Study On Fracture Evolution Law Of Underground Coaland Rock Under Protective Layer Mining In "Three Soft" Coal Seam

Coal and gas outburst is always one of the major disasters of efficient coal mine safety production in our country,especially in the process of the "three soft" in the high stress area coal mining group,the possibility of coal and g as outburst disaster accidents increased greatly.In the prevention measures of coal and gas outburst,the protection layer is the priority area preventive measure.In the process of mining protective layer,coal and rock mass stress will change.Underlying coal and rock in the pressure relief range will occur in varying degrees of deformation,rupture or even fracture,the coal rock permeability greatly improved.This is a positive effect on the control of the underlying coal rock mass.This paper takes 15 th coal seam of 4th mine Pingdingshan Coalmine Group as the object,using elastic mechanics,rock mechanics,damage mechanics and other related theories,through theoretical analysis,similar simulation test,numerical simulation and field test,systematically studied the fissure development,movement deformation,stress change and pressure relief characteristics of the underlying coal and rock mass after the upper protective layer.The research contents mainly include the following three aspects:(1)Measurement of physical and mechanical parameters of "three soft" outburst coal seam in high stress area.Selecting the representative of the high stress area "three soft" prominent coal seam group on the protection layer mining mine,collecting coal and rock samples from the top and bottom of coal seam,experiments were carried out to analyze the physical and mechanical properties of coal;(2)Designing and implementation of similar simulation experiment.Based on the similarity theory and the high stress zone "three soft" outburst coal seam’s occurrence characteristics,a similar material model was established.The test was carried out.The results show that the fissure development,movement deformation,stress change and pressure relief characteristics of the underlying coal seam under theprotective layer of the "three soft" outburst coal seam in the high stress area are obtained;(3)Using the FLAC3 D protective layer on the "three soft" coal seam is used to numerically simulate the process of mining.The numerical simulation is used to calculate the stress law,failure law and pressure relief area of the underlying coal under the protective layer of the "three soft" coal seam in the high stress area.The variation law of the vertical displacement of the underlying coal under different mining conditions is simulated.