The accurate eva‎luation of the shear strength of discontinuities is crucial for ensuring the safety of mining operations, civil engineering projects, and addressing instability issues in rock engineering. This eva‎luation typically employs empirical shear strength criteria, with the base friction angle being a critical parameter. The direct shear and tilt tests are two common methods for determining the base friction angle, with the tilt test preferred for its simplicity and cost-effectiveness. The outcomes of these tests are significantly affected by various factors such as time, temperature, humidity, weathering, and surface conditions of the sample. This study investigates the basic friction angle of three types of rock samples (dolomite, fine-grained sandstone, and coarse-grained sandstone) in both homogeneous and heterogeneous states, under dry and saturated conditions, and at different temperatures (25, 275, 525 degrees Celsius) using the direct shear and tilt test methods. The findings indicate that saturation increases the basic friction angle in fine-grained dolomite and sandstone due to clay-induced cohesion within the rock. Thermal treatment has led to a polished surface on dolomite and fine-grained sandstone samples, resulting in a decreased friction angle in tilt tests. For heterogeneous samples (dolomite-fine-grained sandstone and dolomite-coarse-grained sandstone), the base friction angle approximates the value of the rock type with higher parameters (e.g., sandstone's basic friction angle exceeds that of dolomite, and the base friction angle in the heterogeneous dolomite-sandstone sample, whether fine or coarsegrained, aligns with that of sandstone). The basic friction angle values differ between the tilt test and direct shear test methods, a discrepancy that may be attributed to the normal stress.

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عليرضا باغبانان , سعيد مهدوي