Research On Mechanism And Application Of Energy Absorption And Anti-impact Of Soft Structure For Surrounding Rock In Roadway

Coal bump or rock burst is a dynamic disaster caused by the sudden release of elastic energy under high-stress conditions,resulting in the destruction and instability of coal and rock mass.The root cause of roadway impact failure is that the superposition strength of dynamic and static load is greater than that of roadway support,90%of coal bump occur in the roadway.Therefore,improving the support strength of the roadway and setting up the soft structure for surrounding rock in roadway to dissipate waves and absorb energy is beneficial to the construction the anti-impact structure of soft structure and support structure of coal bump roadway.This study takes the 21170 transportation roadway of Changcun coal in Yima as the engineering background.Given the characteristics of large mining depth of roadway,high mining stress,strong dynamic load disturbance of roof,and impact tendency of the coal and rock seam.Using theoretical analysis,laboratory experiments,numerical simulation,and field tests,focusing on the stability control of roadway surrounding rock,the energy absorption and anti-impact mechanism of soft structure for surrounding rock in roadway under coal bump is studied.The corresponding relationship between the energy absorption effect of soft structure and the key scale parameters is established.The coordination mechanism of energy absorption and anti-impact of soft structure and resistance to impact of the roadway support structure is put forward.The main achievements are as follows:（1）The mechanical properties and energy dissipation laws of coal and rock samples under dynamic load are clarified.The SHPB experimental system was used to analyze the dynamic mechanical properties of coal and rock samples when the impact pressures were 0.25,0.30,0.35,0.40,and 0.45 MPa,and the impact times were 1,2,and 3 respectively.With the increase of impact times,the peak stress decreases,and the weakening degree increases of coal and rock samples.The peak stress weakening coefficients of coal and rock samples under dynamic load are obtained,which are 28.5%～73.2%and 12%～55.8%,respectively,and have a linear weakening relationship with the number of impact times.The energy dissipation law and damage characteristics of coal and rock samples under dynamic load are analyzed.The energy absorption per unit volume of coal and rock samples are 0.46～0.81 J/cm³ and 0.37～0.60 J/cm³ respectively,which are positively correlated with the impact times.It is clarified that in the coal and rock sample there is no interface friction and presents"1"failure under dynamic load without confining pressure,and there is an end effect and presents"Y"failure under dynamic load with confining pressure.（2）The failure process of roadway surrounding rock and the energy absorption characteristics of soft structure under dynamic load are studied.The failure evolution process of surrounding rock of the roadway with and without soft structure is analyzed by using the similar physical experimental model frame of impact dynamic load.The failure process of the roadway is that small cracks appear on the roof,then the damage degree of floor increases,and finally,large cracks and separation layers appear on the roadway roof.The closer it is to the source,the more obvious the roadway damage is.The surface displacement,stress distribution,and acoustic emission characteristics of the roadway under different impact energies are studied.The soft structure for surrounding rock in roadway can reduce the displacement,stress,acoustic emission amplitude and ringing number of roadway is obtained.The energy absorption of soft structures consists of spatial scattering energy absorption,rock-reflected energy absorption,rotational energy absorption,and loose block energy absorption.The soft structure for surrounding rock in roadway can effectively absorb the impact energy and protect the roadway from impact damage.（3）The mechanism of stress wave attenuation and energy absorption and anti-impact in the soft structure area of roadway surrounding rock is revealed.Based on one-dimensional elastic wave theory,motion equation,and energy conservation equation,the mechanical model of energy absorption and anti-impact of soft structure is constructed.The law of velocity reduction of stress waves after reflection,transmission,and scattering in soft structure area is analyzed.The energy absorption of soft structure is mainly related to the initial velocity,stress,and particle diameter of the soft structure is obtained.It is revealed that the particle size of the soft structure for surrounding rock in roadway is the main factor affecting the energy absorption of soft structure.The PFC software was used to verify the effect of particle size on the wave propagation velocity in the soft structure.The smaller the particle,the smaller the velocity and the greater the energy absorption.（4）The key scale parameters of energy absorption and anti-impact of soft structure for surrounding rock in roadway are determined.The FLAC^3Dnumerical simulation software is used to study the failure characteristics of roadway with different impact positions under roof impact,side impact,roof and side impact,and different impact energies of 10⁴,10⁵,10⁶,and 10⁷ J respectively.After the soft structure is set on the two sides of the roadway,the reduction rate of the vertical stress of the roof and the horizontal stress of the side are 9.3%～23.5%and 7.6%～21.4%,respectively.The energy absorption effect of soft structure has a logarithmic function relationship with its size:It has a power function relationship with its fracture degree:The stress reduction rate of soft structures under different sizes and fracture degrees is calculated.The results show that the stress reduction rate is 30%when the size of soft structure of the surrounding rock is 10～15 m and the fracture degree is 30%～40%of coal strength,and the energy absorption effect is good.（5）The coordination mechanism of energy absorption and anti-impact of soft structure for surrounding rock in roadway and resistance to impact of support structure is revealed.The interaction relationship between coal and rock mass strengthened by roadway support structure and soft structure broken and weakened surrounding rock is analyzed.The construction mechanism of soft structure for surrounding rock in roadway caused by repeated borehole drilling is studied.The influencing factors of soft structure energy absorption zone by repeated borehole drilling are analyzed.The control effect of internal steel pipe borehole protection technology on the strength of surrounding rock and the integrity of supporting structure is simulated.The mechanism of"relief in support"and"strong in soft"energy absorption and anti-impact of soft structure and resistance to impact support structure is established.The coordination control effect of energy absorption and anti-impact of soft structure for surrounding rock in roadway and resistance to impact support structure is revealed.（6）The engineering application preliminarily verified the research results.Given the characteristics of large buried depth,concentrated tectonic stress,weathering,and creep of mudstone,and impact tendency of coal and rock.Based on the energy absorption mechanism and key scale parameters of soft structure for surrounding rock in roadway.Field application in 21170 transportation roadway of Changcun coal mine in Yima.The soft structure size of roadway surrounding rock is10 m,and the fracture degree is 30%of the coal strength.The soft structure technology of internal steel pipe borehole protection technology and repeated borehole drilling is adopted.Field application of energy absorption and anti-impact technology of soft structure for surrounding rock in roadway and resistance to impact roadway support structure.Compared with the original support,the range of loose roof and side is reduced by 51%and 67%,respectively.After the soft structure of surrounding rock,the roadway deformation is reduced,and the total energy of microseismic monitoring is reduced by about 40%～50%.The roof separation is effectively controlled and the deformation of roadway surrounding rock is restrained.The roadway control effect is remarkable,which provides a theoretical basis for the stability control of high-stress roadways under similar geological conditions.There are 147 Figures,34 Tables,and 298 References in this paper.