This paper investigates the mechanism of slope displacement using the results of long-term monitoring of the unstable behavior and failure of a large excavated rock slope with an elevation difference about 300 m. The study also evaluates the influence of joint sets on slope behavior through numerical analysis. Then fundamental points regarding the stability of large excavated rock slopes are introduced as follows. The stability of a large excavated rock slope is greatly influenced by the joints and weak layers in the rock, and the relationship between their positions and the positions of the excavated surface. It is important not to fail to notice signs of instability caused by the influences of them early through long-term monitoring started in the early stages of excavation. Based on such monitoring, the need of actions should be determined such as additional investigations, stability analysis, and design modifications and changes.
This paper focuses on a case of failure of a large excavated rock slope with a height (an elevation difference) about 300 m. First, the behavior of each part of the slope is analyzed based on the displacement measurements obtained during a period of about 10 years before the failure. Next, each cross section of the slope is modeled by elasto-plastic equivalent continuum analysis to illustrate that the measurements are explainable. And how the unstable behavior of the slope occurred according to the topographical and geological conditions of the respective cross sections is examined.
Geological structure The slope involved in this case study consists of late Paleozoic to early Mesozoic olistostrome: limestone, shale, tuff, and sandstone. The alterations of shale and tuff include lenses of sandstone, and these layers are overlain by olistoliths of limestone.