Study on Brittle Damage Evolution and Acoustic Emission Characteristics of Limestone

Brittleness is one of the most important mechanical properties in deep rock mass. In order to study the brittle damage evolution mechanism of limestone, the acoustic emission test of limestone under uniaxial compression was carried out, and the relationship between brittleness index and damage variable and b-value was analyzed. The results show that: (1) The ratios of crack closure stress, crack initiation stress and damage stress to peak stress in limestone are 31.3 %, 43.0 % and 85.5 %, respectively. (2) The average brittleness index of limestone is 0.32, and the mean square error is 0.009. With the increase of brittleness index, the damage variable corresponding to the characteristic stress gradually decreases, and the damage variable gradually increases from ‘proportional function’ to ‘concave power function’. The damage acceleration phenomenon exists in the critical failure stage. (3) Under the condition of uniaxial compression, with the increase of brittleness index, the shear failure of limestone decreases and the tensile failure increases, and the brittleness index can better characterize its failure mode. (4) There are four obvious stages in the cumulative ringing count, cumulative energy, cumulative amplitude and time curve of acoustic emission in limestone: slight increase period, quiet period, steep increase period and sharp decrease period. The amplitude of quiet period is less than 80 dB, and the curve shows a step-like upward trend. The larger the brittleness index, the longer the quiet period, the shorter the sharp increase period, and the greater the ratio of the stress corresponding to the b value to the peak stress. (5) The b-value curve shows a trend of rising first and then falling, and the b-value abrupt points are all before the end of the quiet period. These two points can accurately warn the instability and failure of limestone. With the increase of brittleness index, the b-value abrupt point appears later and closer to the peak. The research results provide important reference for surrounding rock stability control and dynamic disaster monitoring and early warning.