Research On Collapse Mechanism And Anti-collapse Technology Of Borehole In Deep Tectonic Coal

Coal and gas protrusion problem crisis mineral safety,pre-pumping of coal seam gas by borehole is one of the main methods to solve the problem of gas outburst.With the increase of coal mining depth,coal seam stress is gradual increase.After the borehole was finished and the borehole is easy to collapse and plug hole.Blocked of gas extraction channel,and the gas extraction concentration was decays too fast or even goes to zero.Therefore,the problem of borehole collapse hole in coal seam is studied.For the borehole make anti-collapse and support to ensure smooth extraction of gas.This is a great significance to reducing the gas protrusion accidents.The gas extraction borehole in tectonic coal seam of Yu Xi Coal Mine in Shanxi Province take as the research object.For the borehole collapse and plug hole to on-sit investigation.The mechanical parameters of coal samples were tested to study the strength variation characteristics of coal seam failure.and analysis the cause of hole collapse and plugging of borehole.Using FLAC 3D software to construct the numerical calculation mode of non-contact between borehole and screen tube,and carry out the numerical simulation analysis of the borehole anti-collapse and support under the different conditions under large deformation.Make a new support plan for gas extraction borehole.Research and development the borehole whole course down screen tube and deep sealing hole equipment.The field industrial verification test of structural coal seam borehole was carried out.The main research results are as follows:(1)Coal body integrity is damaged after the coal seam drilling and forming,and the coal body strength is decreases.The coal rock body around the borehole is broken and fissure development.Stress redistribution of the coal rock body around after borehole pressure relief.The instability of coal body in borehole wall is the main cause of borehole collapse.(2)Borehole deformation increases with increasing coal seam depth.The greater the buried depth of coal seam,the greater the force of borehole support screen tube,and the deformation is more severe;The borehole upper coal rock body move downward to form pressure relief,with increasing depth of burial,the borehole surround coal rock seam area of plastic damage is reduced.(3)With the increase of lateral pressure,the lateral deformation of borehole increases.The plastic failure of coal and rock around the borehole changes from vertical to horizontal.and gradually horizontal development and expand.The vertical stress of boreholes and screen tubes in soft coal is greater than that in hard coal,and the borehole wall of soft coal first contacts with the screen tube.The transverse plastic failure of coal and rock around borehole in hard coal is greater than that in soft coal.(4)The whole-course screen tube support and deep hole sealing technology are adopted in the bedding borehole of gas drainage in tectonic coal seam,and the borehole collapse problem is effectively improved.The borehole gas extraction concentration and pre-pumping time is significantly improved.The borehole utilization is increase.Verified the feasibility value of the collapse prevention support test.The paper contains 42 figures,12 tables and 88 references.