Mining Protection Scope Determination of Low Protective Seam in Contiguous Seams

In order to set up the mining protection scope of No.11223 coal mining face in a protective seam under the contiguous seams in the middle coal group o f Jinjia Mine, six groups boreholes were made in 1118 1 1 roadway and return airway. With the gas desorption value of the borehole measured at site, the seam gas pre ssure of boreholes was calculated with the seam gas parameters of lab. The regression analysis was applied to pressure data. The six groups critical point of the protec tion scope obtained was a theoretical protection scope and the critical points were individually shifted in the boreholes by 1. 30, 1. 10, 17. 51, 16. 52, 3. 20 and3. 90 m. The strike pressure released angle was 55° and the inclined pressure released angle was 54° and 82° individually. In the protection scope, the pure quantity of pressure released gas drainage from protected seam was about 26. 286 3 million m3, the gas drainage rate reached to 80. 69%. The gas desorption index of drilling cuttings was not over the standard.