Experimental Study On Mechanical Properties And Acoustic Emission ChaRActeristics Of Hard Rocks Under Different Loading Methods

In recent years,with the vigorous development of underground engineering,many rock mass projects have gradually shifted to the deep,while the construction of deep hard rock mass projects,they often face the threat of rock engineering disasters such as rock bursts,hindering the smooth progress of the project.It even caused serious casualties and economic losses.The occurrence of these disasters was mainly caused by rock rupture and instability.It is well known that underground engineering rock masses are complicatedly stressed,and the mechanical properties and damage characteristics of rocks are closely related to the load forms they are subjected to.Therefore,it is necessary to conduct in-depth study on the mechanical properties of hard rock under different loading conditions and the process of rupture and instability,so as to provide a basis for revealing the mechanism of rock rupture and instability,and provide a reference for disaster prevention of engineering rock masses.In this paper,three hard rocks,red sandstone,marble and granite,are selected.The ZTRE-210 microcomputer is used to control the rock triaxial test system and the PCI-2 acoustic emission detection system.The acoustic emission test of the rock is carried out.Mechanical properties and acoustic emission characteristics under axial compression test,graded load-keeping test,graded disturbance loading test,graded disturbance loading and unloading test,and multi-cycle loading and unloading test.On this basis,the parametric analysis method proposed in JCMS-III B5706 is introduced to study the fracture types and internal crack evolution of three hard rocks under different loading methods.The main research results obtained are as follows:Rock acoustic emission tests under five different loading methods were carried out on three kinds of hard rocks,and the strength characteristics,basic mechanical parameter characteristics and macroscopic destruction characteristics of the rocks were studied.The research shows that compared with the uniaxial compression test,the other four loading methods strengthen the strength of red sandstone and marble,and degrade the strength of granite;in the graded loading and graded disturbance loading test,the red sandstone and marble The elastic modulus of rock relatively increases,while that of granite decreases.Under the action of cyclic load,the elastic modulus of the three hard rocks increases first and then decreases with the increase of the number of cycles;the Poisson's ratio of the three hard rocks It has been improved to a certain extent under different loading methods;the failure mode of red sandstone under different loading schemes is always shear failure,the main failure mode of marble evolves from axial splitting to inclined plane shear,and the failure mode of granite is from single The splitting failure of the crack through transition to the splitting failure of the multi-fracture penetration eventually evolves into shear failure.The parameters such as ringing count,energy and event of acoustic emission of three kinds of hard rock under different loading modes were compared and analyzed.The research shows that the acoustic emission activities of the rocks under different loading paths are common.Acoustic emission is mainly concentrated in the compaction and destruction stages of the rock.The ringing count and energy value of the acoustic emission of the rock in the early stage of the test are low;each under the same loading scheme The value of the acoustic emission characteristic parameters of the rock and the activity of the acoustic emission are different.The intensity of the acoustic emission of the rock is granite,marble,and red sandstone in order from large to small;the quiet area of the acoustic emission activity before the failure of the granite is the "quiet period" ",And the red sandstone and marble do not appear,indicating that the" quiet period "of acoustic emission is not a necessary attribute of all rocks.According to the acoustic emission parameter analysis method proposed by JCMS-III B5706,the types of internal cracks in the rock under different loading modes are analyzed and the crack evolution law is analyzed.The research shows that the RA-AF scatter plots of rocks under different loading methods all show the characteristics of low RA values corresponding to high AF values,and high AF values corresponding to the characteristics of low RA values,which is important to distinguish tension from shear cracks.Acoustic characterization;the expansion ratio of the number of internal cracks in each rock under different loading methods is characterized by the fact that the proportion of tensile cracks is much larger than that of shear cracks;the loading and unloading effect promotes the expansion of internal shear cracks in the rock,so that the number of shear cracks accounts for Relatively improved.