Research On Instability Characteristics Of Borehole In Soft Coal Seam Under Fluid Solid Stress Coupling Effect

The reason of the drill of soft coal under the action of fluid-structure interaction is not found.The article through granular mechanics,fluid mechanics and solid mechanics,with the help of Hoek-Brown intensity theory,based on numerical simulation and experiment research,analyzed unstability in soft coal borehole.Discussing the influence of coal properties for borehole collapse stress,analyzed the range of forming stabilized borehole in soft coal seam radius;based on traditional stress;with the cohesion and internal friction angle increases constantly,the stress of borehole collapse decreases continuously.Build the seepage mathematical model of double hole borehole.Based on Hoek-Brown intensity theory,introduce residual compressive strength,correction of the coupled formulas;build the unstability model of gassy coal,using multi-physics field software,through quantify the value of GSI,the research shows that(1)The weaker the strength of coal,the bigger the range of the influence of gas,the bigger the plastic zone.(2)For the round drill and elliptic drill,the range of pressure relief is more bigger of elliptic drill.(3)with the development of skewed borehole,the bigger of the plastic zone,continuously extend of the drill,the bottom of the drill easier to hack,the dilatation is more obviously.Based on the experiment of coal and gas coupling research,analyzed the influence of different gas stress for perturbance and transformation around drill,the more enlargement of gas stress,the more range of pressure relief,at the same time,the more bigger of borehole deformation modulus.