Development of fracture processes in Silesian Carboniferous sandstones

The development of fracture processes in selected Carboniferous rocks from the Upper Silesian Coal Basin is described, with particular regard to the behaviour of rock specimens in the post-failure stage. The fracture processes were monitored using the stress-strain relations, coupled with acoustic emission, recorded during loading. Energy accumulation and dissipation phenomena were observed during rock loading. Cracking was recorded on the stress-strain curves as deformation loops, accompanied by significant stress decreases, and as cyclic increases in acoustic emission activity. Observing and analysing stages of high acoustic emission and stress drops enabled determination of three ways ("schemes") in which fracture originated and developed during the post-critical stage. Scheme I is damage and movement of grains and rock cement, scheme II is destruction of single rock grains of particular resistance, and scheme III is a dislocational and slide deformation of the rock medium.