In establishing the seismic design method for underground structures, it is important to make clear the characteristics of underground seismic motions and to know behaviors of structures during an earthquake. Electric Power Development Company (EPDC) has started the seismological observations since 1976 at three existent underground hydro-power plants. In these six years, nearly a hundred earthquakes have been observed including the Miyagiken-Oki earthquake with a magnitude of 7.4. The peak ''accerelation amplitude ratio shows half to one-third for far-field earthquakes. This result is the same as those observed and given in other references. While, for near- and very-near-field earthquakes this ratio evidently shows Smaller. The peak displacement of cavern wall is proportional to the Spectrum Intensity (S.I.) and accerelation amplitude has no correlation to wall displacement.
Hinsichtlich der seismischen Konstruktionsmethode fuer unterirdische Bauten ist wichtig, dass die unterirdischen sęismischen Bewegungscharakteristiken, und das Verhalten der Bauten wahrend eines Erdbebens, erkannt werden. Die Electric Power Development Company (EPOC) hat im Jahre 1976 mit der seismologischen Beobachtung von drei bereits vorhandenen unterirdischen wasserkraftwerken begonnen. Wahrend dieser sechs Jahre wurden etwa einhundert Erdbeben, einschliesslich das Miyagiken Oki Erdbeben mit einer Starke von 7.4. Das maximale Beschleunigung Amplitudeverhaltnis zeigt die Halfte bis zu einem Drittel, Bei entfernten Erdbeben. Dieses Resultat ist das gleiche wie vorherige Resulte, wahrend fuer nahe oder unmittelbare Erdbeben das verhaltnis nachweislich geringer ist. Die maximale Verschiebung von Wanden unterirdischer Hohlraume ist proportional zu Spektrums starke (S.I.) und das Beschleunigungsverhaltnis hat keine Beziehung zur Wandverschiebung.
Au Sujet de la methode d''etude sismique pour les constructions souterraines, il est important de preciser les caracteristiques des mouvements sismiques souterrains, de même que de connaître les comportements des constructions pendant les tremblements de terre. Electric Power Development Company (EPDC) a commence un programme d''observations sis- mologiques en 1976 à trois centrales hydro-electriques existantes. Au cours de ces six dernieres annees, pas loin d''une centaine de trernblements de terre avec une amplitude ont ete observes, y compris le trernblement de terre Miyagiken-Oki avec une magnitude de 7,4. Le rapport d''amplitude d''acceleration maximum diminue de moite jusqu''à un tiers pour les trernblements de terre lointains. Ce resultat est identique aux resultats obtenus precedemment. Alors que pour les trernblements de terre proches et tres proches, ce rapport est evidemment plus faible. Le deplacement maximum du mur d''abri est pro- portionnel à l''lntensitede Spectre (I.S.), et l''amplitude d''acceleration n''est pas en correlation avec le deplacement du mur.
The procedure of seismic design for underground caverns is shown schematically in Fig. -1. Among the items show!'' in the procedure, the following must be specifically examined, 1) whether or not stress-strain characteristics of rock can be known by means of conventional test methods when rock mass is subjected to the large seismic load, 2) whether or not the dynamic stress and strain of non-uniform rock mass including non-linear behavior can be analysed reasonably and accurately by practical means, 3) whether or not the characteristics of input seismic motion underground are different from those at the ground surface ordinally known and 4) how an actual cavern behaves during an earthquake.
In order to clarify these issues, we believe that it is the best way to obtain the underground observation ''data from an actual earthquake and simulate the observations by analysis using an analytical method based on the unified theory.
This seismological observations have been started since 1976 as a part of the study on underground nuclear power plant.
EPDC has 11 underground hydro-power plants. Considering the regional characteristics of seismicity in Japan, the geological conditions, the dimensions of underground caverns and the maintenance conditions of the plant, the earthquake observatory system ''was installed at three plants for observation of earthquake motions. The observed records at the ground surface ''e and underground were then compared. The locations of three plants are shown in Fig.-2 along with the magnitudes and locations of earthquakes observed. Table-l lists an outline of the observation of each of the three plants. The earthquake motions are detected by velocity sensors, and then are recorded by recorder controllers (differential amplifier, integral amplifier). In ''order to prevent the mal-operation of equipment caused by the start-up of a generator or by the air-vibration of line-switches, the recorder is so designed as to start operation, except for the Miboro-plant, when the starters simultaneously detect the earthquake motion of over 0.05 kine in velocity both at the ground surface and underground.
The relatively strong earthquake motion has not yet been observed at the Miboro plant.
