Half a century of weathering process of mudstone cut slope and impact on slope stability

Abstract

Sedimentary soft rocks such as mudstone weather over time when exposed to the surface by cut excavation. And the cut slopes that have been excavated for a long time often caused surface collapse. However, there have been no cases of observing the weathering process of sedimentary soft rocks for decades, and prediction of weathering, stability of cut slopes, and rational measures are major issues. In this study, we conducted field surveys such as elastic wave exploration, soil tests, and X-ray diffraction analysis for about 50 years after excavation of significantly weathered mudstone cut slopes. Then, the weathering mechanism of the slope and its effect on stability were examined. As a result, it was confirmed that the strength of the slope surface layer decreased due to the effects of stress release and repeated dry and wet conditions due to unloading immediately after excavation. On the other hand, chemical weathering such as oxidation and dissolution of clay minerals that compose mudstone is still in progress, and it is expected that weathering will continue in the future.