| In connection with weakening hard roof, a series of research methods have been taken in this paper,including theoretical research, numerical simulation, project implementation and effects monitoring. First, based on the current methods for weakening hard roof, this paper designs a program of deep holes for presplitting topper roofs, partitions hard roof levels and computes destruction radius(crush zone, fractured zone) of theoretical blasting points according to the relevant blasting theory, accomplishing the formost theoretical research. Based on the above results of the calculation, the following chapters study the blasting effect of single and group blast holes, and some design parameters affect the results, including no coupling coefficient, hole spacing, group spacing, charging structure and kits slot width.According to theoretical study for the impact on blasting effect by parameters and combined with the actual situation, this paper defines the reasonable value range of each parameter. Secondly, according to the reasonable range, combined with the N1202 face engineering background, ANSYS / LSDYNA is used to numerical simulated for each parameter. By comparing and analyzing the results of simulation, this paper defines the reasonable design parameters. Based on theoretical calculations and numerical simulation results of the preceding sections, N1202 weakening programs are determined and implemented. During the implementation, the top coal caving case has been recorded and analyzed, the hole wall has been peeked and contrasted the differences before and after blasting. And the concentration of gas and CO between the untreated face and N1202 have been analyzed so as to clear the effect of weakening. Finally, in order to give a comprehensive analysis of whether the roof weakening has achieved the expected effects,a pressure observation in the N1202 working face has been arranged to record support working resistance, strength, step distance and the roadway surface displacement according to inlines and stations.The conclusion:① Based on the mechanical parameters experiment, the formations above the roof have been graded and analyzed according to the model of beam and sheet. The two theoretical models are suitable to N1202 face. Based on key strata theory, this paper has obtained average plate load q and step distance. And according to the blasting theory, this paper has calculated for each formation damage zone radius.② According to N1202 face engineering background and numerical simulation results, the blasting design parameters have been determined. Radial no coupling coefficient values in the range 1.15-1.5, single hole blasts and forms fractured radius in the range of 1.5m-3m, single group blasts and forms fractured radius 3.5m. The hole pitch in one group has been ranged from 3-6m, and group spacing ranges from 7-8m. According to above theoretical research, the hole layout design can ensure the cracks formation between the holes. In addition, the kits lancing can enhance the directional effect. Therefore, kits can groove the width of 15 mm, and based on the numerical simulation results, the kits play a guiding role for blasting fissures and jets of high-energy.③ Based on pressure observation, the results show that the average distance of N1202 first weighting step is 27 m after weakening, contrasted with N1205 face, the distance has been shortened nearly 15 m, the average strength and resistance of stents have decreased during pressure observation and met the requirements of the rated working resistance, the roadway surface displacement amount is small, it tends to reduce the strength of advance support and lower roadway requirements. |
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