| Rock burst caused by excavation of underground construction has an obvious hysteresis effect,and research shows that the occurrence of hysteretic rock burst is closely related to the time-lag damage of the rock.Based on this,considering the actual stress state of the surrounding rock after excavation,a typical sandstone in engineering construction is selected as the research object,and on the basis of theoretical analysis,uniaxial compression and triaxial unloading time-lag damage tests under static and dynamic loads are carried out,and numerical simulation analysis of time-lag damage of sandstone under static and dynamic loads is carried out by PFC3 D particle flow program,and the time-lag deformation damage of sandstone is analyzed comprehensively.The following conclusions and results were obtained.The main relevant conclusions and results are as follows.⑴ Under static load,the stress level has a significant effect on the time-lag deformation and failure of sandstone uniaxial compression,and the damage incubation time decays exponentially as the stress level increases,but far exceeds the incubation time of conventional uniaxial compression damage,while the average axial strain rate in the isokinetic deformation stage increases exponentially;In uniaxial compression time-lag damage,the annular strain and volume strain of the rock sample are significantly larger than the conventional uniaxial compression test,and when the stress level is lower than 90%,the annular strain at the time of damage grows rapidly and exceeds the axial strain,which is the significant feature that distinguishes time-lag damage from conventional uniaxial compression damage.The total energy of uniaxial compression time-lag damage is comparable to that of conventional uniaxial compression in general,but the proportion of dissipated energy increases significantly during time-lag loading,indicating that the time-lag loading phase The rapid growth of circumferential strain in the rock sample during the time-lag loading phase leads to a significant increase in near-axial splitting tension damage cracks,which also leads to a more severe fragmentation of the rock sample damage.⑵ The effect of unloading amount on the time-lag deformation and failure of triaxial unloading under the action of static load is also significant,with the increase of unloading volume,the damage incubation time decays exponentially,while the average axial strain rate in the isokinetic deformation phase tends to increase exponentially;the total energy in the triaxial unloading time-lag damage is approximately the same as that in the conventional triaxial unloading damage,and with the decrease of unloading volume,the dissipated energy in the hysteretic stage of unloading gradually decreases,but the dissipated energy in the time-lag stage of unloading gradually increases,and the shear surface of the time-lag damage in triaxial unloading also gradually curves;the damage in the time-lag damage in triaxial unloading gradually increases with the decrease of unloading volume,when the unloading volume is between 70% and 80%,the accumulated damage in the time-lag stage of unloading is larger than that in the hysteretic stage of unloading,and when the unloading volume is between 85% and 100%,the damage in the time-lag stage of unloading is larger than that in the time-lag stage of unloading.⑶ Compared with the uniaxial compression time-lag failure test under static load,the failure incubation time and average axial strain rate of the uniaxial compression time-lag failure test under dynamic disturbance are generally unchanged with the increase of stress level,but the damage incubation time will decrease by more than 35% and the average axial strain rate will increase by more than 60%;the response ratio,total energy,dissipation energy,and damage variables of the dynamic disturbance phase When the stress level is lower than90%,the loss ratio is lower than 0.5,while when the stress level is higher than 90%,the loss ratio will be higher than 0.5,and the number of damage and cyclic disturbance in the power disturbance stage is S-shaped growth law.⑷ The effects of different amplitude and frequency combinations on the uniaxial compression time-lag deformation and failure of sandstone under the action of dynamic disturbance are also significant,with the increase of disturbance amplitude,the damage incubation time decreases exponentially,while the average axial strain rate of the isokinetic deformation phase increases exponentially;with the increase of disturbance frequency,the damage incubation time gradually decreases and the average axial strain rate gradually increases at the same amplitude.The total energy,elastic strain energy and dissipation energy of the dynamic perturbation phase at the same perturbation frequency gradually increase with the increase of amplitude,and the total energy,elastic strain energy and dissipation energy of the dynamic perturbation phase at the same perturbation amplitude gradually increase with the increase of frequency;the damage variables of the dynamic perturbation phase at different combinations of amplitude and frequency show an S-shaped growth with the number of perturbations of the perturbation cycle The damage variables in the dynamic perturbation phase at different combinations of amplitude and frequency showed an S-shaped growth pattern with the number of perturbations in the perturbation cycle,and the damage gradually increased with the increase of perturbation amplitude and frequency.⑸ Compared with the triaxial unloading time-lag failure test under static load,the failure incubation time and average axial strain rate of the triaxial unloading time-lag failure test under dynamic disturbance are generally unchanged with the increase of unloading amount.,but the damage gestation time will decrease by more than 43% and the average axial strain rate will increase by more than 275%;the response ratio,total energy,dissipation energy,and damage variable of the dynamic disturbance phase of three-axis unloading time-lag damage all increase with increasing unloading volume,while the opposite is true for the elastic strain energy.The loss ratio,total energy,dissipation energy,and damage variable all increase with the increase of unloading,while the opposite is true for elastic strain energy;when the unloading amount is lower than 80%,the loss ratio is lower than 0.5,when the unloading amount is higher than 80%,the loss ratio is higher than 0.5,and when the unloading amount is more than 95%,the loss ratio reaches more than 0.9,and the number of damage and cyclic disturbance in the dynamic disturbance phase shows an S-shaped growth law.⑹ In the numerical simulation test of sandstone uniaxial compression time-lag failure under static and dynamic loads,the total number of cracks at the starting point of time-lag failure is relatively small,while the total number of cracks at the end of time-lag damage increases significantly,and its total number of cracks increases significantly as the stress level decreases,and at the same time,the total number of cracks at different stress levels also increases significantly under the action of dynamic perturbation compared with the action of static loading;the shear-tension ratio at the end of time-lag damage shows a nonlinear The shear-tension ratio at the end of the time-lag damage showed a non-linear growth trend with increasing stress level,and the overall shear-tension ratio was greater than 1.5,while the overall shear-tension ratio under dynamic disturbance was greater than that under static load.In the numerical simulation test of time-lag failure of sandstone triaxial unloading under static and dynamic loads,the total number of cracks at the starting point of time-lag failure is relatively small,while the total number of cracks at the end of time-lag damage increases significantly,and the total number of cracks increases significantly as the unloading amount decreases,and at the same time,the total number of cracks increases significantly under different unloading amounts compared with static loading under dynamic disturbance.The shear-tension ratio at the end of time-lag damage also showed a non-linear growth trend with the increase of unloading amount,and its shear-tension ratio was greater than 2.5 as a whole,and the shear-tension ratio at the end of time-lag damage with different unloading amounts under the action of dynamic disturbance was basically equal to that under the action of static loading. |
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