Experimental investigation on the reformation and strength weakening of hard limestone by acidizing

Several derivative disasters such as ground pressure disasters and methane explosions can be caused by the hard roof in coal mines. For limestone roofs with fine integrity and extreme hardness, collapse is difficult and the effect of conventional roof control methods is limited. Acidizing reformation is an effective way to weaken the strength of roof strata based on acid-rock reaction. In this study, the rock strength damage law and acid reaction characteristics were tested by the limestone acidification experiment. Besides, the strength degradation mechanism of limestone under the acidity effect was analyzed. The results show that the acid corrosion characteristics of limestone are obvious, as numerous mineral grains generate voids under the effects of acid corrosion, and more defects are formed inside. The acid-rock reaction is the most intense at the early stage and then gradually reaches dynamic equilibrium, and the acid corrosion rate of limestone is 4.24% (10% HCl, 360 min). The hard limestone is damaged after acidification. Furthermore, the internal cracks can be induced to rapid initiation and unstable propagation under load, which reduces the strain required for rock failure by 33.33%. The failure morphology is more complicated, and the uniaxial compressive strength and elastic modulus decrease by 52.42% and 34.44% respectively. The strength weakening of hard roof after acidification is due to the defects such as intergranular cracking caused by the corrosion of rock crystals under acidity effect, which accelerate the initiation and propagation of internal cracks with external force. Macroscopically, acidification induced the deterioration of rock mechanical properties by reforming the roof structure. The feasibility of acidizing reformation method to control hard roof is confirmed in this study.