Liquefaction Analysis of Four High Tailings Dams

This is the story of a long, 3-year study on the investigation of the liquefaction analyses of four tailings dams. All of them were built by the upstream construction method and initially considered unsafe. Before this study, liquid limit stability analyses on these four structures indicated a low factor of safety. This work aimed to carry out stress-strain analyses with the NorSand constitutive model. The work started in 2020 when most stress-strain commercial programs did not yet work with NorSand, but in due course, programs improved and enabled the use of this model. Most of the dams had limited in situ and laboratory tests. In situ tests in most dams were short and did not reach the bottom of the tailings. Existing laboratory tests, on the other hand, aimed only to yield strength parameters, not NorSand ones. The authors then used a mix of strength parameters and literature-recommended typical values. The final analysis results indicated that two of the dams were very unsafe, and two others were very safe. The authors compared the results of the liquefaction potential and safety factors obtained by reducing strength parameters. Despite the theoretical limitations of the parameter reduction technique, a good, inverted correlation was found. The authors concluded that limit equilibrium analyses of tailings may be misleading and should be avoided.