Study On The Mechanism Of Destressing Blasting And Stability Of Surrounding Rock In Deep Roadway

During the excavation of deep rock mass,excessive stress concentration of surrounding rock often leads to instability and failure of roadway,which affects safety production.As an effective way of roadway support,pressure relief blasting can achieve the support effect by transferring the stress of rock mass.An in-depth study on the mechanism of pressure relief of blasting under high stress can provide a basis for roadway surrounding rock support and safety evaluation,which is conducive to safe production.Under the background of deep rock mass blasting,this paper takes the surrounding rock mass before and after roadway blasting pressure relief as the research object,the mechanism of blasting pressure reduction is studied from two levels of rock mass around a single hole and surrounding rock mass of roadway by combining theoretical analysis and test and numerical simulation.According to the attenuation index of explosion stress wave in high stress rock mass and considering the strain rate effect of dynamic tensile and compressive strength of deep rock,the range of crushing ring and fissure ring of columnar charge blasting rock mass under different in-situ stress environments is calculated theoretically.Based on the static and dynamic mechanical test of the strong and weak combined rock mass,the deformation energy absorption characteristics of the damaged and weakened rock mass are analyzed,which provides the basis for the pressure relief effect of the weakened rock mass after blasting.From the point of view of blasting damage of surrounding rock,the damage range of surrounding rock is rezoned,and the law of stress and energy transfer of surrounding rock during blasting is analyzed relatively quantitatively.Combined with the blasting test of plate similar model under bidirectional loading,the pressure relief process is reproduced.On this basis,considering the overall stability of the roadway,the blasting damage area is simplified and divided,and by means of FLAC3D simulation software,the stress distribution and energy accumulation in different regions are explored,and the mechanism of pressure relief blasting in deep roadway is further discussed.The main results are as follows:(1)The attenuation law of explosive stress wave in deep rock mass is different from that in shallow rock mass,and the attenuation exponent increases with the increase of in-situ stress.The blasting damage range of rock mass is affected by confining pressure.Under the condition of equal confining pressure,the radius of crushing zone and fracture zone decreases gradually with the increase of confining pressure,and the radius of fracture ring decreases faster.In addition,with the increase of confining pressure,the radius of fracture zone decreases greatly under lower confining pressure,which indicates that crack initiation is sensitive to confining pressure.Under bidirectional unequal pressure,the crack propagation is more likely along the direction of deviatoric stress,while in the direction perpendicular to the deviatoric stress,the crack propagation is inhibited,and the fracture circle formed is elliptical.The larger the deviatoric stress is,the more obvious the promoting or inhibiting effect is.(2)The two components influence each other in the process of static and dynamic deformation and failure of the damaged body.The damaged body promotes the radial deformation and failure of the undamaged body,while the latter has an inhibitory effect on the former.The strain energy accumulated by the damaged body is greater than that of the undamaged body under both static and dynamic loads,and the higher the damage degree,the greater the difference between the two components is.Compared with the single specimen,the fracture degree of the damaged body in damaged combined specimen under dynamic load is greater,while the degree of the intact body is smaller.More than 75%of the energy absorbed in the static and dynamic failure process of the combined body under the specific "damage" form of coal-rock combination is used for the damage of the damaged body,indicating that the damaged rock mass can absorb more energy.(3)The rock mass outside the fractured zone around the hole is still subjected to the large loading effect of the explosion stress wave,so the concept of "strain hardening zone" is proposed on the basis of the traditional blasting damage zone.The formation of "strain hardening zone" is the fundamental reason for the short-term increase of elastic modulus in the loading process of specimen after blasting,and it has certain timeliness.Blasting changes the stress distribution and energy accumulation state of the rock mass around the hole,reduces the peak value of stress and energy density,and transfers the high stress or high energy density accumulation area away from the hole.In addition to the strain energy taken away by the drilling process,the blasting process dissipates a large amount of elastic energy accumulated by the rock mass around the hole,and the deformation process of the rock mass in the distance will further promote the transformation of strain energy into dissipation energy.These factors contribute to the realization of rock mass pressure relief.(4)The test of plate blasting under bidirectional loading shows that the blasting process can achieve the effect of pressure relief.Radial compression and disturbance result in "stress drop".The generation of "stress drop" is similar to the rheological phenomenon under blasting disturbance.The closer the stress state of the specimen is to the strength limit of the specimen during blasting,the more obvious the damage caused by blasting disturbance to the specimen will be.The external stress under bidirectional loading and the internal stress of explosion lead to the splitting failure of specimens.The phenomenon of "stress drop" in blasting test is the result of instantaneous release of strain energy of rock mass around the hole under blasting.The process of energy re-consumption under continuous loading after blasting corresponds to the further compression deformation process of damaged rock mass after blasting of roadway surrounding rock.(5)Three blasting weakening calculation models under different damage degrees and thickness of weakening zone were built by FLAC3D simulation software.The effect of blasting weakening has great influence on the radial deformation of weakening area and internal plastic area.The greater the damage degree and thickness of weakening area,the more obvious the increase of radial displacement,and the smaller the part of displacement increment from external elastic plastic area,and the larger the volume of the weakening zone and the internal plastic zone.(6)The blasting effect reduces the radial stress and tangential stress of the rock mass near the weakening area,increases with the increase of the damage degree and the thickness of the weakening area,and gradually transfers the peak value of the tangential stress to the depth of the rock mass.The blasting weakening process can lead to the energy accumulation of the rock mass in the external elastoplastic zone.The greater the damage degree and the thickness of the weakening zone,the more obvious the energy accumulation in the external elastoplastic zone.The strain energy density accumulated in the rock mass after blasting is less than that before blasting,which shows that the process of blasting weakening rock mass can achieve pressure relief effect.Figure [89] table [9] reference [130]...