A New Method to Investigate the Size Effect and Anisotropy of Mechanical Properties of Columnar Jointed Rock Mass

As a special type of rock mass, the columnar jointed rock masses (CJRMs) present anisotropic mechanical properties and complicated failure modes due to the existence of columnar joints and micro-fractures. The determinations of mechanical properties and representative volume element (RVE) of CJRMs are important for the design, construction, and stability evaluation of hydropower projects. In this paper, the numerical simulations of CJRMs with different inclination angles and sizes under uniaxial and true triaxial compression conditions were conducted to investigate the size effect and anisotropic characteristics of mechanical properties. Results showed the failure modes presented anisotropic and size effect characteristics and the confining pressure influenced the failure modes by providing lateral enhancement. In addition, the mechanical properties first fluctuated and then reached stability as size increased, and the RVE were concentrated in 2 m to 3 m. The RVE were affected by the loading conditions and the CJRMs with inclination angles of 90° and 75° exhibited the smallest and largest RVE respectively. The anisotropy coefficients (ACs) of mechanical properties possessed a RVE of 2.5 m. Based on the simulations, a new method was proposed to investigate the correlation between the size effect and anisotropy of mechanical properties. Results showed the mechanical properties of CJRMs presented most stably at the inclination angle of 90°, and the inclination angles ranging from 40° to 75° were the most unfavorable. Based on this method, the anisotropy of size effect and the size effect of anisotropy, which were difficult to investigate in the past, could be discussed in detail through numerical simulations.