Numerical modelling of pore-fluid-enhanced thermal spallation in granitic rock

Abstract

This paper considers numerically the effect of pore-fluid on thermal spallation of granitic rock. For this end, a numerical model based on the embedded discontinuity finite element approach to rock fracture and an explicit scheme to solve the underlying thermo-mechanical problem is developed. In the present implementation, a displacement discontinuity (crack) is embedded perpendicular to the first principal direction in a linear triangle element upon violation of the Rankine criterion. In the thermo-mechanical problem, the heating due to mechanical dissipation is neglected as insignificant in comparison to the external heat flux. This leads to an uncoupled thermo-mechanical problem where the only input from the thermal part to the mechanical part is thermal strains. This problem is solved with explicit time marching using the mass scaling to speed up the solution. Finally, the fluid trapped into the micro-pores is modelled as a material that can bear only volumetric compressive stresses. A thermal spallation problem of a rock sample under axisymmetry is simulated as a numerical example.