ABSTRACT:

The geological structure at the Sabigawa Pumped Storage Power Plant is characterized by its complexity including highly developed jointing, thus presenting extremely difficult geological conditions for the construction of a large cavern. However, the construction of this large cavern was successfully completed even under the such difficult conditions by introducing an observational construction management system, the objective of which was to secure the stability of the cavern by grasping its behavior in real time during the excavation. This paper reports the process and results of the observational construction management technology which was applied to the construction of this large-scale underground excavation under unfavorable geological conditions.

RESUME:

Le site de la centrale electrique à accumulation par pompage de Sabigawa est caracterisee par la complexite de sa structure geologique, notamment une fissuration très marquee, et presente donc des conditions geologiques extrêmement difficiles pour la construction de gran des cavernes. Cependant, une caverne de grande taille a pu être construite malgre ces conditions grace a système informatique de conception et d'execution visant à assurer la stabilite de la caverne par la saisie de son comportement en temps reel durant tout Ie temps de I'excavation. Le present rapport rend compte de la technologie informatique de conception et d'execution qui a ete appliquee à la construction de cette centrale electrique souterraine de grande taille dans des conditions qeologiques defavorables,

ZUSAMMENFASSUNG:

Die geologishe Struktur um das Pumpspeicherkraftwerk Sabigawa ist durch hohe Komplexitat einshlieβlich hoch ausgebildeter Zerklueftung, gekennzeichnet, so daβ sich extrem schwierige geologische Bedingungen fuer den Bau einer groβen Kaverne ergeben. Der Bau dieser groβen Kaverne wurde Jedoch trotz dieser Bedingungen erfolgreich abgescholssen, indem ein Beobachtungs- Baubetnebssystem angewandt wurde, dessen Ziel es war, die Kavernenstabilitat sicherzustellen, indem das Verhalten der Kaverne unter Echtzeitbedingungen wahrend der Auschachtarbeiten beobachtet wurde. Die vorliegende Abhandlung berichter ueber die Beobachtungs- Baubetriebstechnik, die fuer den Bau dieses groβen Untergrund-Pumpspeicherkraftwerks unter schwierigen geologischen Bedingungen angewandt wurde.

1
GEOLOGY AND SUPPORT DESIGN

The Sabigawa Power Plant is a large-scale pumped storage type underground electric power plant of 900MW which Tokyo Electric Power Co., Inc. constructed in Tochigi Prefecture. The geology at the cavern for the underground power plant consists mainly of various kinds of Neogene rhyolites. The underground powerhouse cavern is located at a depth of approximately 200m below the ground level. The rhyolite is characteristic of highly developed joints of hydrothermal alteration experiences. These fractured zones have a maximum width of 150cm and are filled with clay. Two of these fractured zones (F-I and F-T) were identified in the preliminary investigation stage, but fractured zones F- V and F- W were newly discovered during the arch excavation. A mushroom shape was adopted for the cavern which is 28m wide, 51m high and 163m long, with a cross sectional area of approximately 1,400m2 and an excavation volume of approximately 190,000m3.As shown in Figure 2, a concrete lining was applied to the cavern ceiling and a support system was designed for the cavern walls to secure stability against sliding.

2
OBSERVATIONAL CONSTRUCTION MANAGEMENT SYSTEM
2.1
Composition of observational construction management system

As shown in Figure 3, the observational construction management system is composed of four subsystems, measurement planning, data processing, analysis and design, and observational management. The data processing subsystem not only performs primary data processing, but also secondary data processing including the preparation of graphic presentations of measurement data in cross sections and contours. This subsystem provide to the engineers timely a large quantity of measurement data in a visual form which is easy to use in making judgments.

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