Abstract: In this paper, to accurately measure the effective radius and identify the reasonable arrangement of drainage borehole spacing, the arrangement of drilling holes in the traditional gas pressure measurement were improved appropriately. In the same height, unequal spacing of pressure measurement boreholes and drainage holes were arranged separately, the effective extraction radius was then determined by monitoring the gas pressure changes in different borehole groups, and the field test was practiced in Tingnan coal mine. The stress drop curves show that the gas around the drainage holes flows in a state of linear seepage in the early drainage period, then gradually turns to low-speed nonlinear seepage with extraction time prolonged, while the gas pressure and extraction time basically shows power function correlation in the whole curve. Moreover, the effective drainage radius reaches to 4 meters after 40 days gas extraction, and the influence scope of gas drainage expands no longer after the radius up to 5 meters.

Key words: effective radius, gas pressure, gas drainage, stress drop curve