加载速率效应影响下硬岩失稳破坏试验及前兆分析研究

In order to study the destabilization and damage mechanism of hard rock tunnel peripheral rock affected by loading rate effect,five sets of uniaxial compression-acoustic emission tests with different loading rates were carried out on granite.The rupture evolution process and damage mode of the specimen under each loading rate,the strength change characteristics of the specimen,the distribution characteristics of the acoustic emission parameters of the specimen at each stress stage were studied,and a method of identifying the destructive precursor of granite instability was proposed on the basis of the change rule of the amplitude concentration curve.The study shows that the larger the loading rate is,the shorter the duration of the whole process of specimen damage is,the more intense the damage is,and the worse the integrity of the specimen is after the damage;the peak strength and modulus of elasticity show obvious accelerating effect,but the increase of both of them decreases when the loading rate is more than 0.1kN/s,and the increase of the peak strength decreases from 26%(0.02kN/s-0.05kN/s)to 6.5%(0.2kN/s-0.5kN/s),the increase of modulus of elasticity decreased from 35.6%to 12%,and the peak strain showed a negative correlation with the loading rate;the middle and high frequency signals of the AE ringing counts appeared earlier and earlier,and only a small amount of ultra-high frequency signals were present at the time of damage;the energy of AE was changed from the"lone-type"to the"group-type";The b-value is smaller when the specimen is damaged,from 0.46767(0.02kN/s)to 0.30212(0.5kN/s);The distribution of RA-AF scattering points at each stage shows that the larger the loading rate is,the better the shear crack development is;The slope mutation point between the oscillation stage and the sudden rise stage of the amplitude concentration curve Γ can be used as the precursor information of the destabilization damage of the granite under different loading rates,and the larger the loading rate is,the smaller the intensity corresponding to this mutation point is,from 0.95σc(0.02kN/s)to 0.68σc(0.5kN/s),and the time of appearance is earlier,from 4831s to 186s.