Abstract: Aim at the use of blasting to mining legacy ore pillars in metal mines has the limitations of poor safety and high ore loss rate,High Range Static Cracking Agent (HSCA) which has no vibration characteristics is introduced into the mining of legacy ore pillars. Through the design of HSCA expansion compressive stress tests and static rock breaking tests,the magnitude of HSCA radial expansion compressive stress and its distribution pattern in relation to the water-cement ratio were analyzed,and the feasibility of achieving the safe and low-loss mining of legacy pillars in metal mines through HSCA static rock breaking was demonstrated from the characteristics of the distribution of the expansion compressive stress,the method of controlling the orientation of the main crack,and the timeliness of rock breaking,respectively. The results show that when the water- cement ratio is larger than the theoretical optimum water-cement ratio,the expansion compressive stress decreases with the increase of the water-cement ratio. For an upwardly inclined borehole,the expansion compressive stress tends to increase from the bottom of the borehole towards the mouth of the borehole. Conversely,for a downward inclined hole,the expansion compressive stress tends to decrease. By using HSCA static rock breaking,the main crack direction of the legacy ore pillars can be controlled by pre-cutting slots in the charge holes,adding induced sheet or induced holes,which can effectively reduce the re-injury of the non-rock-breaking area of the ore rock. Therefore,for the areas where blasting is not suitable for mining the legacy ore pillars,using HSCA static rock breaking is not only conducive to ensuring the safety of legacy pillar mining,but also improves the legacy pillar mining rate. The study results can provide reference for further exploring the new rock breaking theory and technology of mining the legacy ore pillars in metal mines.

Key words: static rock breaking,legacy ore pillars,expansion compression stress,main crack,timeliness