Drained cyclic behaviour and minimum freeboard design in tailings dams

Abstract

Classified coarse grained tailings, also called sand tailings, are used to construct the main embankment wall in tailings dams. Due to the importance of this structure  in the global stability of the dam, the wall is designed to resist different type of loading, e.g. monotonic loading, seepage from the pond, dynamic loading, wind erosion, among others. Within dynamic loading, special concern is usually given to the undrained response of the material since it may trigger liquefaction phenomena (e.g. cyclic mobility type of response). On the other hand, the cyclic drained response has usually received little attention despite its potential implications. This is likely due to the series of international standards that specify a minimum operational and total freeboard in the scenario of excessive crest settlements. However, is uncertain if such requirements are adequate for a series of scenarios related to the in-situ characteristics of the wall and earthquake loading. In this context, the present study shows results of a series of drained Direct Simple Shear (DSS) tests conducted on sand tailings prepared under different conditions. Results are presented in terms of settlement versus applied cyclic stress. In addition, monotonic tests were conducted in order to preliminary explore a relationship between the critical state line (through the critical state parameter) and the observed cyclic response.