Abstract: To address the challenges encountered in open-pit limestone mines,including low fragmentation efficiency of
hard rock with high joint density and high compressive strength,difficulty in controlling blasting-induced vibration,and stringent
environmental constraints in ecologically sensitive areas,a liquid oxygen (LOX) transient phase-change rock-breaking
technique suitable for fractured rock masses is proposed. Based on the quasi-static high-pressure generated by the rapid vaporization
and expansion of liquid oxygen,a two-stage rock-breaking mechanism characterized by stress-wave reflection enhancement
and gas wedge-driven crack propagation is analyzed. Field experiments were conducted in a large open-pit limestone mine
in Hebei Province. By systematically deploying vibration monitoring,fragment size statistics,and environmental parameter
measurements,the fracturing effectiveness,vibration propagation characteristics,and environmental impacts of the LOX phasechange
rock-breaking technique were quantitatively analyzed. The results indicate that approximately 70% of the rock fragments
in the free-face zone have particle sizes smaller than 30 cm,demonstrating significantly improved fragmentation uniformity compared
with conventional blasting. At a distance of 40 m from the source,the peak particle velocity is reduced by about 37% relative
to conventional blasting,and the dominant vibration frequencies are stably distributed within the range of 8 Hz to 15 Hz,
effectively avoiding resonance with typical building structures. In addition,no detectable emissions of harmful gases such as
NO_x and SO₂ were observed during the rock-breaking process,and the dust concentration was significantly reduced. These results
demonstrate that the liquid oxygen transient phase-change rock-breaking technique achieves both efficient rock fragmentation
and favorable vibration and environmental performance in high-steep slopes and ecologically sensitive open-pit mines,providing technical support for the engineering application of non-explosive rock-breaking methods and the development of green
mining practices.