Research On The Mechanism And Its Prevention And Control Of Floor Heave In Gob-side Entry Retaining With Hard Roof Of Deep Mine

The development of coal mining to deep is an inevitable trend,and the superiority of gob-side entry retaining as an important development direction of coal mining is self-evident.But the phenomenon of floor heave is very common in gob-side entry retaining,especially in the hard roof of deep mine which its strata behaviors is extremely strong.and the floor heave of it is particularly serious.The safety and efficient production of coal face has seriously affected by the floor heave which has become one of the main restricting factors of the success of gob-side entry retaining.Through physical simulation,numerical simulation and theoretic analysis,this dissertation systematically analyzes deformation and failure mechanism of floor in gob-side entry retaining by investigating the distribution characteristics and its evolution law of stress,strain,displacement and plastic zone of it,and the mechanism of floor heave in gob-side entry retaining with hard roof of deep mine was revealed.Besides,on the basis of the mechanism of floor heave in gob-side entry retaining,an idea that optimizes region stress of floor in it by cutting roof to release pressure is proposed,which indicates prevention and control mechanism of gob-side entry retaining by cutting roof to release pressure.Ultimately,cutting roof to release pressure,pre-mining reinforcement,post-mining treatment technology of floor heave in gob-side entry retaining with hard roof of deep mine is formed and prevention and control technology ideas of floor heave in gob-side entry retaining with such roof of deep mine is presented.it can be concluded as follows:(1)The characteristics of strata behaviors of floor heave in gob-side entry retaining with hard roof of deep mine was studied by physical simulation.The results show that:The floor heave of the gob-side entry retaining with hard roof of deep mine was serious,and floor heave was occurred in the driving stage,but it mainly occurred during primary mining to secondary mining stages.The deep rock mass of roadway floor was always under compressive,and the shallow rock mass of it presented’tension-compression’ strain transition phenomenon.Under the geological conditions,the floor heave of the gob-side entry retaining is mainly composed of compression bending type,shear dislocation type and extrusion fluidity type,the other mainly are tensile failure or tensile shear failure,but also showed large deformation and asymmetrical characteristics.(2)The characteristics of strata behaviors of floor heave in gob-side entry retaining with hard roof of deep mine was studied by numerical simulation.The results show that:The influence range of the roadway floor stress was 60m front of working face to 100m back of working face during mining,the roadway floor stress was considerable influence by mining among the range of 10-30m front of working face and the range of 20-60m back of working face.The plastic range of roadway floor was increasing as stage went on,and it also showed stage and regional.The roadway floor was mainly shear failure during the whole gob-side entry retaining.The deformation of roadway floor was considerable influence by mining and excavation,which among the range from 5m front of driving face to 20m back of driving face during roadway excavation,the range from 30m front of working face to 20m back of working face during primary mining,and the range from working face to 40m front of it during secondary mining.The measure of floor heave was increased rapidly at these stages.(3)The influence factors of floor heave in gob-side entry retaining with hard roof of deep mine was studied by numerical simulation.The results show that:The floor heave in gob-side entry retaining is mainly influenced by floor lithology,roof lithology,mining depth,roadway width,mining height,size and strength of packing body.The primary and secondary orders of influence for floor heave are floor lithology,mining depth,roof lithology,roadway width,mining height,size and strength of packing body.(4)Based on the occurrence stage of the floor heave and its dominant floor heave type at the stage,the mechanical model of floor in gob-side entry retaining which belong to different periods and different types was respectively constructed.The mechanism of its floor heave were analyzed,the calculation method of floor heave,the critical discriminant for instability of deformation and failure of floor,and the calculation method of floor damage depth were deduced.At the same time,the influence factors and stability of the floor were analyzed.The results show that:①The measure of floor heave increases with the increase of the stress of the original rock and the outer boundary of the elastic compression zone of the roadway,and decreases with the increase of the elastic modulus of the floor when the deformation of it was small and occurs off the layer.②The probability of sliding unstable increases with the increase of roadway width and the horizontal stress at both ends,and decreases with the increase of the bending rigidity of the floor and the layering thickness of the strata when slip-bending deformation of the floor occured.③Because of the different of the strength of rock mass,the friction angle in shear dislocation plane and the horizontal squeezing pressure at later stage,the wedge-shaped block structure mainly has three kinds of movement forms,such as sliding instability,detachment instability and crushing instability when the shear dislocation damage of the floor occured.④Failure depth of the floor of left roadway is mainly related to roadway width,packing body width,the width limit equilibrium area of coal side and friction angle in the body of floor rock when extrusion flow deformation of the floor occured.(5)The support resistance of roadway side decreased rapidly after cutting roof to release pressure in gob-side entry retaining with hard roof of deep mine.The region stress of floor was optimized,and the measure of floor heave then decreased.And prevention and control technology ideas of floor heave by cutting roof to release pressure is proposed for gob-side entry retaining with hard roof of deep mine.(6)Base on characteristics and mechanism of floor heave in gob-side entry retaining with hard roof of deep mine,general prevention and control principle of floor heave which composed of "dynamic control of zoning in stages,optimizes region stress of surrounding rock,prevention and control of surrounding rock integrity,matching coordination of surrounding rock supported,strengthening support for key parts,adaptability and economic rationality" was proposed,and specific prevention and control principle of floor heave which composed of "cutting roof to release pressure and roof and floor mutual control,cutting roof to release pressure and strengthening coal side and control floor" was proposed.