- 440 views
- 1084 downloads
CENTRIFUGAL MODELLING OF OIL SANDS TAILINGS CONSOLIDATION
-
- Author / Creator
- Sorta, Amarebh R.
-
A large amount of fluid fine tailings (FFT) is stored in tailings ponds and is continuously accumulating from the extraction of bitumen from oil sands ore in northern Alberta. The FFT are high in water content and have a very slow dewatering behavior that requires many years for them to fully consolidate under their own weight. A better understanding of the geotechnical properties of untreated or treated tailings is needed to evaluate different tailings treatment and disposal options. However, evaluating the long-term geotechnical behavior of the tailings using conventional laboratory and field experiments can be time-consuming and relatively expensive. In response to this dilemma, a centrifuge modelling technique is used in this study to model the self-weight consolidation of oil sand tailings. The technique replicates the prototype self-weight stress in a model and models consolidation that may take many years in a field within a few hours of centrifuge run. A series of centrifuge tests is conducted in the new GeoREF geotechnical beam centrifuge facility at the University of Alberta for modelling the self-weight consolidation of oil sands tailings using consolidation cells equipped with in-flight solids content and pore pressure profile measuring transducers. The repeatability of centrifuge tests and scaling laws is examined by running “model of the model” tests along with duplicate tests. Centrifuge tests are also conducted at the C-CORE centrifuge center at Memorial University of Newfoundland and Labrador, mainly to evaluate the segregation behavior of tailings during high-gravity tests. The concerns of segregation in modelling the self-weight consolidation of oil sands tailings using centrifuge are addressed by defining segregation boundaries at high centrifugal acceleration and Earth gravitational acceleration. The results form a guide for selecting a non-segregating tailing for centrifuge tests. The applications of formulas that relate the undrained shear strength of tailings with their maximum particles size carrying capacity at different accelerations are evaluated. A wait-time is proposed for tailings prior to spinning them in a centrifuge that minimizes particle size segregation during the centrifuge tests. The thixotropic behavior of tailings of different solids and fines content are examined and the effects of thixotropy in centrifuge modelling are evaluated. The time domain reflectometry (TDR) is applied for solids content profile measurements in centrifuge tests after examining various measuring technologies for solids content. A series of tests is conducted to evaluate the TDR probe calibration, measuring range, sensitivity and the effect of chemical additions, soil texture and thixotropy. The TDR calibration equation for deriving solids content from TDR dielectric constant readings is proposed for high-water content material. The proposed equation differs from the commonly used calibration equation for higher solids content materials. Also in the study, a non-contact type laser displacement sensor for tailings interface settlement monitoring is examined and applied to centrifuge tests. A new technique of density profile measuring probe, based on a light scatter technique, is examined in the centrifuge tests program. The consolidation parameters of tailings and kaolinite slurry are determined from centrifuge tests using data collected during the centrifuge flight and at the end of the tests. Large strain consolidation tests are conducted to derive input parameters for numerical models and to compare with centrifuge results. Comparisons of consolidation parameters from the centrifuge and large strain consolidation tests indicate the strain rate effect on compressibility. The strain rates in centrifuge tests and conventional consolidation tests are presented and the effects of strain rates on the compressibility of materials are discussed. The slurry-water interface settlements of tailings are monitored during the centrifuge tests and compared with FSConsol large strain consolidation numerical model prediction. The consolidation rate from FSConsol is found to be slower than the centrifuge results. In addition to the centrifuge tests, the settling, shear strength, permeability and plasticity of oil sands-fines sand mixture tailings at a wide range of solids and fines content are examined at Earth gravitational acceleration.
-
- Graduation date
- Spring 2015
-
- Type of Item
- Thesis
-
- Degree
- Doctor of Philosophy
-
- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.