Study On The Mechanics And Acoustic Emission Characteristics Of Layered And Jointed Rocks

As layered and jointed rocks are the most common rock structures and formations found in mining construction sites,it is important to investigate the damage evolution,damage characteristics and mechanisms of laminated and natural jointed rocks sampled from the original rocks of the project.In this paper,a series of indoor experiments are conducted on layered and jointed rocks taken from engineering sites,and their loading characteristics,mechanical properties and acoustic emission parameters under uniaxial stress conditions are systematically analyzed from macroscopic and microscopic perspectives by combining acoustic emission techniques and digital image correlation(DIC),and then the damage modes and mechanisms of engineering rocks are investigated in depth.A model for predicting the uniaxial compression strength of layered and jointed rocks is developed based on the support vector mechanism.The main research contents and findings of this paper are as follows:(1)An in-depth comparative analysis of the basic mechanical parameters and acoustic emission characteristics of layered rocks was carried out using acoustic emission detection techniques,strain gauges and DIC to explore the variation of mechanical and acoustic emission characteristics of three types of layered rocks at different lamination angles.The results show that the uniaxial compressive strength of the layered rocks tends to decrease first and then increase with increasing lamina angle,and that when the lamina angle is 0°,the rocks have the highest brittleness and are prone to rock burst.AF-RA data from acoustic emissions indicate that shear cracking dominates the damage mode of layered rocks under uniaxial compression.(2)After recording and plotting the full-field axial displacement and axial principal strain at the rock sample surface by the DIC system,it was found that the displacement and strain generated at the rock surface in the first and middle stages of loading were relatively small,when the presence of laminae had little effect on them,and when damage was imminent in the later stages of loading,the rock surface would generate larger displacement and strain,and the extension of its displacement and the extension of the strain field through the The laminae distributed on the rock surface are constrained,indicating that the evolution of damage occurring on the rock in the late loading stage is more influenced by the laminae surface(3)The jointed rock samples were grouped according to the distribution of surface cracks,and indoor experiments including wave velocity tests,rebound tests and uniaxial compression tests were carried out on each group to investigate the mechanical parameters of the natural jointed rocks and to compare their acoustic emission characteristics by means of acoustic emission techniques.The wave velocity and rebound values of the jointed rocks provide a good fit to the peak strength,and the mechanical strength of the rocks can be obtained quickly and accurately in the field using wave velocity meters and smithy hammers.Shear damage generally occurs under uniaxial compression in jointed rocks,with tensile damage being the dominant mode of damage in rock samples with single cracks at larger crack angles and shear damage at smaller crack angles,while the mode of damage in rock samples with cross cracks and mixed cracks is not affected by their dominant crack angles under uniaxial compression(4)Uniaxial compressive strength prediction models for layered rocks and natural jointed rocks were constructed using support vector regression,with wave velocity,density and lamina angle as input parameters from the laminated rock strength prediction model,and crack distribution,crack angle(length),density,wave velocity and rebound value as input parameters for natural jointed rocks.The results show that both GA-SVR and PSO-SVR can be used to predict the uniaxial compressive strength of both layered and jointed rocks,but a comparison of the two models based on MAPE and R~2 evaluation criteria reveals that the performance of the PSO-SVR model is significantly better than that of GA-SVR.