A.Gens E.E.Alonso - Deparmaent Geotechnical Engineering University Politecnica de Cataluunya Barcelona

the paper describes the failure of the tailings dam of a pyrite mine that occurred in 1998. It was a sudden failure that resulted in large discussing the geological setting and the main geotechnical parameters of the material in volved,, a proposal for the failure mechanism is put forward that is consistent with the data and observations obtained in an extensive investigation carried out after the failure. the lack of dissipation of pore pressures over a twenty-year construction period and the development of progressive failure phenomena are important features of the proposed mechanism.