Study On Models Test Of Rock Mass Dynamic Failure And Energy Law

In recent years,as mine engineering,underground transportation,and underground space utilization gradually extend into deep rock masses,many rock mass engineering need to be carried out in a more complex and harsh geological environment,which has led to an increase in dynamic disasters such as pressure bump and rockburst.In particular,the relatively stable engineering area in the shallow rock mass may be subjected to dynamic failure when it is constructed within deep rock mass.The mechanism of the dynamic disaster is extremely complicated,and there is no unified and clear theory to explain it.Classification of rock mass dynamic failure is one of the most fundamental and key scientific problems in underground dynamic disaster research according to its failure mechanism and characteristics.Therefore,it is of great significance to study the classification and mechanism of rock mass failure in areas that are prone to dynamic failure in engineering excavation.In the paper,five kinds of dynamic hazard classification are carried out in the area of rock mass engineering which is prone to dynamic failure,including pillars model,press-shear and extrusion model,inclusion model,the end of mining face model and different groove-vertical fracture model,the mechanical models of five types of damage are simplified,and the failure mechanism of every model is analyzed.The five rock mass dynamic failure models are tested.Based on energy theory,combined with digital image correlation method,high-speed camera shooting and finite element simulation,the deformation and failure modes,energy laws,fragmentation characteristics and failure severity of the model specimens are analyzed,which studies the occurrence mechanism of five types of rock mass dynamic disasters.The influence of these factors on the degree of failure of the model are studied by changing the different stiffness testing machine loaded and specimen sizes(number and width of pillars,length and angle of prefabricated cracks,angle of tipping of inclusions and presence or absence of cementation,overall dimensions of specimen)in the model test.The paper has made the following progress:1.The physical and mechanical parameters and rockburst tendency indicators of the briquette coal,camellia white granite,peninsula red granite,red sandstone,limestone and shale materials used in the five dynamic disaster model specimens are tested.2.The pillar failure in the pillars model is analyzed,and the influence of the number of coal pillars,the type of rock material and the width of the pillar on the model failure is studied:the pillar of the pillars model is small in size relative to the overall model,and the rockburst occurs instantaneously in the ultimate strength of rock.The more the number of pillars,the larger the ejection velocity of the fragments,and the smaller the failure load,the smaller the energy release.The larger the width of the pillar,the greater the severity of the failure and the ejection velocity of the fragments,in other words,the wide pillar is more severely failure than the narrow pillar,the energy release is larger,and the ultimate load is lower in failure of the narrow pillar.The greater the compressive strength and elastic modulus of the rock material,the greater the degree of failure and the ejection velocity of the fragments.The ejection velocity of the fragment is higher under plane strain than the velocity under plane stress in the pillars model.Mine accidents are avoided by reducing the number of goafs,increasing the size of strips and pillars in mining areas prone to disasters.3.The failure mechanism of the press-shear and extrusion model(vertical large cross-section prefabricated oblique arc fractures and small cross-section side prefabricated oblique rectangular fractures)is analyzed,and the effects of different rock materials,fracture size and angle,and different stiffness testing machines loading on the degree of failure are analyzed:due to the stress concentration near the prefabricated crack,the prefabricated fracture tip first reaches the ultimate strength,cracks,expands,and coalesces failure,in other words,the region between the upper and lower fractures expands and penetrates,the fracture tip expands to the top and bottom of the specimen,and the failure of upper and lower fractures form concave rock crater,and the failure gradually extends to the inside of specimen until the rock burst occurs.The smaller overall height of specimen,the horizontal angle and length of the fracture of the press-shear and extrusion model are,the greater the ultimate load during the failure is,the more accumulated energy,the more severe the failure(the greater the ejection kinetic energy),the greater the dissipative energy and the surface freedom energy y of the fracture.The more developed the various primary fractures in the model,the easier the failure of model under lower load,and the degree of failure is weak and tends to be statically destroyed.The drilling pressure relief and blasting unloading are carried out in the dynamic disaster area,and the size and horizontal angle of the drilling and fractures are increased,and the rock mass failure is changed from dynamic to static,thereby reducing the threat to the mining operation.4.The failure mechanism of the inclusion model is analyzed,and the influence of the cementation conditons on the inclusions and the surrounding rock mass,the angle of the inclusions and the presence or absence of prefabricated fractures(length)on the degree of failure of the model are studied:the deformation of the inclusions and the upper and lower regions is inconsistent with other regions,resulting in upward and downward concentrated stress zone at the tip of the inclusions.Therefore,the tip of the inclusions is prone to the initiation and expansion of the upward and downward fractures,including different order of crack propagation failure occurs from the left tip-lower tip-left tip-left tip-right tip,resulting in rockburst in the inclusion body and nearby rock mass.The worse or no cementation of inclusions and surrounding rock mass is,the larger the angle of the inclusions is,the prefabricated fractures near the inclusions and the larger the fracture length are,the smaller the ultimate load in failure,the lower the accumulation energy is,the less severe the failure is,the less the number of fragments is,and the dissipative energy of the fracture surface,the total number of fragments and the equivalent total surface area are relatively small.The inclusions have a barrier effect on the vertical deformation,and the larger the angle of the inclusions is,the more obvious the barrier effect is.Therefore,it is helpful to transform the dynamic failure into static failure of rock mass by reducing the degree of inclusion cementing and increasing the number and length of cracks near the inclusions,thereby reducing the occurrence of inclusion rockburst.5.Analysis of the failure mechanism of the end of mining face model:firstly,stress concentration occurs in the central region groove,the joints of middle groove-upper and lower(top and bottom corners),so the central groove first reaches the ultimate strength,especially different degrees failure of strength or crack propagation failure are most likely to occur at the corners of the left and right sides(the corner of top and bottom,column between the corner of top and bottom),resulting in overall shear failure of the specimen.Therefore,the failure phenomenon of the model is consistent with the occurrence of instability and failure at the end of the mining face in the excavation working face-in-situ mining roadway.The end of the working face needs to be safely supported in the mining operation.The failure mechanism of the model is independent of the size of the model specimen.6.The influence of vertical primary defects on the failure mechanism of circular arc,rectangular and arched roadway in rock mass engineering is studied,which can be summarized as the expansion and penetration failure of vertical primary fracture and different shape groove interface.7.Axial displacement,input energy of test machine system,dissipative energy of fracture surface,equivalent total surface area,number of equivalent fragments,free surface energy y and the failure degree of rock mass dynamic failure model specimen under compression failure of small stiffness testing machine are greater than the corresponding values in the test of the large stiffness testing machine.Therefore,when the stiffness of the mining system(testing machine)is less than the stiffness of the engineering rock mass(model specimen),rockburst is more likely to occur.8.The mechanical conditions of the rock pillar(plate)body structure and the circular roadway with circular steel structure support body where are prone to power failure in mine engineering are deduced.It is proved that the amount of energy released in the destruction of the engineering structure is independent of the selected boundary range.The consistency of the ejection velocity of the fragments in the five classifications of the dynamic failure model and the corresponding engineering bodies are demonstrated.