In recent years there has been a growing interest in reprocessing old tailings storage facilities (TSFs) for economic, environmental, or social issues. However, a series of geotechnical challenges have arisen with these projects since large cuttings on loose and saturated tailings are required. Therefore, tailings' static and dynamic behavior must be fully understood to assure both excavation stability and workers' safety. In this paper, a comprehensive geotechnical characterization of old copper tailings is described to evaluate the stability of the excavation in these materials.
The study includes field and lab testing. Regarding field testing, CPTu tests with shear wave velocity (Vs) measurements were undertaken. These surveys were conducted in two different areas: closer to the dams and in the center of the impoundment. Emphasis was placed on parameters such as Soil Behavior Type (SBT) and the State Parameter (𝜓), computed by a set of empirical calibrations available in the literature. In addition, special interest receives the validation of undrained strength correlations since drainage conditions must be assessed before using the undrained properties.
The laboratory tests were carried out in disturbed and undisturbed samples in the same zone of the CPT tests to define the index properties of the materials and the soil behavior under cyclic and monotonic shearing. For this purpose, drained and undrained monotonic and cyclic tests were performed. From the laboratory tests, strength parameters were obtained from the monotonic tests and the liquefaction cyclic resistance ratio obtained from the cyclic triaxial tests.
The results show that materials in the middle of the pond have a finer Particle Size Distribution (PSD), smaller shear strength parameters, and a slightly higher tendency towards a contractive behavior. However, although the material closer to the dams is coarser and exhibits a higher shear strength, its response is also contractive.
