Research On The Underground Pressure Of Crossing Coal Pillar In Shallow Close Distance Seam

The coal pillars left in the upper coal seam have great influence on the mining of the lower coal seam in shallow close distance seams,and it often leads to the obvious roof weighting in mining of the lower coal seam,even inducing rock burst and other accidents.Therefore,this paper take condition of 12101 working face in Halagou Coal Mine,strata caving characteristics,crack evolution law and stress distribution characteristics when mining under pillars in the lower coal seam are studied,and it has guiding significance for safety production and stable mining of similar working face.Through establishing the mechanical model of upper key block structure in three different stages which are entering pillars,crossing pillars and out of the pillars,and the stability of key block structure is analyzed.By FLAC3 D simulation software and similar material simulation experiment,when mining crossing pillars,the stress distribution of the surrounding rock and the law of overlying strata are monitored,FBG and PPP-BOTDA are used in the simulation experiment to monitor the transformation and movement of the overlying key strata.Combining with the underground pressure observation data of the working face,the law of underground pressure when mining crossing the pillars at the final stage is analyzed.It shows that the overlying pillars rotate at the pucking fracture line of roadway with the inferior key strata,and it leads to the pressure increase of working face suddenly,strong pressure is happened.The maximum values of the advance abutment pressure transfers when entering pillars,crossing pillars and out of the pillars are 2.64 MPa,2.79 MPa and 3.26 MPa,the average factor of stress concentration is 1.48.The advance abutment pressure is transfered from overlying pillars to 12101 working face when crossing the pillar section 1,The pressure comes to the maximum when mining out of the auxiliary roadway and expelling gangue roadway,The analysis of plastic zone shows that the roof of the working face is cutting down broken.The results of site monitoring show that the support resistance is bigger when acrossing abandoned roadway than acrossing the coal pillar.In the similar simulation,the Bragg grating monitoring results are consistent with the law of rock movement,and the maximum value in the right of the Brillouin curve of the fiber H1 is increased suddenly,it shows that the whole overlying pillar sinks in this stage,and it leads to strong pressure behaviors.