Sand tailings dams : design, construction and operation

The design of sand tailings dams for tailings impou ndments in highly seismic regions has been subjecte d to a long development process with continuous improvement mainly because of the general concern originated by several earthquake induced failures. Two important hydraulic sand fills and sand tailings dam failures in the 1960’s (San Fernando dam in California and El Cobre tailings dam in Chile) are the most well-known. Th e development process continued until it achieved the present situation where recent designs show a reas onably high degree of safety and reliability and also rela tively cost effective construction and operational control methods. As a consequence of the knowledge and experience gained mainly over the last 30 years, it has been pos sible not only to design but also to construct and to ope rate sand tailings dams of more than 200 m in heigh t and with rates of production and placement of tailings sand as high as 45,000 tons per day. This achievement is the result of continuous knowledge gained regarding geotechnical behaviour of tailings sands under high confining pressures; hydraulic transport and pumping of sandy slurries; new numerical methods of dynamic stabili ty analysis and the improvement of reliable sand dispo sal and compaction methods. This paper provides a summary of the evolution that occurred over the last 30 years in the design of t ailings impoundments with sand dams. It also describes the fundamental design concepts, the knowledge gained in the behavior of tailings sands under high confining pre ssures and dynamic loads. The paper finally identif ies areas where it is possible to further improve designs, op eration and closure. A large part of the experience and examples presented are related to actual tailings d ams located in Chile, where several high and large dams exist or are planned to be built shortly.