Research Of The Influence Laws Of Bottom Coal Thickness On Roadway Floor Burst Start-up

In recent yasrs,the roadway floor burst disasters occur frequently,which seriously restricts the safe and efficiency of deep mines.The on-site statistical data shows that coal mines,depending on factors such as geology and mining technical conditions,will leave bottom coal with different thicknesses,which is an important factor affecting floor burst start-up.The paper comprehensively uses the true triaxial test,numerical simulation,theoretical analysis,field measurement to study the influence mechanism of bottom coal thickness on the impact force distribution,stress transmission and start-up process in the process of roadway excavation,the following main achievements are obtained:(1)The true triaxial test of the coal-rock combination specimen from roadway floor shows that,rock sample is the main elastic energy storage,while coal sample is the main power release indicator.when the coal sample is thin(the ratio of coal sample to rock sample is 1:2)or thick(the ratio is 0.7),the possibility of dynamic damage of the combined coal-rock combination is greatly enhanced.When the ratio of coal thickness is 0.33 and 0.67,the dynamic failure time is smaller and the impact energy index is higher,the burst liability of overall combination specimen is relatively higher.(2)The numerical simulation analysis of floor with bottom coal in process of excavation shows that the concentration of the lateral stress field of the floor is more concentrated than that of the axial and vertical stress fields,and the stress concentration factor is about 1.4 times that of the latter two.Floor lateral stress field is the dominant source factor of floor burst.(3)The flexural failure mechanics model of the floor coal-rock laminated beam shows that with the increase of the bottomcoal thickness,the elastic energy of the bottom coal gradually increases,and the gradient has a negative correlation with the fourth power reciprocal of the bottom coal thickness.(4)When the roadway is excavated,the floor rock is the main impact energy storage,while the bottom coal is the main power release.The bottom coal thickness affects the tendency of floor burst start-up by changing the area size of the potential burst start-up zone,potential burst energy transfer zone,potential burst pressur behavior zone,the energy storage degree,and the energy transmission capacity,and the spatial dependent position among the three.With the increase of the bottom coal thickness,the tendency of floor burst start-up is gradually strengthened;when the thickness of the bottom coal reaches to 2m,the influence gradient of bottom coal tende to zero.(5)The bottom coal should be avoided in the process of roadway excavation in burst coal seam.When bottom coal must be left,the bottom coal thickness should not exceed 2m.When leaving floor with bottom coal to relieve pressure,it is necessary to take relieving measures for floor rock strata,to block the stress transmission path,to weaken the tend of floor brust start-up.The papar conclusions were applied in the field and the floor has a good anti-danger effect.