| With the continuous development of rock mass engineering,deep rock mass engineering has received more and more attention.Ultrasonic testing technology,as a convenient and nondestructive testing method,has been widely applied in the study of rock mechanics.Studying the propagation and attenuation laws of ultrasonic waves in different jointed rock masses is one of the important topics at present.At present,the relevant theory of ultrasonic propagation in rock mass is based on continuous medium,and the ultrasonic longitudinal wave test is the main means.However,most rock masses in nature belong to discontinuous media,and the continuous media theory is no longer applicable to the study of ultrasonic propagation characteristics in such rock masses.The longitudinal wave velocity will be insensitive,so it is urgent to consider carrying out relevant research on ultrasonic propagation theory in discontinuous media.In this paper,through similar material simulation,single jointed rock mass and equal length cross jointed rock mass are prepared,uniaxial compression and ultrasonic shear wave propagation tests are carried out,and the propagation characteristics of ultrasonic shear wave in jointed rock mass with different degrees of fragmentation are studied in depth.The main conclusions are as follows:(1)The degree of rock fragmentation increased from 10 ‰ to 90 ‰.In different single jointed rock masses,the transverse wave velocity first decreased,then increased,and then decreased nonlinearly.The average wave velocity was 1319.55m/s,while in different equal length cross jointed rock masses,the transverse wave velocity and maximum amplitude nonlinearly decreased,with an average wave velocity of 1092.89m/s;The maximum amplitude and energy of transverse waves in different single jointed rock masses increase nonlinearly,while the ultrasonic energy in different equal length intersecting jointed rock masses first increases and then decreases.The average energy values after failure are 64.9 and 44.03,respectively.(2)The degree of rock fragmentation increases from 10 ‰ to 90 ‰,and the elastic modulus of rock masses with different single joints and equal length cross joints shows an overall nonlinear decreasing trend.The maximum elastic modulus of rock masses with different single joints is 8.13 GPa,the minimum value is 6.79 GPa,and the maximum reduction rate is16.48%;The maximum elastic modulus of rock masses with intersecting joints of different lengths is 10.03 GPa,the minimum value is 8.01 GPa,and the maximum reduction rate is20.14%.(3)The degree of rock fragmentation increases.In the two-dimensional time-frequency map,the distribution trend of ultrasonic frequency in different single jointed rock masses decreases nonlinearly with time,and the frequency shows a layered distribution in the timefrequency map;The ultrasonic frequency in rock masses with intersecting joints of different lengths decreases nonlinearly with time,and the frequency shows a concentrated distribution in the time-frequency map;In the three-dimensional time-frequency map,the frequency spectrum of shear wave signals in equally long intersecting joints and single jointed rock masses shows a single peak shape,showing a nonlinear decreasing trend in both time and frequency dimensions.(4)Based on the correlation analysis between the shear wave acoustic parameters and the mechanical parameters of jointed rock mass with different degrees of fragmentation,the sensitivity analysis and fitting between the elastic modulus of jointed rock mass and different failure thresholds,the shear wave acoustic parameters and the elastic modulus of jointed rock mass with different degrees of fragmentation were carried out.By fitting the empirical formula of regression equation,the estimation model of the elastic modulus of jointed rock mass with different degrees of fragmentation based on the ultrasonic shear wave acoustic parameters was established.(5)Through verification analysis,it was found that when the degree of rock fragmentation does not exceed 70 ‰,the estimation model for the elastic modulus of single jointed rock masses with different degrees of fragmentation based on transverse wave acoustic parameters is more effective;In the estimation model of elastic modulus of equal length intersecting jointed rock masses based on transverse wave acoustic parameters with different degrees of fragmentation,the error of elastic modulus value increases when the degree of fragmentation reaches 50 ‰,and increases when the degree of fragmentation exceeds 70 ‰.This model can provide reference for ultrasonic testing technology of engineering rock mass strength parameters. |
