Experimental study of the inrush of fines events in caving mining

Cave mining has inherent risks, which include rock bursts, collapses, subsidence, and inrushes. Among the inrush events that can occur are the inflows of water, mud, and dry-fine material. The latter type of inflow is one about which we have the least amount of information and little research, despite the fatal consequences that have occurred associated with this phenomenon. In this work, the inrush of fine events was simulated at a laboratory scale to study the main variables that influence these events. An experimental setup consisting of a drawbell filled with different layers of coarse and medium granular material was used as a base. A hang-up was induced in the setup and then fine material was added on top to observe the consequences. Three experimental stages were developed applying three distinct fine materials: glass microspheres, fragmented concrete, and finally clay. It was observed that the magnitude of the inrush event was directly related to lower friction and higher sphericity of the fine material. Finally, the inrush of fine events did not apparently occur due to shear failures in the experimental setup; rather in the simulated scenarios with the presence of coarse material, the removal of a hang-up was always required as a trigger mechanism to generate an inrush of fines event.