Effect of Anisotropy on the Strength and Brittleness Indices of Laminated Sandstone

The strength and brittleness of rocks are among the most important mechanical parameters in the design of geotechnical projects. Anisotropy is one of the prominent factors affecting the rock properties including strength and brittleness. This paper investigates the effect of anisotropy on the strength and brittleness of laminated sandstone samples collected from the northwest of Khorramabad (west of Iran). For this purpose, the laminated sandstone samples were drilled at different lamination angles (beta) of 0 degrees, 30 degrees, 45 degrees, 60 degrees, and 90 degrees. Here, beta is the angle between lamination planes and loading direction. After preparation of specimens, petrographical and physical properties were investigated. Then, uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) tests were carried out on the specimens at different beta angles, and their strengths were determined. Using data analysis, brittleness was indirectly obtained as a function of UCS and BTS. The results showed that the anisotropy of the sample has a significant influence on UCS, BTS, and brittleness. Moreover, UCS and brittleness of the sample showed a shoulder-shaped anisotropy with the maximum value at beta = 0 degrees or beta = 90 degrees and minimum value at beta = 30 degrees. Meanwhile, the BTS of the sample increased with an increase in beta from 0 degrees to 90 degrees. According to the classifications of UCS and brittleness of rocks in the literature, in terms of the beta angle, the sample falls into the different categories of rock classes.