Southern Expansion of the Cerro do Lobo Waste Facility. Mechanical Characterization of Soil-rockfill Mixtures

Abstract

The Southern Expansion of the Cerro do Lobo Waste Facility, inserted in the Neves-Corvo Copper and Zinc Mining Concession, is located in Baixo Alentejo, district of Beja, covering the municipalities of Castro Verde and Almodôvar, Portugal. During the operational phase, the mining waste will be deposited vertically, in stages. At the same time, the deposition area will expand approximately 10%. This enlargement includes the southern expansion of the tailings dam. This dam will contain waste up to level 8 (at elevation 272 m), has a maximum height of 17 m, and its walls have slopes of 1(V):2.5(H) upstream, to allow the application of geosynthetics, and 1(V):2(H) downstream. The body of the dam consists of materials resulting from excavation inside the reservoir (rockfill and soil-rockfill mixtures) and a transition layer (0.30 m thick) to support the materials that constitute the waterproofing system. Soil-rockfill mixtures (SRM) represent an environmentally friendly material that capitalises on the reuse of the material excavated. Recently, it has been giving particular attention to SRM by the fact that many embankments, constructed with such materials, have presented a poor performance and required, in many cases, the implementation of corrective measures. To improve the knowledge about the mechanical behaviour of soil-rockfill mixtures applied in tailings dams and also to prevent the use of a less capable material behaviour, LNEC, in cooperation with the Dam Owner, carried out an experimental study. This paper presents the results of the performed experimental program, which involved undrained triaxial tests among others.