The Kan-etsu tunnel is the longest road tunnel in Japan. In excavation of this tunnel, rock bursts frequently occurred at the cutting face. We introduced acoustic emission monitoring and field stress measurements were performed in the zone with the danger of rock burst. The tunnel face became unstable when it comes close to a particular geological discontinuity. Rock bursts and AE activities in this field are mainly associated with the reduction of normal stress on the discontinuity.
Le tunnel Kan-etsu est le plus au Japon. En creusant ce tunnel, l"eclatement de la roche s"est frequemment produit sur la face coupee. Nous avons observe l"emission acoustique et la mesure de la pression de la roche à la section où il y avait danger d"eclatement de la roche. La face du tunnel etait instable lors de l"approche d"une discontinuite geologique particulière. L"eclatement de la roche et l"activite de l"emission acoustique dans cette section sont principalement lies à la diminution de la pression normale sur la discontinuite.
Der Kan-etsu Tunnel ist der langste Strassentunnel in Japan. Wahrend der Arbeiten fuer diesen Tunnel traten haufig Felsbrueche an den Vortriebsstellen auf. Wir fuehrten Gerauschemissionsueberwachungen und Felsdruckmessungen ein an den Stellen, an denen Gefahr von Felsbruch bestand. Die Vortriebsstellen waren besonders instabil in der Gegend von Verwerfungen der Gesteinschichten. Felsbrueche und Gerauschemissionen sind hauptsachlich mit Verringerung des normalen Drucks bei Verwerfungen in Verbindung zu bringen.
Rock bursts frequently occurred in advance of the Kanetsu tunnel just after blasting. This tunnel is the longest road tunnel in Japan, which is 10,926m long and about 1,000m deep. Rock burst is a serious problem in safety of the tunneling work. Some of these rock bursts resumed activity a few hours later, despite judgments that they had ended. It was possible to specifically locate the direction in which rock noise was generated in front of the face or in the rock ahead of the side wall under quiet condition. Thus, in working areas with a danger of rock burst, it was essential to proceed with work only after fitting safe and adequate support.
Acoustic emission (AE) monitoring was carried out as one of the countermeasures against the abrupt rock burst in the working areas. AE is considered to be a seismic phenomenon associated with mechanical instability within a material (Hardy 1973). Nakajima (1984) showed that the AE monitoring was an available means for the control of the refuge time from working space and for the support design of the tunnel.
Sugawara (1987) and Kaneko (1989) applied AE monitoring to the prediction of coal burst on a long wall face in a multi-layered coal mining field. We assume that the relationship between rock bursts and AE could correspond to the relationship between the main shock and fore shocks in the prediction of earthquakes. It would be highly effective to apply AE to predicting rock burst, which are typical examples of rock failures.
