Materiały konferencyjne SEP 1992

Szkoła Eksploatacji Podziemnej * 92 377 of not caving roof the wider is the yielding zone ahead the front and the crushing of coal is more intensive. Theoretical models ajid experiences show us that the depth of yield zone in such cases could be many meters. And remember that the thickness of the seam is reasonably smal 1 here. In such a way several zones with different gas reglme is formed ahead of the front of coal face. The first zone is formed by crushed coal and is al- most degasified. The second one is the pćirt where primary cracks are developed and widened by high rock stress. By this the volu- me of macropores is increased and it causes partial desorption of gas from coal microstructure to the macropores. Coal seam has irregular błock structure here with pre-generated higher free gas pressure in the macropores. The third zone in conform with the strip of the highest abutment stress ahead the face. Inducing of new macrocracks takes place here but due to high confining stresses the volume of macropores is in fact smaller. The fourth zone is still ahead of the abutment stress zone and represents conditions in the seam prior to the exploitation. The first zone acts as a barrier, the second one as a gas expansion zone and the thlrd as an energy reservoir. As the exploitation is going on degasified barrier is gradually weakened. When the balance between passive forces of the barrier zone and active forces generated by gas pressure in the second zone collapses the process of bursting starts. Gas expands from the second zone pushing the coal barrier towards working area of the coal face, Coal from the second zone is collapsing to smali irregular błock pieces simultaneously. As a volume of opening macropores and a space between broken coal blocks are becoming greater the pro- cess of gas desorption from coal microstructure develops as an additional source of gas expansion energy. Owing to acting of significajit passive forces the desorption process has not so explosive character as it is obvious in "classical" outbursts. In case of roadways the mechanism is similar but increased rock stresses are usually of tectonic type. In inclined or steep seams the gravity acts as additional part of active forces. By short definitions the main features of the mechanism of both types of phenomena could be described as follows: