Research On The Characteristics Of Generalized RQD Based On Development Degree Of The Discontinuities

Traditional Rock Quality Designation(RQD)has become an important index and basic method for characterizing rock mass structure since it was proposed in 1964.However,the standard RQD calculation principle does not consider the rationality of the threshold,and the results cannot fully reflect the anisotropy and size effect of the rock mass.Based on the research of a rock slope in the Xudonggou stope of Anqian Iron Mine,Liaoning,this paper divides the fractures into groups of dominant occurrences,and divides the fractures spacing and persistence grades to generate 35 types of rock mass models with different levels of fractures development.Based on fractures geometric parameters and fractures network simulation technology,combined with statistical analysis,numerical simulation and chart analysis,the relationship between the generalized rock quality index characteristics of rock mass and the development degree of fractures is explored.The main work and research results obtained are as follows:(1)Perform statistical analysis on the occurrence data of fractures,draw the rose occurrence map and pole distribution map through the geological software DIPS,divide them into three dominant groups,and use the MCSDO program to perform function fitting on the occurrence.According to previous research results and related specifications,the fractures spacing and ductility are divided,and the fractures network simulation parameters are determined to generate rock mass models with different degrees of fractures development.(2)According to the modeling parameters of the fractures network model,the DFN section in the 3DEC program is used to complete the establishment of a threedimensional discrete fractures network.Aiming at the shortcomings of traditional drilling and coring method to calculate RQD,the concept of generalized RQD is introduced,and scan-lines are arranged instead of boreholes,and the generalized RQD of this direction is calculated through the intersection of scan-lines and fractures.(3)In order to calculate the threshold of the generalized RQD,the anisotropic survey line is arranged in the selected section of the rock mass model,and the corresponding threshold when the standard deviation of the generalized RQD in each direction reaches the maximum is used as the optimal threshold.Using the best threshold to calculate the generalized RQD can reflect the anisotropy of rock masses most comprehensively and to the greatest extent,making the results closer to the true quality of rock masses.Moreover,the selection of the optimal threshold is closely related to the spacing of the fractures,and increases as the spacing increases.(4)The advantage of the generalized RQD lies in its flexibility to calculate in any direction and arbitrary threshold.Based on this,the generalized RQD is used to discuss the degree of anisotropy of 35 models.The study found that the fractures spacing affects the anisotropy of rock mass.The key factor of the anisotropy decreases with the increase of the spacing between the fractures.(5)The existence of internal fractures of rock mass makes various parameters and properties have obvious size effects.In the fractures network model,measuring lines of different lengths are arranged in the vertical direction,and the research on the size effect of the generalized RQD has been carried out.Analyzing the relationship between the generalized RQD and the length of the survey line in different models,the results show that the generalized RQD changes with the length of the survey line.When the length of the survey line is small,the generalized RQD changes greatly.As the length of the survey line increases,it gradually tends to It is stable and converges to a certain stable value,showing obvious size effect.(6)The study shows that the convergence length of the survey line shows an increase with the increase of the fractures spacing and ductility,indicating that the development degree of the internal fractures of the rock mass has a greater impact on the generalized RQD size effect.When encountering this kind of rock mass in the project,the length of the survey line(drilling hole)should be appropriately increased to ensure the reliability and stability of the results.Through the above research work,guidelines and methods are provided for the measurement and calculation of the generalized RQD,and a certain scientific theoretical basis is provided for obtaining high-quality and high-reliability rock quality indicators in practical engineering.Therefore,it has important practical significance to study the relationship between generalized RQD characteristics and fractures development.