22 / 2020-02-29 06:06:48

Panel destressing strategies for remnant pillar extraction

Destress Blasting,Pre-conditioning,Rockbursts,Numerical Modelling

Rockbursts are one of the most common safety hazards in underground mining. Generally defined as violent brittle failure of rock, rockbursts typically occur in stiff rock masses subjected to high mining induced stresses. Destress blasting or pre-conditioning is a rockburst control technique, where the action of blasting rock in advance of extraction lowers the local stress and stiffness of the rock, in consequence reducing its burst proneness. The technique is commonly practiced in hard rock mines development faces, and in sill and crown pillars which become burst-prone as the orebody is extracted. Large-scale destressing is a variant of destress blasting where panels are drilled off and blasted in the hanging wall of the orebody using longhole, fanning blast pattern from crosscut drifts situated in the host rock. These panels cut off the mining region from high mining induced or far field stresses, improving the region’s mineability or potential for safe extraction.
Numerical modelling back analysis case studies have shown that reducing the panel stiffness and stress can replicate the stress changes measured in the field, and that the application of these two effects in the model provides an immediate beneficial stress reduction in the stress shadow stopes. The aim of this study is to quantify the effect of destressing over the entire extraction sequence of the remnant pillar and to determine the optimal panel geometry.
A typical remnant pillar model is constructed, and the holistic destressing effect is applied to the destress panels with a high rock fragmentation and stress reduction effect. The entirety of remnant pillar is extracted in sequence and the ore at risk in in the pillar is quantified with the brittle shear ratio and burst potential index. The energy release rate of each mining step and development step is also measured. Assuming a best-case scenario for panel destressing, a cost benefit analysis is conducted in terms of improved mineability in the stress shadow and reduced mineability outside the stress shadow. Finally, a parametric study is conducted to evaluate the effect of panel depth, width, and standoff distance on mineability.
It is shown that ore at risk is significantly reduced in the stress shadow stopes over the entire extraction sequence. The energy release rate of each ore extraction step is also reduced over the entire sequence, ameliorating the safety of ore extraction.