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Cavity expansion in locked sand

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If you have a question about this talk, please contact Magdalena Charytoniuk.

The Athabasca oil sand deposit in Northern Alberta, Canada contains approximately 200 billion cubic meters of bitumen. This sand deposit has a dense uncemented locked sand structure (relative density exceeding 100%) with interstitial bitumen filling its pore space. Sample disturbance makes sampling this material in its intact state very difficult. Pressuremeter testing is proposed as an alternative method of reliably determining material parameters for reservoir modelling at insitu stress levels. As far as extraction planning is concerned, one of the most important, yet difficult, parameters to quantify accurately is the insitu permeability. Due to its locked sand structure, this material is highly dilative and its insitu permeability is known to increase significantly when sheared. The aim of this research was to develop a methodology to derive the change in permeability due to shear dilation using cavity expansion theory. A series of laboratory scale cavity expansion experiments were conducted on locked sand to study both its drained and undrained behaviour during cavity expansion. In this seminar a comparison of the drained behaviour of locked sand in its intact and reconstituted states will be presented, as well as the finite element modelling conducted to derive material parameters from the test data. The undrained behaviour of the material during a sequence of loading-holding stages is presented. The evolution of void ratio in the soil annulus surrounding the expanding cavity will be shown and compared to what is commonly assumed in cavity expansion theory.

This talk is part of the Engineering Department Geotechnical Research Seminars series.

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