Study On Mechanism Of Activation Water Inrush Of X9 Collapse Column In Sihe Coal Mine

The mining data and three-dimensional geophysical data of No.16 coal seam in Sihe Coal Mine show that 17 collapse columns are found in the field.Most of the collapse columns are filled and cemented well,without water content and water conductivity,and there is no water gushing in the mining process.However,the location area of X9 collapse column is used as low-lying water area for 30 days,and about 800 m3 / h of Ordovician limestone water gushing occurs.In this paper,the formation mechanism of the collapse column is analyzed,and the activation water conduction mechanism of X9 collapse column is studied by using the methods of theoretical analysis,numerical simulation and experiment.On this basis,the water plugging scheme is proposed.The main research results are as follows :(1)Based on the theory,this paper studies the stress field distribution of the collapse column and surrounding rock,and obtains the stress distribution formula of the column and surrounding rock.The main factors affecting the stress of the column are self-weight,surrounding rock and confined water.The main factors affecting the stress of the surrounding rock are self-weight and the interaction force of the collapse column.Through theoretical analysis,it is concluded that the judgment basis of the activated water conduction of the collapse column,in which the water conduction of the column is mainly two cases:(1)the water conduction of the cement layer section of the collapse column is damaged,(2)the water conduction of the cement layer section of the collapse column is staggered with the surrounding rock strata,and the judgment formula and influencing factors of the water conduction in these two cases are obtained.(2)FLAC3D numerical simulation software is used to simulate the initial stress field and displacement field of the collapse column and surrounding rock.It is found that the stress concentration occurs around the collapse column,and the displacement of the collapse column area increases significantly.FLAC3 D numerical simulation software was used to simulate the plastic zone and displacement field of the collapse column under the action of confined water.It was found that the middle and lower part of the collapse column was the region with the largest displacement.When the confined water was between 1 MPa and 2 MPa,there was an obvious plastic failure zone in this region.FLAC3 D numerical simulation software is used to simulate the distribution of stress field,displacement field and plastic zone of collapse column under mining action.It is found that the stress concentration zone appears at the end of the mining area,and the roof also has a large displacement.There is a continuous plastic failure zone at the end and the roof.When the mining is 30 m from the collapse column,the plastic failure zone will be connected,which may lead to water inrush.(3)Through the experimental study on the strength change of coal in engineering examples with time under water immersion,it is found that when the time reaches a certain value,the strength of coal will gradually approach a value.Taking the strength limit obtained by the experiment as the parameter,the protective coal pillar is assigned to study the change of the plastic zone of the protective coal pillar with the width of the coal pillar,and the limit width of the protective coal pillar under water immersion is obtained.(4)According to the characteristics that water gushing is difficult to control,this paper puts forward the idea of ' changing static into dynamic,static water plugging'.That is to say,five water retaining walls are constructed at different positions,and the water retaining wall is equipped with conduits to drain and reduce pressure.The grouting scheme combining borehole cap grouting and intermittent hydrostatic grouting was used to complete the plugging of Ordovician limestone collapse column channel.This paper contains 31 figures,8 tables and 65 references.