Research On Rockburst Tendency Mechanism And Fracture Characteristics Of Rocks With Different Pore Structures

Rockburst is a dynamic disaster caused by the ejection of rocks from the parent body caused by deep engineering excavation.The influencing factors of rockburst disaster mainly focus on the external stress environment and the rock structure.The deep high stress environment provides external conditions for energy storage,and the energy storage and release process is closely related to the rock structure.The structure of rock itself can be attributed to the pore,grain and mineral composition of rock.Among them,the pore of rock is the most sensitive to energy storage and release,which is an important internal cause of rock burst disaster.Focusing on the influence of rock porosity on the occurrence of rockburst disasters,this paper studies the rockburst tendency mechanism and fracture characteristics of rocks with different pore structure.Taking limestone,granite and red sandstone samples with the same burial depth from three different mines as the research objects,the pore structure characterization test and the rock mechanical property test were carried out.The density,wave velocity and porosity of three kinds of rocks with different pores were compared,and the compactness of rocks with different pores was analyzed.Based on multiple criteria,the rockburst tendency of different pore rocks is comprehensively discriminated,and the rockburst tendency strength grade is obtained.Combined with the energy evolution law and the characteristics of acoustic emission parameters during loading and unloading of three kinds of rocks with different pores,the rockburst tendency mechanism of rocks with different pores is revealed from the perspective of energy.Combined with the macro-fracture mode of rock samples and the micro-morphological characteristics of fractures,and according to the distribution characteristics of acoustic emission RA-AF values in the loading failure process,the fracture modes of three kinds of rocks were identified.The macro-micro fracture characteristics of rocks with different porosity were explored.The main research results are as follows.(1)The difference in porosity between the limestone and granite samples is not significant,much smaller than that of the red sandstone samples,and the relationship between density,specific gravity,longitudinal wave velocity and uniaxial compressive strength is that the limestone sample is the largest,followed by the granite sample,and the red sandstone is the smallest,among which the limestone sample is the densest.The smaller or denser the rock pores,the smaller the ratio of each characteristic intensity to the peak intensity.(2)Based on multiple criteria to comprehensively judge the rockburst tendency of rocks with different pore structures,the limestone samples have strong rockburst tendency,granite samples have weak rockburst tendency,and red sandstone samples have no rockburst tendency.The rockburst tendency is positively correlated with wave velocity,density,compressive strength,etc.,and basically negatively correlated with porosity.Comprehensive analysis shows that rock pore structure(porosity and compactness)is the key inducement of rockburst.(3)The energy densities of total energy,elastic energy and dissipated energy all show nonlinear evolution characteristics under different stress unloading levels of rocks with different pores.The elastic energy has a linear function relationship with the total energy,and the larger the slope,the stronger the energy storage characteristics.The proportion of elastic energy to total energy shows a trend of first decreasing and then increasing,dissipated energy is the opposite.The denser and harder the brittle rock,the better the energy storage properties and the stronger the rockburst tendency.The acoustic emission ring count and energy evolution of limestone samples are much more than that of red sandstone samples,and the quiet period of cumulative ring count and cumulative energy is the shortest.(4)The limestone sample is mainly damaged by tension-shear interaction,the granite sample is similar to limestone,and the red sandstone sample is mainly tensional failure.Under uniaxial compression,the stronger the rockburst tendency,the more obvious the shear damage.The fracture modes identified based on the RA-AF value are consistent with the macromesoscopic fracture characteristics,and the distribution characteristics of the RA-AF value under uniaxial compression have a great correlation with the rock stress stage.