In order to design the section configuration and the orientation of the underground powerhouse cavern, the initial rock measurement has been carried out at the depth of 550m below the surface, by means of the Borehole Deformation Method, the Conical-ended Borehole Technique, the Hydraulic Fracturing Method, and the Acoustic Emission Method. The results obtained are Harmonious with each other, and the magnitude of the maximum principal stress has been evaluated to be about 26MPa. This is much larger than the stresses measured previously at another construction sites of underground powerhouse in Japan. The direction of the maximum principal stress is generally horizontal, and in the east-west direction. These results have been successfully used for the cavern orientation selection and the section configuration designing, and the longitudinal axis of the cavern has been decided in the direction to be coincident with the maximum principal stress, in order to minimize the stress concentration around the cavern.
La measure de la contrainte initiale de la massif rocheux pour conception de configuration et orientation d'une cavite d'une centrale electrique souterraine situee à 550 m soes le surface du sol ont ete faites, à l'aide de quatre methodes de measure differents; methode de measure par liberation des containtes, la technique de trou de sondage à fond conique, fracture hyrauliquement et methode de emission aooustique (AE). La contrainte initiale de la, massif roeheux obtenue par eettes. methodes a revele une containte principal maximum d'environ 26 MPa et cette resultat obtenu avec chacune des methodes a indique une tendenee generale d'harmonisation. Cette valeur'obtenu est maximum au milieu des centrales electrique souterraines actuellement en service en Japon jusqu'ici. La containte principal maximum de la massif rocheux agit quasimenthorizontalement d'est en ouest. Les resultats ont ete utilise dans le conception de la configuration de la cavite et choisir son longue axe. La longue axe de la cavite a ete choisi parallèle à la direction de la containte principal maximum. Ceci a par effect de reduire sur concentration de containtes author la cavite dus à l'excavation.
Um zu entwerfen die Querschnittsform und die Orientierung von der unterirdische Kraftwerkanlage Kaverne, die Messungen des anfanglichen Bodendrucks wurdem in der Tiefe von 500m von druchgefuehrt, mit Boreloch Umformung Methode, konische prundlo;chherstellung Technik, Hydraulischer Bruch Methode und Akustik Emission Methode. Die Meßergebnisse zeigten eine harmonisch Tendenz, und der anfangliche Bodendruckwert wies auf eine maximale Hauptspannung von ungefahr 26 MPa hin, der bisher höchste an allen unterirdischen Kraftwerkanlagen in Japan gemessene Wert ist. Der Bodendruck wirkt dabei in fast horizontaler Richtung von Osten nach Westen. Als Ergebnis dieser Untersuchungen wurde der Kaveme so entworfen, daß die axiale Richtung mit der Ausrichtung der Hauptspannung uebereinstimmt zu mindern der Konzentration von der Spannung im Umfang von der Kaverne.
Underground caverns for the pumped storage power generation have been constructed at more than 20 places in Japan. Recently, the power plant is advanced in making to be further larger capacity, in company with the improvement of pump turbine performance. To obtain a much more effective head, a clear tendency that the depth of the cavern from the surface is getting larger than, before, is observed. In consequence, some of the powerhouse caverns are presently constructed and/or planned at the depth beyond 500m.
Stability of large rock caverns, such as an underground powerhouse cavern, is very much controlled by their orientation with respect to the initial stress field. Thus, when we design the section configuration of the Cavern and its orientation, it is much important to evaluate the initial stress field exactly. In addition to that, in order to design a rational support system and to execute the work safely, it is required that the secondary stress field, which is induced in the surrounding rock mass by, the excavation, should be estimated.
In the present paper, a successful case example of the in situ stress measurement is presented, along with an evaluation scheme of the initial stress field.
