ABSTRACT:

The 40-meter-high underground cavern is situated in rocks containing many joints dipping at steep angles. There was investigated borehole survey and field measurements. It was founded very useful to calculate discontinuum stability analysis of rock mass around cavern to find value of shear strength of joints, when the rock mass is becoming unstable and to find type of possible collapse of cavern for final design of underground opening building technology.

RESUME:

La caverne souterraine de la hauteur de 40 m est situee au massif de roche contenant beaucoup de fissures raides. On a foit ici l'investigation dans les forages et les testes terraine. On a demontre qu'il est tres utile de comptu I'analyse de stabilite du massif discontinu aux environs de la caverne pour destinee la solidite glissement des fissures ou Ie massif cesse d'etre stabile et pour destiner le type colapsus l'eventuele de la caverne ce qui est utile pour fixer Ie project finale de la technologie du travail souterrain.

ZUSAMMENTAFASSUNG:

Die 40 Meter hohe Untergrundkaverne befindet sich im Gesteinsmassiv, das viele steile Spalten enthalt. Hier waren die Bohrforschungen und Feldmessungen durchgefuehrt. Es zeigte sich sehr nutzlich, die diskontinuierliche Stabilitatanalyse des Massives in der Umgebung der Kaverne zu berechnen, um die Schubfestigkeit der Spalten und die Stabilitatgrenze des Gesteinsmassives festzustellen. Es macht auch möglich, eventuelles Kolapstyp der Kaverne zu bestimmen, was fuer den endgueltigen Vorschlag der Technologie des Untergrundwerkes nuetzlich ist.

1. INTRODUCTION

The underground opening as the Hydro-electric Powerhouse, which is in the central part of Honshu Island in Japan, is situated in70 m depth beneath the top of the mountain on the right bank of Kiso River. 1.1. Geology and survey location Geologically, this site is located in the northern part of the late Cretaceous Caldron movement. The surface of the mountain consists of the cenozoic, neogene, Pliocene and quaternary deluvium. Basement rocks are granite porphyry, royalties and slate (Fig. 1). These rocks contain many joints dipping at steep angles (Tanimoto et al.1995). There was investigated the borehole survey in 4 boreholes. Borehole A, B and C, located on the strait line, were vertically drilled down from the same level in the exploratory adit at the intervals of 25 m between A and B, and 34.1 m between B and C as is shown in Fig. 1. 1.2. Joint mapping through borehole survey Prior various field measurements, there was investigated the distribution and the characteristics of joints in boreholes by using the borehole scanner system. The system is based on the direct digital data acquisition of continuous images obtained through a rotating scanner with high observation speed and 360 degree panoramic continuous image in real time in borehole. BSS is able to scan the borehole at the maximum speed of 120 cm/min. The resolution is 0.1 mm or more. The clear colour image provides nonstop information on joint direction and inclination. Several joints are shown (Fig. 2, 4) in the form of sine curves appearing on an entire circumferencial image of borehole wall. A three dimensional view can be displayed from any arbitrary angle. Data obtained from the borehole wall survey of joints can be shown in the form of joint rosettes or stereo net projection. Simplified models by stereo graphic projection (Fig. 3) were used in (Tabata 1995) to show characteristic set of joints and their orientations, which were used in mathematical model.

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