The Analysis Of Discriminant Method Of Ground Drilling Based On The Finite Element Strength Subtraction

Ground gas extraction technology is an effective means rising in recent years togovernance mine gas overrun，but the Ground gas drainage recovery well have toexperience Severe deformation of the overburden of Coal seam，its load-bearing formis more complex。just because of this，the safety assessment of ground gas extractionwells have always been the problem that bothering people。This article apply the finiteelement strength subtraction which is widely used in geotechnical engineering in theground drilling safety assessment，the following several aspects of the research wasconducted of the ground drilling：(1)We learned that displacement and stress of the interface between layers areconcentrated through the numerical simulation of excavation process of coal seam。Especially that，the junction of the critical layer and the lower layer is the high-riskdamage position of the drilling。(2)Establish the three-dimensional model of the ground drilling casing indifferent diameter and different wall thickness，we get the distribution of the tensilestress and shear stress on the ground drilling casing cross section。And we get the rulethat the maximum tensile and shear stress of the ground drilling changing with thediameter and wall thickness。(3)Bring in finite element limit analysis thought，we have been obtainedrespectively tensile and shear safety factor of the ground drilling casing through thereduction of the casing tensile strength and shear strength。And we get the grounddrilling casing tensile and shear failure modes and failure process though the changeof casing plastic zone with reduction factor。(3)We get the tensile and shear safety factor of4308working face in a coalmine， Jincheng coal group，though the method of calculating safety factor bynumerical simulation。And the safety factor and strata displacement monitoring datawere compared, through the analysis of the comparison results proved that the safetyfactor used to evaluate the safety of ground drilling is feasible.