Thermal jet drilling of granite rock: a numerical 3D finite-element study

Abstract

This paper presents a numerical study on thermal jet drilling of granite rock that is based on thermal spallation phenomenon. For this end, a numerical method based on finite elements and a damage-viscoplasticity model is developed for solving the underlying coupled thermo-mechanical problem. An explicit time stepping scheme is applied in solving the global problem, which in the present case is amenable to extreme mass scaling. Rock heterogeneity is accounted for as random clusters of finite elements representing rock constituent minerals. The numerical approach is validated based on experiments on thermal shock weakening effect of granite in dynamic Brazilian disc test. The validated model is applied in 3D simulations of thermal jet drilling with a short duration (0.2 s) and high intensity (3 MW/m2) thermal flux. The present numerical approach predicts the spalling as a highly (tensile) damaged rock. Finally, it shown that thermal drilling exploiting heating-forced cooling cycles is a viable method when drilling in hot rock mass.