Progressive damage characteristics and damage constitutive model of coal samples under long-term immersion
HAN Penghua1，2，ZHAO Yixin1，2，GAO Sen1，2，GAO Yirui1，2，ZHANG Cun1，2，HU Yong3
(1. Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources，China University of Mining and Technology(Beijing)，Beijing 100083，China；2. School of Energy and Mining Engineering，China University of
Mining and Technology(Beijing)，Beijing 100083，China；3. Huaneng Coal Industry Co.，Ltd.，Beijing 100070，China)
Abstract：Water-rock interaction is an essential factor in the weakening of coal rock masses. Long-term immersion as a type of water-rock interaction is widespread in mining engineering and shaft engineering. The progressive damage characterization of coal samples during long-term immersion is obtained by a uniaxial compression experiment. The relationship between mechanical parameters and saturation and immersion time is established，and the macroscopic fracture extension characteristic of coal samples are analyzed. The results show that the soaking process of coal samples can be divided into two stages：unsaturated immersion and long-term(saturated) immersion. The peak stress in coal samples decreases by 46.3% and 34.5% in the unsaturated stage and long-term immersion stage，respectively，which conforms to the exponentially decreasing trend. During long-term immersion，the number of macroscopic cracks produced in coal samples after loading gradually decreases from 6–8 in a dry to 2–3 in a 360 d soaked. The damage mode changes from combined tensile and shear damage for unsaturated coal samples to single shear damage for 360 d soaked coal samples. Based on initial compression characteristics and critical damage strength characteristics in a coal sample，a damage constitutive model describing the whole deformation process of a coal sample under long-term immersion is proposed using continuous damage mechanics and statistical damage theory. According to this model，it can be found that the initial damage increases gradually from 0 in a dry sample to 0.773 for a soaked 360 d sample with the increase of soaking time. In addition，the error and fit between model curves and the experimental data are evaluated by introducing the root mean square error(RMSE) and the coefficient of determination(R2). The theoretical curves of the improved model are found to be the highest matching with the experimental data. The maximum value of RMSE and the minimum value of R2 for the improved model are 1.81 and 0.76，respectively，which are better than the models proposed in existing papers.
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2024, Vol. 43 
