Blast Vibration Damage and Its Monitoring to Underground Rock Cave from Adjacent Open-pit Blasting

摘要

During open-pit mine excavation, blast induced vibrations can cause micro-cracks in nearby transport lane and decrease its strength, even the failure of rock engineering. In this paper, a study was conducted to evaluate the effect of blasting in Nanfen open-pit iron mine on the stability of adjoining underground rock cave workings. The field survey of geological conditions, the geological characteristics of key positions of underground opening in Nanfen open mine, China were carried out, especially how the construction process will affect its stability. Strata monitoring instruments, viz. borehole extensometers, convergence indicators, strain bars, stress capsules and load cells were installed in the roof. Monitoring of strata behavior was carried out before and after the blasts. It is concluded that the Nanfen mine contains structural elements and distinct textural varieties which differ significantly in their response to rock properties testing and to excavation. Data collected in this study demonstrate the highly inhomogeneity internal structure characteristic of apparently homogenous batholiths, and the influence of this inho-mogentiy on rock mass response. Some measures are proposed to take so as to play fully the role of host rock in construction process. The practice showed that the geological/engineering conditions of rock in Nanfen mine are very complex, and it is of importance to monitor rock's structural plane and deformation and to readjust timely the construction schedule and relevant technologies. Major damage was observed when the magnitude of PPV exceeded 180mm/s. It was also observed that the roof of underground level cave vibrated with 1.1～2.8times higher amplitude of vibration compared to the span of level cave. It is stressed that the self-stability mechanism of key positions should be monitored and controlled carefully so as to ply fully the role of self-stability of host rock. What the measures proposed to take and relevant experience will benefit the construction of the other similar projects/rock engineering.