Slope stability analyzes in metamorphic rock masses with anisotropic behaviour

Anisotropy in rocks is that the rock exhibits different strength, deformation and similar properties in different orientations under the effect of fabric, microstructure or existing discontinuities. In underground and surface engineering structures built on rock masses with anisotropic properties, projects are evaluated with the data obtained from the studies, usually taking into account the orientation angles that are perpendicular to the bedding planes or randomly selected. This situation especially affects the safety coefficient values of open pit slopes. In this study, Acacia Maden İşletmeleri A.Ş., located in Hanönü district of Kastamonu province, the effect of the anisotropic properties of the metamorphic rock mass (green schist and mica schist) that cause instability on the slope stability in the copper mine area was investigated practically. Green schist and mica schist containing metamorphic rock masses, which cause stability problems in the field, and whose mechanical behavior can change depending on the directions were evaluated. Rock properties (strength, etc.) perpendicular to the bedding planes are usually at higher values. However, at different degrees of bedding planes, the strength and deformation values of the rock material may also be different. In order to reveal these differences and to determine the effect of anisotropy on slope stability, experimental studies were carried out at different orientation angles (0°, 15°, 30°, 45°, 60°, 75° and 90°) of the anisotropy plane with the vertical. In this context, uniaxial and triaxial compressive strength, ultrasonic sound velocity (P and S), indirect tensile strength, deformation properties (modulus of elasticity) and shear strength values (cohesion (c) and internal friction angle (ϕ)) were determined based on directions. In addition, anisotropy type (U, wavy, shoulder) and degree (low, medium and high) were also evaluated. Mohr-Coulomb and Generalized Hoek-Brown failure criteria are generally used in slope stability studies. In this study, besides these criteria, "Anisotropic Linear" and "Snowden Modified Anisotropic Linear" failure criteria were also used. Maximum slope safety coefficients were obtained at 60° orientation angle and minimum at 0°. In addition, suitable slope geometry (slope height, angle, width) was determined for slope studies to be carried out at these degrees. Slope parameter's results obtained from the slope stability analyzes made by considering the orientation angle will be effective in preventing slope instability in the study area. Keywords: Anisotropic Linear, Green Schist, Mica Schist, Rock Anisotropy, Snowden Anisotropic Linear.