Surrounding Rock Deformation Mechanism And Application For Gob-side Entry Retaining By Pre-splitting And Filling In Thick-layer Soft Roof

In recent years,the development of coal mining tends to be more efficient and economized.And the technique of Gobside Entry Retaining as one of the important technologies of scientific and efficient mining has been widely used.The coal seam with thick-soft roof is widely distributed,because the mechanical characteristics of the roof in the soft rock are loose,broken,low strength and complicated migration of overlying strata,it is difficult to keep Gob-side side Entry Retainging.In view of the above problems,we use experimental research,theoretical analysis,numerical simulation,similarity test and field industrial test.The physical and mechanical properties of the roof in thick-layer soft rock,the law of overlying rock movement,the stability of the surrounding rock along the gob,the characteristics of the supporting structure in the thick layer soft rock by pre-splitting and filling,the expansion of the pre-splitting cracks,and the mechanism of the penetration are systematically studied.The main innovation and research achievements of the paper include the following aspects:(1)The physical and mechanical properties of the the thick layer-soft layer roadway surrounding rock are carried out,and the physical and mechanical parameters,such as uniaxial compressive strength,elastic modulus,internal friction angle and cohesive force,are obtained.Through observing the surrounding rock structure of the deep roadway,we can observe the roof fracture,crack development and the complete extent of the thick soft rock roadway,and get the length of the suspended ceiling of the gob side of the roadway.(2)The structural models of pre-splitting roof angle roof methods that the deflection to the roadway,the side deflection to the roadway and the roof of the vertical roadway are established.By analyzing the bending deformation rule of soft roof,we can know that:the influence of the pre-splitting crack angle on the subsidence in the roof is obvious.The plane mechanical model of the upper stable rock stratum under different elastic parameters of caving fill is built,the results of the study show that:with the increase of the elastic coefficient,the tensile stress of the rock mass will be reduced and the degree of shear stress concentration in the upper stable rock will be restricted,which is beneficial to maintaining the integrity of the rock mass.The variation trend of strain energy of surrounding rock structure under different turning angles is analyzed through the analysis,the results show that:the strain energy produced by uniformly distributed load on the upper stable rock layer is linearly accumulated with the increase of bending subsidence.The strain energy of upper stable rock and thick soft rock increases exponentially.The rate of strain energy decreases with the increase of rotary sinkage.Whether we can control the surrounding rock deformation in a certain range and maintain stability in the early stage of Gob-side Entry Retaining will be the key to the gob side entry entry.(3)According to the occurrence characteristics of thick soft rock,three dimensional calculation model of discrete element is established under the conditions of-5,0,5,10 and 15 degrees respectively.The stress distribution characteristics and the damage scope of the roadside solid coal are analyzed,show that:When the roof breaking angle is 5 degrees,the stress concentration of the roadway side coal body is reduced,and the disturbance and the bearing capacity loss of the roadway roof are alleviated.The caving filling body effectively supports the overlying strata on the gob side of the roadway.When the Gob-side Entry Retaining is located in the inclined coal seam,the fall filling body is located on the coal wall of the alley,and the rock stratum displacement and the plastic damage range of the area are larger in the lower coal wall.During the mining process,the amplitude of stress distribution is more obvious,which is more likely to cause instability of surrounding rock structure in gob-side Entry Retaining.(4)The three dimensional calculation model of the pre-splitting crack interval is 0m,0.5m,1M,1.5m and 2m respectively.By analyzing the horizontal stress,the plastic damage evolution law and the energy dissipation characteristics of crack propagation around the precast cracks,show that:When the pre-splitting crack interval is lm,the stress concentration in the initial section of the retaining lane is well removed.The timely propagation and penetration of precast cracks effectively control the dilatation damage and energy dissipation process of surrounding rock mass,and it is beneficial to the coordination of rock strata.With the increase of buried depth,the vertical stress,horizontal stress and shear stress level around the Gob-Side Entry Retaining will increase.The rock mass around the prefabricated cracks has plastic damage under the action of tensile and shear,and the rock mass around the prefabricated cracks is mainly shear failure.When the prefabricated cracks are interconnected,the surrounding rock mass is dominated by tensile failure.(5)By means of similar material test,studied the movement characteristics and the variation rule of mine pressure in the top overburden strata in Gob-side Entry Retaining,results show that:The main frequency band of the pre-splitting explosive stress wave is mainly about 30HZ.The stress wave caused by the pre-splitting blasting is more lost in the soft rock on the gob side,and the loss of the propagation is small in the hard rock.Therefore,the pre-splitting blasting has little disturbance to the upper strata of the Gob-side Entry Retaining,and it is beneficial to the stability of the overlying masonry structure.The pre-splitting crack not only effectively remoes the stress concentration formed by the stress of the advance support,but also influences the disturbance of the surrounding rock along the Gob-side Entry Retaining due to the isolation of mining disturbance and weak rock caving.In addition,the collapsing bulging support structure is formed in the goaf side,which can relieve the impact load of the high rock stratum rotation and break,and reduce the deformation of the surrounding rock in the gob.(6)In the 5203 return air roadway of Changxin mining in Shanxi,the Gob-side Entry Retaining by pre-splitting and self-filling in thick-soft roof is carried out.It effectively solves the difficult problem of Gob-side Entry Retaining under thick-soft roof,and achieves good application results.Monitoring results of surrounding rock pressure and displacement in retaining roadway indicate that:in the rear of the working face,the 10?15m range is the surrounding rock deformation and the severe pressure area,the 16?25m displacement velocity decreases gradually behind the working face,and the entry pressure decreases gradually,the rear of the working face is more than 40m as the stable area,the deformation of the surrounding rock converges and the pressure tends to be stable.The industrial test verified the key technology of the top filling and gob side entry retaining from different aspects and the rationality and reliability of the conclusions in the previous chapters.The field test has proved that the Gob-side Entry Retaining by pre-splitting and filling is reasonable and reliable,and The reasonableness and reliability of the research conclusions.