Evaluation of strength anisotropy and failure modes of laminated sandstones

In this research, the anisotropic behaviour of laminated sandstones, collected from southwest of Qom (central part of Iran), was evaluated using uniaxial compressive strength, point load and Brazilian tests. For this purpose, the eight rock blocks were selected. The rock samples were drilled at different direction with respect to the inclination angles (beta) of 0, 30, 45, 60 and 90 degrees. After specimen's preparation and assessment of mineralogical and physical properties, specimens were subjected to uniaxial compressive strength, point load and Brazilian tests, and their strength and failure modes were evaluated at different inclination angles (beta) between loading direction and lamination planes. Transitional angle, which indicates the change in dominant failure mode from parallel to the lamination to across the lamination, were also determined. The results indicate that the anisotropic behaviour of selected sandstones in uniaxial compressive strength test is different compared with the point load and Brazilian tests. Based on the results, the compressive strength anisotropy ratio of the studied sandstones is low, whereas for point load tests, the anisotropy ratio is obtained moderate. Finally, the different failure modes were classified for laminated sandstones.