In the upper part of the planned location of the portal of a highway tunnel, there was a steep rock cliff with several unstable rock blocks. It seemed that the risk of those rock blocks to fall was very high. The cut-out to stabilize the rock cliff was monitored with various measuring instruments to prevent the sudden fall of the rock blocks. This paper discusses themeasurement of acoustic emission and interpretation of its result during excavation of the rock cliff. We calculated displacements by integrating the accelerogram twice in terms of time, and demonstrated that slight displacements can be calculated from the measured AEs.

Dans la partie superieure de l'emplacement prevu pour le portail d'un tunnel autoroutier, il y avait un escarpement rocheux raide avec plusieurs blocs rocheux instables. Le risque de chute de ces blocs semblait très eleve. Lors de la coupe pour stabiliser l'escarpement rocheux, le suivi a ete effectue avec differents instruments de mesure pour eviter la chute brutale des blocs rocheux. Cette thèse presente les mesures d'emission acoustique (EA) et l'interpretation de leurs resultats pendant l'excavation de l'escarpement rocheux. Nous avons calcule des deplacements en integrant l'accelerogramme deux fois par rapport au temps, et montre que de petits deplacements sont calculables à partir des EA mesurees.

Im oberen Teil des geplanten Ortes des Stollenmundes eines Autobahntunnels gab es einen steilen Felsen mit mehreren instabilen Felsenblöcken. Die Gefahr schien sehr groß zu sein, dass diese Felsenblöcke einstuerzen können. Beim Abbau um die Stabilisierung des Felsens wurde das Monitoring mit verschiedenen Messinstrumenten zusammengestellt, um den plötzlichen Verfall der Felsenblöcke zu verhindern. Das vorliegende Papier diskutiert die Akustische Emission und die Auslegung deren Ergebnisse wahrend des Abbaus des Felsens. Wir berechneten die Verschiebungen durch zweimalige Integrierung der Accelerogrammen in Bezug auf die Zeit. Die dargestellten kleinen Verschiebungen können aus den gemessten akustischen Emissionen berechnet werden.

1. Introduction

Above the planned south portal position of the Uenohara tunnel in Kagoshima Prefecture on the Higashi Kyushu highway, there was a huge basalt rock cliff called "Tsurugi Iwa". The cliff wall was steep, with columnar joints. Some of the rock blocks were overhanging, and there were numerous boulders of various sizes. Therefore we evaluated this cliff to be very unstable (Fig. 1).

A high risk was anticipated from the viewpoint of long-term maintenance if the portal were constructed in such a cliff. A plan had been drawn that, before the tunnel excavation reached the portal position, the cliff was to be cut to achieve a stable ground geometry. However, the site is near an urban area and the back of the ground including Tsurugi Iwa is in the vicinity of the Kokubu City industrial complex where precision machines are operated. Considering the location, mechanical excavation was selected for cutting the slope.

The excavation plan was as follows. The slope was to be cut downward from the upper part, using a large size hydraulic rock drill and a backhoe.

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