ABSTRACT
In seventies and eighties the technological roof caving was utilized when mining deposit with thickness up to 5 meters located out of protection pillars. Together with inducing the caving, the remnant pillars were blasted out. This method of technological caving had not met the requirements because the blasted roof plate with low loosing factor of the fallen rock had not ensured the appropriate support for upper roof strata. This resulted in periodical stress increase in the solid in front of the mining face and numerous tremors and stress-relieve events caused by emission of elastic energy gathered in the rock-mass due to exceeding the compressive strength. The tremors and stress-release events were often of global nature and covered major part of the mining area. Therefore, intensive investigations on improving the technology of caving and a search for solutions ensuring the required roof support in the mined-out space were carried out. The J-Z mining method with limited (with regard to place and height) roof caving and J-3S method with periodical caving and intensive blasting were introduced. The idea of that solution was giving up blasting of the remnant pillars. At the same time experimental exploitation with roof control by its deflection on the remnant pillars and spontaneous caving of the roof rocks, without its induction by blasting were introduced in the “Rudna” mine.
