Thermo-hydro-mechanical Behavior of Granite under Cyclic Temperature Changes

Meysam Najari, Postdoctoral fellow, Department of Civil Engineering and Applied Mechanics, McGill University, Montreal, QC, Canada and Antony P Selvadurai, William Scott Professor and James McGill Professor, Department of Civil Engineering and Applied Mechanics, McGill University, Montreal, QC, Canada

Contact First Author: Meysam Najari; meysam.najari@mail.mcgill.ca

Previously Published Material: Part of the work was presented in the Environmental Earth Sciences journal by Meysam Najari and APS Selvadurai:http://link.springer.com/article/10.1007%2Fs12665-013-2945-3

Abstract ID#: 34615

 

English Abstract:
This research deals with the computational and experimental investigation of thermo-hydro-mechanical processes that are induced by the boundary heating of a granite cylinder containing a cylindrical cavity. The study is of interest to geomechanics problems associated with the deep geologic disposal of heat-emitting nuclear fuel wastes, the extraction of geothermal energy, oil and gas recovery, and the geologic sequestration of carbon dioxide in supercritical form. Temperature changes can influence a saturated porous geomaterials in several ways: it can cause skeletal deformation due to thermal expansion of the rock; induce fluid flow due to the fluid pressures generated by the differential thermal expansion between the porous skeleton and pore fluid; and alter the physical characteristics of the migrating pore fluid.

A cylindrical granite sample measured 15.24 cm in diameter and 30.48 cm in height containing a sealed fluid-filled cavity with a diameter of 2.54 cm and a depth of 15.24 cm was prepared. Prior to performing the THM experiment the permeability of the sample was estimated using constant flow rate steady state technique. The sample was then subjected to a cycle of temperature changes on its outer surface and the temperature and fluid pressure changes in the fluid-filled cavity were measured. It was observed that regardless of how precisely the cavity was filled with de-aired water, air bubbles can still exist in the cavity and influence the fluid pressure changes. A novel technique was suggested for taking into account the influence of the volume of trapped air and eliminating its effect in the estimation of the fluid pressure changes in the fluid-filled cavity. The experiment was computationally modeled using the finite element code COMSOL MultiphysicsTM and the experimental results were compared with the computational estimates. The computational model took into account the compressibility of the water, the porous skeleton and the solid grains.

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