A novel thermo-mechanical coupling approach for thermal fracturing of rocks in the three-dimensional FDEM
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A novel thermo-mechanical coupling approach for thermal fracturing of rocks in the three-dimensional FDEM Clément Joulin1 · Jiansheng Xiang1 · John-Paul Latham1 Received: 21 June 2019 / Revised: 5 February 2020 / Accepted: 7 February 2020 © The Author(s) 2020
Abstract This paper presents a new three-dimensional thermo-mechanical (TM) coupling approach for thermal fracturing of rocks in the finite–discrete element method (FDEM). The linear thermal expansion formula is implemented in the context of FDEM according to the concept of the multiplicative split of the deformation gradient. The presented TM formulation is derived in the geo-mechanical solver, enabling thermal expansion and thermally induced fracturing. This TM approach is validated against analytical solutions of the Cauchy stress, thermal expansion and stress distribution. Additionally, the thermal load on the previously validated configurations is increased and the resulting fracture initiation and propagation are observed. Finally, simulation results of the cracking of a reinforced concrete structure under thermal stress are compared to experimental results. Results are in excellent agreement. Keywords Thermo-mechanical (TM) · Finite element method (FEM) · Discrete element method (DEM) · Finite–discrete element method (FDEM) · Thermal cracking · Explicit method · Fracture model
1 Introduction Thermally induced deformations and fracturing are significant concerns in many engineering fields such as engine design, nuclear fission reactors, geothermal energy, hydrocarbon production and radioactive waste disposal. When a material is exposed to a temperature gradient, it will deform and cracks may appear, the prediction of those cracks is key in making robust, efficient and safe designs. In geothermal energy exploitation, the injection cycles of cool water in the hot reservoir are likely to induce fractures [37], and in hydrocarbon production, thermal shocks are found to enhance the hydraulic fracturing efficiency [6]. In such applications, the fractures increase the permeability of the reservoirs and have a positive influence on production. On the contrary, in the context of radioactive waste disposal fractures are undesirable as initiating new cracks in the rock is potentially creating new flow pathways for radionuclides to be transported into the biosphere. As high temperatures are expected in the vicinity of a geological disposal facility (GDF), pre-
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Jiansheng Xiang [email protected] Department of Earth Science and Engineering, Imperial College London, London, UK
dicting thermally induced deformations and failure is of importance for safe disposal of the radioactive waste. In radioactive repository applications, the major heat-driven process is the thermal expansion of the rock. Thermal expansion is a strongly coupled process because it requires the mechanical equations to be modified. A typical granite has a coefficient of thermal expansion of 8 × 10−6 /◦ C. For a temperature rise of 50 ◦ C, this is equivalent to a 0.015% volume change. Altho
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