ISRM Suggested Method for Determining the Basic Friction Angle of Planar Rock Surfaces by Means of Tilt Tests

Abstract

The basic friction angle plays a key role when estimating the shear strength of discontinuities for rock engineering projects, since a large body of research has shown that rock joint shear strength models that consider it are able to provide realistic results (Barton 1973; Barton and Choubey 1977; Kulatilake et al. 1995; Grasselli and Egger 2003; Xia et al. 2014; Tang and Wong 2016). The concept behind the basic friction component of shear strength is related to the angle of repose observed for solid bodies on inclined surfaces or granular materials. Based on this analogy, the basic friction angles of planar rock surfaces can be determined by means of tilt tests. Gravity provides both the shear and normal stress components in tilt tests. In this suggested method, the testing device, specimen preparation, shapes and sizes, and testing procedure are described. In addition, other issues related to the tilt test and basic friction angle, such as the effect of vibrations caused by acceleration on the testing machine are also briefly presented in the last section.