Strength And Deformation Characteristics Of Precast Arc-Fractured Rocks Under Different Stress Paths

Under natural conditions,rock masses are subjected to complex geological effects,and they exist in various stress states.The interior of the rock mass often contains a large number of irregular fissures.In tunnel excavation,roadway boring,coal mine underground mining and other rock projects,it is common to encounter rock masses with internal fissures that resemble arcs.When the external load is applied,the stress concentration will be generated at the tip of the fissure in the working face,leading to the destabilization and deformation of the fissured rock mass,resulting in engineering disasters.Previously,the analysis of the mechanical characteristics of rock masses containing arc fissures was not sufficient,in order to refine the characteristic law of arc fissures under different conditions and guarantee the engineering safety,it is important to study the mechanical characteristics,energy evolution law and acoustic emission characteristics of prefabricated arc fissure rock masses under different stress paths.In this paper,prefabricated arc-shaped and linear fractured rock masses are processed by waterjet.The sandstone specimens were subjected to conventional uniaxial compression,triaxial compression,and triaxial unconfined compression tests.The effect of arch height and dip angle on the strength-deformation characteristics,energy evolution characteristics and acoustic emission characteristics of the arc fissure under different stress paths is studied.The main results obtained are as follows:(1)Based on the test results under different stress paths,it is found that the peak strength,elastic modulus and peak strain of prefabricated fissure rock mass under different conditions are gradually decreasing with the increase of fissure arch height and gradually increasing with the increase of fissure dip angle.Under the same conditions,the strength and elastic modulus of linear fissure rock mass are higher than those of arc fissure rock mass,and the triaxial compression strength is greater than the unloading confining pressure strength,and the rock mass is more likely to be destabilized in the triaxial unloading confining pressure test.The increase of the dip angle of the arc fissure has an optimal effect on the mechanical properties of the rock,and the arch height plays a deteriorating role.Splitting damage occurs in all rock masses with different arch height fissures.The dip angle from 0° to 90° rock mass shows a changing pattern of splitting damage to shear damage to splitting damage.The strength of the fractured rock mass is severely degraded and more easily deformed and damaged,and the strength,peak strain and elastic modulus of the arc fractured rock mass are much smaller than those of the intact rock samples.(2)Based on the principle of energy calculation,the energy evolution law of the prefabricated arc fissure rock mass under different conditions is analyzed.It was found that the larger the arch height of the arc fissure in the triaxial compression and unloading test,the smaller the energy value of the fissure rock at the peak strength,the greater the proportion of elastic energy,and the smaller the proportion of dissipated energy and BIM value.With the increase of the dip angle of the arc fissure,the energy values tend to increase and reach the maximum value at 90°,the ability of the rock mass to absorb and store energy can be effectively enhanced by the larger dip of the arc fracture.The proportion of elastic energy,the proportion of dissipated energy and the BIM value of the rock mass in the unloading pressure test tend to increase.The percentage of elastic energy of linear fracture rock increases with the increase of inclination angle,and the percentage of dissipation energy and BIM value decrease with the increase of inclination angle.The total energy and elastic energy of linear fractured rock mass are larger than that of curved fractured rock mass under the same inclination angle,and the dissipation energy is smaller than that of curved fractured rock mass when the inclination angle is small.Each energy value of the arc fracture rock sample is smaller than that of the intact rock sample,and the energy absorption rate and release rate are even lower.(3)Based on the acoustic emission test data,it is found that the peak ring count rate and peak amplitude of rock mass tend to decrease with the increase of prefabricated fissure arch height.The smaller the fissure arch height,the more active the acoustic emission and the more violent the damage.With the increase of the dip angle,the peak ring count rate and the peak amplitude both show an increasing trend.The larger the fissure dip angle is,the more acoustic emission events,the larger the peak amplitude value and the more violent the damage.The triaxial compression acoustic emission activity is more active in linear fissures than in arc fissures at the same dip angle,and the peak acoustic emission occurs later in arc fissures than in linear fissures.Each energy value of the arc fracture rock sample is smaller than that of the intact rock sample.The peak ringing count rate is close to the moment of peak amplitude appearance,and the correspondence is strong.They both appear after the peak stress,and the acoustic emission hysteresis effect is obvious.When the dip angle is large in the unloading pressure test,the effect of fracture dip angle on the rock mass acoustic emission exceeds the effect of fracture line shape on it.The amplitude of the fissure rock mass is widely distributed and low in amplitude in the early stage,and the distribution range is small and high in amplitude in the later stage.