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UBC Theses and Dissertations

A new approach for modeling the non-linear one dimensional consolidation behaviour of tailings Ahmed, Syed Iftekhar


The management of tailings largely depends on its consolidation behaviour. Extensive works on this sector have been performed as it plays a significant role in economic and environmental considerations of a tailings management facility. To resolve these issues, consolidation theories had been developed for one, two or three dimensional condition with numerical solutions for soft soils like tailings which behave differently from natural soils. Eventually, large strain consolidation tests have experienced at its advance level for precise determination of experimental data because non-linear behaviour of compressibility and hydraulic conductivity fits to a wide range of functions. This non-unique behaviour of tailings is believed to be an aftermath of the combination of flocculation, sedimentation, consolidation, segregation, deposition, freeze-thaw and desiccation phenomena. Similarly, a consequence of several factors combined called “apparent over-consolidation” is a mystery to the tailings industry and the reasons for this occurrence are not fully understood. It is believed to be the result of the combination of several contributing factors at low effective stresses. Previously, it was assumed that tailings are normally consolidated or consolidating under the load of mounting deposited materials and numerical modeling had been performed by different researchers based on this assumption. However, the apparent compressibility behaviour of tailings was noticed for different types of tailings at a wide range of solids content and various types of testing procedures. Conducting statistical analysis, a new compressibility function, one of the forms of Weibull distribution, is proposed to fit the void ratio-effective stress relationship considering pre-consolidation behaviour. A fully implicit model was developed by introducing that proposed compressibility equation to predict the tailings long term consolidation behaviour. A case study was performed for different types of tailings to predict the consolidation behaviour followed by the sensitivity analysis of the developed model. Significant effects of apparent consolidation have been observed on void ratio, effective stress, excess pore water pressure and tailings settlement for a period of 50 years. The major outcome of this study is the consideration of apparent over-consolidation behaviour during the early stage of the deposition helps to formulate the model more precisely.

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