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INTRODUCTION The No.1 Takaseyama Tunnel was constructed In Tochigi-Prefecture, 120 km north of Tokyo as part of the Yagan Railway Line, It is a Single-track No.1-type tunnel, and has a length of 346m and a sectional area of 30mBoth the drilling of rock debris to the tunnel and the excavation of the tunnel itself were carried out by applying NATM method. Actual examples of the application of NATM in the excavation of the whole tunnel length have, up to now, been few. However, drilling of the rock debris bas almost always been carried out with conventional excavation methods which use the Side driff method. This is particularly true at situations where the tunnel entrance has been covered with a deep layer of rock debris. In many cases however, use of conventional methods has resulted in problems such as landslides caused by loosening of the bedrock. The use of the NATM method right from the drilling of the tock debr' of the tunnel entrance on the No.1 Takaseyama tunnel resulted in favourable conditions and avoided such Problems as loosening of the bedrock. it is believed that these results will greatly widen the application of the NATM method and that they moreover confirm its surperiority to other conventional methods. the following report contains a summary of the excavation work and the results of measurements. Particular attention is given throughout the excavations involved in the drilling of the rock debris of the tunnel entrance. CHARACTERISTICS OF TOPOGRAPHY AND GEOLOGY The Takaseyama tunnel is located approximately 120 km north of Tokyo in the region where the Ojika River, which flows south from the border of Fukushima-Prefecture, changes its course from south to east. (See Fig. 1) (Figure in full paper) Geologically speaking, the region is composed of a Mesozoic sill of granitic diorite which is covered with a discordant layer of Neocene tuffaceous psephite. For approximately 150m from the north entrance to the No.1 tunnel, the principal component of the excavated material was granitic diorite, whereas the remainder was tuffaceous psephite. After large quantities of granitic diorite had been extracted from the first 40mat the north entrance of the tunnel (the area of excavation which is the subject of this report), there successively appeared later intrusions of quartz porphyry at right angles to the tunnel shaft. The area, then, is composed of geologically complex zones including regions of dense faulting. Furthermore, it was detected at the earlier stage of the construction that the rock debris layer at the tunnel entrance might extend to a depth of some 20m along the shaft of the tunnel. This rock debris layer composed of accumulations of weathered granite. Coarse and fine grained material, as well as gravel, are packed loosely into the crevice between the irregular agglomerations of angularly shaped rocks. The natural slope of the rock debris at the tunnel entrance was rather steep ranging 35–45 degrees.
- Asia > Japan > Tōhoku > Fukushima Prefecture (0.54)
- Asia > Japan > Kantō > Tokyo Metropolis Prefecture > Tokyo (0.45)
ABSTRACT: Pinglin tunnel, which is 12.9 km in length, is under construction in Taiwan. Three tunnels, including two separated main tunnels with 12m in diameter and one pilot tunnel with 5m in diameter, are parallel in direction and were constructed simultaneously. Large deformation of main tunnels and the pilot tunnel were observed during the excavation of main tunnels. A detail study based on the monitoring results has been performed to gain more understanding on the behavior and stability of the rock mass surrounding the tunnels. ABSTRACT: Le tunnel de Pinglin, qui a l2.9kms de long, est maintenant en cours de construction a Taiwan. Les trois tunnels, dont deux tunnels principaux de 12m de diamètre et un tunnel pilote de 5m de diamètre, sont parallèles et construits simultanement. L'excavation des tunnels principaux a provoque d'importantes deformations de ceux-ci et des ruptures du soutènement primaire du tunnel pilote. Une etude detaillee prenant en compte les resultats d'instrumentation et la reaction du système de soutènement a ete realisee en vue d'obtenir une comprehension valable du comportement et de la stabilite du massif rocheux autour des tunnels. ZUSAMMENFASSUNG: Der Bau des 12,90 km langen Pinglin Tunnels in Taiwan hat begonnen. Drei Tunnel, die beiden Haupttunnel mit einem Durchmesser von 12 m und ein Pilotstollen mit einem Durchmesser von 5 m, verlaufen parallel und werden gleichzeitig aufgefahren. Grosse Deformationen in den Hauptstollen sowie Beschadgungen des primaren Ausbaus im Pilotstollen wurden durch den Vortrieb der Hauptstollen herbeigefuehrt. Aufgrund von Messergebnissen sowie dem Verhalten des Tunnelausbaus wurde eine detaillierte Studie erstellt, um zu einem guten Verstandnis zu gelangen ueber das verhalten des Gesteins und der umliegenden Gebirgsmasse. 1. INTRODUCTION The rugged Central Mountain Range runs through Taiwan roughly in the north-south direction, which makes the land transportation difficult between Taipei city on the west and Ilan country on the east. The Taipei-Han expressway project is aimed to shortening the travel time between the two places. The expressway, totaling 31km in length and two lanes in each direction, starts at Nankang in Taipei city and ends at Toucheng in Han county, passing through Shihting and Pinglin on the way (see Fig. 1). Due to the craggy topographical condition of the mountainous terrain, five tunnels account for 20km in length will be constructed. The longest tunnel is the Pinglin tunnel with 12m in diameter and 12.9km in length. There are two parallel main tubes, west bound and east bound, to be constructed for the Pinglin tunnel (see Fig.2). To minimize uncertain geological risk and to ensure progress rate for the main tunnels construction, a pilot tunnel, 5m in diameter and located between the main tubes, has been implemented in advance in order to perform detailed geological investigation and to treat weak zones, if necessary. Fig. 2 illustrates the layout of the two main tunnels and the pilot tunnel. The distance between two main tunnels are in general 60m apart except at the portal being reduced to 42m. The pilot tunnel locates in the middle location between these two main tunnels, and the elevation of the pilot tunnel is lightly lower than the main tunnel. The purpose of this paper is to utilize the monitoring instruments installed in the first eight hundred meters tunnel excavation from the eastern portal, which was completed by drilling and blasting (D&B) construction method in april 1996, in order to gain more understanding on the behavior of rock mass during excavation.
ABSTRACT: Many places in Scandinavia and elsewhere non-gravitational; semi-horizontal or surface parallel rock stresses far higher than the gravitational stresses may be encountered. If the stresses are high enough, rock failure may occur at the surface. In areas with fairly homogeneous and competent rocks with limited weathering and scarce vegetation, such failure may be observed. Two different types of failure may be identified, namely surface parallel extension cracks known as exfoliation, and distinct shear failure. Sometimes combinations of the two modes are found, and even buckling of exfoliation slabs may occur. This paper describes surface phenomena observed in the Tysfjord - Kobbelv region in Northern Norway, where an abundance of stress related failures may be seen over wide areas with easy access from public roads. In-situ rock stress measurements have been carried out in a number of tunnels excavated in connection with hydropower projects, roads and mining. Heavy spalling was experienced in the roof of most of the tunnels during excavation, sometimes at a depth less than 25 m. The combination of in-situ rock stress measurements results, observation of spalling in tunnels, and surface observations gives a unique opportunity to verify the relation between the in-situ rock stress pattern and surface failure. RÉSUMÉ: Dans plusieurs endroits en Scandinavie, et ailleurs, on peut trouver des tensions de roche non-gravitationnelles, demihorizontelles ou parallèles à la surface, bien plus fortes que celles de la gravitation. Si la tension est assez fort, la roche peut se fis- surer à la surface. Dans les endroits où l'on trouve une roche solide et homogène, où la desagregation est assez limitee et la vegetation rare, de telles fissures peuvent être observees, On peut identifier deux types de ruptures: une exfoliation dûe des fissures d'extension parallèle à la surface, et une rupture par cisaillement. On peut parfois trouver un combination des deux types, et même une cassure des plaques exfoliees. Cette etude decrit un phenomène de surface dans la region de Tysfjord-Kobbelv au nord de la Norvège, d'accès facile par la route, où une grande quantite de fissures dûes à la tension peut être observee sur une grande etendue. Des mesure de tension de la roche ont ete faites in situ dans plusieurs tunnels creuses lors de la construction de centrales electriques, de routes et de mines. Un fort ecaillement à ete observe dans le plafond de la plupart des tunnels pendant l'excavation, parfois à une profondeur de moins de 25 m de la surface. ZUSAMMENFASSUNG: In vielen Gegenden Skandinaviens und anderswo können die nicht-gravitationsbedingten, semi-horizontalen oder oberflachenparallelen Gebirgsspannungen deutlich höher sein als die gravitationsbedingten Spannungen. Sind die Spannungen hoch genug, kann an der Oberflache Gesteinsbruch auftreten. In Gebieten mit verhaltnismaßig homogenen und kompetenten Gesteinen, begrenzter Verwitterung und sparlicher Vegetation können solche Brueche observiert werden. Zwei unterschiedliche Bruchtypen können auftreten, oberflachenparallele Dehnungskluefte, bekannt als Exfoliation, und deutliche Scherbrueche. Manchmal kommen auch Kombinationen dieser zwei Bruchtypen und sogar geknickte Exfoliationstafeln vor. Dieser Beitrag beschreibt Oberflachenphanomene, die in der Tysfjord-Kobbelv-Region in Nordnorwegen wahrgenommen werden können. Dort können eine Fuelle von spannungsbedingten Bruechen von öffentlichen Straßen aus ueber große Entfernungen hinweg leicht verfolgt werden. In-situ-Spannungsmessungen sind in vielen Tunnels durchgefuehrt worden, die in Verbindung mit Wasserkraftprojekten, Strassen und Bergbau gebaut wurden. Heftiger Abbruch und Bergschlag im Hangenden der moisten Tunnels konnte wahrend des Ausbruchs beobachtet werden, und dies manchmal in einer Tiefe yon weniger als 25 m. Die Kombination von Resultaten von In-situ-Spannungsmessungen, Beobachtungen von Abbruechen und Bergschlagen in Tunnels und Oberflachenobservationen ergibt eine einmalige Gelegenheit, den Zusammenhang zwischen In-situ-Spannungsverhaltnissen und Trennflachengefuegen an der Oberflache zu verifizieren. Auf dieser Grundlage ist es möglich, erste: Hinweise bezueglich- hoher horizontaler Spannungen zu erhalten, ohne In-situ-Spannungsmessungen durchzufuehren. 1 INTRODUCTION Many places in Scandinavia and elsewhere considerable rock stress problems nay be encountered even at shallow depth. As measurements of in situ rock stress were made possible, it became evident that the stress problems in these cases were connected to semi-horizontal or surface parallel rock stresses far higher than the gravitational stresses. It was also observed that if the stresses were high enough, rock failure might occur even at the rock surface. This is particularly the case in areas with homogenous and competent rocks with scarce vegetation. The Tysfjord - Kobbelv region in Northern Norway is an area where an abundance of stress related surface failure phenomena may be observed from easily available public roads. At the same time, in situ rock stress measurements have been carried out in a number of tunnels in the area in connection with hydropower projects, road constructions, and mining. Heavy spalling and bursting was observed in the roof and sometimes also in the invert in most of the tunnels. The combination of stress measurement results, observation of spalling in tunnels, and surface failure observations has given a unique opportunity to verify the relation between in situ rock stresses and surface failure.
- Energy > Renewable > Hydroelectric (0.95)
- Transportation > Infrastructure & Services (0.75)
- Transportation > Ground > Road (0.75)
Abstract An overburden height of about 1.5 times the tunnel diameter is known to be critical with regard to the stability of an underground excavation. The near-surface zone is usually affected by heavy weathering and represents the border area between hard and soft rock. Due to the variability of the rock mass parameters, a most accurate determination is required to allow for an adequate geotechnical design. For these geological conditions, it is vital to take a more "creative" approach to determine rock mass parameters rather than sticking too close to standard tests and existing classification systems. For numerical calculations and for the interpretation of monitoring results different strengths of the rock mass are taken into account as the ground behavior is sensitive when varying the input parameters. 1 Introduction The geotechnical design of an underground excavation nowadays is a well-known procedure regulated by the Guideline for the Geotechnical Design of Underground Structures with Conventional Excavation (Austrian Society for Geomechanics 2010). Laboratory tests of rock to derive rock mass parameters are executed according to national standards. The latter also provide classification systems to describe rock and rock mass for engineering purposes. This practice is suitable for most cases, but some rock types require a different approach to describe them sufficiently for engineering purposes. Most of them lie within the border area between hard and soft rock. Regarding the geotechnical design, it also represents the transition zone between "stable" and "unstable" conditions. These kinds of rocks therefore demand special attention, but just in these cases the determination of rock mass parameters is extremely difficult. We encountered the issue described above during the excavation of the Pummersdorf Tunnel, a 3.45 km NATM-Tunnel near the federal capital of St. Pölten. The prevailing overburden height of approximately 1.5 times the tunnel diameter (D) is critical with regard to the stability of an underground excavation (Vavrovsky 1987 and Poisel 2005). Rock failure in the crown up to the surface forming a chimney is an often monitored collapse phenomenon. This is a very critical failure mechanism, especially in horizontally layered rock. As it was observed during various tunnel excavations in the past, even little differences in the rock mass strength led to a collapse of the cavity (Vavrovsky 1993). These differences were often so little that they could not be determined on site by the geologist or the tunnel engineer. The paper emphasizes the challenges of dealing with ground types described above for geologists and tunnel engineers.
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
ABSTRACT: Tseung Kwan O - Lam Tin Tunnel project will be developed to improve connectivity between the Central and Eastern Kowloon areas of Hong Kong. The twin tube road tunnel is 2.6 km long requiring excavation spans ranging from 16 m to 34 m. The underlying geology of the site is dominated by jointed granite and highly fractured volcanic tuff. The rock will be excavated using drill and blast techniques, but with the appropriate restrictions applicable to the urban area setting. At Lam Tin Interchange (LTI) Portal, a 9 m span pilot adit, enlarged to a permanent portal span of 25 m is required to obtain early access one of the main tunnel drives. The key challenge at this location, is that the adit and main drive junction pass directly beneath existing metro lines, with vertical separation less than 10 m at the closest point. What further complicates matters is that in this particular zone there is a mapped fault running through this location. It is a requirement of the rail authority, Mass Transit Railway, MTR, that any tunnel excavation induced deformation and vibration within the existing metro is monitored and controlled to pre-determined levels. If these allowable limits are exceeded, tunnelling works are suspended. This paper presents the detailed construction impact assessment which was carried out using advanced numerical modelling techniques to predict the potential effects on the metro tunnels. A comparison between the predicted and measured ground conditions and ground response to the tunnelling is presented to compare actual with predicted observations. The paper will serve as a useful reference for analytical techniques employed at critical existing infrastructure locations where impacts must be tightly controlled to ensure acceptable ongoing operational and safety measures are maintained.