Damage Model For Coal And Rock Under Coupled Thermal-Hydraulic-Mechanical Conditions And Its Application

The creation of an excavation damaged zone (EDZ) is expected around all man-made openings in geologic formations. In underground engineering such as deep mining, nuclear waste disposal and geothermal exploiting, the deep rock mass is in harsh environment of high ground stress, water pressure and temperature. The formation and its subsequent spatial and temporal evolution of EDZ in such environment are considered as a coupled process among thermal, hydraulic and mechanical (THM) fields. Understanding the physico-mechanical properties evolution in EDZ is of great importance for evaluating the engineering stability and safety, and for optimizing the supporting parameters. In addition, recognizing the gas migration and coal seam damage process under coupled thermal, hydraulic and mechanical conditions is also critical for deep coal mining, coalbed methane exploiting and CO2storage in unminable coal seam.Therefore, the present paper begins with the characterization of rock mass heterogeneity, based on which a coupled THM model considering rock damage process is proposed. The model is solved by programming on the basis of finite element software and validated by a laboratory experiment for thermal cracking test in granite. The initiation and propagation of primary cracks is vividly reproduced with the numerical simulation, which provide a numerical tool for studying the damage zone evolution under coupled THM conditions.Secondly, the proposed model is used to study the EDZ evolution under different in situ stress and elevated temperature.Thirdly, the proposed model is used to study the pillar stability in nuclear waste disposal based on the Aspo Pillar Stability Experiment (APSE) at Aspo Hard Rock Laboratory. Numerical model for KBS-3repository is carried out to predict the pillar stability under conditions of excavation, groundwater seepage, temperature variation and bentonite swelling.Fourthly, a fully coupled THM model for gas migration in deep coal seam is also established. A general permeability model under the combined influence of gas adsorption-induced solid deformation and thermally-induced gas desorption is developed and is implemented into the fully coupled THM model for gas transport. A numerical model for deep coal bed methane extraction is carried out to analysis the influence of different factors, especially thermal field, on gas drainage.Finally, combined with the actual coal seam conditions and in-situ measurement date, the coupled THM model for gas migration is used to predict the variation of gas pressure and gas content with depth.