Investigation of the thermo hydro mechanical behaviour of large scale experiments - including parametric studies on various critical factors

• Main Author: Tey, Chun Yean
• Published: Cardiff University 2004
• Subjects: 624.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.583499

This thesis presents an investigation into the thermo/hydro/mechanical interactions occurring in two large scale experiments with different geometry setup designed for deep geological disposal of nuclear waste. The analysis of flow and deformation through unsaturated soils was performed using the proposed constitutive model. The following mechanisms are accommodated moisture flow in liquid and vapour forms, dry air flow including the movement of bulk air and the transport of dissolved air in the pore water, heat transfer by conduction, convection and latent heat of vapourisation, and the elasto-plastic deformation of unsaturated soils. The governing differential equations are solved spatially using a finite element technique and temporally using a finite difference technique. The numerical model was subsequently applied to two large scale experiments: AECL's Buffer/Container Experiment and AECL's Horizontal Canister In-room geometry. The analyses involved modelling the coupled thermo/hydro/mechanical interaction between the engineered buffer and the host rock, and the swelling phenomena at the buffer/rock interface. A comprehensive set of material parameters was determined for use in the numerical code. A theoretical formulation was developed to describe a time-dependent adsorption/desorption process associated with the micro/macro swelling phenomena occurring in bentonite-based buffer materials. This was implemented within the numerical model. The transient swelling behaviour of bentonite-based buffer materials was found to be influential in the simulation of an underground repository, in particular the resaturation behaviour in expansive clay. Sensitivity analyses on critical parameters identified for both geometry setups are presented and shown to affect the resaturation processes to varying degrees. This investigation has provided valuable insights into the repositories' behaviour.