A case study on a geotechnical investigation of drainage methods for heightening a tailings dam

Safe disposal of contaminated tailings is recognized as the single largest environmental challenge facing the mining industry worldwide. Because suitable land for a new tailings pond is becoming rare and expensive, more and more mine operators tend to heighten the existing tailings dams to improve their storage capacity. However, this could lead to a decrease in the stability of the tailings dams. Based on comprehensive geotechnical investigations of a tailings dam in China, this paper presents a successful case study on heightening an existing tailings dam and extending its operational lifetime using a new drainage technique named the upward bending drain pipes system. The proposed system has 60 upward bending drain pipes arranged in the dam wall. The drain pipes are designed with combinations of slots and holes. With this arrangement, seepage on the hole surfaces changes to seepage on the slot surface, which increases the seepage capability by about 20 times compared with traditional drain systems. Based on a dam stability analysis, it is found that the value of the factor of safety of the dam can be improved around 20 % after slope drainage at an elevation of 2015 m. By using the proposed drainage system, the height of the tailings dam of this mine can be increased from 45 m (elev(tion 2015 m) up to 60 m (elevation 2030 m), which will increase by 8 million cubic meters the wet tailings storage and will satisfy mine operation for 5 years.