Evaluation of energy accumulation, strain burst potential and stability of rock mass during underground extraction of a highly stressed coal seam under massive strata-a field study

Abstract

Severe geotechnical problems like strain burst, side spalling, roof fall, irregular caving, the premature collapse of rib/remnant pillars, etc. are frequently observed during the mining of highly stressed coal seams under massive overlying strata. In this study, different underground structures and adequate support systems under such complex geological conditions are designed by evaluating energy accumulation, strain burst potential, stress conditions and stability of the rock mass. An energy-based safety factor is derived and implemented through numerical modelling to identify the yield zones in the surrounding rock mass. The strain burst potential in different locations is also evaluated by the elastic energy accumulation and the Burst Potential Index (BPI) whose maximum values reach 628 kJ/m3 and 47.6% respectively during depillaring operations. These values indicate the significant strain burst and side spalling conditions which are corroborated by the field investigations and monitoring data by geotechnical instruments. Control measures have been taken by leaving the optimum size of rib/remnant pillars in the goaf and installing adequate support systems in the working areas. It is observed in the field that rib/remnant pillars, designed with a safety factor of ∼0.17 are found suitable for regular caving of overlying massive strata in the goaf. The side spalling and the strain burst are minimised by installing the glass-reinforced plastic (GRP) bolts and the wire mesh. The uncontrolled caving of the overlying massive strata in the working area is prevented by installing closely spaced two rows of rock bolts at the goaf edge. This study would be helpful to design different underground structures and to ensure the safety of working areas during the extraction of highly stressed coal seams under massive strata.