Mechanism Of Strong Ground Pressure While Crossing The Overlying Roadways In Close Distance Shallow Seams

The vertical distance between close distance shallow seams is small,and the coal pillars left over from upper coal seam mining has a great influence on the appearance of mining pressure on the lower coal seam.Influenced by the coal pillars left by the upper coal,abnormal mineral pressure is easily occurred in the process of mining in the lower coal seam.Previous studies have focused on the appearance of abnormal ground pressure in the incoming and outgoing stage,focusing only on the impact of coal pillars on the mining of lower coal seams.There is little research on the presence of overlying roadways in coal pillars,especially in the case of multiple overlying roadways.Due to the existence of overlying roadways,the load slabs of the lower coal seam slabs are not uniform,abnormal strong ground pressure appears frequently,and the risk of roof accidents is greater.Therefore,it is necessary to study the phenomenon of strong ground pressure in the process of crossing theoverlying roadways in close distance shallow coal seams,reveal its behavior mechanism,and propose corresponding solutions.This paper takes the example of working face 21305 of Daliuta Coal Mine and the Shigetai 31201 working face in Shendong mine area as the engineering background.Combinied with the means of on-site measurement data,physical simulation and numerical simulation,and studies the appearance of the strong ground pressure in the close distance shallow coal seams.And exploring the mechanism while crossing the overlying roadways strong ground pressure accident prevention and control ideas and measures.The main findings are as follows:(1)Based on the analysis of the pressure data of the 21305 working face of the Daliuta Coal Mine,the strong ground pressure stage is analyzed,and the characteristics of the pressure appearing when the working face is pushed below the concentrated coal pillars are summarized.At the same time,combined with the example of a strong underground pressure accident in the 31201 working face of Shigetai Coal Mine under the overlying roadway,the breaking motion of the overburden rock when the working face passes through the overlying roadway is analyzed,and the results show that the shear breakage above the overlying roadway causes the lower coal roof breaking,slipping and instability,and finally caused the accident.(2)The study of the broken rock in the stage of the working face cross theoverlying roadways is studied by using the method of physical simulation.The results show that the presence of overlying roadways can lead to the change of the key stratum break step distance.The stability of the block articulation is poor due to the reduction of the break distance of the rock below the overlying roadways.When the fissure line position is above the overlying roadways the working face of the overlying roadways is prone to slipping and unsteady.(3)The study was carried out on the working face 31201 of Shigetai Coal Mine,and the simulation was carried out using UDEC software.Analysis can be seen that the overlying roadways will change the collapse pattern of the working face rock and thus cause the cut and fall of the cladding rock,at the same time,the overlying roadways affects the stress distribution of coal seam cladding rock,resulting in the increase of the pressure of thefore coal block.(4)The idea and countermeasure are put forward for the prevention and control of strong ground pressure in the working face while crossing the overlying roadways.The main ideas are roadway treatment,mining design optimization.Specific measures to take pre-explosion boundary coal pillars、fillings and reducing the length of the working face and slowing the speed of the working face to ensure that the working face safe and efficient while crossing the overlying roadways.There are 40 figures,13 tables and 99 references in this thesis.