Assessment of stress around mine workings at the time of rockburst occurrence

Abstract

This article deals with a specific rockburst case in the ČSM Mine in the Ostrava-Karviná Coalfield (OKC), Czech Republic. Determination of the magnitude of acting stress is based on the constant weight of the overlying rocks. The rule that the force of stress relief of a mined-out space is equal to the force of additional load in the surrounding unmined area holds true. The magnitude of stress relief is influenced considerably by whether the total thickness of strong overlying layers is disturbed. The state of complete failure of overlying layers is assessed on the basis of undermined surface subsidence measurement. In the case considered, multiple seams were mined; thus, stress transfer to overlying as well as underlying layers is dealt with. In the individual stages of the calculation of acting stresses, the basic rule that the constant weight on the whole affected area, corresponding to the whole roof, was checked. Stress is determined at the time of rockburst occurrence. The maximum magnitude of acting stress around the mine workings reaches up to approximately 100 MPa, which is five times the original geostatic pressure.

Keywords:

• rockburst
• underground mining
• longwall mining
• stress distribution
• surface subsidence
• overlying strata disintegration

Acknowledgements

This work was performed with the financial support of Grant 105/09/P277 from the Grant Agency of the Czech Republic.