Influencing factors analysis of hard limestone reformation and strength weakening under acidic effect

Abstract

Roof disaster has always been an important factor restricting coal mine safety production. Acidic effect can reform the rock mass structure to weaken the macroscopic strength characteristics, which is an effective way to control the hard limestone roof. In this study, the effects of various factors on the reaction characteristics and mechanical properties of limestone were analyzed. The results show that the acid with stronger hydrogen production capacity after ionization (pK_a<0) has more prominent damage to the mineral grains of limestone. When pK_a increases from −8.00 to 15.70, uniaxial compressive strength and elastic modulus of limestone increase by 117.22% and 75.98%. The influence of acid concentration is manifested in the dissolution behavior of mineral crystals, the crystal defects caused by large-scale acid action will lead to the deterioration of limestone strength, and the strength after 15% concentration reformation can be reduced by 59.42%. The effect of acidification time on limestone has stages and is the most obvious in the initial metathesis reaction stage (within 60 min). The key to the strength damage of acidified limestone is the participation of hydrogen ions in the reaction system. Based on the analytic hierarchy process method, the influence weights of acid type, acid concentration and acidification time on strength are 24.30%, 59.54% and 16.16%, respectively. The research results provide theoretical support for the acidification control of hard limestone roofs in coal mines.

Keywords

hard roof / acidic effect / structural reformation / strength weakening / influencing factors

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Foundation item: Project(2021YFC2902102) supported by the National Key Research and Development Program of China; Project (52374142) supported by the National Natural Science Foundation of China; Project(JSTU-2022-066) supported by the Young Talent Support Project of Jiangsu Association for Science and Technology, China