A-BQ, a classification system for anisotropic rock mass based on China National Standard

Abstract

The rock mass in nature is in most cases anisotropic, while the existing classifications are mostly developed with the assumption of isotropic conditions that not always meet the engineering requirements. In this study, an anisotropic system based on China National Standard of BQ, named as A-BQ, is developed to address the classification of anisotropic rock mass incorporating the anisotropy degree as well as the quality of rock mass. Two series of basic rating factors are incorporated including inherent anisotropy and structure anisotropy. The anisotropy degree of rock mass is characterized by the ratio of maximum to minimum quality score and adjusted by the confining stress. The quality score of rock mass is determined by the key factors of anisotropic structure occurrence and the correction factors of stress state and groundwater condition. The quality of rock mass is characterized by a quality score and classified in five grades. The assessment of stability status and probable failure modes are also suggested for tunnel and slope engineering for different quality grades. Finally, two cases of tunnel and slope are presented to illustrate the application of the developed classification system into the rock masses under varied stress state.