Strength and deformation behavior of columnar jointed rock masses under different confining pressures

Columnar-jointed rock mass (CJRM) has significant anisotropic mechanical characteristics, due to that they have abundant columnar joints. Consequently, their mechanical properties are always up to the angle between the orientation of the columnar joints and loading direction. It is very important to figure out their engineering characteristics. In this work, a series of triaxial tests were conducted on CJRM physical models for different joint orientations ( β ). The joint orientation β is chosen as 0, 15, 30, 45, 60, 75, and 90°. Based on the result, the non-linear strength characteristics of CJRM are studied. The results represent a low strength is up to the special joint characteristic. The strength of the CJRM is anisotropic, exhibiting a special “U” shape versus the loading orientation. With the increase of confining pressure, the mechanical anisotropy gradually decreases. In the study, different failure modes are observed when subjected to different joint orientations and confining conditions: (a) splitting failure through the sample, (b) sliding failure along the critical joint, and (c) shearing failure through the sample. Furthermore, two empirical non-linear strength criteria are used to predict the triaxial compression strength of the CJRM and are proven to be effective.