Study on shear failure characteristics of jointed rock mass with different lithology based on the difference of acoustic emission parameters

Lithology is one of the basic factors controlling the shear properties of jointed rock mass. Based on acoustic emission monitoring technology, three-dimensional scanning and three-dimensional engraving technology, this study carried out direct shear laboratory tests of granite, sandstone and limestone under the same three-dimensional joint surface morphology and normal stress gradient (0.5g1/3/6Mpa), and systematically analyzed the characteristics of acoustic emission parameters and the evolution law of acoustic emission b value during the shear process of each lithologic sample. The main conclusions are as follows: (1) the peak shear strength increases monotonously with the normal stress. Sandstone and limestone show strain softening characteristics after the peak, while granite shows strong stress oscillation characteristics after the peak; (2) Lithology difference controls microcrack damage and energy release: granite has a long silence stage and releases high energy, sandstone has a very short silence stage and energy is scattered, limestone has a very low ring count, and AE cumulative ring count and AE energy jointly characterize the three-stage damage evolution (silence → accelerated growth → deceleration); (3) The RA-AF distribution shows that the tensile failure is the main type of the three rock properties, and the proportion of tensile/shear cracks is affected by the normal stress; (4) The b value is significantly controlled by lithology, and the three kinds of lithology show the evolution characteristics of "sudden drop rise fluctuation" in the loading process, but there are significant differences in the specific curve shape; (5) To overcome the universal limitation of the traditional b-value threshold, a "b-value energy coordinated sudden drop point" is proposed as an early warning criterion for shear slip instability of jointed rock mass. The sudden drop occurs before the peak value of the three lithologies, and the occurrence time of the sudden drop point is related to the lithology and normal stress, which provides a new method for monitoring rock damage. Through the analysis of multi-dimensional acoustic emission characteristics, this study deepens the understanding of shear failure mechanism of jointed rock mass, and promotes the development of dynamic monitoring technology of rock engineering stability.