ROCK MASS STRENGTH AND SIESMICITY DURING CAVING PROPAGATION AT THE EL TENIENTE MINE, CHILE

Rock masses of primary copper ore at the El Teniente mine have been described as very competent and massive during caving operations. Underground mining operations have been accompanied with intense induced seismicity, and severe seismic failures have been experienced in pass years during caving propagation. Major factors causing seismicity have been analysed through back analysis studies undertaken at the Esmeralda mine sector during caving initiation and propagation. These studies included, rock structure characterization, data analysis of the recorded seimicity and the production records, and numerical modelling to assess the state of the stress in three different mine sectors. Mining parameters such as the extraction rate that influence caving propagation, were found to be similar between the studied sectors, however, the recorded seismicity of completely caved rock masses of similar volumes were found to be very different from each other. The numerical model results indicated that the stress path in a rock type from one particular sector during caving propagation moved in a direction where severe seismicity should be expected, however the recorded seismicity was benign compared to the observed seismicity in other studied sectors. This rock mass response is only possible for a rock mass with low strength, which can be described through the application of a novel definition of weak discontinuities. The results agree with the concept that the low rock mass strength correlates with the abundance of weak discontinuities, and therefore these rock mass features that to be considered in any kind of seismic risk analysis at the mine site.