The Law Of Strata Pressure Behaviors Under The Couple Effect Of Coal Pillar And Interbedded Hard Rocks In Exploitation Of Double-system Coal Seams

Datong Mining area is a typical double-system coal field for exploitation in China.As Jurassic coal seam in Datong mining area has been completely mined and a large number of coal pillars are left in the mining area.At present,exploration is being done mainly on the Carboniferous thick coal seam and the double-layer layers are hard and difficult.During the mining process of the Carboniferous coal seam,with the large area of the roof cracking in the goaf,the hydraulic support is obviously enlarged,the safety valve is opened frequently and the column is damaged,which severely influences on safety of the working surface,and brings about many difficulties in safe and efficient production of mines.Therefore,it is very important to study the effect of the hard rock coupling between the coal pillar and the double layer on the influence of the strata.In this paper,aiming at the problem of breaking and couple effect of the coal pillar and hard strata on the strong and abnormal strata pressure behavior in the mining face.Tongxin mining area as the object,through theoretical analysis,similar simulation experiment,numerical simulation exploring the law of breaking and couple effect of the coal pillar and hard strata on the strong strata pressure behavior in mines from the span of the key layer of the stope,the form of the overlying strata fracture and the stress distribution of the overlying strata,even verified by the law of the working face support drag along with advancing distance;providing reference for exploitation safely in similar "double-system" mines that have remaining coal pillars.Main achievements made in this paper are as follows:(1)Based on the distribution of the load of hard rock strata between the remaining coal pillars and the double strata,a mechanical model is set up for hard rocks interbedded;the formula for solution of the initial breaking span of the key stratum interbedded under the action of coal pillars is deduced combined with the thin and thick-plate theory;(2)According to the similar simulation experiment study the breaking and instability rules of double-system hard rocks interbedded under the action of coal pillars and hard rocks: When the working surface is advanced under the Jurassic left coal pillar,the primary key stratum of the interlayer is broken by the concentrated stress of the pillar,and the rock strata formed by the primary key layer are bent and sank together.,And at this time the vertical fissure fully developed extension,forming through the cracks,and finally through the double-goaf area,resulting in structural instability of the overburden,the formation of a huge impact on the working face;(3)According to the numerical simulation has explored the influence of three effect models of single-coal-pillar,single-hard-rock and their coupling on the the distribution of stresses of stope,and the results show that the coupling effect between coal pillar and hard rock strata has a stronger effect on the stress field of overlying strata than that of coal pillar and hard rock formation.It is easier to induce the formation of high stress field in stope;(4)According to field measurement of the support drag has verified the rules of coupling effect between coal pillar and hard rock on the strata pressure behavior: under the coupling of the coal pillar and the hard rock,breaking of the inferior key stratum interbedded occurs with a large roof weighting step,distinct increase of resistance in support and other large strata pressure phenomena;when the key stratum interbedded breaks,motion of the overlaying rock spreads to the Jurassic mining goaf,causing a huge impact on the working surface,thus developing a second large strata pressure.