Study On Key Technology Of Static Cracking Agent In Large Verhanging Roof Area At Fully Mechanized Mining End

The long time large overhanging roof at the end of the header of the header mining face is easy to cause the accumulation of gas and large area to pressure in the upper and lower corner,which seriously affects the normal mining and safe production of the mine.The method of replacing the above materials with static expanders,combined with the large overhanging roof at the end of the header,is proposed to be applied scientifically and standardized to solve the cracking problem of hard roofs in mines.In order to solve the problems of hard suspended roof cracking and not easy to collapse,taking the 8119 working face of Baidong Coal Mine as the research background,the formation reasons of hard roof and rock breaking mechanism of static cracking agent in fully mechanized mining face were analyzed by combining theoretical analysis,laboratory experiment,numerical simulation and field industrial experiment.The reaction time and expansion pressure of the cracking agent were analyzed under the conditions of different material ratio,water-cement ratio,water temperature and pore diameter,and the optimal parameters were obtained.FLAC^3Dsimulation software was used to establish the model,and the transits of the plastic zone,the stress distribution around the borehole and the displacement of the model were observed under the radial pressure.Coal rock samples were collected and lithology determination was carried out for the roof of the working face.Based on rock strata parameters,the construction scheme was designed.The effect of large area suspended roof caused by static expansion agent was evaluated by ore pressure observation and borehole peep.The results show that:(1)The bulk expansion of calcium oxide hydration reaction is the main reason for the expansion pressure of static cracking agent;(2)The expansion pressure produced by static cracking agent increases with the increase of calcium oxide content and pore size,and decreases with the increase of water-cement ratio.Water temperature affects the reaction rate,and water-cement ratio affects the fluidity.(3)When the radial pressure is 50.17 MPa and the hole spacing is less than or equal to 80 cm,the simulated rock can be broken;(4)The best parameters obtained are applied to the cracking of the suspended roof at the end of the working face,and the periodical pressure step distance and stress of the roof are reduced,and the cracking effect of the roof is good.The paper has 42 figures,12 tables and 60 references.