Application of CMRI-ISM RMR for Stability Analysis of Development Workings for Ballarpur Underground Coal Mine - An Empirical and Numerical Approach

Abstract

Roof bolt failures in the mine generally occur due to the poor identification of the weak rock layers and considered as a major concern for underground coal mines in terms of its productivity and safety. The triggering factor responsible for underground roof failure is the presence of weak bedding planes and various geological discontinuities. Geological disruptions present in the mine roof seriously affect the continuity of the rock layers resulting in block failure. However, numerous improved methods have been suggested by a number of researchers but still, the upholding of the accidents due to roof fall is considered as a major challenge for underground mine workings. Thus, it is necessary to give proper emphasis on characterization of the roof fall so that stability of the mine workings could be increased and movement of the weak and layered strata can be arrested by applying an adequate roof bolting system. This mechanism of roof support gives the composite binding between the rock layers by restricting the roof fall. The stability of mine workings can be also increased by proper application of rock mass classifications system and adequate design of support system and finally, by extensive simulation methods and statistical methods like FLAC 3D numerical and statistical modelling to ascertain the stability of the workings. CMRI-ISM RMR (Central Mining Research Institute – Indian School of Mines Rock Mass Rating System) classification system is the most popular and practiced method for roof support design in Indian coal mines which is being successfully used from last several years for roof support design in Indian geo-mining conditions. This forms the basis to estimate the rock load and support design. In this paper attempt has been made to assess the stability of workings and pillars below the railway track by using empirical and numerical approach. After both the studies it can be said that, the galleries and pillars underlying the railways track are stable, as factor of safety in each case is more than 2. Later on, the study was also extended to see the effects of subsidence on the surface which reveals that, there shall be no such effect on the surface due to underground workings as the value of NEW (non-effective width) is less than 0.4 for both the cases.