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Title: An investigation of the influence of elevated temperatures on the thermal-hydraulic-mechanical response of unsaturated soils
Author: Siddiqua, S.
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2008
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Abstract:
This thesis presents an investigation of the influence of elevated temperatures, defined in this thesis as within the range of 70°C-200°C, on the thermal-hydraulic-mechanical response of unsaturated soils. At elevated temperatures, high pore gas pressures develop due to an increase in both dry air pressure and vapour pressure. This gas pressure drives the flow of both gas and vapour, therefore advective flow of vapour dominates over diffusion flow. Moreover, elevated temperatures impact standard thermal/physical parameters of the various phases in the soil-water system. Based on Luikov's approach to thermal-hydraulic behaviour of capillary porous bodies, and an existing thermal-hydraulic-mechanical model, a new thermalhydraulic- mechanical formulation is developed within a mechanistic framework for unsaturated soils, applicable for elevated temperatures. Key advances carried out include the development of a new pore gas transfer equation as opposed to dry air transfer, changes to velocity of pore gas expression to account for elevated temperatures and the inclusion of thermo-osmotic flow of liquid due to temperature gradient. Also temperature sensitive parameters in the energy conservation equation have been considered as a function of temperature. A numerical solution is used to solve the theoretical formulation. A finite element method is presented to achieve spatial discretisation and temporal discretisation is achieved through the use of a finite difference technique. The performance of the model is explored via the simulation of two laboratory based experiments subjected to elevated thermal loads to cover the range of 70°C-200°C. Firstly, thermal and thermal-hydraulic experiments have been simulated to study the thermal-hydraulic response for a temperature boundary condition of 85°C. The new model shows a significant rise in pore gas pressure due to the elevated temperature. Consequently pore gas pressure gradients dominate the vapour flow. The advantages of the new model over an alternative model where elevated temperature effects are not considered are demonstrated via comparison of moisture distribution results. The new model shows much improved accuracy. A second simulation is carried out with an applied boundary temperature to a value of 150°C. The new model's performance again shows a significant increase in pore gas pressure due to the elevated temperature. Again the results yield a much improved solution compared to the alternative model.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.525634  DOI: Not available
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