Study On Mechanism Of Pre-splitting Blasting Of Roof For Gob-side Entry Retaining

Great pressure of the roof and difficult supporting of the roadside have become urgent problems in the process of gob-side entry retaining. The cantilever length of roof can be reduced by using the method of pre-splitting blasting, which can alleviate the support pressure of the roadside and ensure the process of retaining roadway smoothly. Therefore, it is of great theoretical and practical significance to study the mechanism of pre-splitting blasting for gob-side entry retaining roof.Taking the air return way in 5203 gob-side entry retaining working face of Changxing coal mine as the engineering background, using the method of theoretical analysis, laboratory test, numerical computation, and in-situ test, mechanism of pre-splitting blasting in roof is systematically studied, principle of pre-splitting blasting and crack initiation are deeply analyzed,significance and optimization of parameters are mainly discussed,effect of cutting seam and deformation law of roof are analyzed. The results are as follows:(1) Through physical and mechanical characteristics test of surrounding rock,density, compressive strength, tensile strength, elasticity modulus, poisson’s ratio,mechanical parameters under dynamic loading conditions of coal and rock are obtained. Stress-strain relationship is analyzed.(2) Principle of pre-splitting blasting and crack initiation are researched. Charge weight, decouple coefficient, distance between holes and other parameters which have strong impact on the effect of blasted result are analyzed and appropriate values of parameters are selected(3) Numerical calculation model is established by LS-DYNA. The impact of charge weight, decouple coefficient, distance between holes on the pre-splitting blasting are compared. Through similar model experiment, charge weight, decouple coefficient, distance between holes are optimised.(4) Similar material test of pre-splitting blasting for gob-side entry retaining roof is developed, process and effect of pre-splitting blasting are analyzed. Function and mechanism of pre-splitting blasting are researched. Stress characteristics and deformation law of roof by pre-splitting blasting are studied.(5) Mechanical model of natural hanging roof structure and cutting hanging roof structure of roadway are established. The analytical solution of internal force and displacement are obtained Change law of internal force and displacement areanalyzed.(6) Scheme of roof cutting with pre-splitting blasting is put forward, which is successfully implemented in Changxing coal mine and has achieved remarkable results.