Classification of “Loosened Rock Mass” Based on Cases of Dam Construction

In Japan, dams have been built in the mountainous area of many even now. However, sites that contain rock is not suitable as the basis of the dam is increasing recently. “Loosened rock mass” is one of the bedrock that is not suitable for the foundation of the dam. For this reason, if there is a “loosened rock mass” on the site, it is necessary to countermeasures. For example, excavation of loosened rock mass, modification of dam position, etc. In addition, the range and properties of looseness are different for each site by the terrain, the geology, the geological structure, the formation process of slope. Therefore, in the construction site of the dam, in order to understand exactly the properties and nature of looseness, it is necessary to careful survey. In this study, we tried to systematic classification of loosened rock mass in order to be able to compare the range and properties of the looseness of the site in dam construction in the future. When classifying systematically loosened rock mass, we focused on the following points as an element of the classification. “Slope movement pattern”, “range regulation factor”, “property regulating factor”. We have set five slope movement pattern. And, combining “range regulation factor” and “property regulating factor”, we have classified into 15 types and 9 pattern.