ARMR, a new classification system for the rating of anisotropic rock masses

Abstract

The engineering behavior of rock masses is strongly dependent on anisotropy, which is present at different scales, from the microscale in the intact rock due to the alignment of rock crystals (inherent anisotropy) to the macroscale in rock masses with anisotropic rock structure, characterized by distinct bedding or schistosity planes. This paper presents a new rock mass classification system, Anisotropic Rock Mass Rating (ARMR), specifically developed for the classification of anisotropic rock masses. ARMR considers the following rating parameters: (a) anisotropy strength index, RC; (b) uniaxial compressive strength of intact rock; (c) degree of structure anisotropy; (d) corrected rock quality designation (RQD); (e) condition of anisotropy surfaces; and (f) groundwater conditions. Its use is illustrated and explained by application to specific case studies in anisotropic rock masses, and the advantages and limitations of the classification system are outlined. The strength of anisotropic rock masses is determined using the modified Hoek–Brown criterion (Saroglou and Tsiambaos, Int J Rock Mech Mining Sci 45:223–234, 2008), which is extended to rock masses with the use of ARMR.