Tailings dam constructed on very loose, saturated sandy silt

Abstract

This paper discusses the design and performance of a tailings dam constructed over very loose, saturated sandy silt foundation soils. A major slide in an iron tailings disposal area in 1948 resulted in liquefied tailings flowing through a valley and depositing up to 6 m of very loose tailings over glacial till. The properties of the saturated tailings foundation soils were critical to the overall dam design. The new dam will eventually reach a height of 30 m.The paper discusses consolidation and strength parameters of the foundation tailings, design considerations including the potential for foundation and stored tailings liquefaction, and the result of monitoring programs during construction of the starter dam which reached a height of about 9 m. During construction the most critical stability conditions developed during placing of the initial 1.2 m lift of pit-run gravel. After foundation pore pressures dissipated additional fill was placed with no further problems. Contrary to experience with other fine grained angular soils having few clay sized particles, the iron tailings foundation soils consolidated significantly under applied load. It was computed that consolidation under the weight of the starter dam would be sufficient to increase the relative density to a value that would remain stable under maximum anticipated earthquake loadings.