Abstract: Coal mining leads to overburden breakage and ground subsidence, and the dynamic evolution process of height of fractured zone could be revealed by the law of overburden and surface migration. Because the ground subsidence lags behind the coal mining, after the mined-out area is abandoned, the height of fractured zone is lower than mining process due to long-term compaction. Based on the characteristics of the subsidence velocity of surface point, the evolution process of the height of fractured zone is divided into two stages. The first stage corresponds to the process of rock layer breaking and gradually passing upward, then the second stage with subsidence of fractured zone corresponds to the process of separation of layers and closure of cracks, deformation and rebound of fractured rock layers after compression, and natural compaction of broken rock masses. This paper focused on the influence of compaction on the height of fractured zone. According to the quantitative relationship between the thickness of coal seam, the rock deformation in caved zone and fractured zone, and the ground subsidence, the prediction model of the height of fractured zone in the second stage was established, which was verified with the actual measurement results of Taiping coal mine. The control variable method is applied to further analyze the evolution characteristics of the height of fractured zone in the abandoned goaf under the influence of each single factor. The results show that the height of fractured zone is related to the uniaxial compressive strength of block in the caved zone, the initial bulking coefficient in the caved zone, the maximum height of fractured zone during mining process and the corresponding height of the caved zone, the depth of coal seam, and the amount of grounding subsidence. After 15 years of mining in Taiping coal mine, the measured value of the height of fractured zone is 11.36?13.00 m, which verifies the reliability of prediction model with predicted value of 12.75 m. Finally, the prediction model was used to carry out theoretical calculations on the height of fractured zone 2002?2003 in the abandoned goaf of Wu’an coal mine (closed mine), combined with ground-airborne transient electromagnetic system to determine the ideal location of ground gas drainage borehole, by which a ground borehole gas drainage test was successfully carried out.

Key words: abandoned goaf, the height of fractured zone, compaction, ground-airborne transient electromagnetic system