Prediction of amount and nature of abutment loading under varying overlying strata on the basis of empirical formulation
Safety of a pillar basically involves two parameters: (a) strength of the pillar and (b) mining induced stress on the pillar. In practice, assessment of mining induced stress on the pillar is rather more complex than the determination of the pillar strength. CMRI[1] has developed empirical relationship among different geomining parameters to estimate pillar strength but lack of information about mining induced stresses, in and around the extraction face under the existing massive overlying strata of shallow coal mines, directly affected mining feasibility.
Monitoring of the nature and amount of mining-induced stresses over pillars was undertaken at different coal seams with shallow depth cover and varying overlying strata conditions. The development of abutment loading on the coal pillars facing goaf line is visualised by the analysis of the in situ observations at different sites with varying geo-mining conditions. The rock properties and depositional conditions of the immediate roof strata at each site were studied and incorporated in terms of caveability index. Considering the relevant geo-mining parameters, which influenced the pillar loading, empirical relationships are attempted to estimate the range of influence and the value of ultimate induced stress (vertical) over the coal pillars of shallow depth cover.
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[1] Sheorey, P. R., Das, M. N., Barat, D., Prasad, R. K. and Singh, B., 1987. Coal pillar strength estimation from failed and stable cases. International Journal of Rock mechanics and Mining Sciences, 24: 347-355.