| The morphological characteristics of rock joint are the key factors affecting the deformation characteristics,failure characteristics and strength characteristics of rock masses.Therefore,measuring the surface roughness of joint is of great significance for evaluating the stability of rock masses.The classic JRC-JCS shear strength is widely used in evaluating the stability of engineering rock masses.The important parameter joint roughness coefficient(JRC)in this model often needs to be evaluated by the profiles of the joint surface.The mechanical measuring instrument with low cost is one of the important ways to obtain the profiles of the joint surface.This paper takes into account the scale effect of the joint surface,and studing the influence of the profiles interval to the morphological characteristics of rock joint.Determining an appropriate sampling interval that can not only meet the accuracy requirements of joint shear strength analysis,but also reduce the time-consuming and labor-intensive.The research are as follows:(1)The three-dimensional laser scanner and the mechanical profiler were used to obtain the profiles of the joint surface at the same position,and the measurement accuracy and reliability of the profiler were evaluated by quantitatively comparing the digital information obtained in the two measurement methods.Comparative analysis shows that,compared with the measurement results of the three-dimensional laser scanner,the comprehensive measurement accuracy of the profilometer in the horizontal and vertical directions of the joint is 5.92% and 6.26%,respectively,and has good stability,which shows that profilometer can be used for the measurement of the joint morphology when considering engineering cost.(2)Using three-dimensional scanning technology and 3D printing technology,a number of joint samples with natural morphological characteristics were produced.15 profiles with different intervals were extracted on the surface of the joint,combined with the JRC-JCS theoretical shear strength formula to evaluate the shear strength estimates of the joint under different normal stresses,and compared with the results of the shear test.The results show that the sampling distance of the profiles affects the evaluation of the shear strength of the joint,and the larger the distance,the greater the dispersion and volatility of the estimation results.(3)In order to determine the appropriate profiles sampling interval of the joint surface,the roughness values of the joint surface under 30 different intervals and 10 series sizes are compared.It can be found that with the change of the sampling interval of the joint surface profiles,the roughness value of the joint surface shows a certain difference,which has a obvious effect of the sampling interval.Specifically,the sampling interval of profiles is within 0-5mm,and the roughness(JRC)value of the joint shows good stability(the difference is not more than 2%);for maxmum-sized joint,when the acceptable fluctuation difference is 5%,the sampling intervals of the profiles can be expanded to 40 mm.In addition,the analysis results show that although the JRC values of the joint shows a certain difference with the sampling interval of the profiles,the regularity of the scale effect is not affected by the sampling interval. |
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