This paper investigates the mechanism of slope displacement, the effectiveness of stabilization measures, using the results of long-term monitoring of the unstable behavior of two large excavated rock slopes with elevation differences of about 300 m. The study also evaluates the influence of joints on slope behavior through numerical analysis. Finally, technical guidelines for the stabilization of large excavated slopes are introduced.
Cet expose porte sur 1'etude du mecanisme du glissement de terrain en roches qui ferment des parois d'excavation inclinees, ainsi que sur I'efficacite des mesures visant à leur stabilisation, à l'aide des resultats d'observation à long terme de deux grands paquets de couches rocheuses qui tendent à glisser, sur des parois d'excavation inclinees, dont la hauteur atteint quelque 300 m. De plus, I înfluence des diaclases sur le comportement des parois inclinees sera etudiee au moyen d'une analyse numerique. En dernier lieu, des regles de conduite techniques sont indlquees, pour assurer des parois inclinees de grandes excavations.
Diese Studie untersucht den Mechanismus der Böschungsverschiebungsowie die Wirksamkeit von Maβnahmen zur Stabilisierung unter Verwendung der Ergebnisse von langfristiger Überwachung des instabilen Verhaltens zweier ausgegrabener Gesteinsböschungen mit Höhenunterschieden von etwa 300 m. Die Studie bewertet auch den Einfluβ von Fugen auf Böschungsverhalten durch numerische Analyse. Schlieβlich werden technische Richtlinien fuer die Stabilisierung groβer ausgegrabener Böschungen vorgestellt
The present study focuses on two large excavated rock slopes with elevation differences of about 300 m or more and of different rock structure. Both slopes were monitored over years from the occurrence of the first unstable behavior to the stabilization or collapse. On the basis of the data obtained from these measurements, this paper investigates the mechanism of slope movement and the effectiveness of stabilization measures in terms of both measurement data and numerical analysis results.
(1) Geological structure and changes in unstable behavior This slope is composed of alternations of Triassic ~ Jurassic sandstone and slate layers. As shown in Figure 1, the layer dip at about 40° to 60° toward the mountain. The slate layers SI-3, SI-4 and SI-5 are at least about 20 m thick each. These layers contain highly sheared zones, which are thought to have been created as a result of creep. The lower half of S1–4 contains argillized weak zone. SI-3 and SI-5 also have sheared zones, but they are much, smaller than those in SI-4. Figure 2 shows a plan view of the slope. Excavation of the slope began in April 1985 at around EL 1420 m by bench cutting. In May 1989, when the excavation at EL 1180 to 1160 m (road) began, the stability of the slope, particularly in the right side from the intersection line (A-A) where the slope surface changes direction began to fall sharply until the entire slope surface became unstable. The maximum rate of displacement, according to electro-optical distance measurement (hereafter termed "distance measurement") results, was about 6 mm/day, and a cumulative displacement of more than 250 mm occurred locally during the one year from April 1989. Therefore, excavation was suspended, and stabilization measures including drainage tunnel (length: 100 m) and prestressed anchors (about 350 anchors; 22 to 34 m in length) were taken. As a result, the slope movement stopped. The slope angle for subsequent excavation below the road was changed, and in July 1990 excavation was resumed.
