Discussions on rockburst and dynamic ground support in deep mines

Abstract

Abstract The paper is a summary of discussions on four topics in rockburst and dynamic ground support. Topic 1 is the mechanisms of rockburst. Rockburst events are classified into two categories in accordance with the triggering mechanisms, i.e. strain burst and fault-slip burst. Strain burst occurs on rock surfaces when the tangential stress exceeds the rock strength in hard and brittle rocks. Fault-slip burst is triggered by fault-slip induced seismicity. Topic 2 is prediction and forecasting of rockburst events. Prediction for a rockburst event must tell the location, timing and magnitude of the event. Forecasting could simply foresee the probability of some of the three parameters. It is extremely challenging to predict rockbursts and large seismic events with current knowledge and technologies, but forecasting is possible, for example the possible locations of strain burst in an underground opening. At present, the approach using seismic monitoring and numerical modelling is a promising forecasting method. Topic 3 is preconditioning methods. The current preconditioning methods are blasting, relief-hole drilling and hydrofracturing. Defusing fault-slip seismicity is difficult and challenging but has been achieved. In very deep locations (>3000 m), the fracturing could extend from the excavation face to a deep location ahead of the face and therefore preconditioning is usually not required. Topic 4 is dynamic ground support against rockburst. Dynamic ground support requires that the support system be strong enough to sustain the momentum of the ejecting rock on one hand and tough enough on the other hand to absorb the strain and seismic energies released from the rock mass. The current dynamic support systems in underground mining are composed of yielding tendons and flexible surface retaining elements like mesh/screen and straps. Yielding props and engineered timber props are also used for dynamic support.