Numerical modelling is increasingly being used to evaluate ground stability and to assist in the long-term planning of mining operations. However, selection of appropriate constitutive material behaviour and input parameters for the rock mass is still debated amongst the rock mechanics community. A case study of a hard rock mine practising sublevel open stoping has been simulated using 3D finite difference method (FLAC3D). The mine was modelled using four types of constitutive material models-Mohr-Coulomb with post-peak cohesion-softening/friction-softening, bi-linear Mohr-Coulomb with post-peak cohesion-softening/friction-softening, Mohr-Coulomb with post-peak cohesion-softening/friction-hardening and the improved unified constitutive model (IUCM). The outcome of all approaches has been compared with measured ground performance. The comparison revealed that the numerical model using the IUCM provides the most realistic match to the observations in the mine including the failure of the crown pillars.
Stability of wall slopes is the basic in-gradient for carrying out economic and safe extraction of mineral at any open pit mine. At Rampura Agucha Mine open pit (India) this assumes a greater emphasis as its footwall is achieving its final configuration while hangwall is on dynamic stage. During blasting, back break was the main concern as despite of carrying out pre-splitting, the benches experienced substantial back break adversely affecting the stability. The back break damages the remaining rock and reduces rock mass strength too.For addressing these issues, an experiment involving 22 blasts was conducted to identify and understand factors causing rock damage. The investigations consisted of collection of ground characteristics (comprehensively termed as Rock Mass Rating) for each test blast site and the blast results including extent of the back break, fractured zone, their orientation, etc were recorded. Based on these observations, a number of measures like modification in firing front orientation, rationale explosive energy concentration vis a vis rock characterization have been initiated commensurate with rock characteristics. It has led to significant improvement in stability of the pit as authenticated by safe standing of the footwall for 25 benches. These measures have instilled confidence to the mine management that the pit will provide sustainable business targeted production till its designed life.
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