Numerical simulation study on stability analysis of crown pillar—a case study

The transition from an open-pit to an underground space is inevitable to exploit deposits from greater depth. Crown pillar, a remnant ore usually left in between open-pit to underground mining that supports the terrain and aids in carrying out underground mining operations safely and its stability is vital. The design of crown pillar is majorly influenced by its thickness, span, slope angle, ore dip, depth of open-pit mining, rock mass quality, cohesion and friction angle. When the crown pillar is situated near the surface (shallow depth), it is synonymously named as the surface crown. The behaviour of the crown pillar is different from the surface crown due to variation in geo-mining conditions. As underground mining progresses, displacements around the crown pillar are generated and stresses reorients around it. This can be assessed through numerical simulation. To have a better understanding, this paper concentrates on crown pillar’s stability and geometrical parameters influence on its stability. The field study is carried out at Ramrama manganese ore mine, where the transitioning takes place at shallower depth and FLAC3D 5.0 is used for numerical simulation work to analyse the behaviour of the crown pillar. From the results interpreted, it is found that the maximum amount of principal stresses decreases for the lower span, 8 m, of crown pillar with increase in slope angle and for the larger span as in case of 22 m span; the stresses generated are reduced in case of 38° slope angle and increased for 45° slope angle. Higher dip of orebody generates high amount of stresses in the pillar and with an increase in the depth of mining, high amount of displacements and stresses are observed around the crown pillar.