Abstract: The water coning of coal seam permeability coefficient and adsorption characteristic has seldom been studied at home and abroad. Aiming at that, the theory model of dynamical water coning breaking through boundary of drilling hole was established. The analysis presents that when evacuation during the process of gas pressure determination, gas flow amount is maximum, breaking through velocity of water coining is fastest, and the influence of gas flow decreasing after borehole sealing is smaller. Additionally, the relation between the time of breaking through boundary of drilling hole and the gas flow amount, thickness of coal seam, drilling depth and the porosity of coal mass in the rising process of dynamic water coning has been derived, and the times of water coning breaking through the boundaries with different flow rate, coal seam thickness and length of borehole were calculated. It is found that the breaking through time greatly reduces with the increase of flow rate. As the flow rate keep a constant, with the increase of the drilling depth, the breaking through time first undergoes a smaller variation process, and then decreases significantly. Moreover, using the ball direction flow field to determine the gas pressure in engineering , the influence of coal seam water coning to the gas pressure determination can be avoided by shorten the evacuation time.

Key words: gas pressure, water coning effect, coal-rock mass