed material. Below the four sliding masses stable fractured paragneiss is located, treated here as bedrock. The slope movements range from 3 to 4 per year in the lower part. The displacement vectors are mainly aligned parallel downwards the slope suggesting a translational sliding mechanism. Based on these results a computer model was build (Fig. 3). The two lines display the two different groundwater levels in the calculations. Even though a horizontal groundwater level is not a realistic assumption in this case, it allows to demonstrate the effects of (Figure in full paper) MEASUREMENTS The slope is observed geodetically, five of the geodetic points (spheres), see Figure 4 and the storage water level are measured frequently. For each of the recorded points a monthly moving mean is calculated. In the exploration adit (gray line, Fig. 4) deformation between the underlying, more stable rock (sliding mass 3) and sliding mass 4 is measured with a wire extensometer and recorded automatically (Tentschert 1998). Also the initiations of the different sliding zones are displayed in the figure.
ZUSAMMENFASSUNG: Beim Bau des Schachtkraftwerkes Kuehtai wurda zunachst der oberste Teil der Schachtauskleidung in offener Baugrube hergastellt und mit Überlagerungsmaterial hinterfuellt. Das wait ere Abteufan im Fels erfolgte sektorweise fortschreitand nach einer Wendelflache von 3m Ganghöhe. In Eruebrigung jeglicher temporarer Sicherungsmaβnahmen wurde gleich die endgueltige Ausklaidung hergestellt, die als spiralenförmiger Betonstreifen von 3 m Höhe und 60 cm Mindestwandstarke dem Ausbruch an der Schachtsohle unmittelbar folgte. Dieses auf Versuche, Rechnung und Messungen gestuetzte Bauverfahren erwies sich als zeitsparend, sicher und wirtschaftlich. SUMMARY: After constructing the upper part of the shaft lining for the Kuehtai shaft power station in an open pit and backfilling the overburden, the subsequent shaft sinking in rock has been carried out along a helical surface of 3 m pitch, advancing by sectors. Rendering any temporary support unnecessary, the permanent lining kept following up the excavation closely as a helical concrete strip of 3 m height and 60 cm minimum thickness. Based on tests, computations and measurements, this procedure proved to be time-saving, economic and safe. RÉSUMÉ: Lors de la construction du puits de la centrale de Kuehtai, la partie superieure du revêtement du puits fut realisee dans une fouille à ciel ouvert, qui fut remblayee par la suite. Le fonfçage ulterieur du puits dans le rocher fut execute en procedant par secteurs, selon une surface helicoldale de pas egal à 3.00 m. Sans prendre des mesures de securite temporaires, le revetement definitif fut realise à l'aide d'une bande helicoldal de beton, de 3 m de haut et d'epaisseur minimum de 60 cm, qui suivit immediatement l'excavation du radier du puits. Sur la base d'essais, de calculs et de measures, cette methode de construction s'est averee sure et economique et a permis de gagner du temps. 1. ALLGEMEINE VORAUSSETZUNGEN Die Oberstufe Kuehtai (Abb. 1) der zur Zeit ca. 30 km westlich von Innsbruck im Bau befindlichen Kraftwerksgruppe Sellrain-Silz (Gesamtleistung 761 MW) der Tiroler Wasserkraftwerke Aktiengesellschaft wird als Pumpspeicherwerk Angelegt, um im Sommer das dem Zwischenspeicher Langental zuflieβende Wasser eines ausgedehnten Beileitungssystems ueber eine geodatische Höhe von 319 bis 440 m in den Jahresspeicher Finstertal zu fördern, sowie um ganzjahrig zusatzlichen Walzbetrieb zu ermöglichen. Die zur Erzeugung des im Pumpbetrieb erforderlichen Gegendrucks notwendige tiefe Anordnung der beiden reversiblen Maschinensatze (Mittelebene der Pumpenturbinen 48 m unter dem Absenkziel des Speichers Langental) fuehrte in der gegebenen topographischen Situation zum Entwurf eines Schachtkraftwerkes, uebrigens dem bisher gröβten hinsichtlich der Schachtabmessungen (30 Meter Ausbruchsdurchmesser.,82 m Schachttiefe). von einer Talverflachung unterhalb des Langentaldammes aus auf einem nur wenige Meter ueber der Schachtsohle liegenden Niveau einen 1.2 km langen Entwasserungs- und Schutterstollen bis an den Kraftwerksschacht heranzufuehren, bestimmten dessen Entwurf und Ausfuehrung in entscheidendem Maβe (Abb. 3). 2. UNTERGRUNDVERHÄLTNISSE, SONDIERUNGEN, FELSMECHANISCHE VERSUCHE Oer Fels befand sich an der Baustelle unter einer rund 25 m tiefen Überlagerung aus Moranenmaterial und Hangschutt (Abb. 3). Nachdem seine zum Langentaler Becken geneigte Oberflache durch Brunnen und Bohrungen abgetastet und die Schachtachse ungefahr fastgelegt worden war, wurde das Gebirge im unmittelbaren Schachtbereich durch ein wei teres Bohrloch (mit Pressiometerversuchen) sowie nach entsprechendem Voraushub durch einen Sondierschacht von 3 m Durchmesser ueber die volle Tiefe erkundet. Es handelt sich um eine Wechsellagerung von Schiefergneis und Amphibolit mit einigen Zwischenlagen von Glimmerschiefer, die als Ganzes stark verfaltet ist und in der Aufnahme ein recht kompliziertes Bild zeigt. Das Gebirge erwies sich aber trotzdem schon im Sondierschacht als standfest und kaum wasserfuehrend und brachte auch spater beim Vollausbruch in dieser Hinsicht keinerlei unliebsamen Oberraschungen. Es trug sehr zur Sicherung schon bei der Planung des Schachtes und bei der Wahl des darauf abgestimmten Bauverfahrens bei, daβ man das Gebirge beizeiten gerade im Bereich des Schachttiefsten besonders gut erschlossen und erkundet hatte. Dies ermöglichte der schon erwahnte Entwasserungsstollen, den man im Zuge der Vorarbeiten auf der Höhe der Druckschacht-Flachstrecke an den kuenftigen Krafthausschacht herangefuehrt, zur Druckschacht- Flachstrecke verlangert und in dieser als Pilotstollen fortgesetzt hatte. Eine anschlieβend ausgebrochene doppelte Verbindung zum Fuβ des Pilotschachtes, einmal senkrecht zum Entwasserungsstollen und einmal in der Achse der Druckschacht-Flachstrecke, bot eine vorzuegliche Gelegenheit zur Durchfuehrung einiger in-situ-Versuche in reprasentativen Felspartien sowohl im Schiefergneis als auch im Amphibolit im Bereich der spateren Schachtwandung [Abb.4]. Neben einem Versuch mit per TIWAG-Radialpresse, den zwei nahgelegene Meβstrecken im Druckschacht erganzten, wurden an vier Stellen Schlitzentlastungsversuche mit Verformungskompensation und Überkernen vorgenommen [Ausfuehrung Interfels - LNEC]. 3. SCHACHTENTWURF UNO BAUPHASEN IM ALLGEMEINEN Der Entwasserungsstollen brachte nicht nur wesentliche Vorteile fuer die Erkundung sowie fuer die Entwasserungund Schutterung wahrend der Bauausfuehrung. Sein Vorhandensein und die Erfahrung, daβ er trotz des darueber befindlichen Grundwassersees praktisch trocken geblieben war, ermöglichten auch erst den gewahlten Typ der zweischaligen Schachtauskleidung [Abb. 3, Langsschnitt]. Oberhalb der bis einschlieβlich Generatorboden direkt an den Fels anbetonierten Maschinengeschoβe sind namlich die Kraftwerkseinrichtungen in einem freistehenden Stahlbetonzylindervon 40 cm Wandstarke untergebracht, den ein offener Ringspalt von 60 cm Breite von der Auβenverkleidung des Schachtes trennt.