Abstract
Rock quality designation (RQD) is widely adopted as a fundamental tool in characterizing rock masses since it was devised in 1964. Since the conventional RQD calculation is limited due to its dependence on the selected threshold, previous research introduced generalized RQD to adequately reflect the anisotropy and scale effect of RQD. However, the influence of the joint development inside rock mass on generalized RQD remains unclear. The objective of this work is to investigate characteristics of the generalized RQD in view of different development degrees of discontinuities in rock mass, including spacing (density) and trace length. Three-dimensional fracture network modelling is employed to simulate the actual rock mass of open-pit iron mine in China. Virtual scanlines are set to obtain RQD values in different directions. The results primarily show that the generalized RQD should be introduced to calculate the RQD with different thresholds to fully reflect the anisotropy of rock mass. The optimal threshold can be obtained based on an anisotropic coefficient, which is defined by (RQDmax-RQDmin). It is also indicated that the fracture spacing has a great influence on both the anisotropy of RQD and the selection of the optimal threshold. The optimal threshold of the generalized RQD increases with the increase in the fracture spacing. In addition, the scale effect of RQD in different models is discussed by changing the length of the scanlines. The longer the scanlines we set, the more stable RQD value can be obtained in the model. It is recommended to fit much longer scanline to get realistic RQD in heavily fractured rock mass.
Highlights
Rock quality designation (RQD) is widely adopted as a fundamental tool in characterizing rock masses since it was devised in 1964
Virtual scanlines are set to obtain RQD values in different directions. e results primarily show that the generalized RQD should be introduced to calculate the RQD with different thresholds to fully reflect the anisotropy of rock mass. e optimal threshold can be obtained based on an anisotropic coefficient, which is defined by (RQDmax-RQDmin)
Conclusions is study used 3D structural plane network simulation technology to generate 35 rock mass models with different structural plane spacing and ductility, arranged survey lines inside the model instead of drilling holes, obtained enough values of the generalized RQD, and studied the relationship between the generalized RQD characteristics and the development of discontinuities. e specific conclusions are as follows: (1) e traditional method using 0.1 m as the only threshold for RQD has significant limitations. It cannot fully reflect the anisotropy and scale effect of the rock mass. e generalized RQD concept is introduced, and the optimal threshold is obtained based on the degree of RQD anisotropy. e results show that the degree of joint development affects the selection of the optimal threshold. e optimal threshold increases with the increase in the spacing, while of the discontinuities have a minimal influence on the selection of the optimal threshold
Summary
Characteristics Analysis of Generalized Rock Quality Designation (RQD) Based on Degree of Joint Development. E objective of this work is to investigate characteristics of the generalized RQD in view of different development degrees of discontinuities in rock mass, including spacing (density) and trace length. Predecessors have conducted extensive research on the limitations of the traditional method to calculate the generalized RQD, how the development of the discontinuities in rock mass will affect the characteristics of the generalized RQD remains unclear. Erefore, this study adopts 3D fracture network simulation [32, 33] to generate numerous models of an actual rock mass by considering different jointing degrees. E scale effect of generalized RQD is studied by changing the length of the scanline, which provides a certain theoretical basis for selecting a reasonable drilling depth of rock projects. With the increase in the sample to a certain critical value, the parameters of rock mass tend to be stable
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