Investigating the cyclic response of layered densified tailings deposits to drying–wetting phases: insights from shaking table tests

Over recent decades, advances in thickening technology have enabled the adoption of highly densified tailings (HDT) (thickened and paste tailings) disposal as a viable alternative to conventional slurry tailings disposal. However, the geotechnical response and liquefaction potential of HDT subjected to drying and wetting cycles (e.g. heavy rainfall) under cyclic loading is well understood, especially in seismic regions. This study investigates the impact of drying and heavy rainfall on the behaviour and liquefaction susceptibility of layered HDT under cyclic loading, using a shaking table. Heavy rainfall was simulated to replicate extreme events in Quebec, Canada. A flexible laminar shear box equipped with various sensors and instruments (e.g. pore pressure transducers, 5TEs, cable displacement transducers) was used to simulate depositing of thin layers in the field. Results showed that excess porewater pressure (PWP) in HDT (thickened and paste tailings) deposits (initially exposed or not to drying and wetting phases) developed rapidly during shaking. However, the excess PWP ratio was found to be lower than 0.8 in the layered HDT deposits that were initially exposed to drying and wetting phases, indicating they did not liquefy. In contrast, thickened tailings not exposed to drying and wetting phases liquefied, with PWP ratios reaching 1.0. Post-shaking, the layered thickened and paste tailings deposits initially exposed to a drying and wetting phase exhibited greater resistance to liquefaction compared to those that were not, with excess PWP ratios ranging from 0.8 to 0.9. Contraction and dilation responses were seen in the layered thickened and paste tailings deposits (initially exposed to a drying and wetting [heavy rainfall] phase or not) during the shaking. The layered tailings deposits (initially exposed to a drying and wetting phase) had similar horizontal displacement response to the layered tailings deposits that were not initially exposed to a drying and wetting phase.