Influence mechanism and application analysis of bottom coal layer thickness on floor rock burst

For thin and medium-thick bottom coal layer with thickness of less than 3 m,in order to study the influence mechanism of bottom coal layer thickness on floor rock burst,based on the impact characteristics of floor in excavation roadway and theoretical analysis,the mechanical model of deflection failure of coal-rock laminated beam of floor was established.The deflection deformation curve of floor coal and rock has the development characteristics of synchronization and different amplitudes.The formula calculation shows that with the increase of bottom coal layer thickness,the accumulation elastic energy of bottom coal layer gradually increases,and the increase gradient gradually becomes gentle,which has a negative correlation with the reciprocal of the fourth power of coal thickness.The FLAC3D numerical simulation was used to analyze the main stress,elastic-plastic zone and elastic energy.The results show that the floor rock layer of roadway is the main impact dynamic energy storage body,and the bottom coal layer is the main power release manifestation.The bottom coal layer affects the energy storage and transfer mechanism between the bottom coal and rock by affecting the scope of the potential rock burst start-up zone,the potential energy transfer zone,the potential rock burst occurrence zone,the stored energy,and the dependence between the three zones.This will affect the formation process of the floor rock burst.Bottom coal layer has a weak elastic energy storage capacity relative to the floor rock layer.The thickness of bottom coal layer is a key factor affecting the storage of elastic energy of bottom coal.The thickness of bottom coal layer affects the floor rock burst hazard by affecting the elastic energy transfer ability between coal and rock.With the increase of bottom coal layer thickness,the floor rock burst hazard gradually increases and the gradient gradually decreases.When the thickness of bottom coal layer increases to 2 m,the increase of bottom coal layer thickness has no obvious superimposed effect on the floor rock burst hazard,showing the threshold effect of bottom coal layer thickness on the floor rock burst.When the pressure of floor with bottom coal layer is relieved,it is necessary to take measures to eliminate the danger of the floor rock,block the stress transmission path,reduce the energy accumulation of the floor,and thus reduce the risk of floor rock burst.The application of the research results was analyzed and validated on site.Monitoring by the method of drill bits showed that the effect of eliminating the danger was good.