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

酸效应下坚硬石灰岩改造及强度弱化的影响因素研究

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 pKa 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.

顶板灾害是制约煤矿安全生产的重要因素,酸效应可改造岩体结构以弱化宏观强度特性,是坚硬石灰岩顶板控制的有效途径。本研究分析了各因素对石灰岩反应特性和力学特性的影响。结果表明:电离后产氢能力更强的酸(pK_(a)<0)对灰岩矿物颗粒的破坏作用更为突出。当pKa从−8.00增加到15.70时,石灰岩的单轴抗压强度和弹性模量分别增加了117.22%和75.98%。酸浓度对石灰岩影响主要表现为矿物晶体的溶蚀行为,大规模酸作用产生的晶体缺陷会引发石灰岩强度的劣化,经15%浓度酸化改造后的强度可降低59.42%。酸化时间对石灰岩影响具有阶段性,在前期复分解反应阶段(60 min内)的表现最为明显。酸化石灰岩强度损伤关键在于酸-岩反应体系中氢离子参与程度,基于AHP法得到酸类型、酸浓度和酸化时间对强度影响的权重分别占24.30%、59.54%和16.16%。研究结果为煤矿坚硬石灰岩顶板酸化控制提供了理论支撑。