Evaluation of structurally controlled rockfall hazard for underground excavations

Authors: Fuentes-Espinoza, MA; Andersson, UB; Zhang, P Download Paper

Cite As:
Fuentes-Espinoza, MA, Andersson, UB & Zhang, P 2024, 'Evaluation of structurally controlled rockfall hazard for underground excavations', in Daniel Johansson & Håkan Schunnesson (eds), MassMin 2024: Proceedings of the International Conference & Exhibition on Mass Mining, Luleå University of Technology, Luleå, pp. 1066-1082.



Abstract:
Sublevel caving is used in Kiirunavaara mine at large depths. Seismicity started in the mine in 2007 / 2008 and since then, large rockfalls controlled by structures have occurred in many parts of the mine, despite the use of dynamic rock support systems. A novel “fork layout” for sublevel caving operations is considered for implementation in Kiirunavaara mine. The effect of implementing the fork layout on the rockfall hazard potential for structurally controlled rockfalls has not been studied yet. Historical rockfalls with volume larger than 15 m3 that occurred in different parts of the mine during the period from November 2009 to December 2022 were analysed with respect to their adjacent structures, rockfall location and type of excavation. Ground motion parameters were obtained after processing seismic source parameters of the events that triggered these rockfalls. The rockfall hazard in the fork layout was tested in drift intersections in two production blocks, taking the traditional layout as a point of comparison. Considering various structure combinations and excavation orientations, wedge volumes were obtained at the intersections by using UnWedge. The variations in wedge volumes were used as a proxy for rockfall potential evaluation. It was observed that rockfalls in footwall drift intersections occurred more often at certain footwall drift orientations. Many seismic events that triggered these rockfalls are located close to the ore passes and generated ground accelerations between 0.5 to 10 times the gravity acceleration. Depending on the intersection angle, the fork layout can increase or decrease the rockfall hazard potential.