ARMA 12-159 The Influence of Drilling Direction on RQD Values of Rock Mass with Multiple Sets of Discontinuities and RQD Data Acquisition for In-depth Analysis

摘要

The RQD values are frequently used as an important index in rock mass rating systems for convenient assessments of rock mass quality. It has been revealed that RQD values are strongly correlated to the distribution of discontinuities. However, many argued that, although convenient to be acquired from rock cores, RQD has its limitations to be used to characterize the rock quality. Some claimed that RQD is unreliable and can be of widely ranged values that vary significantly with drilling directions. In this paper, studies are conducted to statistically analyze the relationship between the drilling direction and the RQD. With the assumption of negative exponential distributions for discontinuity spacings, which has been commonly accepted in rock mechanics studies, a statistical model is developed to characterize fractures of drill cores acquired in rock masses with multiple sets of discontinuities. Studies have indicated that RQD may vary significantly over different drilling directions, especially when the number of discontinuity sets in the rock mass is small. In order to fully characterize and understand the rock properties, a practical approach is proposed in this study to utilize RQD values from multiple drill holes/scanlines at different directions to acquire detailed probability distribution parameters for individual discontinuity sets. Analysis indicates that it is necessary to have the number of nonparallel drill holes and scanlines equal to the number discontinuity sets in rock mass in order to solve for all the probability distribution parameters. With the probability distribution parameters estimated for each individual discontinuity sets, the distribution of RQD values over any direction range in the rock mass can then be evaluated.