| The stability of rock masses is related to engineering safety and construction cost,which is always the focus of the research in the field of rock engineering.The rock joint roughness coefficient(JRC)is an important parameter which determines the shear strength and stability of rock masses.Therefore,the research on the quantitative evaluation of JRC is of great significance to investigate mechanical parameters of rock joints,evaluate rock masses stability and reduce safety risks of underground engineering construction.The results show that rock joint roughness coefficient has many characteristics like scale effect,anisotropy and heterogeneity.However,evaluation results are quite different in existing studies due to considering little about sampling methods and evaluation methods.At present,there is no effective method for JRC evaluation.To this end,this paper proposed a refined quantitative evaluation method of rock joint roughness based on 3D scanning technology and analyzed the influence of sampling method on scale effect and anisotropic evaluation results.The main contents of this paper are as follows:(1)In this paper,the research on rock joint roughness at home and abroad has been carried out.The research of data acquisition method,roughness coefficient evaluation method and roughness characteristics of rock joint have been summarized.(2)This paper introduced methods and steps of obtaining the rock joint data by 3D scanning technology.The influence of scanning accuracy and three-dimensional scanning technology on JRC evaluation results were discussed.It is found that the higher the scanning accuracy is,the greater the JRC evaluation results are.What's more,3D laser scanning technology is more suitable for the acquisition of rock joint data than 3D structured light scanning technology.This paper introduced a basic method to obtain equidistant point cloud data of rock joint by image processing and point cloud data processing.The influence of sampling interval on the evaluation results of JRC was discussed.It is found that the smaller the sampling interval is,the larger the JRC measurement results are.(3)The accurate coordinate data was obtained by digitizing Barton standard rock joint contour.This paper put forward a method based on EDJRC,and evaluated existing JRC quantitative methods to select the accurate JRC formula.The quantitative evaluation and mathematical statistics analysis of JRC were realized in batches through computer program.(4)Based on the quantitative evaluation method of rock joint roughness proposed in this paper,the JRC scale effect of three typical rock samples was evaluated.The influence of the sampling size as well as the sampling position on the measured results of JRC were investigated.The results show that the spatial heterogeneity of rock joint roughness is the intrinsic cause of the variation of measured JRC in different areas.Therefore,the measured results of JRC vary significantly due to the changes of sampling size and sampling position.A so-called full data sampling method was proposed to overcome the scale effect in JRC measurement.The full data sampling method can effectively overcome the shortcomings of existing methods and obtain the stable measured values of JRC.(5)This paper proposed a rotation sampling method to evaluate the anisotropy of JRC in different sampling scale.Based on the comparison analysis of a typical rock joint sample,the influences of single contour sampling method and rotation sampling method on the anisotropy evaluation results of JRC were investigated.The results show that the existing single profile sampling method makes the JRC anisotropy data discrete and therefore requires larger sampling size to improve its accuracy of the obtained JRC data.The proposed rotation sampling method can overcome the problem of JRC anisotropy data dispersion and obtain accurate and reliable JRC data for anisotropy evaluation. |
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