SUMMARY:

A study is made on the stability against an earthquake in the case that the'' rock caverns are placed parallel to one another. If the caverns are placed with more than a certain interval in the rocks having the larger dynamic strength than the static strength, it is generally assumed that the cavern which completed the excavation properly is also stable against the strong earthquake to be considered.

ZUSAMMENFASSUNG:

Die Forschung handelt ueber die Stabilitta gegen ein Erdbeben fuer den Fall, wo sich die Felsenhoöhlen miteinander parallel definden. Wenn Höhlen in mehr als einem gewissen Abstand im Felsen liegen, des sen Starke mehr dynamisch als statisch ist, ist es im allgemeinen angenommen, die Höhle, die die Aushöhlung angemessen vollendet hat, auch gegen das starke Erdbeben stabil sein soll.

RESUME:

Une etude est faite sur la stabilite contre un tremblement de terre dans le cas ou les cavernes rocheuses sont placees en parallele a l''une de l''autre. Si les cavernes sont placees avec un intervalle plus grand gu''un certain intervalle guand les roches ont la resistance dynamique plus grande que la resistance statique, generalement c''est assume que la caverne dont l''excavation est accomplie comme il faut, est aussi bien solide contre un fort tremblement de terre considere.

INTRODUCTION

With regard to the underground Pumped-storage power plant constructed in Japan, the examination of the stability against earthquake acting on the cavern has almost never been done so far because the structure built inside the cavern after the excavation increases the Safety to the cavern. However, it Will be necessary to make an aseism¬ic design upon the large cavern such as underground nuclear power plants.

Researches concerning the method to analyze the stability of the rock around caverns during the earthquake as well as observations on the behaviours of the cavern during the actual earthquake are carrying eagerly. And yet, the aseismic design standard has still not been established.

This paper deals with the way to make a rough estimate of the stability of caverns against an earthquake upon carrying out the aseismic design of caverns to be built parallel to one another.

(Figure in full paper)

ASSUMPTIONS USED IN THE STUDY

Seismic Waves Acting on the Cavern All the above-ground nuclear power plants are built on the rock foundation in Japan. As to the aseimic design, the active fault located some distance away from the power plant is assumed as the hypocenter, and the seismic analysis is done in consideration that the ground motion having a particle velocity and a peak acceleration, which are obtained by Figure 1 as Kanai proposed.

In many cases, the input of seismic wave is made where the rigid base is placed approximately 200 meters deep below ground level. Figure 2 shows the result of computation on the distribution of seismic acceleration from the rigid base to the ground surface at a certain nuclear power plant construction site. The quality of rock at the said site was not so preferable. However, the magnitude of acceleration is a same grade at the depth of about 50 meters or deeper, which is about 40 percent of that at the ground surface.

Similar results were obtained at the other sites as well. Therefore, to make a seismic analysis for the cavern deeper than 100 meters, it can be said that the magnitude of acceleration shall be the same as that of the rigid base, which means that the earthquake forces to be considered are much smaller than that of the surface structures.

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